WO2002004548A1

WO2002004548A1 - Polymer compositions with energetically degradable crosslinker

Info

Publication number: WO2002004548A1
Application number: PCT/US2000/031643
Authority: WO
Inventors: Albert I. Everaerts; Charles M. Leir; Roger A. Mader; Peter A. Stark
Original assignee: 3M Innovative Properties Company
Priority date: 2000-07-07
Filing date: 2000-11-09
Publication date: 2002-01-17
Also published as: AU2001217737A1

Abstract

The present invention is directed toward compositions that are chemically different after application to a substrate as compared to the composition prior to its application. Advantageously, compositions of the invention are easily applied to a substrate, but yet they possess adequate cohesive strength after application. A method of the invention comprises a method of transitioning a crosslinked polymer composition from a first chemical state to a second at least partially crosslinked chemical state.

Description

POLYMER COMPOSITIONS WITH ENERGETICALLY DEGRADABLE CROSSLINKER

Field of the Invention The present invention relates generally to crosslinkers useful in preparing crosslinked polymer compositions and further, at least partially crosslinked, compositions therefrom.

Background of the Invention Polymers are generally crosslinked to increase the cohesive strength, rigidity, heat resistance, or solvent resistance ofa polymer composition. However, the use of certain crosslinkers can make it difficult to apply the compositions to a substrate in, for example, the form ofa coating. Certain compositions that are hot-melt processable materials must have a sufficiently low viscosity upon melting, such that they can be readily hot-melt processed (e.g., applied to a substrate). The presence of crosslinks in a material generally increases the melt viscosity of the material, many times making it impossible to hot-melt process the materials.

In an attempt to provide materials having sufficient cohesive strength and/or rigidity, as well as processability, thermally reversible crosslinks have been used. It is well known to incorporate thermally reversible crosslinks into polymers. Upon heating, the crosslinks dissociate or break. Upon cooling, the crosslinks reform. This sequence can be performed repeatedly. Thermally reversible crosslinks find many uses, for example, in hot-melt processable and re-moldable (or recyclable) materials. By incorporating thermally reversible crosslinks into polymers, a composition can be heated to form a coating or mold from the composition and then return to its original crosslinked state.

For examples of thermally reversibly crosslinked polymers, see U.S. Patent Numbers 3,435,003 (Craven); 4,617,354 (Augustin et al); and 5,641,856 (Meurs). Also see, PCT Publication Numbers WO 95/00,576 (Heyboer) and WO 99/42,536 (Stark et al), as well as Canary et al, "Thermally Reversible Crosslinking of Polystyrene via the Furan-Maleimide Diels- Alder Reaction," Journal of Polymer Science Part A: Polymer Chemistry. Vol. 30, pp. 1755-9 (1992) and Chujo et al, "Reversible Gelation of Polyoxazoline by Means of Diels-Alder Reaction," Macromolecules. Vol. 23, pp. 2636-41 (1990).

Further examples of thermally reversibly crosslinked polymers are thermoplastic elastomers, such as those described in Kirk-Othmer Encyclopedia of Chemical Technology. 4^th Edition, Wiley: 1994, Vol. 9, pages 15-37. Such thermoplastic elastomers have many of the physical properties of rubbers (e.g., softness, flexibility, and resilience), but, in contrast to conventional rubbers, they are hot-melt processable. With such thermoplastic elastomers, the transition from a processable hot-melt to a solid, rubberlike composition is rapid, reversible, and takes place upon cooling. Such thermoplastic elastomers are often multiphase compositions in which the phases are intimately dispersed. In many cases, the phases are chemically bonded by block- or graft-polymerization. At least one phase consists ofa material that is relatively hard or glassy at room temperature, but becomes rubbery upon heating. Another phase consists ofa softer material that is rubberlike at room temperature (i.e., an elastomer). For example, a simple structure ofa multiphase thermoplastic elastomer is an A-B-A block copolymer, where A is a hard phase and B is an elastomer (e.g., poly(styrene-t)- elastomer-έ-styrene)). Examples of these materials are included in, for example, U.S. Patent Numbers 3,639,517 (Kitchen et al.) and 4,221,884 (Bi et al), and Japanese Patent Publication Number 52[11977]-129795. References describing the use of these materials in formulating adhesives include, for example, U.S. Patent Numbers 4,444,953 (St. Clair); 4,556,464 (St. Clair); 3,239,478 (Harlan); and 3,932,328 (Korpman).

It may be desired, however, to provide a composition that is chemically different (e.g., having different adhesive properties) after application to a substrate as compared to the composition prior to its application. Thermally reversibly crosslinked compositions are typically chemically the same prior to and after application to a substrate. While thermally reversible crosslinks are advantageous for easily applying the compositions to a substrate, the applied compositions may not possess enough cohesive strength desired or required for certain applications.

U.S. Patent Number 3,909,497 (Hendry et al) describes solid polymers that are thermally degradable to flowable (or at least softened) compositions. The polymers contain heat-sensitive groups that cleave at a temperature substantially lower than that at which the thermal degradation would occur in their absence. Cleavage is effected essentially in the absence of materials reactive with the resulting molecular fragments. The degradation products are useful as adhesives, plasticizers, fillers, etc. Although the compositions therein are chemically different after thermal degradation, as opposed to prior to thermal degradation, usefulness of flowable compositions is limited. For example, it may be desirable to provide compositions with enough cohesive strength after application to a substrate in order to prevent the composition from being flowable. Further compositions that are chemically different (e.g., leading to compositions having different adhesive properties) after application to a substrate as compared to the composition prior to its application are desired. It is desired to provide compositions that are easily applied to a substrate, but yet possess adequate cohesive strength after application to the substrate.

Summary of the Invention The present invention is directed toward compositions that are chemically different after application to a substrate as compared to the composition prior to its application. Advantageously, compositions of the invention are easily applied to a substrate, but yet they possess adequate cohesive strength after application.

In one embodiment, compositions of the invention comprise a crosslinked polymer composition comprising at least one conventionally crosslinked polymer and at least one degradable crosslinker incorporated into the at least one conventionally crosslinked polymer, wherein the degradable crosslinker comprises at least one energetically labile moiety. For example, compositions of this nature may be indicative of those in a first chemical state, prior to applying the compositions to a substrate. In further embodiments, such compositions comprise a mixture of at least two degradable crosslinkers incorporated into the at least one conventionally crosslinked polymer. Preferably, the degradable crosslinker comprises at least one energetically labile moiety selected from the group of aldoxime esters, aldoxime carbonates, amide esters, and mixtures thereof. The conventionally crosslinked polymer can be, for example, physically crosslinked, ionically crosslinked, or chemically crosslinked.

The crosslinked polymer compositions can be tacky to the touch or essentially nontacky at room temperature. In certain embodiments, the composition is at least partially tacky at room temperature. Tackiness of the composition is adjustable by tailoring the composition according to the desired application. Certain applications benefit from providing the composition in a free-flowing form. To facilitate this form, the composition may further comprise at least one ofa dusting agent and a coating agent.

The crosslinked polymer composition may be blended with other polymers. For example, in one embodiment, the crosslinked polymer composition further comprises a polymer that interacts ionically with the at least one conventionally crosslinked polymer. A method of the invention comprises a method of transitioning a crosslinked polymer composition from a first chemical state to a second at least partially crosslinked chemical state, the method comprising the steps of: (1) providing at least one crosslinked polymer composition selected from the crosslinked polymer compositions described above and a crosslinked polymer composition comprising at least one polymer derived from at least one degradable crosslinker; and (2) activating at least a portion of the crosslinked polymer composition by applying an external energy source to at least a portion of the crosslinked polymer composition to fragment at least a portion of the degradable crosslinker. In a further embodiment, the polymer derived from at least one degradable crosslinker is a crosslinked polymer composition comprising at least one polymer derived from at least two different degradable crosslinkers.

In preferred embodiments of this method, the external energy source is a thermal energy source. The step of activating can occur prior to applying the crosslinked polymer composition to at least a portion ofa substrate, while applying the crosslinked polymer composition to at least a portion ofa substrate, or after applying the crosslinked polymer composition to at least a portion of a substrate.

According to this method, further steps may also be performed. For example, the method can further comprise the step of catalyzing fragmentation of the at least one degradable crosslinker. The method can further comprise the step of applying the crosslinked polymer composition to at least a portion ofa substrate. Also disclosed are polymer compositions comprising a polymer that is at least partially chemically crosslinked and at least two pendant moieties on the polymer, wherein the pendant moieties are the reaction product of fragmentation ofa degradable crosslinker comprising at least one energetically labile moiety. For example, compositions of this nature may be indicative of those in the second chemical state.

Detailed Description of the Preferred Embodiments

Crosslinkers of the invention are useful for providing a wide variety of compositions that are chemically different (e.g., having different adhesive properties) after activation and, optionally, application to a substrate, as compared to the composition prior to its activation. As a result ofa change from a first chemical state to a second chemical state, certain physical properties of the composition are altered. Advantageously, the compositions maintain at least some degree of crosslinking after application to a substrate, providing cohesive strength to the applied composition.

In one embodiment, the crosslinkers are useful in providing compositions having varying levels of tack and/or compliance, and therefore adhesion, before and after activation of the composition (i.e., fragmentation of at least a portion of the crosslinkers in the composition). The varying levels of tack and compliance may enable tapes, for example, incorporating the compositions to be more easily repositionable and/or removable before activation as compared to after activation. Furthermore, varying levels of tack may facilitate easier handling and processing of the composition. According to one aspect of this embodiment, a crosslinked polymer composition is essentially non-tacky before activation, but becomes tacky, enabling it to be used as an adhesive (e.g., a pressure-sensitive adhesive), after activation. According to another aspect of this embodiment, the crosslinked polymer composition is tacky before activation, becoming even more tacky after activation. Thus, multi-layer constructions, such as those described by Callahan, Jr. et al. (U.S. Patent Number 5,322,731) and Hamer et al. (U.S. Patent Number 5,804,610), are advantageously not necessary with the present invention.

In a preferred embodiment, the crosslinked polymer composition is "free- flowing" before activation. "Free-flowing" crosslinked polymer compositions are those compositions containing a multitude of solid state particulates that do not substantially agglomerate (i.e., the particulates are capable of being moved by gravitational forces alone) at temperatures below the activation temperature of the degradable crosslinkers. Free-flowing crosslinked polymer compositions contribute to easier feeding and delivery methods. For example, free-flowing crosslinked polymer compositions facilitate feeding hot-melt coating compositions. Furthermore, shipping and handling associated with free-flowing crosslinked polymer compositions is typically less expensive and more convenient than shipping and handling associated with bulk polymer compositions.

A wide variety of other uses for crosslinkers and crosslinked polymer compositions of the invention will be apparent to those of ordinary skill in the art. Generally, the crosslinkers and compositions of the invention are useful in any application where a change from a first chemical state to a second chemical state is desired, as well as a minimum degree of crosslinking associated with the second chemical state.

Crosslinkers Compositions of the invention contain degradable crosslinkers, but may include other types of crosslinkers as well. "Degradable crosslinkers" are those crosslinkers comprising at least one covalent bond, wherein the covalent bond fragments (or degrades) upon activation. Preferably, the degradable crosslinkers fragment irreversibly (i.e., the fragments cannot recombine in any manner and they cannot react with any other portion of the polymer in which they are incorporated to form a new covalent crosslink) upon activation. Depending on the exact chemical nature of the degradable crosslinker, fragmentation may occur, for example, by an elimination or cyclization chemical reaction.

At least two fragments remain incorporated as pendant moieties on the polymer in which the degradable crosslinker was incorporated. In some embodiments, however, more than two fragments are produced and not all of the fragments remain incorporated as pendant moieties on the polymer. Nevertheless, the sum of the molecular weights of the total fragments is essentially the same as the molecular weight of the degradable crosslinker prior to fragmentation. The degradable crosslinkers are generally storage-stable until activation.

"Storage-stable" degradable crosslinkers and compositions containing degradable crosslinkers are those degradable crosslinkers that remain essentially unfragmented (or crosslinked in the case of compositions containing the degradable crosslinkers) when formed and until activation of the degradable crosslinker (also referred to as "activation of the composition"). The shelf life of the degradable crosslinker is generally long enough to permit the use of the degradable crosslinker and compositions therefrom in the desired application. Preferably, the shelf life of the degradable crosslinker is at least about three days, more preferably at least about one month, even more preferably at least about six months, and most preferably at least about one year. That is, the degradable crosslinkers do not prematurely fragment to substantially affect properties of the composition in which they reside.

Activation of the degradable crosslinker occurs by application of an external energy source (e.g., heat or thermal radiation, as well as ultraviolet radiation) to the degradable crosslinker. Typically, and preferably, the external energy source is a thermal energy source (e.g., heat). Thus, preferred degradable crosslinkers are thermally degradable crosslinkers.

