NO150689B - MEMBRANE FOR ELECTROCHEMICAL CELL AND ELECTROCHEMICAL CELL INCLUDING SUCH A MEMBRANE - Google Patents

Description

Pressure-sensitive adhesives of copolymers containing units of N-alkyl substituted imides or monoamides of ethylenically unsaturated dicarboxylic acids, especially maleic acid.

The invention relates to pressure-sensitive adhesives which consist of copolymers of alkyl esters of acrylic or methacrylic acid and N-alkyl substituted imides or monoamides of ethylenically unsaturated dicarboxylic acids, as well as optionally an ethylenically unsaturated compound that can be copolymerized with this.

The properties of polyacrylates largely depend on the type of alcohol or mixture of alcohols with which the acrylic acid is pre-esterified. As the number of carbon atoms in the straight-chain alkyl group in the alcohol increases, the properties of the homopolymers change as follows: First tough, rubbery and medium-hard polymers, then soft, less tough and more rubbery polymers, then soft sticky polymers, and finally hard, brittle and waxy polymers. The homopolymer of n-butyl acrylate is soft and sticky, and the tendency towards softer and stickier polymers continues until the n-alkyl group in the ester contains about 8 carbon atoms. Then the direction goes towards hard, brittle crystalline and waxy polymers (of e.g. n-hexadecyl acrylate and n-octadecyl acrylate). The molecular weight of the polymers also influences such properties as rubberiness, stickiness, softness, toughness, hardness and brittleness. Acrylates, which are known to form solid, sticky-soft polymers, are esters of acrylic acid and secondary alkyl alcohols containing from 4 to approx. 12 carbon atoms. Esters of acrylic acid and tertiary alkyl alcohols, such as t-butyl alcohol and t-amyl alcohol, are homopolymerized into relatively hard and non-adhesive polymers. Polymethacrylates show a similar tendency in their properties, but they are generally without significant stickiness and are more rubbery, firmer and tougher than the corresponding poj-acrylates.

The variations in the properties that can be obtained with polymers of acrylate and methacrylate monomers make these polymers attractive for many applications. Polymers that are rubbery, tough, soft, sticky have been used extensively as various types of adhesives, including lamination adhesives, hot melt adhesives and pressure sensitive adhesives. Particularly suitable for the production of pressure-sensitive adhesives are the polymers of acrylate monomers which themselves polymerize into a pressure-sensitive adhesive state. In general, the acrylate monomers that form soft, adhesive, though not aggressively adhesive, polymers are limited to esters of acrylic acid and non-tertiary alkyl alcohols where the alkyl groups contain on average from 4 to 12 carbon atoms, and where, in addition, the main chains contain at least 50% of the carbon atoms in the alkyl group. In general, these acrylate monomers amount to no less than approx. 75% of the entire amount of monomer from which the polymer powder is made. The balance between stickiness, adhesion and cohesion can be regulated by other monomers that can be copolymerised with the acrylics. Pressure sensitive adhesive polymers containing significant amounts

of methacrylates, is unknown.

A common type of pressure-sensitive adhesive polymer is produced by polymerizing alkyl acrylates containing from 4 to approx. 14 carbon atoms in the alkyl group. The alkyl acrylates can also be mixtures comprising methyl acrylate, provided that the average number of carbon atoms in the alkyl group is not less than approx. 4. U.S. Reissue Patent 24 906 and German interpretation documents no.

1 079 768 and no 1 096 524 state that these adhesives are improved if they contain an ethylenically unsaturated acid or an unsubstituted

amide of such, copolymerized with the above-mentioned acrylates.

German specification document no. 1 079 768 also describes the addition of

an organic peroxide to these copolymers and then heating the mixture in situ on a support. German specification No. 1 096 524 also describes the use of a polyvalent organic compound to crosslink the copolymers. The technical progress compared to this known technique is explained in the following, in connection with table VII.

According to the invention, a pressure-sensitive adhesive is provided which consists of copolymers of alkyl esters of acrylic or methacrylic acid and N-alkyl-substituted amides of ethylenically unsaturated carboxylic acids, as well as optionally an ethylenically unsaturated compound that can be copolymerized with this. The adhesive is characterized in that the copolymer is a copolymer of: (A) N-alkyl-substituted amido monomers of the general formula (B) ester monomers of the general formula where the weight ratio between monomer (A) and monomer (B) lies within the interval between 1:19 and 3:1, and where the molar ratio between monomer (A) and monomer (B) does not exceed 1:1, in which formulas (1) R and R' is hydrogen or methyl,

(2) The R^ groups are alkyl groups containing up to 28 carbon atoms, where the average number of carbon atoms of the alkyl groups is not greater than 24, and the alkyl groups containing more than 6 carbon atoms are mainly branched, the extent of

branching is increased when the size of the alkyl groups is increased.

(3) the R 2 groups are alkyl groups, containing up to 14 carbon atoms, where at least 50% of the molecules of the ester monomer have the R o groups bonded to the oxygen atom at non-tertiary carbon atoms, and (4) the R 3 groups are hydrogen or alkyl groups , containing up to 10 carbon atoms, where the alkyl groups containing more than 6 carbon atoms are mainly branched alkyl groups, and optionally (C) ethylenically unsaturated monomers of the following types: monocarboxylic acids or dicarboxylic acids or esters, amides, imides or anhydrides thereof, vinyl esters or ethers or alkenic hydrocarbons, which are copolymerizable with the monomers (A) and (B), in an amount up to 50% by weight of the sum of the monomers

(A) and (B) .

The ratio between these monomers in the pressure-sensitive adhesives

polymers and the degree of stickiness and adhesion that the polymers exhibit depends on the type of monomers chosen, the number of carbon atoms in their respective alkyl groups, the configurations of the alkyl groups and the extent to which primarily monomer (A) and to a lesser extent monomer (B) consists of mixtures of molecules with different alkyl groups.

