CA1249387A - Self-curable latex compositions - Google Patents

Abstract

ABSTRACT OF THE INVENTION

Self-curable latex compositions contain particles of an oxazoline-modified polymer and particles of a coreactive polymer. These latex compositions are curable, yielding films and other articles having good tensile and elongation properties and excellent resistance to water and aqueous fluids. In addition, these latex compositions are self-curing at room temperature.

Description

~L2~387 SELF-CURABLE LATEX COMPOSITIONS

This invention relate~ to self-curing polymer latexes.

Diverse self-~uring polymer latexes are k~own in the art~ For example, blends of a carboxylated latex such as an a~~rylic acid/styrene/butadiene terpoly-mer latex with a melamine formaldehyde or urea formal-dehyde resin are known to be self-cu A ng, i.e., they ~orm a curable composition which cures at elevated temperatures.

Other self-curable latex systems employ a car~oxylated latex which is cxosslinked with a polyvalent cation or with a cationic polymer. Such latexes have ~he disadvantages of being pH dependent and of forming films which are highly sensitive to water, solvents or other chemicals.

Consequently, a self-curable latex which is free of the disadvantages of previously known self--curable latexes would be highly desirable.

31,759-F -1-*

__ ~Z4~3~7 This invention is such a self-curable latex~
The latex of ~his invention is a curable latex composi-tion comprising an aqueous dispersion of (a) discrete particles of an oxazoline modified addition polymer containing pendant oxazoline groups which polymer has been prepared in an emulsion polymerization process from (1) an oxazoline as represented by the formula:

R2 fR2 Q N

Rl wherein Xl is an acyclic organic radical h~ving addition polymerizable unsaturation; each R2 is independently hydrogen, halogen or an inertly sub~tituted organic radical and n is 1 or 2 and (2) at least one other addition polymerizable monomer which is copolymerizable with said oxa~oline and is not a coreactive monomer or an oxazoline and (b) discrete particles of a coreactive polymer containing pendant coreactive groups which coreactive polymer has been prepared in an emulsion polymerization process from tl) an addition polymerizable coreactive monomer containing pendant groups which are capable sf reacting with an oxazoline group to form a covalent bond thereto and (2) at least one other monomer which is copolymerizable with said coreactive monomer.

Surprisingly, the latexes of this invention, when dried to form films, coatings, or other articles, exhibit excellent tensile and elongation properties and are surprisingly resistant to aqueous and organic 31,759-F -2-~2~931~7 fluids. ~lso surprising is that many of the latexes of this invention are self-curable at room temperature, i.e., crosslinking of the latex occurs without heating the latex and without the addition of curing agents.

The composition of this in~ention contains discrete particles of an oxazoline modified polymer.
Said oxazoline modified polymer has been prepared by - the emulsion polymeriæation of certain addition polym-erizable oxazolines and at least one other copolymeriz-able monomer.

The oxazolines employed herein are as repre-sented by the general structure:

R2 ~R2 l ~2) R2-l- ~ ~n ~ lC~
Rl wherein R1 is an acyclic organic radical having addi-tion polymeri~able unsaturation; each R2 is indepen-dently hydrogen, halogen or an inertly substituted organic radical and n is 1 or 2. Preferably, R1 is ~2C=C-wherein R3 is hydrogen or an alkyl radical. Most preferably, R1 is an isopropenyl group. Each R2 is preferably hydrogen or an alkyl group with hydrogen 31, 759-F -3-~Z49387 being most preferred; and n is preferably 1. Most preferably the oxazoline is 2-isopropenyl-2-o~azoline.

The oxazoline modified polymer also contains repeating units derived from at least one monomer which is not an oxazoline and which is copolymerizable with the aforementioned oxazoline. A broad range of addition polymerizable monomers are copolymerizable with said oxazoline and are suitable herein. Suitable monomers include, for example, the monovinyl aromatics, alkenes, esters of Q, ~-ethylenically unsaturated carboxylic acid; car~o~ylic acid esters wherein the ester group contain~ addition polymerizable unsaturation; halo-genated alkenes; acyclic aliphatic conjugated dienes and the ll~ke. Small amounts of crosslinking monomers 15 such as divinylbenzene may also be employed.