"Thermally degradable crosslinkers" typically fragment according to the invention when subjected to temperatures greater than the polymerization temperature of the polymer in which they are integrated, preferably when subjected to temperatures at least about 20°C greater than the polymerization temperature of the polymer in which they are incorporated. Preferably, the degradable crosslinker fragments at a temperature less than the temperature at which the polymer in which it is integrated degrades (i.e., the temperature at which the polymer becomes useless for its intended purpose, such as by uncontrollably crosslinking or charring). The temperature at which a thermally degradable crosslinker fragments within about two hours or less is referred to as its "activation temperature." When incorporated into polymers, the activation temperature of the crosslinked polymer composition is typically the same as the activation temperature of the thermally degradable crosslinker (or the thermally degradable crosslinker having the lowest activation temperature) incorporated therein. Preferably, the activation temperature is about 80°C to about 200°C, more preferably about 80°C to about 180°C. Compositions containing the degradable crosslinkers are subjected to any suitable temperature to transform the composition from a first chemical state into the desired second chemical state. The length of exposure is adjusted, for example, depending on the proportion of degradable crosslinkers of which fragmentation is desired. In a further embodiment, in addition to using an external energy source, activation of the degradable crosslinkers can occur by catalysis. Catalysis can accelerate the fragmentation rate of the degradable crosslinker and/or lower the activation temperature of the degradable crosslinker. In catalysis, the catalyst does not become incorporated into the degradable crosslinker or fragments therefrom, but merely acts to accelerate the fragmentation of the degradable crosslinker.

In one embodiment where fragmentation of the degradable crosslinker is catalyzed, an acid or base is added to the degradable crosslinker and compositions containing the same. For example, fragmentation of an aldoxime ester into a nitrile and a carboxylic acid can be facilitated by the addition of either an acid or a base. Bases that can be used to initiate acid/base catalyzed fragmentation include, for example, organic bases such as tertiary amines and mixtures thereof. Acids that can be used to initiate this type of fragmentation include, for example, sulfuric acid, p-toluene sulfonic acid, oxalic acid, and mixtures thereof.

Fragmentation of other degradable crosslinkers can also be initiated in this manner or using other appropriate mechanisms as recognizable to those of ordinary skill in the art. The catalyst can be introduced into the composition in either an active or latent state (e.g., a catalyst that does not become active until irradiated with ultraviolet radiation). Generally, the catalyst is added after polymerization of the polymer in which the degradable crosslinker is incorporated. By adding the catalyst after polymerization, one need not be concerned with activation of the degradable crosslinker prior to, or during, formation of the polymer.

For acid-/base-catalyzed fragmentation, any suitable amount of an acid or base is added to the composition in order to accelerate the fragmentation rate of the degradable crosslinker and/or lower the activation temperature of the degradable crosslinker. Then, the mixture is heated to a temperature sufficient to initiate fragmentation of the degradable crosslinker (i.e., the activation temperature). Typically, the activation temperature is lower than those activation temperatures where catalysis is not used, such as those described above with respect to thermal activation of degradable crosslinkers. Any suitable chemistry can be used for the degradable crosslinker so long as the crosslinker contains at least one energetically labile moiety (i.e., a moiety that fragments upon activation by an external energy source). A degradable crosslinker may contain more than one energetically labile moiety. The energetically labile moieties may or may not be the same throughout the degradable crosslinker.

Suitable chemistries for the degradable crosslinker include, for example, those containing esters or carbonates, particularly those containing the following esters or carbonates: aldoxime esters, aldoxime carbonates, amide esters, tertiary alkyl esters, tertiary alkyl carbonates, and mixtures thereof. Particularly preferred esters and carbonates are aldoxime esters, aldoxime carbonates, amide esters, and mixtures thereof. This preferred class of degradable crosslinkers produces fragments that are essentially free of free radicals and ethylenic unsaturation. Thus, crosslinked polymer compositions incorporating these degradable crosslinkers tend to be more stable and less susceptible to degradation after activation.

Mixtures of various degradable crosslinkers can be used in accordance with the present invention. For example, if a multiple-tier degradation is desired, a mixture of different thermally degradable crosslinkers may be useful. That is, some of the crosslinkers may fragment at lower temperatures than other degradable crosslinkers in the composition. Furthermore, a mixture of degradable crosslinkers that fragment when subjected to different external energy sources (e.g., a mixture containing at least one thermally degradable crosslinker and at least one degradable crosslinker that fragments upon exposure to ultraviolet radiation) can be used in compositions of the invention. The crosslinkers can then be degraded in a stepwise manner, if desired, providing intermediate compositions having increasingly lower levels of crosslinking density and, thus, increasingly different chemical states.

Each degradable crosslinker preferably contains at least two free radically polymerizable groups (e.g., ethylenically unsaturated groups) when the degradable crosslinker is used to crosslink polymer compositions. The free radically polymerizable groups are generally copolymerizable with monomers used to prepare the polymers in the composition. Preferably, the free radically polymerizable groups are part of (meth)acrylate moieties in the degradable crosslinker. By using (meth)acrylate degradable crosslinkers, incorporation of the degradable crosslinkers into (meth)acrylate polymers is facilitated. That is, (meth)acrylate degradable crosslinkers have similar polymerization reactivities as (meth)acrylate monomers, with which they may be copolymerized.

The presence of the free radically polymerizable groups facilitates incorporation of the degradable crosslinker into a polymer during polymerization. By incorporating the degradable crosslinker into the polymer, crosslinking of the polymer results. As free radical polymerization is the preferred polymerization method, the degradable crosslinker preferably does not contain any groups that interfere with (i.e., slow the rate of, or prevent any) free radical polymerization.

The degradable crosslinkers are further described below, with reference to certain terms understood by those in the chemical arts as referring to certain hydrocarbon groups. Such hydrocarbon groups, as used herein, may include one or more heteroatoms (e.g., oxygen, nitrogen, sulfur, or halogen atoms), as well as functional groups (e.g., oxime, ester, carbonate, amide, ether, urethane, urea, carbonyl groups, or mixtures thereof). Depending on the chemistry, the functional groups may also be degradable according to the present invention. The term "aliphatic group" means a saturated or unsaturated, linear, branched, or cyclic hydrocarbon group. This term is used to encompass, alkyl, cycloalkyl, alkylene (e.g., thioalkylene and oxyalkylene), alkenylene, alkenyl, cycloalkenyl, aralkylene, aralkenylene, cycloalkylene, and cycloalkenylene groups, for example.

The term "alkyl group" means a saturated, linear or branched, monovalent hydrocarbon group (e.g., a methyl, ethyl, isopropyl, t-butyl, heptyl, dodecyl, octadecyl, amyl, or 2-ethylhexyl group, and the like).

The term "cycloalkyl group" means a saturated, cyclic, monovalent hydrocarbon group.

The term "alkylene group" means a saturated, linear or branched, divalent hydrocarbon group. Examples of particular alkylene groups are thioalkylene and oxyalkylene groups. The term "thioalkylene group" means a saturated, linear or branched, divalent hydrocarbon group with a terminal sulfur atom.

The term "oxyalkylene group" means a saturated, linear or branched, divalent hydrocarbon group with a terminal oxygen atom. The term "alkenylene group" means an unsaturated, linear or branched, divalent hydrocarbon group with one or more carbon-carbon double bonds.

The term "alkenyl group" means an unsaturated, linear or branched, monovalent hydrocarbon group with one or more carbon-carbon double bonds (e.g., a vinyl group).

The term "cycloalkenyl group" means an unsaturated, cyclic, monovalent hydrocarbon group with one or more carbon-carbon double bonds.

The term "aralkylene group" means a saturated, linear or branched, divalent hydrocarbon group containing at least one aromatic group.

The term "aralkenylene group" means an unsaturated, linear or branched, divalent hydrocarbon group containing at least one aromatic group and one or more carbon-carbon double bonds.

The term "cycloalkylene group" means a saturated, linear or branched, divalent hydrocarbon group containing at least one cyclic group.

The term "cycloalkenylene group" means an unsaturated, linear or branched, divalent hydrocarbon group containing at least one saturated or unsaturated cyclic group and at least one carbon-carbon double bond.

The term "aromatic group" means a mononuclear aromatic hydrocarbon group or polynuclear aromatic hydrocarbon group. The term includes both aryl groups and arylene groups.

The term "aryl group" means a monovalent aromatic group. The term "arylene group" means a divalent aromatic group.

Oxime Esters and Oxime Carbonates

Any suitable oxime ester or oxime carbonate can be used so long as it meets the definition of degradable crosslinkers of the invention. Most preferred are degradable crosslinkers containing at least one aldoxime ester moiety, aldoxime carbonate moiety, or mixtures thereof. Aldoxime esters and aldoxime carbonates were found to be more readily thermally degradable as compared to oxime esters and aldoxime carbonates in general.

Aldoxime esters (including, for example, aldoxime esters and aldoxime thioic esters) and aldoxime carbonates (including, for example, aldoxime carbonates, aldoxime xanthates, and aldoxime trithiocarbonates) generally disassociate into a nitrile fragment and an acid fragment and generally conform to the following structure (I):

(I) R¹ is a moiety that contains a free radically polymerizable group (e.g., a (meth)acrylate, (meth)acrylamide, styrene, vinyl ester, or fumarate group). For example, R¹ can comprise an alkylene, thioalkylene, oxyalkylene, alkenylene, alkenyl, cycloalkenyl, aralkylene, cycloalkylene, aralkenylene, cycloalkenylene, or arylene group linked to the carbonyl group (including thiocarbonyl group) of the ester or carbonate. When R¹ comprises, for example, an oxyalkylene or thioalkylene group linked to the carbonyl group (including thiocarbonyl group, if Y is a sulfur atom) through its respective terminal oxygen or sulfur atom, the degradable crosslinker is an oxime carbonate (including thiocarbonates if Y is a sulfur atom). The R¹ moiety may also be substituted with one or more heteroatoms (e.g., O, S, N, halogens, etc.) or functional groups (e.g., oximes, esters, carbonates, amides, ethers, urethanes, ureas, carbonyl groups, or mixtures thereof) in the hydrocarbon chain that are inert to free radical polymerization. The acid corresponding to R¹ (i.e., R^IC(Y)XH) preferably has a pK_a value of greater than one for increased storage stability.

R² is a moiety that may or may not contain a free radically polymerizable group (e.g., a (meth)acrylate, (meth)acrylamide, styrene, vinyl ester, or fumarate group). Typically, R² comprises a hydrocarbon group linked to the carbon atom of the aldoxime by a carbon atom. For example, R² can comprise an alkylene, cycloalkenyl, alkenyl, alkenylene, aralkylene, aralkenylene, cycloalkylene, cycloalkenylene, or arylene group linked to the carbonyl group (including thiocarbonyl group) of the ester or carbonate. The R² moiety may also be substituted with one or more heteroatoms (e.g., O, S, N, halogens, etc.) or functional groups (e.g., oximes, esters, carbonates, amides, ethers, urethanes, ureas, carbonyl groups, or mixtures thereof) in the hydrocarbon chain that are inert to free radical polymerization. X and Y are independently selected from oxygen (O) and sulfur (S), depending on the type of aldoxime ester or aldoxime carbonate.

The following examples are provided based on the assumption that R¹ is linked to the carbonyl (or thiocarbonyl) group of the ester (or carbonate) by a carbon atom. If R¹ terminates in an oxygen or sulfur atom, however, nomenclature would be adjusted as understood by those of ordinary skill in the art. When X is oxygen and Y is oxygen, the aldoxime ester is an aldoxime ester. When X is sulfur and Y is oxygen, the aldoxime ester is an aldoxime thioic S-ester. When X is oxygen and Y is sulfur, the aldoxime ester is an aldoxime thioic O-ester. When X and Y are both sulfur, the aldoxime ester is an aldoxime thioic ester. The subscript "n" is an integer of one or greater. When n is one, R² contains a free radically polymerizable group. When n is greater than one, R² may or may not contain a free radically polymerizable group.

Particularly preferred aldoxime esters and carbonates in the class include those where R¹ is independently selected from the following moieties:

V^CHs

H A H and

and those where R² is independently selected from the following moieties:

where a is 3, 4, 5, or 6,

and

Further preferred embodiments of degradable crosslinkers of the invention are those where n is 2 and R¹ is selected from:

and

andR is:

The aldoxime esters and carbonates can be prepared using any suitable method as recognizable to those of ordinary skill in the art. Aldehydes are a general starting material for preparation of the aldoxime esters and carbonates. For example, difunctional (meth)acrylate (i.e., methacrylate or acrylate) aldoxime esters and carbonates can be prepared from diethers of salicylaldehyde. The aldehyde either contains a free radically polymerizable group or is linked to a free radically polymerizable group through a functional group in the aldehyde. During preparation of the aldoxime esters and carbonates, aldehydes are converted to aldoximes with hydroxylamine.

The aldoximes are generally esterified with an acid chloride containing a free radically polymerizable group to make aldoxime esters. Those of ordinary skill in the art will understand that the reactants and/or reaction sequence can be varied to arrive at the same products.

Alternatively, when making aldoxime carbonates, the aldoxime is reacted with a phosgene instead of esterifying the aldoxime. The reaction product is then further reacted with an alcohol to form an aldoxime carbonate. Alternatively, the aldoxime is reacted with a chloroformate instead of esterifying the aldoxime to arrive at an aldoxime carbonate. Again, those of ordinary skill in the art will understand that the reactants and/or reaction sequence can be varied to arrive at the same products.