THE COMPOSITION OF MONOMER A

As indicated by the above formulas, the N-substituted monomer (A) may be an amide acid or an imide derivative of monoethylenically unsaturated dicarboxylic acids. It should be emphasized that monomer (A) can be composed of only one monomer or mixtures of monomers. Furthermore, the molecules of any monomer may include molecules in which the size of the R 1 -alkyl groups is the same or different, either straight or branched, and mixtures thereof. The term "size", as used here for alkyl groups, refers to the number of carbon atoms in the alkyl radical, and the term "average size" refers to the average number of carbon atoms in all alkyl radicals of any R class (R^ or R ^). Thus, a monomer (A) of the amide acid class can consist of amide acid molecules that all have the same size of the R^-alkyl groups with the same or different configuration, mixtures of amide acid molecules where the R^-alkyl groups are of different sizes, or mixtures of molecules where R^ -groups differ from each other in that they are isomeric and homologous.

The R groups in the mixtures of molecules of the monomer (A) may exceed an average of 24 carbon atoms by a few carbon atoms. in that case, however, the number of different R<1->substituted molecules and the extent of branching in the R^ groups, especially when the size of the R^ groups increases, must be increased.

In general, the R₁ groups in monomer (A) can all be the same, both with regard to size and configuration. As the size of the R^-alkyl groups increases, they must be increasingly branched, and the monomer (A) molecules must increasingly be mixtures of molecules where the branched alkyls are different, either as isomers or homologous. The point at which the size of the R^ groups is such that branching is required, and the point at which monomer (A) must be molecules with different R^ alkyl groups, depends on several factors. Among these are the degree of stickiness and adhesion desired in a pressure-sensitive adhesive polymer,

and the composition of monomer (B).

The preferred (A) component for pressure-sensitive adhesive polymers with a fixed adhesive value of at least approx. 100 grams, determined as described below, is a mixture varying from liquid to crystalline solid, soluble in water and in the (B) component with which monomer (A) is to be copolymerized, or mixtures thereof. The monomer (A) component is sufficiently soluble to allow emulsion polymerization. In general, the less crystalline the (A) component, the higher the stickiness of the produced polymer.

If the R 1 -alkyl groups in the monomer contain less than approx. 11 carbon atoms, component (A) can either be a liquid or a crystalline solid. The R 1 -alkyl groups should essentially all be branched when the R 1 -alkyl groups are all of the same size within the range of approx. Cg-C^0, and it applies to N-monoalkyl substituted amide acids. In the case of an imide monomer (A), the R 1 -alkyl groups in the molecules can contain around 8 to 10 carbon atoms before significant branching is necessary.

If the average size for R^ is greater than about approx. C^q, depending on monomer (A), then the monomer (A) composition must have a state form between a liquid and an essentially non-crystalline, viscous, semi-solid, soluble in (B) -

the component as previously mentioned. It should be remembered here that the individual monomer components of the (A) mixture do not necessarily have to satisfy the aforementioned physical properties. On the contrary, the monomeric components may individually be insoluble or crystalline or both, only when mixed with the other components they give a substance which is either liquid or an essentially non-crystalline solid, soluble in water or in monomer (B) . These requirements for physical properties are met when the average size of increases to over approx. 10 carbon atoms, when the degree of branching of R^ increases, and when the degree of mixing for molecules with different branched R^ groups increases. Particular examples of this are given below. v

The significance of the non-crystalline and liquid or semi-solid monomer (A) mixtures where R^ has an average of over approx. C^q, is that the use of such allows a wider selection of monomer (B) mixtures and a wider range for the quantity ratios between the monomers (A) and (B).

These numerical limitations placed on the number of carbon atoms in R 1 to indicate the point at which branched alkyl R 1 groups and further also various alkyl groups must be present are limitations that can be used to produce pressure sensitive adhesive polymers having a tack as indicated above. These limitations are to be correlated with the monomer (B) mixtures and conditions that yield pressure-sensitive adhesive polymers. As will be apparent from an overall consideration of the invention, these limitations are approximations that can be deviated from to a certain extent.

The R 1 -alkyl groups contain from 1 to 10 carbon atoms.

The R 1 -alkyl groups which contain from approx. 6 to 10 carbon atoms, are branched alkyl groups, although branching in each and every R 3 alkyl group in the monomer (A) which is N-substituted with secondary alkyl is not essential. In general, the degree of branching in the R₁ alkyl groups need not be as great as in R₂ to obtain a liquid or substantially non-crystalline monomer (A) mixture. In this patent it should be understood that the largest alkyl group on the amido-nitrogen atom is the R^ group.

As used herein, the term "non-branching carbon atoms" means carbon atoms having no more than two carbon atoms directly attached. A branching carbon atom is a carbon atom that is directly linked to more than two carbon atoms,

and the term also includes a carbon atom directly linked to the nitrogen atom in the amides or imides. The possible number of branch-forming carbon atoms and thus the possible number of branches is naturally a function of the number of carbon atoms in the alkyl group. One can thus achieve a greater degree of branching not only by increasing the number of side chains on the main chain of the alkyl groups, but also by branching in the side chains. A minimum degree of branching that is generally applicable to the alkyl groups that require branching as explained above is that where the branched alkyl groups contain a maximum of from 5 to 6 consecutive, non-branching carbon atoms.

The effect of the branching with regard to eliciting

the above-mentioned level of stickiness is further enhanced as the degree of mixing of monomer molecules with different R^ groups increases. If such R^ groups are different but all straight-chain alkyl groups, then there is little advantage in mixing, however. However, the beneficial effect of such mixing is evident when mixing molecules with different branched alkyl groups, even when these are closely homologous. This applies, for example, to t-octyl, t-nonyl, t-C^ °9 ci4"amic acid monomers.

It turns out that when you mix t-nonyl monomers and t-C^ monomers, the effectiveness of the mixture increases as the number of different components in the mixture increases. The terms "heterogeneity" or "complexity", as used here, mean the combined effect of branching and mixing.

The preferred monomer (A) mixtures are soluble, liquid to viscous semi-solid mixtures of molecules with different, highly branched R^ groups containing up to 28 carbon atoms, where the average number of carbon atoms in R^ is from about 8 to 24, and the R-^ groups essentially - with regard to the number of carbon atoms - lie within this range. Among the mixtures of alkylamines which contain such alkyl groups, and which can be used as starting materials for the preparation of said monomer (A) mixtures, are "Primene 81-R" and "Primene JM-T",

The amines in these mixtures are stated to be t-alkyl primary amines with highly branched alkyl groups where the primary amino nitrogen is directly linked to a tertiary carbon atom so that they contain the structural element

These mixtures mainly consist of amines with alkyl groups in the range cn~ ci2' "Pr:i-mene 81-R" consists of approx. 90% of C-3 to C-3-alkylamines. "Primene JM-T" basically consists of C18 to C22 alkylamines.