The term "monovinyl aromatic monomer" is intended to include those monomers wherein a radical of the formula:

CY2=C-(w~erein R is hydrogen or a lower alkyl such as an alkyl having from 1 to 4 carbon atoms~ is attached directly to an aromatic nucleus containing from 6 to 10 carbon atoms, including those monomers wherein the aromatic nucleus is substituted with alkyl or halogen substitu-ents. Typical of these monomers are styrene; ~-methyl-styrene; ortho-, meta- and para-methylstyrene; ortho-, meta-and para-ethylstyrene; o,p-dimethylstyrene;

31,759-F -4-~2~93~7 o,p-diethylstyrene; isopropylstyrene; o-methyl p-iso-propylstyrene; t-butyl styrene; p-chlorostyrene;
p-bromostyrene; o,p-dichlorostyrene; o,p-dibromostyrene;
vinylnaphthal~ne; diverse vinyl (alkylnaphthalenes) and vinyl ~halonaphthalenes) and comonomeric mixtures thereof. Because of considerations such as cost, availability and ease of use, styrene and vinyltoluene are preferred and styrene is especially preferred as the monovinyl aromatic monomer.

Alkenes suitably employed herein include the monounsaturated aliphatic organic compounds such as ethylene, n- and isopropylene, the diverse butenes, pentenes, and hexenes as well as alkenes containing diverse substituent groups which are inert to the polymerization thereof. Preferred are unsubstituted C2 C8 alkenes with C2-C4 unsaturated alkenes being most pre~erred.

Esters of a,~-ethylenically unsaturated carbcxylic acids useful herein include typical~y soft acrylates, those whose homopolymers have a glass transition temperature (Tg) of less than about 25C.
~xamples of these include ben~yl acrylate, butyl acrylate, sec-butyl acrylate, cyclohexyl acrylate, dodecyl acrylate, ethyl acrylate, 2-ethylbutyl acrylate, 2-ethylhexyl acrylate, heptyl acrylate, hexyl acrylate, isobutyl acrylate, isopropyl acrylate, methyl acrylate and propyl acrylate. Hard acrylates, those whose homopolymers have a Tg of greater than about 25C, can also be used. Examples of these include 4-biphenylyl acrylate and tert-butyl acrylate. Soft methacrylates are also suitable for use. Examples of such include butyl methacrylate and hexyl methacrylate. Also useful 31,759-F -5-~4g387 in the present invention are hard methacrylates such as sec-butyl methacrylate, tert-butyl methacrylate, cyclo-he~yl methacrylate, ethyl methacrylate, isobutyl methacrylate, isopropyl methacrylate, methyl methacrylate and propyl methacrylate. The cost, availability and known properties of butyl acrylate and ethyl acrylate make these monomers preferred among the acrylates. The cost, availability and known properties of methyl methacrylate make it preferred among the methacrylates.

Halogenated alkenes useful herein include, for example, vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, and the diverse polychloro-, polyfluoro- and polybromo alkenes.

Acyclic aliphatic conjugated dienes usefully employed herein include typically those compounds which have from 4 to 9 carbon atoms, for example, 1,3-butadiene;

2-methyl-1,3-butadiene; 2,3-dimethyl-1,3-butadiene;
pentadiene; 2-neopentyl-1,3-butadiene and other hydro-carbon analogs of 2,3-butadienes, such as 2-chloro--1,3-butadiene and 2-cyano-1,3-butadiene; the substituted straight chain conjugated pentadienes; the straight chain and branched chain conjugated hexadienes; other straight and branched chain conjugated dienes having from 4 to 9 carbon atoms; and comonomeric mixtures thereof. The 1,3-butadiene hydrocarbon monomers such a~ those mentioned hereinbefore provide interpolymers having particularly desirable properties and are therefore preferred. The cost, ready availability and the excellent properties of interpolymers produced therefrom makes 1,3-butadiene the most preferred acyclic aliphatic -conjugated diene.
-31,759-F -6-~249387 Mixtures of two or more of the foregoing monomers may, of course, be employed herein, if desired.
Of the foregoing monomers, most preferred are styrene, mixtures of styrene and butadiene, butyl acrylate, methyl methacrylate and vinyl acetate.