Subsequent reaction with multifunctional ethylenically unsaturated compounds, such as (meth)acryloyl chlorides, to impart additional free radically polymerizable groups to the aldoxime ester or carbonate, may then be performed, if desjred. Specific preparation examples are provided in the Examples section, infra.

Amide Esters An amide ester, as used herein, is a compound containing at least one amide group and at least one ester group. Amide esters (including, for example, amide esters, amide thioic esters, and amide dithioic esters) generally cyclize to an imide, eliminating an alcohol or thiol and generally conform to the following structure (II):

(II)

R³ is a moiety that contains a free radically polymerizable group (e.g., a

(meth)acrylate, (meth)acrylamide, styrene, vinyl ester, or fumarate group) and links to the oxygen atom of the ester (if X and Y¹ are both oxygen) or thioic O-ester (if X is oxygen and Y¹ is sulfur), or links to the sulfur atom of the thioic S-ester (if X is sulfur and Y¹ is oxygen) or dithioic ester (if X and Y¹ are both sulfur). For example, R³ can comprise an alkenylene, alkenyl, cycloalkenyl, alkylene, aralkylene, aralkenylene, cycloalkylene, cycloalkenylene, or arylene group linked to the oxygen atom of the ester (if X and Y¹ are both oxygen), thioic O-ester (if X is oxygen and Y¹ is sulfur), thioic S- ester (if X is sulfur and Y¹ is oxygen), or dithioic ester (if X and Y¹ are both sulfur). The R³ moiety may also be substituted with one or more heteroatoms (e.g., O, S, N, halogens, etc.) or functional groups in the hydrocarbon chain (e.g., oximes, esters, carbonates, amides, ethers, urethanes, ureas, carbonyl groups, or mixtures thereof) that are inert to free radical polymerization. R⁴ is a moiety that may or may not contain a free radically polymerizable group

(e.g., a (meth)acrylate, (meth)acrylamide, styrene, vinyl ester, or fumarate group). For example, R⁴ can comprise any hydrocarbon group linked to the nitrogen atom of the amide by a carbon atom. For example, R⁴ can comprise an alkyl, cycloalkyl, alkylene, thioalkylene, oxyalkylene, alkenylene, alkenyl, cycloalkenyl, aralkylene, aralkenylene, cycloalkylene, cycloalkenylene, aryl, or arylene group linked to the nitrogen atom of the amide. The R⁴ moiety may also be substituted with one or more heteroatoms (e.g., O, S, N, halogens, etc.) or functional groups (e.g., oximes, esters, carbonates, amides, ethers, urethanes, ureas, carbonyl groups, or mixtures thereof) in the hydrocarbon chain that are inert to free radical polymerization.

R⁵ is a moiety that links to the amide carbonyl (if Y¹ is oxygen) or amide thiocarbonyl (if Y² is sulfur) with at least one carbon atom and to the ester carbonyl (if Y¹ is oxygen) or ester thiocarbonyl (if Y² is sulfur) with at least one carbon atom. R⁵ may or may not contain a free radically polymerizable group (e.g., a (meth)acrylate,

(meth)acrylamide, styrene, vinyl ester, or fumarate group). However, one, but not both, of R⁴ or R⁵ contains a free radically polymerizable group. Examples of R⁵ include those moieties capable of becoming incorporated into a 5- or 6-membered ring, which ring includes R⁵ and the imide, upon cyclization of the degradable crosslinker to an imide.

As such, typically R⁵ contains two or three atoms in a chain, with the terminal atoms each being carbon. When there are three atoms in the chain, the center atom may be, for example, carbon or a divalent heteroatom (e.g., oxygen or sulfur). The chain may also contain pendent hydrocarbon groups therefrom, such as when R⁵ contains a free radically polymerizable group. One or more atoms in the chain may also be part ofa ring structure. Preferably, R⁵ comprises an alkylene or arylene (e.g., ortho arylene) group.

X, Y¹, and Y² are independently selected from oxygen (O) and sulfur (S), depending on the type of amide ester. That is, each Y constituent (Y¹ and Y²) occurring within an amide ester may be the same or different from other Y constituents. Similarly,

X may be the same as one or both of the Y constituents. Alternatively, X may be different from each of the Y constituents.

When X is oxygen, Y¹ is oxygen, and Y² is oxygen, the amide ester is an amide ester. When X is oxygen, Y¹ is oxygen, and Y² is sulfur, the amide ester is a thioamide ester. When X is oxygen, Y¹ is sulfur, and Y² is oxygen, the amide ester is an amide thioic O-ester. When X is oxygen, Y¹ is sulfur, and Y² is sulfur, the amide ester is a thioamide thioic O-ester.

When X is sulfur, Y¹ is sulfur, and Y² is sulfur, the amide ester is a thioamide dithioic ester. When X is sulfur, Y¹ is oxygen, and Y² is sulfur, the amide ester is a thioamide thioic S-ester. When X is sulfur, Y¹ is sulfur, and Y² is oxygen, the amide ester is an amide dithioic ester. When X is sulfur, Y¹ is oxygen, and Y² is oxygen, the amide ester is an amide thioic S-ester.

Particularly preferred amide esters in the class include those where R³ is:

, R⁴ is:

-[CH₂]₂-CH₃ and R is:

The amide esters can be prepared using any suitable method as recognizable to those of ordinary skill in the art. Anhydrides are a general starting material for preparation of the amide esters. The anhydride is generally combined with a free radically polymerizable alcohol to form an ester acid. The acid moiety is then converted to a more chemically reactive derivative, such as an acid chloride, that can react with a primary amine, such as an amino alcohol or diamine. Upon reaction with the primary amine, an amide ester is formed. Subsequent reaction with multifunctional ethylenically unsaturated compounds, such as (meth)acryloyl chlorides, to impart additional free radically polymerizable groups to the amide ester may then be performed, if desired. Those of ordinary skill in the art will understand that the reactants and/or reaction sequence can be varied to arrive at the same products. Specific preparation examples are provided in the Examples section, infra.

Tertiary Alkyl Esters and Tertiary Alkyl Carbonates

Tertiary alkyl esters (including, for example, tertiary alkyl esters, tertiary alkyl thioic esters, and tertiary alkyl dithioic esters) and tertiary alkyl carbonates (including tertiary alkyl carbonates, tertiary alkyl thioic carbonates, tertiary alkyl xanthates, and tertiary alkyl trithiocarbonates) generally dissociate into fragments comprising an olefin and an acid and generally conform to the following structure (III):

(III) R⁶ is a moiety that contains a free radically polymerizable group (e.g., a (meth)acrylate, (meth)acrylamide, styrene, vinyl ester, or fumarate group). For example, R⁶ can comprise an alkenyl, cycloalkenyl, alkylene, thioalkylene, oxyalkylene, alkenylene, aralkylene, aralkenylene, cycloalkylene, cycloalkenylene, or arylene group linked to the carbonyl group (including thiocarbonyl group, if Y is a sulfur atom) of the ester or carbonate moiety. When R⁶ is, for example, an oxyalkylene or thioalkylene linked to the carbonyl group (including thiocarbonyl group, if Y is a sulfur atom) through its terminal oxygen or sulfur atom, respectively, the degradable crosslinker is a tertiary alkyl carbonate. The R⁶ moiety may also be substituted with one or more heteroatoms (e.g., O, S, N, halogens, etc.) or functional groups (e.g., oximes, esters, carbonates, amides, ethers, urethanes, ureas, carbonyl groups, or mixtures thereof) in the hydrocarbon chain that are inert to free radical polymerization.

R⁷ is a moiety that may or may not contain a free radically polymerizable group (e.g., a (meth)acrylate, (meth)acrylamide, styrene, vinyl ester, or fumarate group). R⁸ is a moiety that may or may not contain a free radically polymerizable group (e.g., a (meth)acrylate, (meth)acrylamide, styrene, vinyl ester, or fumarate group). R⁹ is a moiety that may or may not contain a free radically polymerizable group (e.g., a (meth)acrylate, (meth)acrylamide, styrene, vinyl ester, or fumarate group). One of R⁷, R⁸, and R⁹ contains a free radically polymerizable group. Furthermore, at least one of R⁷, R⁸, and R⁹ contains a hydrogen atom attached to a saturated carbon atom adjacent to the tertiary center. The moiety of R⁷, R⁸, and R⁹ that contains a free radically polymerizable group may or may not be the same moiety that contains a hydrogen atom attached to a saturated carbon atom that is adjacent to the tertiary center.

R⁷, R⁸, and R⁹ are independently selected from moieties that comprise an alkyl, cycloalkyl, alkylene, alkenylene, alkenyl, cycloalkenyl, aralkylene, aralkenylene, cycloalkylene, cycloalkenylene, aryl, or arylene group attached to the tertiary center of the tertiary alkyl ester or carbonate. Each of these moieties may also be substituted with one or more heteroatoms (e.g., O, S, N, halogens, etc.) or contain functional groups in the hydrocarbon chain (e.g., oximes, esters, carbonates, amides, ethers, urethanes, ureas, carbonyl groups, or mixtures thereof) that are inert to free radical polymerization.

X and Y are independently selected from oxygen (O) and sulfur (S), depending on the type of tertiary alkyl ester or carbonate.

The following examples are provided based on the assumption that R⁶ is linked to the carbonyl (or thiocarbonyl) group of the ester (or carbonate) by a carbon atom. If R⁶ terminates in an oxygen or sulfur atom, however, nomenclature would be adjusted as understood by those of ordinary skill in the art. When X and Y are both oxygen, the tertiary alkyl ester is a tertiary carboxylic ester. The tertiary carboxylic esters also include aromatic tertiary carboxylic esters, such as tertiary benzoic esters, which dissociate into two fragments, an olefin and a benzoic acid. When X is sulfur and Y is oxygen, the tertiary alkyl ester is a tertiary thioic S-ester. When X is oxygen and Y is sulfur, the tertiary alkyl ester is a tertiary alkyl thioic O-ester. When X and Y are both sulfur, the tertiary alkyl ester is a tertiary alkyl dithioic ester.

Particularly preferred tertiary alkyl esters and carbonates in the class include those where X and Y are both oxygen, R⁸ and R⁹ are both methyl groups (CH₃), R⁶ is:

and R⁷ is:

The tertiary alkyl esters and carbonates can be prepared using any suitable method as recognizable to those of ordinary skill in the art. For example, a tertiary alcohol and acid chloride can be reacted in the presence of a base to form a tertiary alkyl ester. Those of ordinary skill in the art will understand that the reactants and/or reaction sequence can be varied to arrive at the same products.

When making tertiary alkyl carbonates, the tertiary alkyl ester is further reacted with an alcohol. Alternatively, the tertiary alcohol is reacted with a phosgene instead of the acid chloride to make a tertiary alkyl carbonate. The reaction product is then further reacted with an alcohol to form the tertiary alkyl carbonate. Alternatively, the tertiary alcohol is reacted with a chloroformate instead of the acid chloride to arrive at a tertiary alkyl carbonate. Those of ordinary skill in the art will understand that the reactants and/or reaction sequence can be varied to arrive at the same products. Subsequent reaction with multifunctional ethylenically unsaturated compounds, such as (meth) acryloyl chlorides, to impart additional free radically polymerizable groups to the tertiary alkyl ester or carbonate, may then be performed, if desired.

Specific preparation examples are provided in the Examples section, infra.

Preparation of Crosslinked Polymer Compositions Comprising the Degradable Crosslinker

The degradable crosslinkers can be used in a wide variety of polymers. Depending on the amounts and types of components in the crosslinked polymer compositions, the crosslinked polymer compositions can be tacky to the touch or essentially non-tacky to the touch at room temperature.

According to the invention, crosslinked polymer compositions of the invention maintain at least some degree of crosslinking after activation. The level of crosslinking maintained varies widely according to the intended application for the compositions. The crosslinking facilitates compositions that are easy to handle, store, and apply to a substrate, but yet have adequate cohesive strength after activation and application to a substrate.

The crosslinking maintained in the composition after activation can be imparted by one or more of several methods. For example, the crosslinking may be provided by degradable crosslinkers of the invention that have not been activated (e.g., when a mixture of different degradable crosslinkers is used or when a crosslinked polymer composition has not been activated for a sufficient amount of time to fragment all of a certain type degradable crosslinker). Furthermore, the crosslinking may be provided by conventional crosslinking within the polymer composition. Conventional crosslinking includes, for example, physical crosslinking, ionic crosslinking, chemical crosslinking, and mixtures thereof.

In one embodiment, the crosslinking maintained after activation of the composition is provided by conventionally crosslinked polymers. In this embodiment, a mixture of degradable crosslinking and conventional crosslinking is used in the crosslinked polymer compositions. Conventional crosslinking, which includes all crosslinking formed by crosslinks that do not meet the requirements of degradable crosslinks of the present invention, may or may not contain energetically labile moieties. Compositions containing the conventionally crosslinked polymers are subjected to an external energy source to activate the degradable crosslinkers, causing fragmentation of all, or a portion, of the degradable crosslinkers. In any event, the remaining composition still retains some degree of crosslinking, which is imparted by the conventional crosslinking.