MONOMER (B) COMPOSITION

I. ACRYLATE MONOMERS (B) .

The R2 alkyl groups in acrylate monomer (B) are alkyl groups containing from 1 to 14 carbon atoms, the average number of carbon atoms depending on the average size of R^, the degree of branching in R-^, the extent to which monomer (A) is a mixture of molecules containing various R 1 -alkyl groups,

and whether monomer (A) is the same class of monomer or a mixture of monomer classes. In general, the number of carbon atoms in R,, in the acrylate monomer is on average from approx. 3 to 13 when monomer (A) is an amide derivative of dicarboxylic acids, and R 1 is a lower alkyl containing not more than about 6 carbon atoms. If the average size of R^ is increased within the range of 7-10 carbon atoms, and the degree of branching is increased, R2 can have from 2 to 13 carbon atoms on average. If the average size of R^ is increased within the range of 11 - 24 carbon atoms, and the degree of branching and mixing is increased, R2 can average from 1 to about 13 carbon atoms.

The R 2 alkyl groups can be straight-chain alkyl groups and mixtures of such, branched alkyl groups and mixtures of such, and mixtures of these groups. The R2-alkyl groups that contain more than approx. 9 carbon atoms, should preferably be branched alkyl groups. Mixtures of types of acrylate monomer (B), and especially those where the R 2 alkyl groups are higher alkyl groups, allow greater leeway for the composition of monomer (A). At least 50 mole percent of acrylate monomer (B) must consist of acrylates where the R2~ groups are directly linked to the oxygen atoms at non-tertiary carbon atoms.

The dependency between applicable (A) and (B) components

and the permissible mixing ratios are shown in Table i as a general guide. It is emphasized that the data in table i must be interpreted

in the context of the entire description of the invention, and it should not be understood as a complete presentation.

As shown in table i, the maximum ratio can be increased to approx.

2:3 when the average number of carbon atoms in the R^ groups increases from 1-6 to 7-10 and the alkyl groups are branched. Also, a larger range of alkyl acrylates can be used in the monomer (B) composition. The maximum should not exceed approx. 1:3 if practically all R^ groups are the same.

If one adds branched<e><c>7<->Cl0~ alkyls and especially various branched C^-C^ alkyls to the lower to Cg alkyl groups, then this allows a gradual increase in the maximum ratio for monomer (A), because the addition causes a gradual increase in the average number of carbon atoms in the alkyl groups. Thus the maximum of 2:3 is reached for the third group in Table i as the R-^ groups of monomer (A) consist of an increasing number of branched c^-C^O-N-substituted monomer (A) molecules.

The effect of increased branching and increased degree of mixing on the width of the proportion range is shown in the tables in the fourth group.

In the fifth group in table i, the effect of increased branching and mixing in connection with increasing number of carbon atoms in R.^ is further illustrated. As stated above, the maximum ratio does not exceed a 1:1 molar ratio of monomer (A) to monomer (B). As is generally shown in the five groups in the table, the average number of carbon atoms in R 2 may decrease as the average number of carbon atoms and the complexity of the R 1 -alkyl groups increase. The minimum amount of monomer (A) is greater than 1:19 if R 2 has on average 1-2 carbon atoms, the amount increasing as the average number of carbon atoms and the complexity of the R 2 -alkyl groups decrease.

II METHACRYLATE MONOMERS (B)

The repeating units of methacrylate monomer (B) in the adhesive polymers correspond to esters of methacrylic acid and non-tertiary alkyl alcohols containing from 1 to 14 carbon atoms, on average 4-14 carbon atoms. The non-tertiary alkyl alcohols can have straight-chain or branched alkyl groups, mixtures of branched alkyl alcohols are preferably used.

Table II is analogous to table I and shows that the smallest number of carbon atoms in R2 decreases from approx. 8 to approx. 4 as the complexity of the monomer (A) mixture increases with increasing number of carbon atoms in R^ within the previously described range. The minimum ratio in which monomer (A) can be combined with methacrylate monomer (B) decreases, and the maximum ratio increases, as the average magnitude of R 1 increases and the complexity of the monomer (A) composition increases. Within each proportionality range, the ratio of monomer (A) increases to the maximum of the range as the average size of R 1 and R 2 increases, and the complexity of monomer (A) and (B) increases. Preferably, the molar ratio between monomer (A) and methacrylate monomer (B) should not exceed 1:2. The greatest width for the composition of the methacrylate (B) composition and the ratio between (A) and (B) is obtained with the highly complex monomers

(A) compositions, especially those which are liquid to viscous semi-solid compositions.

There are different ways to prepare polymers according to the invention. (B) monomers and the anhydrides of the dicarboxylic acid can be copolymerized, followed by amidation of the polymer formed. The polymer can also be made by copolymerizing the monomer

(A) and monomer (B), either in solution in an inert solvent or in an aqueous emulsion. The preferred method to

produce polymers according to the invention is the emulsion polymerization process with a redox catalyst system. This polymerization can be carried out both as a continuous and batch process.

Several types of catalysts can be used for this polymerization. Examples of the peroxide type are inorganic peroxide and barium peroxide; organic peroxides such as dicumyl peroxide, ditertiary butyl peroxide, cumyl hydrogen peroxide, diacetyl peroxide and dibenzoyl peroxide; and inorganic peracids such as ammonium persulfate, potassium persulfate and potassium percarbonate. These initiators can be used alone or preferably together with reducing agents such as ferrous salts, monovalent copper, thiosulphate, hydrogen sulphite and tetrathionate salts, dimethylaniline, triethanolamine and alkylene polyamides. Other types of initiator systems can also be used, e.g. ultraviolet light in the presence of organic peroxides or photosensitizers such as benzophenone.