The proportion of monomers used in the oxazo-line modified latex may vary considerably depending on the particular end use of the composition. Typically, however, the oxazoline is employed in ~elatively minor amounts, e.g. from 0.1 to 20, preferably from 1 to 10, weight percent of the monomers. In general, the oxazoline monomer is employed primarily to impart the desired self-curing characteristics to latex composition and the other monomers are employed to impart the other desired properties to the composition. For example, in a preferred oxazoline modified styrene/butadiene latex, the oxazoline modified polymer will advantageously exhibit physical properties ~e.g., gla~s transition temperature and hardness) similar to those commonly associated with styrene/butadiene polymers. However, certain properties of the polymer, especially adhesion and crosslinking, will generally be enhanced by the inclusion of the oxazoline monomer.

The latexes are conveniently prepared by conventional emulsion polymerization techniques in an agueous medium with conventional additives. Thus, for example, the mono~er charge desired to be employed for -- the oxazoline modified latex is dispersed in an aqueous - -- medium with agitation with from 0.5 to 5 weight percent - 30 (based on the monomer charge) of conventional anionic _ _ -~ and/or nonionic emulsifiers ~e.g., potassium n-dodecyl sulfonate, sodium isooctobenzene sulfonate, sodium 31,759 F -7-~Z~931~7 laurate and nonylphenol ethers of polyethyl~ne glycols) and thereafter polymerizing the resulting aqueous dispersion.

Conventional emulsion polymerization catalysts can be employed in the foregoing latex polymerization and common examples thereof include peroxides, persul-fates, azo compounds such as sodium persulfate, potassium persulfate, ammonium persulfate, hydrogen peroxide and azodiisobutyric diamide. Also suitable are catalysts (e.g., redox catalysts) which are activated in the water phase (e.g., by a water-soluble reducing agent).
The type and amount of catalyst, as well as the particular polymerization conditions employed, will typically depend primarily on the other monomers which are used, and polymerization conditions will be generally selected to optimize the polymerization of such other monomers.
Typically, the catalyst is employed in a catalytic amount, e.g., ranging from 0.01 to 5 weight percent based upon the monomer weight. In general, the ~0 polymerization is conducted at a temperature in the range of from -10 to 110C (preferably from 50 to 90C). Since the oxazoline group of the oxazoline monomer will hydrolyze or react with other monomers at high or low pH, the polymerization is conducted at such pH such that said hydrolysis or reaction is minimized.
Typically, a pH of 3-11, preferably 6-11 is suitable.
More preferably, a pH of 7 to 10 is suitable. The polymerization may be conducted continuously, semi-continuously, or batch-wise.

Similarly, conventional chain transfer agents such as, for example, n-dodecyl mercaptan, bromoform and carbon tetrachloride can also be employed in the 31,759 F -~-~L24931~7 normal fashion in the aforementioned polymerization to regulate the molecular weight of the polymer formed therein. Typically, when such chain transfer agents are used, they are employed in amounts ranging from 0.01 to 10 (preferably from 0.1 to 5) weight percent based upon the weight of the monomers employed in the polymerization. Again, the amount of chain transfer agent employed depends somewhat on the particular chain transfer agent employed and the particular monomers being polymerized.

Suitable latex polymerization procedures are taught, for instance, in U.S. Patent Nos. 4,325,856;
4,001,163; 3,513,121; 3,575,913; 3,634,2g8; 2,399,684;
2,790,735; 2,880,189; and 2,949,386.

The latex of this i~vention further comprises discrete particles of a coreactive polymer. Said coreactive polymer particles are prepared in an emulsion polymerization process from an addition polymerizable monomer containing pendant groups which are capable of reacting with an oxazoline group to form a covalent bond thereto (hereinafter "coreactive monomer") and at least one other monomer which is copolymerizable with said coreactive monomer.