According to one aspect of this embodiment, thermally reversibly crosslinked polymers (e.g., polymers that are ionically or physically crosslinked, such as those described in the Background of the Invention) are used in conjunction with degradable crosslinkers of the invention. When the conventionally crosslinked polymer is ionically crosslinked, the composition typically contains a polymer that interacts ionically with the conventionally crosslinked polymer, such as described in PCT Publication Number WO 99/42,536 (Stark et al). This aspect of the invention provides crosslinked polymer compositions that are particularly suitable for applying the compositions to a substrate by hot-melt processing due to the thermally reversible nature of the conventional crosslinking.

Preferably, for increased cohesive strength, the conventionally crosslinked polymers are crosslinked through chemical bonds (e.g., covalent bonds). Chemical bonds typically have a higher bond strength than those bonds that are thermally reversible. The higher bond strength contributes to increased cohesive strength of the composition after activation. To impart the chemical bonds, a chemical crosslinking agent is typically incorporated into the composition.

Chemical crosslinking agents are selected according to the polymerization and application method used. Preferred crosslinking agents for polymer compositions prepared via photopolymerized, solventless, bulk methods include multifunctional acrylates, such as 1,6-hexanediol diacrylate and those disclosed in U.S. Patent Number 4,379,201 (e.g., trimethylolpropane triacrylate; pentaerythritol tetracrylate; 1,2-ethylene glycol diacrylate; and 1,12-dodecanediol diacrylate). Other useful chemical crosslinking agents include substituted triazines, such as those disclosed in U.S. Patent Numbers 4,329,384 and 4,330,590 (e.g., 2,4-bis(trichloromethyl)-6-p-methoxystyrene-S-triazine), and chromophore halomethyl-S-triazines. Additional useful chemical crosslinking agents for this type of polymerization method include mono-ethylenically unsaturated aromatic ketones, particularly 4-acryloxybenzophenone described in U.S. Patent Number 4,737,559, and multifunctional crosslinking agents, such as l,5-bis(4- benzoylbenzoxy)pentane described in PCT Publication Number WO 97/07,161 and 1,4- butanedi[4-benzoylphenoxy]acetate described in U.S. Patent Number 5,407,971. Chemical crosslinking agents useful in solution-, emulsion- and suspension- polymerized polymer compositions are those that are free radically copolymerizable and/or that effect crosslinking through exposure to radiation, moisture, or heat following polymerization. Typically, to maintain processability and coatability of the composition, crosslinking occurs following polymerization and application of the composition. Photoactivated chemical crosslinking agents include the above-mentioned photoactive substituted triazines, multifunctional crosslinking agents, and mono-ethylenically unsaturated aromatic ketones. Hydrolyzable, copolymerizable crosslinking agents include mono-ethylenically unsaturated mono-, di- and tri-alkoxy silane compounds (e.g., methacryloxypropyl trimethoxysilane, vinyldimethylethoxysilane, vinylmethyldiethoxy silane, vinyltriethoxysilane, vinyltrimethoxysilane, vinyltriphenoxysilane, and the like). Heat-activated, copolymerizable crosslinking agents (e.g., N-methylol acrylamide and acrylamido glycolic acid) are also useful with these polymerization methods.

Generally, the degradable crosslinker is copolymerized with the monomer component (i.e., one or more monomers that are copolymerizable with the degradable crosslinker) and other conventionally crosslinked polymer components (if used, and if copolymerizable with the monomer component) used to prepare the polymers. The components are copolymerized according to any suitable method, as recognizable to those of ordinary skill in the art. Any suitable monomer, or combination thereof, may be used. Preferably, monomers of the present invention are ethylenically unsaturated monomers, preferably monoethylenically unsaturated monomers, such that they can be copolymerized with the degradable crosslinkers. Preferably, the monomers are selected from (meth)acrylates, (meth)acrylic acids, vinyl esters, (meth)acrylamides, and combinations thereof. However, when the crosslinking maintained after activation of the crosslinked polymer composition is at least partially derived from conventional crosslinking, the monomers are generally selected, as recognizable to those of ordinary skill in the art, to provide conventionally crosslinked polymers.

Particularly preferred monomers are (meth)acrylate monomers, including monoethylenically unsaturated monomers, such as (meth)acrylate esters of non-tertiary alkyl alcohols, the alkyl groups of which comprise from about 1 to about 18 carbon atoms, preferably about 4 to about 12 carbon atoms, and mixtures thereof. Examples of suitable (meth)acrylate monomers useful in the present invention include, but are not limited to, methylacrylate, ethylacrylate, methyl methacrylate, ethyl methacrylate, n-butyl acrylate, decyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, hexyl acrylate, isoamyl acrylate, isodecyl acrylate, isodecyl methacrylate, isononyl acrylate, isooctyl acrylate, lauryl acrylate, 2-methyl butyl acrylate, 4-methyl-2-pentyl acrylate, ethoxyethoxyethyl aciylate, isobornyl acrylate, isobornyl methacrylate, 4-t- butylcyclohexyl methacrylate, cyclohexyl methacrylate, phenyl acrylate, phenylmethacrylate, 2-naphthyl acrylate, 2-naphthyl methacrylate, and mixtures thereof. Particularly preferred are 2-ethylhexyl acrylate, isooctyl acrylate, lauryl acrylate, n-butyl acrylate, ethoxyethoxyethyl acrylate, and mixtures thereof.

Examples of other ethylenically unsaturated monomers include, but are not limited to, vinyl esters (e.g., vinyl acetate, vinyl pivalate, and vinyl neononanoate); vinyl amides; N-vinyl lactams (e.g., N-vinyl pyrrolidone and N-vinyl caprolactam); (meth)acrylamides (e.g., N,N-dimethyl acrylamide, N,N-dimethyl methacrylamide, N,N- diethyl acrylamide, and N,N-diethyl methacrylamide); (meth)acrylonitrile; maleic anhydride; styrene and substituted styrene derivatives (e.g., α-methyl styrene); and mixtures thereof.

Optional acidic monomers may also be used. Useful acidic monomers include, but are not limited to, those selected from ethylenically unsaturated carboxylic acids, ethylenically unsaturated sulfonic acids, ethylenically unsaturated phosphonic acids, and mixtures thereof. Examples of such compounds include those selected from acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, maleic acid, β-carboxyethyl acrylate, 2-sulfoethyl methacrylate, styrene sulfonic acid, 2-acrylamido- 2-methylpropane sulfonic acid, vinyl phosphonic acid, and the like, and mixtures thereof. The following polymerization techniques, which are described infra, can be used for polymerizing the monomer component, degradable crosslinker, and other conventionally crosslinked polymer components (if applicable). Those of ordinary skill in the art will understand that not all of these techniques can be used for preparing each crosslinked polymer composition of the invention. For example, when conventional crosslinking is used to impart crosslinking to the composition after activation, the polymer derived from the degradable crosslinker is also conventionally crosslinked. The following polymerization techniques include, but are not limited to: the conventional techniques of solvent polymerization, dispersion polymerization, emulsion polymerization, suspension polymerization, solventless bulk polymerization, and radiation polymerization, including processes using ultraviolet light, electron beam, and gamma radiation. The starting materials may comprise any suitable additives, such as a polymerization initiator, especially a thermal initiator or a photoinitiator, ofa type and in an amount effective to polymerize the components. When polymerized using emulsion, suspension, or dispersion polymerization, the resulting crosslinked polymer compositions are advantageously capable of being readily made into storage-stable, free-flowing polymer compositions. "Free-flowing" polymer compositions are those compositions containing a multitude of solid state particulates that do not substantially agglomerate (i.e., the particulates are capable of being moved by gravitational forces alone) at temperatures below the activation temperature of the degradable crosslinkers. Preferably, the free-flowing polymer compositions do not substantially agglomerate at the storage temperature and pressure.

The free-flowing polymer compositions are especially useful in certain feeding, blending, and delivery methods. For example, free-flowing polymer compositions facilitate feeding hot-melt coating compositions. Conventional feeding equipment, such as hopper feeders and powder conveyers, can be used with free-flowing polymer compositions of the invention. Furthermore, shipping and handling of free-flowing polymer compositions is typically less expensive and more convenient than shipping and handling associated with bulk polymer compositions. Free-flowing polymer compositions can also be easily dry-blended, without the need for solvents or melt blending. The free-flowing polymer compositions can be prepared using any suitable method. In one embodiment, the particulates are filtered to a dryness of about 75% to about 95% solids using any suitable filtering technique, such as using a NUTSCHE filter (commercially available from Northland Stainless, Inc.; Tomahawk, Wisconsin). The filtered particulates are then blended with silica (such as that commercially available from Degussa Corporation; Ridgefield Park, New Jersey, under the trade designation, AEROSIL R-972), using any suitable blending technique, such as using a ribbon blender. The coated particulates are then dried using any suitable technique. For example, the coated particulates can be air-dried in an oven. The coated particulates can also be air-dried in a fluid bed dryer, such as those commercially available from Glatt Air Techniques Inc.; Ramsey, New Jersey.

Solvent Polymerization Method

Solvent polymerization is well known in the art and described in various sources such as U.S. Patent Numbers Re 24,906 (Ulrich) and 4,554,324 (Husman et al).

Briefly, the procedure is carried out by adding the monomers, degradable crosslinker, other conventionally crosslinked polymer components (if applicable), a suitable solvent such as ethyl acetate, and an optional chain transfer agent to a reaction vessel. Then, a free radical initiator is added to the mixture. Many suitable free radical initiators are commercially available, such as those available from E.I. duPont de Nemours & Company; Wilmington, DE under the VAZO trade designation. Specific examples include VAZO 64 and VAZO 52, which are described below in the Table of Abbreviations. Suitable initiators also include hydroperoxides, such as tert-butyl hydroperoxide, and peroxides, such as benzoyl peroxide and cyclohexane peroxide. After purging with nitrogen, the reaction vessel is maintained at an elevated temperature, typically in the range of about 40°C to about 100°C, until the reaction is complete. Typically, the reaction takes about one to about twenty hours to complete, depending on the batch size and reaction temperature. Dispersion Polymerization Method

Dispersion polymerization typically is carried out as single-phase reaction ofa mixture consisting ofa solution of monomers, degradable crosslinker, other conventionally crosslinked components (if applicable), initiator, and steric stabilizer in a solvent that does not dissolve the resulting polymer. The initial stage of the polymerization is a typical solution polymerization and the polymer chains grow in size until they become insoluble in the reaction mixture. As the polymer starts to precipitate out of the mixture, the steric stabilizer adsorbs on the surface of the polymer, preventing coalescence of the polymer particles as they form. The reaction will continue until all of the monomer is consumed, resulting in the formation of crosslinked polymer particles that are insoluble in the reaction medium in which they are formed.

Emulsion Polymerization Method Emulsion polymerization is also described in U.S. Patent Number Re 24,906

(Ulrich). For example, the monomers are mixed with the degradable crosslinker, other conventionally crosslinked polymer components (if applicable), distilled water, an emulsifying agent, and suitable initiators in a reaction vessel. Then, the reaction vessel is purged with nitrogen and heated, with agitation, to a temperature in the range of about 25°C to about 80°C, until the reaction is complete.

For ease of handling and/or to employ emulsion-polymerized polymers as powders, the emulsion-polymerized polymer is typically spray-dried using conventional drying techniques. To prepare such powders, the emulsion-polymerized base copolymer can be fed to a nozzle that sprays the emulsion into a stream of hot gas. The aqueous emulsion medium evaporates first, forming a small droplet of concentrated polymer. As aqueous medium removal nears completion, the droplet is transformed into a powder particle or clusters thereof. See, for example, U.S. Patent Number 3,772,262 (Clementi) and K. Masters, "Spray Drying," 2nd ed., Wiley: 1976.

Suspension Polymerization Method Crosslinked polymer compositions can also be prepared in bead form using suspension polymerization methods. Such suspension methods are described, for example, in European Patent Application Number 0 853 092 (Minnesota Mining and Manufacturing Co.). This suspension process involves mixing the monomers, degradable crosslinker, other conventionally crosslinked polymer components (if applicable), free radical initiator, chain transfer agent, and other desired additives to form a premix. A suspension stabilizer, such as dextrin or a dextrin derivative, is combined with water and then with the premix to form an oil-in-water suspension. The resulting suspension typically comprises from about 10 to about 50 weight percent premix and from about 90 to about 50 weight percent water phase.

Polymerization is then initiated, typically thermally, and carried out for about two to about sixteen hours at a temperature of about 40°C to about 90°C. The crosslinked polymer beads can be isolated by a variety of means and generally have a diameter of one to 5,000 micrometers. Similar to the emulsion process, smaller suspension-polymerized particles may also be capable of being spray-dried to recover the polymer. Larger particles may be capable of being isolated, for example, by simple filtration and air-drying.