As is well known in polymerization technology, the choice of catalyst depends on many factors: The nature of the monomers to be polymerized and whether it is a solution, mass or emulsion. In general, the amounts of initiators used in the preferred emulsion polymerization system can vary from approx. 0.1 to approx. 2 parts per 100 parts monomer.

Different types of emulsifiers can be used. The emulsifier types used in emulsion polymerization are anionic, not ionic or cationic. Emulsifiers from these groups, which are usually used in the emulsion polymerization of acrylate and methacrylate systems, have been used successfully in the present case, as can be seen from the following examples. The polymer emulsion can be used as such, thickened with thickeners such as polyvinyl alcohol, water-soluble polyacrylates, water-soluble cellulose derivatives, etc. The polymer substance can also be separated from the polymerization medium by coagulation with acids, salts or by freezing. The resulting coagulum can then be washed and dried.

The following examples show the breadth of variation in the properties of the polymers produced, and they show in particular how pressure-sensitive adhesives can be "tailored" even with acrylates and methacrylates which have not previously been used in large quantities in such polymers. The measured data with regard to adhesiveness, adhesion and cohesion are not listed for all the substances, but the example material is sufficient to show the combinations of adhesiveness, adhesion and cohesion that are possible according to this invention.

As the examples show, the polymers can be cross-linked either with organic peroxides or by means of multifunctional compounds which can react with free carboxyl groups in the polymer. It is possible to achieve extraordinary improvements in the cohesive strength of these adhesive polymers, in many cases without significant or detrimental effect on adhesiveness and adhesion.

The polymerization reactions in the following polymer examples were carried out in a glass reaction vessel, equipped with stirrer, thermometer, cooler and inlet and outlet for nitrogen. The reaction vessel was always flushed with nitrogen, and a positive nitrogen pressure was maintained during the polymerization. Where it was necessary to heat the reaction mixture, this was done with a water bath. Where the reaction mixture had to be cooled, it was done either with

a water bath or an ice bath.

The amide acid monomers used in the following examples

on emulsion polymerization, was generally made by amidating the anhydride of the dicarboxylic acid in an inert solvent such as benzene. They were separated from the benzene before being used for the polymerization. In several cases, they were produced by adding

add the amine monomers to the anhydride in the presence of a portion of the acrylate monomer as a solvent. The resulting solution of amide acid monomers in acrylate monomer was used for the polymerization without purification to remove unreacted amines and anhydride. The amounts of amide acid monomers that are reproduced in the following examples,

is based on the assumption that all the amine has reacted with all the anhydride, although this was not always the case. In any case, the amidation reaction was sufficiently complete for practical purposes, insofar as there was no significant difference between a polymer prepared from amide acid monomers, purified with

water and hydrochloric acid, and one which was made of amide acid monomers containing some unreacted substances. The polymers produced from washed acid amides had a higher molecular weight. The monomer amounts are the amounts added to the polymerization batch, as indicated above, and they are not necessarily the exact amounts in which the monomers exist as repeating units in the polymer.

The N-alkylamide derivatives which are prepared from the above-mentioned technical mixture ("Primene 81-R") of mainly tertiary C-j^ to C^-alk<y> lamins are referred to in the examples as N-t-C^-3111^ derivatives. The derivatives which are prepared from the above-mentioned technical mixture of essentially tertiary c,Q to alkylamines ("Primene SM-T"), are referred to in the examples as N-t-C2l~derivatives, and those made from the above-mentioned technical mixture , called t-nonylamine, are referred to in the examples as N-t-Cg derivatives. The molar ratios for these derivatives are based on the molecular weight of derivatives of a C12H25~ainine (neutralization equivalent 191) of a <C>^H^-j-amine (neutralization equivalent 315), and of a CgH1g-amine (neutralization equivalent 142).

N-t-butylmaleamic acid (or -maleic acid monoamide) is a soluble, crystalline, solid. The corresponding N-t-1,1,3,3-tetramethylbutylamine derivative is also a soluble, crystalline,

solid. An "N-t-nonyl"-maleamic acid, prepared by the amidation of maleic anhydride with a mixture of highly branched t-alkyl-

primary amines consisting essentially of N-t-Cg and N-t-C^Q branched amines is a partially soluble crystalline solid, generally soluble in the monomer (B) component. N-t-nonylmaleamic acid is less crystalline than the t-octyl derivative. The effect of mixtures of alkyl groups - especially branched alkyl groups, as the number of carbon atoms increases above 10/ is illustrated by a mixture of "N-t-C±2-branched alkyl" rnalamic acids. This monomer (A) is a mixture which consists of a large number of highly branched alkyl groups, especially t-C-^ to t-C^-alkyl groups with an average of around t-C-^" as described in more detail below. This N-t-C-j^-maleic acid derivative is a very viscous liquid. in contrast, the "N-straight-chain C14" derivative, prepared from maleic anhydride and a mixture of straight-chain alkyl fatty acid amines containing from 10 to 18 carbon atoms and averaging about 14 carbon atoms, is insoluble and crystalline. If the straight-chain amines are replaced by branched isomers, the mixture will increasingly increase in solubility and decrease in crystallinity.

Unless otherwise stated, the catalyst used was potassium peroxosulfate/sodium bisulfite. The quantities of this combination of initiator and reducing agents are correspondingly indicated (ie separated by slashes) in the examples. in most cases the polymer was coagulated by the addition of sodium chloride solution. In other cases, the polymers were coagulated by adding acetic acid or calcium chloride. In most cases, the coagulated polymer was first washed with water and then purified by dissolving in methyl ethyl ketone (MEK) and skimming from there with water. The precipitated polymer was then again washed with water.

An emulsion of these monomers in 200 parts water was made. Solutions of initiator and reducing agent, which were each dissolved in 20 parts of water, were added to the emulsion. The polymerization was started at approx. 53°C. The temperature rose to 62°C and stayed there for approx. 10 minutes further addition of catalyst did not increase the temperature. The polymer was then separated from the emulsion and purified.

The polymer was white and soluble in toluene, chloroform

and MEK. It was insoluble in n-heptane. Yield 92.3%, limiting viscosity number 1.35, Huggins constant 0.521, Brookfield viscosity 870 (15% in MEK).