The coreactive monomers employed herein are those which contain pendant coreactive groups which are capable of reacting with an oxazoline group to form a covalent bond thereto. It is understood that the reaction of such coreactive groups with the oxazoline group will typically, but not necessarily, cause the oxazoline ring to open.

31,759-~ _9_ ~LZ4~387 , --10--Typically, the pendant coreactive group on the coreactive monomer wilI contain a reactive hydrogen atom. Exemplary coreactive groups containing an active hydrogen atom include strong and weak acid groups;
aliphatic alcohols; aromatic alcohols, i.e., phenols;
amines; and amides, i.e., -CONH2 and -CONH- groups. In general, the more reactive of such groups, i.e., those having the more labile hydrogen, such as the acids and aromatic alcohols, are preferred herein. Such more reactive groups will generally react with the oxazoline ring more readily under milder conditions than the less reactive groups such as the amines and aliphatic alcohols.
Amide groups are generally intermediate in reactivity.

Especially preferred are monomers containing pendant strong or weak acid groups or acid anhydride groups. Such monomers include those ethylenically unsaturated monomers containing acid groups, such as carboxylic acid and sulfonic acid groups, or acid anhydride groups. Sulfoethyl acrylate is an example of a suitable monomer containing a sulfonic acid group.
Exemplary of suitable monomers containing carboxylic acid groups include itaconic acid, acrylic acid, methacrylic acid, fumaric acid, maleic acid, vinylbenzoic acid and isopropenylbenzoic acid. The more preferred species include acrylic, methacrylic, fumaric, itaconic and maleic acids. Maleic anhydride is an exampl~ of a suitable monomer containing an acid anhydride group.

Suitable coreactive monomers containing phenolic groups include ortho- and meta-vinyl phenol.

31,759-F -10-~249387 Suitable coreactive monomers containing aliphatic hydroxyl groups include, for example, hydroxyethylacrylate, hydroxypropyl methacrylate and N-hydroxymethyl-N-methyl acrylamide. Derivatives of styrene having aliphatic hydroxyl groups are also useful herein.

Suitable coreactive monomers containing amide groups include acrylamide, methacrylamide, vinyl acetamide and ~-chloroacrylamide. N-methylacrylamides and N~methyl-m~thacrylamide are examples of monomers containing~CONH~ g~oups.

Suitable coreactive monomers containing amin~
groups include allyl amine, 2-aminoethylacrylate and 2-aminoethylmethacrylate.

The other monomers suitably employed in the coreactive polymer particles are those which are copolym-erizable with the coreactive monomer. In general, those monomers described hereinbefore as being useful in the preparation of the oxazoline modified polymer are also useful in the preparation of the coreactive polymer. In fact, it is often desirable to "match" the polymer backbone of the coreactive polymer to that of the oxazoline modified polymer; that is, except for the oxazoline and coreactive monomers, to employ the same monomers in the same proportions in both the coreactive and oxazoline modified polymers. It is understood, however, that different monomers may be employed in the preparation of the oxazoline and coreactive polymers in order to obtain the particular characteristics desired.

31,759-F -11-~2~93g~' As with the oxazoline modified polymer, the coreactive polymer generally contains only a minor portion of repeating units which are derived from the coreactive monomer. In general, the coreactive monomer is employed in amounts sufficient to impart the desired auto-curable properties to the latex composition and the other monomers are employed to impart the properties which are typically associated with polymers made from such monomers. In general, the coreactive monomer will lLO comprise from 0.1 to 50, preferably from 0.1 to 20, most preferably from 1 to 10, weight percent of the monomers employed in the preparation of the coreactive pol~mer.

The coreactive pol~mer particles are conven-iently prepared in an emulsion polymerzation process similar to that described hereiDbefore for the prepara-tion of the oxazoline modified polymer. When the coreactive monomer is one containing pendant weakly acidic groups such as carboxyl groups, the polymerization is advantageously conducted under conditions sufficiently acidic to promote the copolymerization of the weakly acidic coreactive monomers with the other monomers being employed. Preferably the pH is maintained between 1 and 6, more preferably between l and 4.
Then, following the polymerization reaction, the pH of the agueous phase is typically adjusted with base to raise the pH to 7.5 to 9, in order to prevent hydrolysis of the oxazoline rings in the oxazoline--modified latex upon subsequent blending.