In certain embodiments, after isolating from suspension and drying, the suspension beads can show some blocking resulting from tackiness of the suspension beads. Due to this blocking, the suspension beads can partially, or even completely, lose desired free-flowing characteristics. To prevent this loss of flow, a dusting agent, such as hydrophobic silica (e.g., AEROSE R-972, commercially available from Degussa Corporation; Ridgefield Park, NJ), can be added immediately after isolating the beads. When treated in this manner, suspension beads can also be used in processing methods and delivery techniques that advantageously exploit the powder-like nature of these materials.

Solventless Polymerization Method

Solventless polymerization methods, such as the methods described for polymerizing packaged polymerizable compositions in U. S . Patent Number 5,804,610 (Hamer et al), may also be utilized to prepare the crosslinked polymer compositions. In one embodiment, from about 0.1 to about 500 grams ofa polymerizable mixture comprising monomers, degradable crosslinker, other conventionally crosslinked polymer components (if applicable), initiator, and optional chain transfer agent is completely surrounded by a packaging material. In another preferred embodiment, the polymerizable mixture is disposed on the surface ofa sheet, or between a pair of two substantially parallel sheets, of the packaging material.

The packaging material is made ofa material that, when combined with the resulting polymer, does not substantially adversely affect the desired polymer characteristics. The packaging material should be appropriate for the polymerization method used. For example, with photopolymerization, it is necessary to use a film material that is sufficiently transparent to ultraviolet radiation at the wavelengths necessary to effect polymerization. Polymerization can be effected by exposure to ultraviolet (UV) radiation as described in U.S. Patent Number 4,181,752 (Martens et al). In a preferred embodiment, the polymerization is carried out with UV black lights having over 60 percent, and preferably over 75 percent, of their emission spectra between about 280 to about 400 nanometers (nm), with an intensity between about 0.1 to about 25 mW/cm^.

In another solventless polymerization method, crosslinked polymer compositions of the present invention are prepared by photoinitiated polymerization methods according to the technique described, for example, in U. S . Patent Number 4, 181 ,752 (Martens et al). For example, the monomers and photoinitiator can be mixed together in the absence of solvent and partially polymerized to make a coatable syrup. Coatable syrups generally have a viscosity in the range of from about 500 centiPoise to about 50,000 centiPoise. In yet another way, the monomers can be mixed with a thixotropic agent, such as fumed hydrophilic silica, to achieve a thickened monomer mixture having a coatable thickness. The degradable crosslinker, other conventionally crosslinked components (if applicable), and any other ingredients are then added to the prepolymerized syrup or thickened monomer mixture. Alternatively, these other ingredients (preferably, with the exception of the degradable crosslinker and other conventionally crosslinked polymer components (if applicable)) can be mixed with the monomers prior to partial polymerization or thickening of the monomer mixture. The resulting polymerizable composition is coated onto a substrate (which may be transparent to UV radiation) and polymerized in an inert atmosphere (i.e., an oxygen- free, such as nitrogen, atmosphere) by exposure to UV radiation. A sufficiently inert atmosphere can also be achieved by covering a layer of the polymerizable coating with a plastic film that is substantially transparent to UV radiation and irradiating through that film, as described in U.S. Patent Number 4,181,752 (Martens et al), using a UV light source. Alternatively, instead of covering the polymerizable coating, an oxidizable tin compound may be added to the polymerizable composition to increase the tolerance of the composition to oxygen, as described in U.S. Patent Number 4,303,485 (Levens). The UV light source preferably has 90% of the emissions between about 280 and about 400 nanometers (more preferably between about 300 and about 400 nanometers), with a maximum emission at about 350 nanometers.

Additives A wide variety of conventional additives can be mixed with the crosslinked polymer composition. In fact, when the crosslinked polymer composition is essentially non-tacky at room temperature, blending of additives with the crosslinked polymer composition is often easier. The components (i.e., crosslinked polymer composition and additives) are even able to be dry-blended, as opposed to the more costly and complicated melt-blending techniques.

Any suitable additive can be blended with the crosslinked polymer composition. For certain applications, expandable microspheres, glass bubbles, and chemical blowing agents may be useful additives. Those of ordinary skill in the art will recognize a wide variety of additives that may be useful when preparing crosslinked polymer compositions of the invention for specific applications.

For example, tackifiers can be added to the crosslinked polymer composition to increase the composition's tack. Plasticizers can also be added to the crosslinked polymer composition. For example, when the polymer is derived from a high proportion of relatively high glass transition temperature (Tg) monomers, addition ofa plasticizer can increase the tack of the composition.

If the crosslinked polymer composition is tacky to the touch at ambient temperature and pressure, it may be desirable to use a coating agent, such as the shell materials described in U.S. Patent Number 5,322,731 (Callahan, Jr. et al), or a dusting agent, such as hydrophobic silica or the like, in order to facilitate easier handling of the crosslinked polymer compositions prior to their application to a substrate. Preferably, when using a coating agent or dusting agent for this purpose, the amount of the coating/dusting agent used is an effective amount to render the composition non-tacky to the touch at ambient temperature and pressure.

Application/Processing of the Crosslinked Polymer Compositions The crosslinked polymer compositions can be applied to a wide variety of substrates to form a coating thereon. The substrate can take any suitable form, such as, for example, a sheet, a fiber, or a shaped article. The coating thickness will vary depending upon various factors such as, for example, the particular application, the crosslinked polymer composition formulation, and the nature of the substrate (e.g., its absorbency, porosity, surface roughness, amount of creping, chemical composition, etc.). For example, a porous or rough substrate will typically require a thicker coating than less porous or smoother substrates. As another example, pressure-sensitive adhesive coatings typically have a thickness of about 25 microns to about 250 microns. The method of processing the composition, or applying it to a substrate, will vary depending on the desired use of the composition and the types of conventional crosslinking used in the composition, if any. Those of ordinary skill in the art will understand that not all of these techniques can be used for applying/activating each crosslinked polymer composition of the invention. For example, when conventional crosslinking is used to impart crosslinking to the composition after activation, the polymer derived from the degradable crosslinker is generally also conventionally crosslinked. Thus, when the conventional crosslinking is chemical crosslinking, it is generally preferred to use methods other than hot-melt coating or solvent coating for applying the composition to a substrate.

In one embodiment, activation of the composition occurs prior to applying the composition to a substrate. In another embodiment, activation of the composition occurs after applying the composition to a substrate. In another embodiment, the composition is activated while it is being applied to a substrate.

To activate the composition (fragmenting at least a portion of the degradable crosslinker, also referred to as "activating the degradable crosslinker" or a similar phrase), an external energy source is applied to at least a portion of the composition. The energy source used to activate the composition can be diffuse, so as to activate broad areas of the composition, or focused, so as to activate discrete, predetermined portions of the composition. Any suitable energy source can be used, such as a thermal source (e.g., oven, infrared radiation lamp or laser, slot burner, or microwave source (when used in conjunction with a receptor for microwave radiation)).

In one embodiment, the external energy source is applied to a discrete portion of the composition, thereby activating the degradable crosslinker in only a portion of the composition. Resulting compositions may, thus, have varying chemical states throughout, depending on whether the degradable crosslinker was activated in that particular portion. In another embodiment, the external energy source is applied to substantially all of the composition, thereby activating the degradable crosslinker in substantially all of the composition. Resulting compositions, thus, having substantially identical chemical properties throughout.

Activation Followed by Application

In certain embodiments, the crosslinked polymer composition is first activated (to fragment at least a portion of the degradable crosslinker) and then applied to a substrate in separate processing steps. That is, the crosslinked polymer composition is first transformed to a composition having reduced crosslink density by fragmenting at least a portion of the degradable crosslinkers incorporated therein. The composition is then applied to a substrate using any suitable method. For example, organic solvent coating and hot-melt coating techniques, which are described infra, may be used.

Any conventional coating technique can be used to apply the compositions to target substrates from organic solvent solutions. Useful coating techniques include brush, roll, spray, spread, wire, gravure, transfer roll, air knife, or doctor blade coating. Hot-melting coating techniques are also useful. For example, the compositions may be introduced into a vessel to melt and activate the composition. The composition is subjected to a temperature sufficient to melt and activate the composition and thoroughly mix any additional components, after which the composition is coated onto a substrate. This step can be done conveniently in a heated extruder, bulk tank melter, melt-on-demand equipment, or hand-held hot-melt adhesive gun.

The hot-melt compositions can be coated onto a substrate using any suitable method. For example, the compositions can be delivered out of a film die and coated by contacting the drawn hot-melt composition with a moving web (e.g., plastic web) or other suitable substrate. Using this method, the hot-melt material is applied to the moving preformed web using a die having flexible die lips, such as a rotary rod die. A related coating method involves extruding the composition and a coextruded backing material from a film die and cooling the layered product to form a multi-layered construction, such as an adhesive tape. After forming by any of these continuous methods, the resulting films or constructions can be solidified by quenching using both direct methods (e.g., chilled rolls or water baths) and indirect methods (e.g., air or gas impingement).

Activation With Application In other embodiments, the crosslinked polymer composition is activated (to fragment at least a portion of the degradable crosslinker) while applying the composition to a substrate in essentially a single processing step.

For example, the composition may be activated and applied using a reactive flame spray technique. The flame spray technique is a process whereby the deposition of a largely molten material is enabled by using a highly directional gas stream. Flame spray methods include flame spraying and reactive flame spraying. Flame spraying involves the introduction of a material to be deposited into a flame that is typically generated external to the gas introduction apparatus. The composition is activated while applying it to a substrate by using reactive flame spraying, wherein the composition, which is typically in the form ofa powder, is at least partially activated during spraying. In flame spray techniques, the kinetic energy of the feed gases typically transports the molten material in a transport gas stream. However, an additional transport gas stream may be utilized. The thermal energy in a flame spray system is determined by the flow rates and composition of fuel and oxidizer gases that are used. Flames are typically created from acetylene and oxygen in order to produce a relatively hot flame. Lower temperature systems, for the deposition of thermally sensitive materials, can be provided by using propane/air flames.

All material introduction methods typically have the same ultimate goal - to produce small, potentially liquified particles that collide with the receiving surface. Commercial flame spray systems are available that use either particle or wire feeds.

Other systems have been described that utilize liquid feeds (K. A. Gross, et al, Journal of Thermal Spray Technology. 8, 583-589 (1999). For example, several flame deposition systems have been reported that describe the spraying of a liquid in, or near, a flame to achieve deposition. Material to be deposited in powder form is typically introduced to a depositing flame in a pressurized transport gas stream. This transport gas stream is typically either the oxidizer for the flame or a designated transport gas stream. Powders can be gravity fed or mechanically fed into the transport gas stream. Alternatively, powders can be drawn into a transport gas stream from a contained, fluidized bed due to the venturi effect of the transport gas stream. Depositing material typically reaches only a fraction of the flame temperature during the flame residence time. Control of this residence time is a key process variable in flame spray deposition. The precise residence time needed for a given system will be determined by the characteristics of the flame spray system and the depositing material. This residence time can be modified, for example, by changing the flow rate ofa designated transport gas stream or by changing the precise point of introduction of the depositing material into the flame.

Depositing material may also be modified by further exposure to the flame. Likewise, a surface to be coated may also be modified, such as by heating with a flame or other thermal source prior to deposition, in order to allow the depositing material to remain in a softened, or fluid, state for a longer time on the receiving surface. Flames generated in typical flame spray systems are viewed exclusively as sources of thermal energy to provide a phase change of the depositing material, such as from a solid particle to a molten droplet. Accompanying this phase change is a change in the rheological properties of the material. Incidental oxidation of the depositing material may also occur in typical flame spray processes. However, reactive flame spraying utilizes the thermal energy of the flame to fragment at least a portion of the degradable crosslinker, which allows the particles to flow more readily when they impinge the substrate and also increases the pressure-sensitive adhesive tack of the applied composition. This fragmentation is a result ofa chemical reaction that occurred due to the thermal energy. That is, a flame spray process that specifically utilizes the flame to fundamentally alter the composition of the injected material is considered reactive flame spraying.

Application Followed by Activation In yet other embodiments, the crosslinked polymer composition is first applied to a substrate and then activated (to fragment at least a portion of the degradable crosslinker). The composition can be applied to a substrate using any suitable method. For example, aqueous solution coating, aqueous dispersion coating, solventless coating (followed by polymerization), thermal deposition, and powder coating can be used. Any conventional coating technique can be used to apply the compositions to target substrates from aqueous solutions, including emulsions and dispersions. Useful coating techniques include brush, roll, spray, spread, wire, gravure, transfer roll, air knife, curtain, slurry, or doctor blade coating.

As another example, the composition can be applied to a substrate using the solventless coating and polymerization method described in U.S. Patent Number 4,181,752 (Martens et al), supra. In this embodiment, the degradable crosslinker is added to a partially polymerized, or thickened, monomer mixture. The resulting composition is then coated onto a substrate and polymerized. After the composition is polymerized, it is activated. Yet another example of this embodiment involves thermal deposition of the crosslinked polymer composition. Particles of the composition are coated on a substrate and then heated using a suitable thermal source, such as those described in PCT Publication No. WO 99/03,642 (Minnesota Mining and Manufacturing Co.). Optionally, the substrate on which the heated particles are coated is softened to facilitate adhesion of the particles to the substrate. If softened, the substrate is generally softened by thermal energy or thermal radiation. For example, the substrate can be softened using heat from the same thermal source that is used for coating and heating particles of the composition.