This polymer can be used as a pressure-sensitive adhesive. It can be applied from a solution to the usual substrates used for pressure-sensitive adhesives. The sticky film on an adhesive tape thus produced gave good adhesion to stainless steel. The tape could be removed from this surface without breaking or separating from the adhesive film. The removal of the tape from the steel surface took place in jerks. Adhesives that are removed in jerks have been called "harsh" adhesives.

The monomers and the soap were added to 300 parts of water with stirring until a good emulsion was obtained. This was heated to 51°C. Initiator and reducing agent were added separately, each dissolved in 50 parts water. The temperature rose to a maximum of 74°C during approx. 5 minutes, in total the polymerization was carried out for 45 minutes.

Part of the polymer emulsion was coagulated with salt. The precipitated polymer was washed with water and dried. The polymer was dissolved in MEK, precipitated with water and then washed with water. This purification was repeated. This washing method ensures that soap and other contaminants present in the polymer are removed.

The polymer is soluble in toluene, ethyl acetate, acetone and MEK. It is insoluble in n-heptane.

Yield 99%, specific viscosity 1.60, Huggin's constant

0.47, Brookfield viscosity 765 (15% in MEK).

This polymer is a pressure-sensitive adhesive polymer. It is softer and more adhesive than the polymer in the previous example. The creep resistance of this polymer, as a measure of the cohesive strength, is less than the creep resistance of the previous polymer. From a solution of this polymer, clothing tape was made by spreading a coating of it on polyethylene terephthalate films. In addition to the polymer, the solution contained 0.8% hexamethylenediamine. The diamine compound then cross-linked the polymer upon heating. An exceptionally high creep resistance was obtained. In some cases, the tape did not creep even after 60 days of creep resistance testing.

Other polymers according to the invention are shown in Table III where acrylate and methacrylate comonomers are listed together with the molar amounts in which they were present in the polymerization rate for each mole of N-t-C-j^-maleamic acids. These polymers were produced by the polymerization process that is generally described above and illustrated in examples 1 and 2. The catalysts used were the redox combination of potassium peroxosulfate/sodium hydrogen sulfite in all examples, except in examples 4, 7 and 11. The polymers in examples 4, 7 and 11 were prepared with hydrogen peroxide/ferroammonium sulfate initiator/activator combinations.

The emulsifier used to make the polymer

in Example 4, sodium lauryl sulfate and isooctylphenyl polyethoxyethanol were in amounts of 3 and 5% respectively relative to the weight of the monomer charge. The emulsifier used in examples 5, 10 and 20 was in each case sodium lauryl sulfate and polyalkylene glycol ether in respective amounts of 6.1 and 4.1% in example 5 and 2.8 and 1.6% in example 10 and 2.0 and 3% in Example 20. The N-t-C12 maleic acid monomers in Example 5 were purified by extraction with hydrochloric acid before being added to the polymerization batch. The emulsifier in Example 11 was 5% ammonium laurate. in Example 19, the emulsifiers were 2.7% sodium lauryl sulfate and 2.5% nonylphene poly(ethyleneoxy)ethanol.

In all the other examples in table iii, the emulsifier was sodium lauryl sulfate which was used in amounts from approx. 2% to approx. 8% by weight of the monomers. The temperatures for the polymerization mixtures in these examples were within the range from approx. 10°C to approx. 80°C. In most cases, the starting temperature was around 48-50°C and the maximum temperature approx. 60-70°C.

All polymers listed in Table III exhibited adhesive properties, except for the polymer of Example 8. A film cast from a solution of this N-t-Cl2 maleamic acid/t-butyl acrylate copolymer was hard and plastic.

Although the t-butyl acrylate, as the only acrylate, together with the amide acid did not yield a pressure-sensitive adhesive polymer, it can be used in pressure-sensitive adhesive polymers with other acrylate esters of non-tertiary alkyl alcohols. The other acrylates do not have to be alkyl acrylates which in themselves are capable of being copolymerized into a pressure-sensitive adhesive; see Example 7. This N-t-C^2-mal-e amic acid/ethyl acrylate/t-butyl acrylate terpolymer is tacky and suitable as a one-component pressure-sensitive adhesive polymer. It is elastic and softer than the polymer of Example 8, although it does not have the degree of softness usually characteristic of many common rubber resin pressure sensitive adhesives. A softer polymer with t-butyl acrylate can be obtained by mixing with higher alkyl acrylates or by using larger amounts of either non-tertiary alkyl acrylates

leter or the amide acid.

The polymers in examples 1-7 contain alkyl acrylates where the alkyl chains contain on average less than four carbon atoms. The polymer in example 5 had a rather low molecular weight. Cross-linking or curing this polymer with 1% of an epoxy compound (Epoxide 201) and 0.5% tetraethylenepentamine leads to improved cohesive strength. The molecular weight of a polymer of the monomers used in example 5 can be increased by known methods whereby the cohesive strength is improved.

The polymer in example 3 has a higher molecular weight than that in example 2, which is evident from their respective limiting viscosity numbers (polymer in example 2: 1.60 in example 3: 2.55) The cohesive strength in these polymers, measured by the creep resistance, is shown in Table VI.

The polymer in example 4 is a coarse pressure-sensitive adhesive. The polymer of Example 6 is softer than the polymers of Examples 1, 2, 3 and 7, indicating a trend towards softer polymers in this series with increasing length of the alkyl acrylate monomer (or average acrylate monomer) in the polymer.

In the polymer series in examples 8-11, where the only acrylates are butyl acrylates, the tendency towards softer polymers goes from t-butyl, to isobutyl, to n-butyl acrylates. The polymer in Example 9 is

a coarse pressure-sensitive adhesive, fairly firm and stiff, but softer than the amide acid/t-butyl polymer (Example 8) previously described.

The continuing tendency towards less rigid and rough, more flexible and softer, more sticky polymers is evident from the polymers in examples 12-16. The pressure-sensitive adhesive polymers in Examples 12

and 13 is softer than that of Example 2. The polymer of Example 14 is also a suitable single component pressure sensitive adhesive polymer. With regard to softness, it is roughly equivalent to the polymers in examples 12 and 13. The polymers in examples 15 and 16 have a fairly low molecular weight, are quite soft and sticky. They are suitable as an adhesive for labels. The creep resistance of these polymers is improved if they are cured or cross-linked, without this having any significant detrimental effect on stickiness and adhesion.