The curable latex composition of this invention is advantageously prepared from the oxazoline modified latex and the coreactive latex by simple 31,759-F-12-~24931~7 blending of the respective latexes in the desired proportion. In general, the relative proportions of oxazoline modified and acidic latexes are chosen such that the resulting self-curable latex composition contains from 0.05 to 20, preferably from 0.2 to 5, more preferably from 0.5 to 2, equivalents of acid groups per equivalent of oxazoline group. In addition, better water and solvent resistance, as well as greater tensile strength is generally seen when the latex composition contains comparable amounts of particles of oxazoline-modified polymer and coreactive polymer.
Preferably, the latex contains 0.1 to 10, more preferably 0.2 to 5, most preferably 0.40 to 2.5, particles of oxazoline-modified polymer per coreactive polymer particle. Such blending is advantageousIy performed at room temperature with mild agitation. The resulting product is an aqueous dispersion containing discrete particles of the oxazoline modified polymer and discrete particles of the acidic polymer.

Advantageously, the respective particle sizes of the oxazoline-modified and the coreactive polymers, and the respective particle size distributions are such that the particles tend to pack together well to form dense, coherent films. The particles may all be of relatively uniform size, or may have different sizes such that the packing together of said particles upon film formation is enhanced.

The curable latex composition of this invention may be used for a variety of applications including paper coating compositions, adhesives, binders and fibrous, nonwoven fabric compositions.
Such compositions are especially suitable for 31,759 ~ -13-~Z49387 those applications in which a self-curable, curable polymer composition is desired.

The latexes of this i~vention may be employed as adhesives, films or binders by applying the latex to the desired substrate, then dewatering the latex and curing the dewatered polymers. T~e dewatering step may be performed by merely allowing the aqueous phase to evaporate under ambient conditi~ns. Alter~atively, elevated (i.e., 50-165C) temperatures may be employed to dewater the latex. Curing of the polymer may, likewise, be performed at ambient temperatures. Such ambient temperature curing is an unexpected property of the latexes of this invention. Such room temperature curing is generally conducted over a period of several hours to several days depending on the particular polymers employed, the amounts of oxazoline and acidic groups in the polymer, the thickness of the film adhesive or binder layer, the amount of crosslinking desired and like factors. Curing may also be effected by heating the polymers preferably to 105 to 165C, more preferably 135 to 150C for short periods. The foregoing drying and curing points may not be distinct steps but may be carried out simultaneously if desired.

The following examples are intended to illus-trate the invention but not to limit the scope thereof.
All parts and percentages are by weight unless otherwise indicated.

Exam~le A. Pre~aratlon of Carboxylated Latex Into a 0.0038 cubic meter (l-gallon), jacketed reactor equipped with FMI lab pumps to deliver monomer 31,759-F -14--~249387 and aqueous feeds were added 590 g of water, 7 g of a 1 percent active aqueous pentasodium diethylene triamine pentaacetate solution and 24.4 g of a 29 percent solids seed latex. The seed latex contained polystyrene particles having a volume average particle size of about 0.0275 micrometers (~m), i.e., 275 A.

The reactor was purged with nitrogen and heated to 9OC. Then, over a 3-hour period, was added a monomer stream containing 455 g of butyl acrylate, ~11 g of styre~e and 2~ g of acrylic ~cid. Added to the reaction mixture continuously over a four-hour period, beginning simultaneously with the start of the monomer stream, was 245 g of deionized water, 15.56 y of a 45 percent active aqueous surfactant solution, 14 g of a 10 percent aqueous sodium hydroxide solution and 4.9 g of sodium persulfate. Following the addition of the monomer in aqueous streams, the reaction mixture was heated at 90C for 1 additional hour and then cooled.
The product was a 44.8 percent solids latex of a butyl acrylate/styrene/acrylic acid polymer in a 65/31~4 weight ratio.