A still further example of Application Followed by Activation involves conventional, as opposed to reactive, flame spraying of the crosslinked polymer composition. The conventional flame spray technique was described above with respect to "Activation with Application."

One of the advantages of using crosslinked polymer compositions of the present invention is the ability to deliver the crosslinked polymer composition using powder coating techniques. In addition to the spray-dried, emulsion-polymerized compositions and the free-flowing, suspension- or dispersion-polymerized particles described above, the crosslinked polymer composition in powdered form can also be prepared using mechanical techniques such as cryo-grinding or hammer milling.

The capability of delivering the crosslinked polymer compositions as powdered coatings offers several advantages and alternatives over crosslinked polymer compositions coated using conventional techniques. For example, when the crosslinked polymer composition is in the form of particulates, the crosslinked particulates can be coated on a substrate in the Z-direction (i.e., the direction perpendicular to the substrate) using powder coating techniques, described infra, and then activated to fragment at least a portion of the degradable crosslinkers. Upon fragmentation, the particulates fuse together to form a continuous coating on the substrate. By applying the crosslinked polymer composition to a substrate in this manner, the resulting coating is less oriented, and thus has reduced stress, as compared to coatings applied by conventional hot-melt coating methods, such as die-extrusion. These process-related effects can compromise the performance of the resulting coatings. Hot-melt coating also has its limitations when three-dimensional, or rough, surface coverage is desired. Furthermore, hot-melt coating of wide sheets, or substrates, requires bulky and expensive custom coating dies that are not readily available. By using powder coating techniques to coat all or a portion of such substrate surfaces with crosslinked polymer compositions of the present invention, all of these disadvantages associated with hot-melt coated compositions can be avoided. Yet, another advantage of powder format of the crosslinked polymer composition is the ease of blending the crosslinked polymer composition with other powdered components. The other powdered components may be other crosslinked polymer compositions of the current invention with different chemistries or crosslinking densities. Alternatively, the other powdered components can be other organic (e.g., polymeric materials) or inorganic materials.

Useful techniques for powder coating of the crosslinked polymer compositions include fluidized-bed coating and electrostatic spray processes. In the fluidized-bed coating process, the crosslinked polymer composition is placed in a container having a porous plate as its base. Air is passed through the plate, causing the composition to expand in volume and fluidize. In this state, the composition possesses some of the characteristics ofa fluid. A substrate is then heated in an oven to a temperature above the melting point of the crosslinked polymer composition. The substrate is dipped into the fluidized bed where the fluidized composition melts on the substrate to form a coating. Depending on the rheology and crosslink density of the crosslinked polymer composition, activation will either fuse the coating into a smooth coating or all or part of the particulate nature of the crosslinked polymer composition can be maintained. Alternatively, a cold substrate can be run over a bed of fluidized particles that are tribo- charged and, thus, cling to the substrate. The coated substrate can then be passed through a heated zone, or nip, to fuse the coating. In the electrostatic spray process, the powdered material is dispersed in an air stream and passed through a corona discharge field where the particles acquire an electrostatic charge. The charged particles are attracted to and deposited on the grounded substrate. The substrate, usually electrostatically coated at room temperature, is then placed in an oven where the powder melts and forms a coating. See for example, Kirk-Othmer Encyclopedia of Chemical Technology. 4^th Edition, Wiley: 1993, Vol. 6, pages 635-636. In all embodiments of application/processing of the crosslinked polymer composition, further processing steps may be performed after application and activation of the crosslinked polymer composition. For example, if applicable, conventional crosslinking in the composition may need to be induced, for example, by radiating (e.g., using electron beam or ultraviolet radiation) the composition. A wide variety of other processing steps may also be performed on the resulting polymer compositions.

Examples These examples are merely for illustrative purposes only and are not meant to be limiting on the scope of the appended claims. All parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight unless indicated otherwise. All reagents were obtained from Aldrich Chemical Company; Milwaukee, WI, unless otherwise noted. All solvents were obtained from VWR Scientific; West Chester, PA, unless otherwise noted.

Table of Abbreviations

Test Methods

Gel Test

A polymer was prepared by incorporating the desired amount ofa degradable crosslinker into a monomer mixture containing 90 parts of IOA and 10 parts of AA. First, a 90: 10 mixture of IOA: AA was prepared and placed in a container with 0.04 part of ESACUR KB-1 per 100 parts IOA:AA. The container was purged with nitrogen and closed. As the nitrogen purging continued, the mixture was irradiated with an ultraviolet (UV) black light (40 Watt UV SYLVANIA BLACKLIGHT, commercially available from Osram Sylvania; Danvers, MA) to form a partially polymerized syrup having a coatable Brookfield viscosity estimated to be about 3,000 centiPoise. An additional 0.1 part ESACUR KB-1 and the desired number of parts of the degradable crosslinker were added to the syrup. After mixing, the composition was knife-coated to a thickness of about 50 micrometers between two transparent, siliconized polyester film, each having a thickness of about 37 micrometers. The laminate was exposed to an UV radiation dosage of about 450 milli Joules per centimeter squared using UV black lights having 90% of the emission spectra between 300 and 400 nanometers, with a maximum emission at about 350 nanometers.

The resulting polymer was then divided into portions. The divided polymer portions were placed on a pre-weighed screen and the liners were removed. The weight of the polymer was obtained.

Then, the polymer was exposed to heat at a specific temperature for a specified amount of time. The temperature was typically 175°C for 0, 1, 5 and 15 minutes, but the exact time and temperature is specified for each test.

The polymer and screen were placed in ajar containing ethyl acetate and allowed to soak for 24 hours. After soaking, any remaining polymer was removed from the screen and dried at 65°C for 20 minutes. After drying, the sample was again weighed to obtain the weight of the polymer that remained on the screen. The percent gel is calculated as the ratio of the weight of polymer remaining on the screen after soaking as compared to the original weight of polymer, multiplied by 100.

Probe Tack Test

Probe tack measurements were made following the test method described in ASTM D 2979-95 using a POLYKEN probe tack tester, Series 400 (commercially available from Testing Machines Inc; Amityville, New York). The probe tack value is an average often readings per sample. Tape Tests

The following test methods were used to characterize pressure-sensitive adhesive compositions produced in the following examples:

180° Peel Adhesion

This test is similar to the test method described in ASTM D 3330-90, substituting a glass substrate for the stainless steel substrate described in the test. For the present purpose, this test is also referred to as the "glass substrate peel adhesion test." Adhesive coatings, having a thickness as indicated in the particular example, on polyester film were cut into 1.27 centimeter by 15 centimeter strips. Each strip was then adhered to a 10 centimeter by 20 centimeter clean, solvent- washed, glass coupon using a 2-kilogram roller passed once over the strip. The bonded assembly dwelled at room temperature for about one minute. The bonded assembly was then tested for 180° peel adhesion using an BVIASS

SLIP/PEEL TESTER (Model Number 3M90, commercially available from Instrumentors Inc.; Strongsville, Ohio) at a rate of 2.3 meters per minute (90 inches per minute) over a five second data collection time. Two samples of each composition were tested. The reported peel adhesion value is an average of the peel adhesion value obtained from testing each of the two samples.

Shear Strength

This test is similar to the test method described in ASTM D 3654-88. Adhesive coatings, having a thickness as indicated in the particular example, on polyester film were cut into 1.27 centimeter by 15 centimeter strips. Each strip was then adhered to a stainless steel panel such that a 1.27 centimeter by 1.27 centimeter portion of each strip was in firm contact with the panel, with one end portion of the strip hanging free. The panel with the strip attached was held in a rack such that the panel formed an angle of 178° with the extended strip free end that was tensioned by application ofa force of one kilogram applied as a hanging weight from the free end of the strip. The 2° less than 180° was used to negate any peel forces, thus ensuring that only shear strength forces were measured, in an attempt to more accurately determine the holding power of the tape being tested.

The time elapsed for each sample to separate from the test panel was recorded as the shear strength. Failures were noted as adhesive (denoted A, no residue on panel) or cohesive (denoted C, adhesive failed internally with adhesive residue remaining on both the backing and panel). Each test was terminated at 10,000 minutes, unless the adhesive failed at an earlier time (as noted).

Synthesis of PIC

In a glass bottle, 80 grams of EHA, 120 grams of DMAEMA, and 300 grams of ethyl acetate were mixed. To this mixture, 0.6 gram of VAZO 64 was added. The bottle was then made inert with nitrogen gas and sealed. The sealed bottle was tumbled in a 55°C water bath for 24 hours. The resultant polymer was coated on a siliconized polyester release liner and oven dried for 15 minutes at 65°C to recover the dried polymer.

Examples 1-15 Synthesis of Aldoxime Esters Example 1 Step I: Synthesis of

2-(5- [2-(hydroxyiminomethyl)phenoxy] pen tyIoxy)benzaldehyde oxime

In a flask equipped with a stirrer, nitrogen inlet, reflux condenser, and addition funnel, 1,350 grams of ethanol and 113 grams of potassium hydroxide were placed. The mixture was stirred until all of the potassium hydroxide dissolved. To this stirred mixture, 208 grams of salicylaldehyde was added. A precipitate formed. The reaction mixture was then heated to 80°C to dissolve the precipitate. To this mixture, 132 grams of 1,5-dibromopentane was added over a period of one hour. The mixture was maintained at 80°C for 8 hours, followed by cooling to 25°C and the addition of 118 grams of hydroxylamine hydrochloride and 112 grams of potassium hydroxide.. The reaction temperature rose to 50°C. After cooling to 40°C, this temperature was maintained for two hours. The mixture was then cooled to 25°C and 1,565 grams of water was added. The mixture was stirred for 15 minutes, filtered, and the precipitate was dried to give 189 grams of 2-(5-[2-(hydroxyiminomethyl)phenoxy]pentyloxy)benzaldehyde oxime.

Step II: Synthesis of

2-(5-[2-(hydroxyiminomethyl)phenoxy]pentyloxy)benzaldehyde oxime dimethacrylate ester

In a flask equipped with a stirrer, nitrogen inlet, cooling bath, and addition funnel, 189 grams of 2-(5-[2-(hydroxyiminomethyl)phenoxy]pentyloxy)benzaldehyde oxime (prepared in Step I of Example 1), 1,817 grams of tetrahydrofuran, and 124 grams of triethylamine was placed. The solution was cooled to 0°C and 127 grams of methacryloyl chloride was added over a period of 45 minutes while maintaining the temperature below 15°C. The mixture was held at 15°C for 30 minutes following completion of the addition of the methacryloyl chloride. Then, the mixture was allowed to warm to room temperature.

To the room temperature mixture, 363 grams of hexane and 727 grams of water were added. The resulting mixture was stirred for 15 minutes. After stirring, the phases were allowed to separate into an aqueous phase and an organic phase. The aqueous phase was discarded. The organic phase was washed with a premix of 191 grams of concentrated hydrochloric acid and 727 grams of water followed by 2 water washes of 363 grams each.

Phenothiazine was added to the organic phase. The solvent was removed using a rotary evaporator. To the resulting solid, a premix of 128 grams of ethyl acetate and 283 grams of hexane was added. The slurry was stirred, filtered, and washed with hexane. The resulting solid was dried, yielding 170 grams of 2-(5-[2-

(hydroxyiminomethyl)phenoxy]pentyloxy)benzaldehyde oxime dimethacrylate ester.

Example 2 Step I: Synthesis of 2-(5-[2-(hydroxyiminomethy.)phenoxy]hexyloxy)benzaIdehyde oxime The same procedure described in Example 1, Step I was followed, except using 334 grams of salicylaldehyde and 225 grams of dibromohexane in place of the dibromopentane and hydroxylamine hydrochloride. The reaction yielded 285 grams of 2-(5-[2-(hydroxyiminomethyl)phenoxy]hexyloxy)benzaldehyde oxime.

Step II: Synthesis of

2-(5- [2-(hydroxyiminomethyl)phenoxy] hexyIoxy)benza!dehyde oxime diacrylate ester

The same procedure described in Example 1, Step II was followed, except using 285 grams of 2-(5-[2-hydroxyiminomethyl)phenoxy]hexyloxy)benzaldehyde oxime (prepared in Step I of this example) and 172 grams acryloyl chloride. The reaction yielded 227 grams of 2-(5-[2-(hydroxyiminomethyl)phenoxy]hexyloxy)benzaldehyde oxime diacrylate ester instead of 2-(5-[2-(hydroxyiminomethyl) phenoxy] pentyloxylbenzaldehyde oxime and methacryloyl chloride, respectively.

Example 3 Step I: Synthesis of 2-(5-[2-(hydroxyiminomethyl)phenoxy]pentyloxy)benzaIdehyde oxime

The same procedure described in Example 1, Step I was followed.