The polymers in examples 17-19 are pressure-sensitive adhesive polymers made from methacrylates where R2 has an average of less than 6 to 10 carbon atoms. The polymer in Example 17 can be classified

as a rough, pressure-sensitive adhesive.

Table IV lists polymer compositions containing different types of monomer (A) units and different compositions thereof with respect to the complexity of the R₂ groups. All polymers in Table IV are pressure-sensitive, adhesive polymers, whether monomer (b) is of the acrylate or methacrylate type. However, the polymer of Example 25 was nearly tack-free when cast from solution as a thin film on a flexible strip of poly(ethylene terephthalate) sheet. This thin polymer film appeared to be partially crystalline. Upon heating to 176°C for 2 minutes, the polymer became extremely tacky, lost its crystalline appearance, and remained tacky throughout the months the tape was observed and tested. The tertiary-octylmaleic acid monoamide from which the polymer in Example 25 was made was a virtually pure monomer, and as previously described, it was crystalline in the monomer state.

Footnotes to Table IV:

(a) Mixture of maleic acid monoamides with the isomeric groups

tertiary butyl, isobutyl and n-butyl - produced by reacting 1

mol of maleic anhydride with 1/3 mol of each of these primary butylamines. (b) Mixture of N-dialkyl acid monoamides prepared from maleic anhydride and a mixture of equimolar amounts of di-n-butyl-diisobutyl, diamyl and dipropylamines.

As previously explained, the N-t-Cg monomer (A) is a partially crystalline solid. The polymer of Example 22 made from this apparently showed no crystallinity and was pressure sensitive in its preparation. t-Butyl monomer (A) is a crystalline solid, but the polymer thereof, in Example 24, apparently showed no crystallinity. It was pressure-sensitive during preparation, which shows that complex monomer (A) mixtures are not necessary when it comes to monomer (A) components containing lower N-alkyl. A polymer prepared from the crystalline mixture of N-n-alkyl maleleptamic acids with an average of approx. 14 carbon atoms in the alkyl groups (as previously described) and a mixture of ethyl-

and butyl acrylates were crystalline and not tacky. This polymer contained about 34% amide acids and 66% acrylates by weight.

The pressure-sensitive adhesive according to the invention can

as stated also contain other components, which do not adversely affect the pressure-sensitive, adhesive properties of the polymer seed to a greater extent. These components can be other monomers that are copolymerizable with monomer (A) and monomer (B) y or other substances that are mixed with the polymer, such as thickening resins, plasticizers, antioxidants and stabilizers.

Illustrative examples of copolymerizable compounds

- according to point C of the claim: Acrylic and methacrylic acids, nitriles, unsubstituted amides and alkyl-substituted amides where the alkyl substituents can contain from J.-28 carbon atoms; and esters of acrylic and methacrylic acid and alcohols selected from a group consisting of a) aromatic substituted alkyl alcohols, b) monocyclic and polycyclic alkyl alcohols, c) halogen substituted alkyl alcohols, d) amino substituted alkyl alcohols, e) cyanoalkyl alcohols,

and f) alkoxyalkyl alcohols. Examples of the previously mentioned alcohol classes are benzyl alcohol, dehydroabiethyl alcohol, dihydroabiethyl

alcohol, tetrahydroabiethyl alcohol, cyclohexyl alcohol, terpene alcohols, chloroethyl alcohol, fluoroethyl alcohol, N-dimethylethyl alcohol, cyanoethyl alcohol and ethoxyethyl alcohol. Other copolymerizable monomers are monoethylenically unsaturated dicarboxylic acids and anhydrides, unsubstituted imide and amide derivatives thereof, and esters of said acids and alkyl alcohols and alcohols described above for the acrylic and methacrylic acids.

Vinyl esters, vinyl ethers and certain olefinic hydrocarbons can also be polymerized together with the monomers (A) and (B). Examples are vinyl acetate, vinyl propionate, vinyl hexanoate, methyl vinyl ether, propyl vinyl ether, octyl vinyl ether, tridecyl vinyl ether, vinyl chloride, vinylidene chloride and styrene.

Preferred copolymerizable monomers are acrylic acid, methacrylic acid, alpha-beta and alpha-alpha unsaturated dicarboxylic acids and anhydrides and styrene. Particularly preferred monomers are those containing polar reactive groups, such as free carboxylic acid groups. The ability of long-term adhesion has been observed in polymers containing polar groups. The free carboxylic acid groups offer opportunities for cross-linking. The copolymers according to the invention can contain relatively large amounts of free carboxylic acid groups. This will be dealt with in more detail in connection with the comparison examples. Cross-linking of the polymers can be effected within seconds.

The examples in Table V indicate representative polymers

with a content of a (C) component. All the polymers in Table V

were pressure-sensitive adhesive polymers as prepared, except for the polymer in Example 35. This was adhesive-free when made.

It can be used as a binder for non-woven fabrics or as a thermoplastic adhesive. A pressure-sensitive adhesive was made from this polymer by softening with glycerol. In general, the polymers that contain acrylic acid monomer (C) are somewhat tougher than polymers that do not contain this acid.

Acrylonitrile works so that the polymers become stiffer. The polymer in example 36 is thus stiffer than the polymer in example 11. It is suitable for use as a one-component pressure-sensitive adhesive and can be classified as a coarse adhesive. If a more sticky polymer of the monomers in example 36 is desired, the acrylonitrile content can be reduced. A tackier and softer polymer that is less coarse can also be obtained with substituted acrylates of larger size, preferably mixtures of acrylates, instead of the butyl acrylate used in the polymer in Example 36.

If the cyano group is attached to the alkyl chain of the alkyl acrylate, the effect on tackiness and other properties is quite different from the effect of the cyano group if its nitrogen groups are attached directly to a terminal carbon atom of the acrylic monomer, such as in acrylonitrile. The cyanoethyl acrylate-containing polymer in Example 37 was less rigid than the polymer in Example 36, the latter showing much lower stickiness and adhesion.