B. Preparation of Oxazoline Modified Latex Into a 0.0038 cubic meter (1-gallon), jacketed reactor were added 146 parts deionized water, 0.01 part of a 1 percent agueous pentasodium diethylene triamine pentaacetate solution, 5.0 parts of DresinateTM 214 surfactant (available commercially from Hercules, Inc.) and 0.5 part of sodium persulfate. The reactor was agitated and purged with nitrogen. To the stirred reactor was then added a mixture of 25 parts of styrene, 5 parts of 2-isopropenyl-2-oxazoline (IPO), and 0.5 part t-dodecyl mercaptan. Then, 70 parts of butadiene were 31,759-F -15-~2493~37 added and the mixture polymerized at 60C for 8 hours.
The reactor was then opened, and 0.5 part o~ sodium dimethyl dithiocarbamate were added. The latex was then steam distilled to remove any unreacted monomers.
The resulting latex contained 33.5 percent solids and had polymer particles of a butadiene/styrene/IPO
terpolymer in a 70/25/5 weight ratio. This oxazoline modified latex was designated as Latex No. 1 in Table I
following.

Oxazoline modified Latex Nos. 2, 3 and 4 and Comparative Latex Nos. C-1, C-2 and C-3 were prepared using the general procedure employed in preparing Latex No. 1 except that the amounts of butadiene/styrene/IPO
and t-dodecyl mercaptan were varied as indicated in Table I followingO In those latexes containing 50 parts butadiene, no sodium dimethyl dithiocarbamate was added. These latexes are components which are blended with the above-described carboxylated latex to prepare latex compositions according to the present invention or, in some uses, Comparative latexes which present invention.

31,759-F -16-~2~938~

TABLE I

Latex PARTS ~Y WEIGHT
No. Butadiene Styrene IPO TDDMl % Solids 1 70 25 5 0.5 33.5 5 C-l* 70 30 0 0.5 3~.0 2 70 25 5 1.0 41.7 C-2* 70 30 0 1.0 39.3

3 50 45 5 0.5 4~.9

4 50 40 10 0.5 37.2 10C-3* 50 50 0 0.~ 38.4 * Not an example of this invention.
T-dodecyl mercaptan.

Self-curable latex compositions were prepared by stirring together at room temperature equal weights ~based on solids) of IP0 modified Latex No. 1 and the carboxylated latex. The IPO modified latex and the carboxylated latex were compatible at all proportions.
The resulting blend was designated as Latex Composition No. 1 in Table II following. In like manner, Latex Composition Nos. 2, 3 and 4 and Comparative Latex Composition Nos. C-l, C-2 and C-3 in Table II below were prepared by mixing IP0 modified Latex Nos. 2, 3 and 4 and Comparative Latex Nos. C-l, C-2 and C-3 from Table I above on an equal weight solids basis with the carboxylated latex. Sample No. C-4 was the carboxylated latex alone. Multiple films were prepared from Latex Composition Nos. 1 through 4 and Comparative Latex Composition Nos. C-l through C-3 by drawing down a 31,759-F -17-1;~4938 17 0.51 millimeter (20 mil~ thick film onto a Teflon brand coated steel plate and then drying the film at ambient temperatures until it becomes transparent. The trans-parent films were then peeled from the plate and further dried at ambient temperature for about 24 hours. Some of the resulting films were then cured for 5 minutes at 80C, 120C or 150C. The resulting films were then cut into stips 13 millimeters (0.5 inch) wide and tested on an Instron tensile tester for elongation at break and tensile strength. In addition, duplicate samples were soaked for 5 minutes in a 0.5 percent aqueous surfactant solution and the thus wetted ~ilms were tested on the Instron for elongation at break and tensile strength. The results were as r~corded in Table II following. The Elongation values are in percent and the Tensile values are in megapascals (MPa).

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--OZ--1~493~7 As can be seen from Table II, the latex compositions of this invention generally formed films having higher tensile strength and somewhat lower elongation than the comparative latex compositions.
The data presented in Table II clearly illustrates the improved resi tance to water exhibited by the latex - compositions of this invention. Films prepared from the ~omparative latex compositions exhibited decreases in the range from about 30 to 70 percent in ten~ile strength upon wetting. By contrast, the latex compositions of thls invention typically lost only about 10 to 25 percent of their tensile strength.
Thus, the films prepared from the latex composition of this invention are clearly significantly less water sensitive than the films prepared from the comparative latex compositions. In addition, the films prepared from the latex compositions of this invention exhibit an excellent combination of good elongation and high tensile strength both in the dry and wet samples.