Step II: Synthesis of

2-(5-[2-(hydroxyiminomethyl)phenoxy]pentyloxy)benzaldehyde oxime diacrylate ester

The same procedure described in Example 1, Step II was followed, except that acryloyl chloride was used in place of methacryloyl chloride.

Example 4 Step I: Synthesis of 2-(5-[2-(hydroxyiminomethyl)phenoxy]propyIoxy)benzaIdehyde oxime The same procedure described in Example 1, Step I was followed, except that

1,3-dibromopropane was used in place of 1,5-dibromopentane. Step π: Synthesis of

2-(5-[2-(hydroxyiminomethyl)phenoxy]propyIoxy)benzaIdehyde oxime dimethacrylate ester The same procedure described in Example 1, Step II was followed.

Example 5 Step I: Synthesis of 2-(5-[2-(hydroxyiminomethyl)phenoxy]propyloxy)benzaIdehyde oxime The same procedure described in Example 4, Step I was followed.

Step II: Synthesis of

2-(5- [2-(hydroxyiminomethyl)phenoxy] propyloxy)benzaldehyde oxime diacrylate ester The same procedure described in Example 2, Step II was followed.

Example 6 Step I: Synthesis of 2-(5-[2-(hydroxyiminomethyI)phenoxy]butyloxy)benzaldehyde oxime The same procedure described in Example 1, Step I was followed except that

1,4-dibromobutane was used in place of 1,5-dibromopentane.

Step H: Synthesis of

2-(5-[2-(hydroxyiminomethyl)phenoxy]propyloxy)benzaldehyde oxime dimethacrylate ester

The same procedure described in Example 1, Step II was followed.

Example 7 Step I: Synthesis of 2-(5-[2-(hydroxyiminomethyl)phenoxy]butyloxy)benzaldehyde oxime

The same procedure described in Example 6, Step I was followed. Step II: Synthesis of

2-(5-[2-(hydroxyiminomethyl)phenoxy]butyloxy)benzaldehyde oxime diacrylate ester The same procedure described in Example 2, Step II was followed.

Example 8 Step I: Synthesis of 2-(5-[2-(hydroxyiminomethyl)naphthoxy]decyloxy) naphthylaldehyde oxime The same procedure described in Example 1, Step I was followed except that 2- hydroxy-1-naphthaldehyde was used in place of salicylaldehyde and 1,10-dibromodecane was used in place of 1,5-dibromopentane.

Step II: Synthesis of 2-(5-[2-(hydroxyiminomethyl)naphthoxy]decyloxy) naphthylaldehyde oxime dimethacrylate ester

The same procedure described in Example 1, Step II was followed.

Example 9 Step I: Synthesis of 3,5-dimethyl-2-(5-[2-(hydroxyiminomethyl)3,5- dimethylphenoxy] pentyloxy)benzaldehy de oxime

The same procedure described in Example 1, Step I was followed except that 2,4-dimethyl-6-hydroxybenzaldehyde was used in place of salicylaldehyde.

Step II: Synthesis of 3,5-dimethyI-2-(5-[2-(hydroxyiminomethy_)3,5- dimethyIphenoxy]pentyIoxy)benzaIdehyde oxime dimethacrylate ester

The same procedure described in Example 1, Step II was followed.

Example 10 Step I: Synthesis of 4-hydroxy-4-methyI-2-pentanone oxime In a flask equipped with a stirrer, nitrogen inlet, reflux condenser, and addition funnel, 100 milliliters of methanol, 20.0 grams of diacetone alcohol (4-hydroxy-4- methyl-2-pentanone), and 23.7 grams of finely ground sodium carbonate were placed. To this stirred mixture, 14.4 grams of hydroxylamine hydrochloride was added. The reaction temperature rose slightly and the mixture was stirred for 2.5 hours.

The mixture was then filtered, the precipitate was discarded, and the solvent was removed from the filtrate. The resulting solid was dissolved in 150 milliliters of tetrahydrofuran and filtered to remove additional precipitate. The tetrahydrofuran was removed using a rotary evaporator to yield 4-hydroxy-4-methyl-2-pentanone oxime.

Step II: Synthesis of 4-hydroxy-4-methyI-2-pentanone oxime diacrylate

In a flask equipped with a stirrer, nitrogen inlet, cooling bath, and addition funnel, 5.0 grams of 4-hydroxy-4-methyl-2-pentanone oxime (prepared in Step I of this example), 40 milliliters of tetrahydrofuran, and 8.0 grams of triethylamine were placed. The solution was cooled to 5°C. Then, a solution of 7.05 grams of acryloyl chloride dissolved in 20 milliliters of tetrahydrofuran was added over a period of 1.5 hours. The mixture was allowed to warm to room temperature and stirred for two hours. The tetrahydrofuran was removed.

The resulting solid was extracted twice with 50 milliliters of ethyl acetate, washed with a saturated aqueous solution of sodium chloride, dried over magnesium sulfate, and filtered. The solvent was removed to yield 4.7 grams of 4-hydroxy-4- methyl-2-pentanone oxime diacrylate.

Example 11 Step I: Synthesis of 2-(5-[2-(hydroxyiminomethyl)phenoxy]pentyloxy)benzaldehyde oxime

The same procedure described in Example 1, Step I was followed.

Step II: Synthesis of 4,5-dichlorophthalic anhydride

In a flask equipped with a stirrer, nitrogen inlet, and DEAN-STARK trap, 10.0 grams of 4,5-dichlorophthalic acid, 150 milliliters of xylene, and several crystals of toluenesulfonic acid were added. The mixture was heated to reflux and water was collected in the DEAN-STARK trap over a period often hours. The xylene was distilled off and the solid was collected in a BUCHNER funnel and allowed to air dry, yielding 8.3 grams of 4,5-dichlorophthalic anhydride.

Step HI: Synthesis of l-acryloxy-2-propyl-4,5-dichlorophthaIate In a flask equipped with a stirrer, nitrogen inlet, reflux condenser, and addition funnel, 4.5 grams of 2-hydroxypropylacrylate, 3.4 grams of triethyl amine, and 25 milliliters of tetrahydrofuran were added. To this stirred mixture, a solution of 6.9 grams of 4,5-dichlorophthalic anhydride (prepared in Step II of this Example) dissolved in 55 milliliters of tetrahydrofuran was added over a period of 0.5 hour. The resulting mixture was stirred for 18 hours.

Trace amounts of the inhibitors, MEHQ and phenothiazine, were added and the tetrahydrofuran solvent was removed using a rotary evaporator. The resulting solid was dissolved in 150 milliliters of ethyl acetate and 50 milliliters of dilute (3%) aqueous hydrochloric acid solution. The mixture was washed with water and a saturated aqueous sodium chloride solution. The mixture was separated into an aqueous phase and an organic phase. The organic phase was dried over MgSO₄ and filtered. The solvent was removed using a rotary evaporator at 30°C to yield 10.5 grams of 1- acryloxy-2-propyl-4, 5 -dichlorophthalate. Step IV: Synthesis of bis-(l,5-pentanedioxy-2-benzaldehydeoxime)-l-acryloxy-2- propyl-4,5-dichlorophthalyl-4,5-dichlorophthalate

In a flask equipped with a stirrer and a nitrogen inlet, 1.0 gram of 2-(5-[2- (hydroxyiminomethyl)phenoxy]pentyloxy)benzaldehyde oxime (prepared in Step I), 3.46 grams of l-acryloxy-2-propyl-4,5-dichlorophthalate (prepared in Step III), and 50 milliliters of ethyl acetate were placed. The resulting mixture was stirred to form a solution. A solution of 3.35 grams of dicyclohexylcarbodiimide in 15 milliliters of ethyl acetate was added to the stirred oxime solution. The resulting mixture was stirred for 18 hours, filtered, and the solvent was removed using a rotary evaporator at 30°C to yield bis-(l,5-pentanedioxy-2-benzaldehydeoxime)-l-acryloxy-2-propyl-4,5- dichlorophthalyl 4, 5-dichlorophthalate.

Example 12 Step I: Synthesis of 2-(5-[2-(hydroxyiminomethyl)phenoxy]pentyloxy)benzaldehyde oxime

The same procedure described in Example 1, Step I was followed.

Step II: Synthesis of l-acryloxy-2-propyl phthalate

The same procedure described in Example 11, Step III was followed except phthalic anhydride was used instead of 4,5-dichloro phthalic anhydride.

Step πi: Synthesis of bis-(l,5-pentanedioxy-2-benzaldehydeoxime)-l-acryloxy-2- propylphthalyl phthalate

The same procedure described in Example 11, Step IV was followed except 1- acryloxy-2-propyl phthalate was used instead of l-acryloxy-2-propyl-4,5-dichloro phthalate.

Example 13 Synthesis of salicylaldoxime dimethacrylate ester In a flask equipped with a stirrer, a nitrogen inlet, and an addition funnel, 13.7 grams of salicylaldoxime and 150 milliliters of tetrahydrofuran were placed. The resulting stirred solution was cooled with an ice water bath to 5°C. Then, 30.8 grams of triethylamine was slowly added. To this solution, 30.0 grams of methacryloyl chloride was added over a period of one hour while maintaining the temperature at 5°C. After 10 minutes of mixing, 100 milliliters of hexane was added, followed by 100 milliliters of water (the temperature was kept below 10°C during the water addition).

The resulting mixture was allowed to separate into an aqueous phase and an organic phase. The aqueous phase was separated and discarded. The organic phase was dried over sodium sulfate. A trace of phenothiazine was added and the solvent was removed using a rotary evaporator. The resulting residue was purified by column chromatography on a silica gel column eluted with a 1 : 1 mixture of hexane and ethyl acetate to yield 7.8 grams of salicylaldoxime dimethacrylate ester.

Example 14 Synthesis of 3-(2-hydroxyethoxy)benzaldoxime dimethacrylate ester In a flask equipped with a stirrer, a nitrogen inlet, and an addition funnel, 5.17 grams of 3-(2-hydroxyethoxy)benzaldoxime, 6.36 grams of triethylamine, and 150 milliliters of tetrahydrofuran were placed. The resulting solution was cooled to 0°C. Then, 8.95 grams of methacryloyl chloride was slowly added. The mixture was warmed to room temperature and stirred for one hour. To this mixture, 150 milliliters of hexane and 75 milliliters of water were added. The aqueous phase was removed and the organic phase was washed with a 3% aqueous hydrochloric acid (HC1) solution followed by washing with a saturated aqueous sodium chloride solution. The organic layer was dried over anhydrous magnesium sulfate and the solvent was removed to yield 2.6 grams of 3-(2-hydroxyethoxy)benzaldoxime dimethacrylate ester.

Example 15 Synthesis of terephthalaldoxime dimethacrylate ester

In a flask equipped with a stirrer, a nitrogen inlet, and an addition funnel, 3.3 grams of terephthalaldoxime, 4.9 grams of triethyl amine, and 40 milliliters of tetrahydrofuran were placed. The resulting solution was cooled with an ice water bath to 5°C. Then, 5.0 grams of methyacryloylchloride was added over a period of 15 minutes. The mixture was stirred for one hour followed by the slow addition of 30 milliliters of water. The solid formed was filtered and washed with a 1 :1 water and acetone mixture to give, after drying, 2.3 grams of terephthalaldoxime dimethacrylate ester.

Example 16 Synthesis of 2-(5-[2-(hydroxyiminomethyl)phenoxy]hexyloxy)benzaldehyde oxime di-2-acryloxyethylcarbonate

In a flask cooled by an ice water bath and equipped with a stirrer, a nitrogen inlet, a dry ice condenser, and a caustic scrubber, 12 grams of phosgene was placed. To this mixture, a solution of 8.4 grams of 2-methyl-2-butene in 50 milliliters of tetrahydrofuran (precooled in an ice water bath) was slowly added. To the resulting 5°C mixture, 12.8 grams of 2-hydroxylethyl acrylate was added over a period of 30 minutes. During the addition, the mixture temperature was maintained below 8°C. The mixture was warmed to 22°C and 20 milliliters of solvent was removed using a stream of nitrogen vented through the scrubber. A vacuum, via a water aspirator, was then applied and the remainder of the solvent was removed to yield the chloroformate ester of 2-hydroxyethyl acrylate.

The chloroformate ester of 2-hydroxyethyl acrylate was added to a 5°C solution of 13 grams of

2-(5-[2-(hydroxyiminomethyl)phenoxy]hexyloxy)benzaldehyde oxime (prepared in Example 2, Step I) in 50 milliliters of tetrahydrofuran over 40 minutes (the temperature was maintained at 10-15°C throughout the addition). The reaction was slowly warmed to 22°C, stirred for 30 minutes, and 30 milliliters of 3% aqueous HC1 and 30 milliliters of ethyl acetate were added. To the resulting emulsion, 50 milliliters of ethyl acetate and 30 milliliters of hexane were added.

The resulting mixture was allowed to separate into an aqueous phase and an organic phase. The aqueous phase was separated and discarded. The organic phase was separated, washed with aqueous potassium chloride, and dried over sodium sulfate. The solvent was removed and the solid residue was washed with 50 milliliters of a 1 : 1 mixture of hexane and ethyl acetate to give 10.5 grams of a white solid that was recrystallized from ethyl acetate and hexane to yield 8.4 grams of 2-(5-[2-(hydroxyiminomethyl)phenoxy]hexyloxy)benzaldehyde oxime di-2-acryloxyethylcarbonate.