The pressure-sensitive adhesive polymer in Example 38 can be characterized as a heat-setting adhesive. As prepared, the polymer had a creep resistance of about 9 minutes. After heating for approx. 10 minutes at 176°C, the creep resistance improved to approx. 19 hours. It appears that this polymer is capable of cross-linking itself.

The polymers contain one free carboxyl group per repeating amide acid unit in the polymer. These are reactive groups that enable further reaction, such as cross-linking. By cross-linking, it is possible to improve the cohesive strength of the polymer. As shown by the adhesive tape examples in Table VI, cured or cross-linked polymers have been produced with substantially improved cohesive properties without any failure of adhesion and without detrimental effect on adhesiveness. Thermosetting pressure-sensitive adhesive polymers have also been made. The degree of thermosetting depends on the amount of crosslinking agent used in the polymer.

(a) Ester of acrylic acid and tridecyloxo alcohol.

(b) "Abitol" is technically hydroabiethyl alcohol, and alcoholic mixture made from resin acids which have been hydrogenated to reduce their unsaturation. It contains about 15% non-alcoholic substance, while the alcohol part is about 45% tetrahydroabiethyl alcohol,

40% dihydroabiethyl alcohol and 15% dehydroabiethyl alcohol.

cr Suitable agents for cross-linking or curing the polymer, multifunctional organic compounds, organic peroxides, epoxy compounds, formaldehyde resins and polyvalent metals which can react with free carboxylic acid groups. The cross-linking can also take place by irradiation, with ultraviolet light or electrons.

The multifunctional organic compounds include polyamines, polyhydroxy compounds and polyisocyanates, cyanoguanidine and 1,4-butanediol. Organic peroxides that have been used successfully are benzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide and cumene peroxide. Zinc hydroxide and calcium oxide are useful polyvalent metal compounds. Suitable formaldehyde resins are phenol/formaldehyde resins, and melamine/formaldehyde resins.

The pressure-sensitive adhesive tapes in the following examples were prepared by spreading the adhesive from a solution onto a film of poly(ethylene terephthalate) or a paper substrate. Solutions of the polymers were made in MEK with and without cross-linking agents. After the pressure-sensitive adhesive polymer was placed on the substrate, the tapes were allowed to dry for several hours at room temperature. The dried adhesive coatings ranged from 0.025 to 0.050 mm in thickness. During storage, the adhesive coatings were covered with a sandpaper.

The pressure-sensitive adhesive polymers to which cross-linking agents were added were cured in an air circulation oven at 65

to 204°C for different times. The adhesive properties of the hardened adhesive tapes described in the following are properties of the adhesives which have been hardened without sandpaper protective covering over the adhesive surface, unless otherwise stated. In many cases, there appeared to be less reduction in stickiness if they were cured

without the sandpaper covering the adhesive.

The creep resistance is indicated by "IK" in Table VI if

the tape did not creep more than 3 to 6 mm after at least 48 hours. The tapes in examples 38 6g~ 40 did not creep even after 60 and 40 respectively

days of testing. In many cases, the creep resistance was so great that the tapes had to be subjected to extraordinary conditions during the test to determine the limits of the creep resistance. Adhesives cross-linked with hexamethylenediamine, benzene peroxide and calcium oxide,

did not creep at either 71 or 115°C, even with a 2 kg load.

The pressure sensitive adhesive polymer of Example 2, crosslinked with diamine, did not creep even at 160°C at 2 kg load for one week. When the tape was removed from the sample plate, it appeared that this polymer had been thermoset. In contrast, tapes made with the polymer of Example 2 with the diamine and exposed to temperatures of up to 115°C for two and three months were still tacky and had high adhesion.

In some examples, two values are given in the adhesion column. the values in parentheses are the tape's adhesion measured after testing for creep resistance.

Footnotes to table vi:

(a) The sandpaper on during curing.

(b) The adhesive tore during the test.

(c) During 20 days at 121°C.

(d) After 35 days of testing very sticky to the touch.

(x) "Instron" adhesive values; all the others were "Probe-tack"

adhesive values (explained in the last part of this patent document).

The tape was exposed to ultraviolet light irradiation in the presence of air. The creep resistance of the irradiated tape was significant

greater than the creep resistance of unirradiated tape.

The diamine in the crosslinking agent column is 1,6-hexanediamine; ^ 2°2 Sr t,enz°y1Peroxide; BDCL is 1,4-butanediol; DiCup is dicumyl peroxide; the epoxy compound is a dicyclic diepoxycarboxylate (Epoxide 201); TEPA is tetraethylenepentamine; Bu 2 O 2 is di-t-butyl peroxide; CuOOH is cumene hydroperoxide,; MFR is melamine/formaldehyde resin and MFRZ is the same resin plus a small amount of zinc chloride; and TY is a mixture of TEPA and "Epoxide 201". The numbers given after the cross-linking agents are the percentage of cross-linking agent in relation to the polymer weight.

The degree of cross-linking decreases as the size of the alkyl group in the acrylates increases. The cross-linking reaction with the multifunctional agents is quite rapid, especially in adhesives of the polymers containing acrylic acid. If it concerns cross-linking agents that react with the acid groups, the cross-linking is carried out within a few minutes at temperatures around 120°C

and for less than one minute at a temperature of approx. 180°C.

The combination of tetraethylenepentamine and the epoxy compound is somewhat better than either the amine or the epoxy compound alone. The epoxy compound appears to reduce the curing speed and the number of crosslinks. The degree of cross-linking can be regulated by varying the ratio between epoxy compound and amine.

Among the adhesive tape examples, there are examples of cross-linking or curing which serve to transfer a cohesion-wise rather weak pressure-sensitive polymer material into a pressure-sensitive adhesive polymer suitable for use in strapping etc. See tape examples 61, 70, 72, 76 and 78. In addition to improving cohesive strength, cross-linking can also increase the polymers' resistance to solvents.