In order to measure degree of crosslinking and resistance to solvents, the swelling index and percent gel of the above-prepared films which have been cured at room temperature, 100, 120 and 150C were determined as follows.

Duplicate film samples were prepared from Latex Composition Nos. 1 and C-1, using a 0.51 millimeter (0.020 inch) casting bar. Each film was allowed to dry until clear and was peeled off as a continuous film.
One film was evaluated without curing; others were evaluated after 5 minute cures at 100, 120 and 150C, respectively. The film being tested was weiyhed and placed into a centrifuge tube. To the tube was added 31,759-F -21-~29L9387 30 g of toluene. The tube was sealed and shaken vigorously for 90 minutes. The tube was then centrifuged at about 18,000-19,200 rpm for 1 hour. The toluene was then poured off and the remaining wet gel was weighed. The

5 gel was then dried in a vacuum oven until a constant weight was obtained. Percent gel was calculated as:

weight of dry gel x 100%
weight of film sample Swelling index is calculated as:

10 w 'ght wet qel-weiqht dry gel weight dry gel The results obtained were as reported in Table III following.

TABLE III

Latex Com~osition Latex Composition No. 1 No. C~l*
Swellinq Index R.T. Cure 13.86 23.3 100C Cure 7.58 22.62 20 120C Cure 8.23 27.41 150C Cure 7.02 23.88 % Gel R. T . Cure81.3 42.03 100C Cure 81.65 49.83 25 120C Cure 80.87 46.38 150C Cure 82099 49.66 * Not an example of the invention.

As can be seen in Table III, films prepared from the latexes of this invention exhibit greatly 31,759-F -22-~249387 -23- .

incxeased resistance to solvents and greater proportions of insoluble material than did the comparative samples.
Testing of films prepared from Latex Composition Nos. 2, 3 and 4 showed similarly improved sol~ent resistance and higher amounts of insoluble material as compared to the relevant controls.

31,759-F -23-

Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A curable latex composition comprising an aqueous dispersion of (a) discrete particles of an oxazoline modified addition polymer containing pendant oxazoline groups, which polymer has been prepared in an emulsion polymerization process from (1) an oxazoline as represented by the formula:

wherein R1 is an acyclic organic radical having addition polymerizable unsaturation; each R2 is independently hydrogen, halogen or an inertly substituted organic radical and n is 1 or 2 and (2) at least one other addition polymerizable monomer which is copolymerizable with said oxazoline and is not a coreactive monomer or an oxazoline and (b) discrete particles of a coreactive polymer containing pendant coreactive groups which coreactive polymer has been prepared in an emulsion polymerization process from (1) an addition polymerizable coreactive monomer containing pendant groups which are capable of reacting with an oxazoline group to form a covalent bond thereto and (2) at least one other monomer which is not a coreactive monomer or an oxazoline which is copolymerizable with said coreactive monomer.

2. The latex of Claim 1 wherein the coreac-tive polymer particles contain from 0.5 to 2 equiva-lents of coreactive groups per equivalent of oxazoline group contained in the oxazoline modified polymer particles.

3. The latex of Claim 1 wherein the coreac-tive monomer contains pendant strong or weak acid groups.

4. The latex of Claim 3 wherein the coreac-tive monomer is an addition polymerizable carboxylic acid.

5. The latex of Claim 1 wherein R1 is as represented by the structure:

wherein R3 is an alkyl group.

6. The latex of Claim 5 wherein the oxazoline is 2-isopropenyl-2-oxazoline.

7. The latex composition of Claim 1 wherein the oxazoline-modified polymer is a polymer of styrene, butadiene and 2-isopropenyl-2-oxazoline.

8. The latex composition of Claim 7 wherein the coreactive polymer is a polymer of butyl acrylate, styrene and acrylic acid.

9. A film formed from the latex composition of Claim 1.