Example 17 Synthesis of 6-(3-[(ethylamino)carbonyI]-3-butenoyIoxy)hexyl-3- [(ethylamino)carbonyl]-3-butenoate

In a flask equipped with a stirrer, nitrogen inlet, and addition funnel, 11.2 grams of itaconic anhydride, 5.9 grams of 1,6-dihydroxyhexane, and 0.1 gram of phenothiazine were placed. The resulting mixture was heated on a steam bath for 3 hours. The mixture was cooled and 50 milliliters of chloroform and 13 grams of thionyl chloride were added. The mixture was heated at reflux for one hour. The solvent was then removed under vacuum. Heptane was added and then stripped to remove the last traces of thionyl chloride. The residue was slowly added to a solution of 11.8 grams of n- propylamine in 75 milliliters of tetrahydrofuran. The reaction was cooled throughout the addition so as to maintain a temperature of 20^°C. After the addition was complete, the mixture was stirred for 15 minutes. Then, 50 milliliters of 1% aqueous hydrochloric acid and 50 milliliters of ethyl acetate were added. The organic phase was separated, washed with saturated potassium chloride solution, and dried over sodium sulfate. The solvent was removed under vacuum and the residue recrystallized from ethyl acetate/hexane to yield 4.3 grams of 6-(3- [(ethylamino)carbonyl ] -3 -butenoyloxy)hexyl 3 - [(ethylamino)carbonyl] -3 -butenoate.

Example 18

Synthesis of 3-(methacryIoyloxy)-l,l-dimethylbutyl-2-methylacrylate

A solution containing 5.9 grams of 2-methyl-2,4-pentanediol and 11.1 grams of triethylamine in 75 milliliters of tetrahydrofuran was cooled to 5°C. Then, 11.5 grams of methacryloyl chloride was added over a period of 15 minutes while keeping the temperature below 10°C. The mixture was slowly warmed to room temperature and held at that temperature for one hour. Then, 70 milliliters of hexane and 50 milliliters of water were added sequentially to the mixture.

The organic phase was separated and washed with 50 milliliters of 3% aqueous hydrochloric acid (HC1) solution and 50 milliliters of 10% sodium chloride solution. The organic phase was dried over sodium sulfate. Then, 0.01 gram of phenothiazine was added. The solvent was removed under vacuum to yield 10.5 grams of 3- (methacryloyloxy)- 1 , 1 -dimethylbutyl-2-methylacrylate.

Examples 19-23 Polymers containing degradable crosslinkers were prepared and tested according to the Gel Test method. The type and amount of the degradable crosslinker used is noted in Table 1. The results of the Gel Test are provided in Tables 2-3. Time and temperature for each Gel Test are noted in the Tables.

Table 1

Table 2

Table 3

Examples 24-34

A suspension-polymerized crosslinked polymer composition was prepared according to the method described in European Patent Application No. EP 0 853 092 (Minnesota Mining & Manufacturing Co.) with the following modifications: The reaction was carried out in a flask equipped with a condenser, thermowell, nitrogen inlet, stainless steel motor-driven agitator, and a heating mantle with temperature control. To the reaction flask, 450 parts of deionized water and 36 parts of methylcellulose stabilizer (17,000 grams/mole) were added. The reaction flask was heated to, and maintained at, 45 °C while the contents were agitated and purged with nitrogen. A premix containing the (meth)acrylate monomers, degradable crosslinker, and other ingredients shown in Table 4 (amounts are in parts by weight) was added to the reaction flask while stirring vigorously at a rate of about 500 to about 950 revolutions per minute. The temperature of the reaction mixture was adjusted to 55°C, the nitrogen purge was maintained, and the reaction was allowed to continue to completion. The resulting, roughly 85% solids, partially tacky crosslinked polymer beads were collected by filtration. The partially dried beads were mixed with 1 part of AEROSIL R-972. The resulting beads were then further dried, either by air evaporation or vacuum drying at 70°C, to give free-flowing beads.

Table 4

Example 35

The reaction was carried out in a flask equipped with a condenser, thermowell, nitrogen inlet, stainless steel motor-driven agitator, and a heating mantle with temperature control. To the reaction flask, 150 parts of deionized water, including 0.6 part of methyl cellulose stabilizer (17,000 grams/mole), was added. The reaction flask was heated to, and maintained at, 45°C while the contents were agitated and purged with nitrogen.

A premix containing 87.5 parts EHA, 5 parts MAA, 7.5 parts AA, 1 part of the degradable crosslinker prepared in Example 1, 0.25 part ABP, and 0.075 part IOTG was added to the reaction flask while the mixture was stirred vigorously at a rate of about 500 to about 950 revolutions per minute. The temperature of the reaction mixture was adjusted to 80°C, the nitrogen purge was maintained, and the reaction was allowed to continue to completion. The resulting, roughly 85% solids, partially tacky crosslinked polymer beads were collected by filtration. The partially dried beads were mixed with 1 part of AEROSIL R-972. The resulting beads were further dried by air evaporation to give free-flowing beads having a gel content of 66%.

Example 36 A sample (designated HMM + Press) of the free-flowing beads prepared in

Example 35 was placed in a hot-melt mixer and heated to 175°C to activate the degradable crosslinker. The hot-melt mixer contained three chambers and a valve to discharge mixed polymer. The three chambers were configured as upper, middle, and lower chambers. The middle chamber contained the valve for discharge of the mixed polymer and the static mixing elements. All three chambers were heated.

Free-flowing beads were placed in the top chamber. A heating period then transferred heat from the chamber walls to the beads. A piston drove beads from the upper chamber, through the middle chamber over the static mixing elements, and into the bottom chamber. After the beads had fully entered the bottom chamber, a piston in the bottom chamber forced the beads back through the middle chamber and across the static mixing elements again. This process was repeated as many times as was necessary to adequately mix the beads.

The mixed, heated beads were pressed between two siliconized liners in a hot- melt press set at 175°C and pressed at 69 MegaPascals for 2 minutes. One of the liners was removed and the exposed sample was then laminated to a 37-micrometer-thick, aminated, polybutadiene-primed polyester film.

A separate sample (designated "Press") of the free-flowing beads prepared in Example 35 was coated between liners in the same manner, but was not hot-melt-mixed before coating. The sample was also placed in a hot-melt press set at 175°C. After sitting for 5 minutes, the sample was pressed at 69 MegaPascals for 2 minutes.

For the "HMM + Press" and "Press" methods, the samples were removed from the press and the siliconized polyester liner was removed. The resulting samples each had an adhesive thickness of 64-89 micrometers.

Additional samples (Examples 36B-D and 36F-H) were further cured using a Fusion Systems (Gaithersburg, Maryland) ultraviolet (UV) processor with an "H" bulb at the UV dosages listed in Table 5. The samples were then tested for 180° Peel Adhesion and Shear Strength following the test methods described above.

Table 5

ND = Not Determined Example 37 A sample of the free-flowing beads prepared in Example 35 was placed in the hot-melt mixer described in Example 36 and mixed and heated to 175°C to activate the degradable crosslinkers. The mixture was allowed to cool to room temperature and was then dissolved in ethyl acetate to give a 35% solids solutions.

To a sample of the solution, 1 part PIC was added. The solution was solvent- coated onto a 37-micrometer-thick, aminated, polybutadiene-primed, polyester film and dried in a 70°C oven for 20 minutes. The resulting adhesive coating had a thickness of 50 micrometers. Additional samples (Examples 37B-D and 37F-H) were further cured using a Fusion Systems ultraviolet (UV) processor with an "FT bulb at the UV dosages listed in Table 6. Samples of the resulting tapes were tested for 180° Peel Adhesion, Gel, and Shear Strength according to the test methods described above.

Table 6

ND = Not Determined

Example 38

A sample of the free-flowing beads prepared in Example 35 was placed in the hot-melt mixer described in Example 36 and mixed and heated to 175°C to activate the degradable crosslinker and form a molten polymer. The molten polymer was then coated onto a 37-micrometer-thick, aminated, polybutadiene-primed, polyester film. The resulting adhesive coating had a thickness of 25-50 micrometers.

To another sample of the molten polymer, 1 part PIC was added before placing it in the extruder and coating it as described above. Additional samples (Examples 38B- D and 38F-H) were further cured using a Fusion Systems ultraviolet (UV) processor with an "H" bulb at the UV dosages listed in Table 7. Samples of the resulting tapes were tested for 180° Peel Adhesion, Gel, and Shear Strength according to the test methods described above. Table 7

ND = Not Determined

Example 39

A sample of the free-flowing beads prepared in Example 35 was placed in an extruder and coated onto a 37-micrometer-thick, aminated, polybutadiene-primed, polyester film. The resulting adhesive coating had a thickness of 38 micrometers. Another sample of the free-flowing beads prepared in Example 35 was co-extruded with 1 part PIC and also coated as described above. Additional samples (Examples 39B-D and 39F-H) were further cured using a Fusion Systems ultraviolet (UV) processor with an "H" bulb at the UV dosages listed in Table 8. Samples of the resulting tapes were tested for Shear Strength according to the test method described above.

Table 8

Example 40

Polymers containing degradable crosslinkers from Example 2 and HDDA crosslinkers were prepared according to the Gel Test method. The amount of each crosslinker used is noted in Table 9. Probe tack of the polymers, both before and after heating at 175°C for 5 minutes, was then determined according to the Probe Tack Test described above.

Table 9

Various modifications and alterations of the invention will become apparent to those skilled in the art without departing from the spirit and scope of the invention, which is defined by the accompanying claims. It should be noted that steps recited in any method claims below do not necessarily need to performed in the order that they are recited. Those of ordinary skill in the art will recognize variations in performing the steps from the order in which they are recited.

Claims

What Is Claimed Is:

1. A crosslinked polymer composition comprising: at least one conventionally crosslinked polymer; and at least one degradable crosslinker incorporated into the at least one conventionally crosslinked polymer, wherein the degradable crosslinker comprises at least one energetically labile moiety.

2. The crosslinked polymer composition of claim 1, wherein the composition comprises a mixture of at least two degradable crosslinkers incorporated into the at least one conventionally crosslinked polymer.

3. The crosslinked polymer composition of claim 1, wherein the composition is essentially nontacky at room temperature.

4. The crosslinked polymer composition of claim 1, wherein the composition is at least partially tacky at room temperature.

5. The crosslinked polymer composition of claim 1, wherein the composition is free-flowing.

6. The crosslinked polymer composition of claim 1, further comprising at least one ofa dusting agent and a coating agent.

7. The crosslinked polymer composition of claim 1, further comprising a polymer that interacts ionically with the at least one conventionally crosslinked polymer.

8. The crosslinked polymer composition of claim 1, wherein the degradable crosslinker comprises at least one energetically labile moiety selected from the group of aldoxime esters, aldoxime carbonates, amide esters, and mixtures thereof.

9. The crosslinked polymer composition of claim 1, wherein the at least one conventionally crosslinked polymer is physically crosslinked.

10. The crosslinked polymer composition of claim 1, wherein the at least one conventionally crosslinked polymer is ionically crosslinked.

11. The crosslinked polymer composition of claim 1, wherein the at least one conventionally crosslinked polymer is chemically crosslinked.

12. A substrate at least partially coated with the crosslinked polymer composition of claim 1.

13. A method of transitioning a crosslinked polymer composition from a first chemical state to a second at least partially crosslinked chemical state, the method comprising the steps of: providing at least one crosslinked polymer composition selected from: the crosslinked polymer composition of claim 1, and a crosslinked polymer composition comprising at least one polymer derived from at least one degradable crosslinker; and activating at least a portion of the crosslinked polymer composition by applying an external energy source to at least a portion of the crosslinked polymer composition to fragment at least a portion of the degradable crosslinker.

14. The method of claim 13, wherein the external energy source is a thermal energy source.

15. The method of claim 13, further comprising the step of catalyzing fragmentation of the at least one degradable crosslinker.

16. The method of claim 13, further comprising the step of applying the crosslinked polymer composition to at least a portion ofa substrate.

17. The method of claim 16, wherein the step of activating occurs prior to applying the crosslinked polymer composition to at least a portion ofa substrate.

18. The method of claim 16, wherein the step of activating occurs while applying the crosslinked polymer composition to at least a portion ofa substrate.

19. The method of claim 16, wherein the step of activating occurs after applying the crosslinked polymer composition to at least a portion ofa substrate.

20. The method of claim 13, wherein the crosslinked polymer composition comprising at least one polymer derived from at least one degradable crosslinker is a crosslinked polymer composition comprising at least one polymer derived from at least two different degradable crosslinkers.

21. A polymer composition comprising: a polymer that is at least partially chemically crosslinked; and at least two pendant moieties on the polymer, wherein the pendant moieties are the reaction product of fragmentation ofa degradable crosslinker comprising at least one energetically labile moiety.

22. A substrate at least partially coated with the polymer composition of claim 20.