EXAMPLE 100

Adhesive tape was produced with a polymer, made from N-t-C12 maleamic acid, ethyl acrylate, 2-ethylhexyl and ethylene glycol dimethacrylate in the molar ratio 1:1:4:0.056. This polymerizate was prepared with a hydrogen peroxide/ferroammonium sulfate catalyst; the emulsifier was a combination of ammonium lauryl sulfate and nonylphenoxypoly(ethyleneoxy)ethanol. After the polymerization was complete, 2% methylethyl cellulose was added to the emulsion in relation to the polymerizate. A 0.0038 cm thick film of the polymer was sputtered directly from this emulsion onto a polyethylene terephthalate film and dried. The tackiness of the adhesive film was 630 g. Its peel adhesion was 223 g/cm. The tape did not creep, even after 4 days of testing at 71°C.

The above comparative examples shall serve to illustrate the important function of monomer A in the pressure-sensitive adhesive polymers of the acrylate/acrylic acid type. The data for these different polymers are summarized in Table VII.

In comparative examples 1 and 2, one mole of maleic mpnoamide is replaced by 2 moles of 2-ethylhexyl acrylate. The polymer of Example 1 is to be compared with the polymer of Example 34, and the polymer of Comparative Example 2 is to be compared with the polymer of Example 35. It is to be noted that the peel adhesion values for the polymers of Comparative Examples 1 and 2

is lower than that of Examples 34 and 35. This is the case even though the weight percent amount of acrylic acid in the polymers of Comparative Examples 1 and 2 is approximately the same as in Examples 34 and 35. However, it should be noted that the weight percent of carboxyl groups is reduced.

However, comparative examples 3-8 illustrate best

that monomer A plays a significant role in these polymers. The comparison examples with different numbers should be compared with example 34, and the examples with the same number should be compared with example 35.

In comparative examples 3 and 4, 1 mol of 2-ethylhexyl acrylate is used instead of 1 mol of maleic acid monoamide. As shown, a reduced peeling adhesion is obtained when the maleic acid monoamide is omitted from the polymer and 1 mol of 2-ethylhexyl acrylate is added.

In comparative examples 5 and 6, the maleic acid monoamide is omitted, and an equal molar amount of acrylic acid is added. Both the amount of acrylic acid and the amount of carboxyl groups in examples 5 and 6

is greater than the amounts in examples 34 and 35, respectively. The peel adhesion for these polymers is significantly lower than the peel adhesion for the polymers according to examples 34 and 35.

Comparative examples 7 and 8 are included to illustrate what happens when monomer A is omitted without any other monomer being introduced to replace it. In both of these examples, the weight of the acrylic acid is far above the amount by weight recommended for the previous pressure-sensitive adhesive polymers of the acrylate type. The relative amounts of the free carboxyl groups are, however, approximately the same as for the polymers in examples 34 and 35. Although there is thus a certain similarity here, it should be noted that the peel adhesion is far better for the polymers according to examples 34 and 35.

It should be emphasized that the examples which best illustrate the advantages according to the invention are comparative examples 5 and 6. It is well known that the introduction of free carboxylic acid groups into the polymer is a problem in connection with pressure-sensitive adhesive polymers. This is clear from the opposed German patent document 1 079 768. The presence of free carboxylic acid groups improves the adhesiveness of the pressure-sensitive adhesive polymer, but the maximum

amount that can be introduced into the polymer (through the acrylic acid monomer),

is limited because the adhesive becomes "rough" (harsh) at high concentrations. Thus, although the adhesiveness of the polymer can be improved, it becomes undesirably "rough". By adding 1 mol of N-t-C^-maxeins<y>remonoamicl', which also provides 1 mol of free carboxylic acid groups, it is possible to introduce an amount of free carboxylic acid groups into a pressure-sensitive adhesive polymer that far exceeds the amount that can be used according to German patent 1 079 768.

For a given acrylate mixture, ever-increasing amounts will

of acrylic acid result in an increasingly harder, coarser pressure-sensitive adhesive. Over approx. 12% acrylic acid is the combination of tackiness, adhesion and cohesion such that the polymer is not a commercially practical adhesive. Although the acrylic acid gives the polymer good properties as a pressure-sensitive adhesive, the stiffness-producing effect of the acid will at a certain point make the copolymer unusable. According to the present invention, this limit is raised significantly in terms of the total amount of acid monomers.

This has been achieved by adding the maleic acid monoamide, and this monomer contributes additional amounts of polar groups, namely a carboxyl group and an amido group.

The difference between rough and soft pressure-sensitive sheet materials will be explained in more detail. Coarse pressure-sensitive adhesives are particularly useful for special applications where permanent or particularly strong bonding is desired, but are considered unsatisfactory for general purposes due to uneven unrolling from rolls of adhesive tape. In the U.S. patent document 2 601 016 describes pressure-sensitive copolymers of isoamyl acrylate and acrylonitrile or methacrylonitrile. These adhesives have no recognized commercial utility because they

are rough and yet do not provide a permanent bond. in contrast to these, it is coarse, pressure-sensitive adhesive sheet material that is be-

written in the aforementioned "Reissue" patent 24,906, in production on a large scale for such purposes which require a strong, permanent bond. Soft pressure-sensitive adhesives, on the other hand, are used commercially in such cases where it is important that they can be easily removed from a non-sticky backing, such as in adhesive tape rolls for use at home or in the office.

Two methods were used to test the stickiness. By

one was used an "instron machine", and the values measured with

this, is called "Instron adhesive values". The second and preferred method uses an apparatus described below. This method is referred to here as "probe tack test", and the values measured with this method are called "probe tack" or "probe-tack values".

The apparatus used in the "probe tack test" consists of

four functional parts: (1) A 0.636 cm diameter cylindrical steel rod attached to a compression-loaded spring of (2) "Series L Hunter Mechanical Force Gage" (Hunter Spring Company, brochure

750/FG, revised February 1961), (3) a ring with an opening slightly larger than the diameter of the rod and (4) a carrier for the ring which is moved downwards to bring the ring around the rod and then upwards to remove the ring from it. This carrier moves 2.54 mm per second.

At the beginning of the test, the carrier is at the highest point

in its path, and the ring rests on the wearer. The ring lies on the carrier in such a way that the opening in the ring is in line with the rod placed below it.

A strip of adhesive tape is attached to the ring with the adhesive side down, so it covers the ring opening. As the carrier is moved downward by a synchronous motor, the adhesive surface exposed above the opening is brought into contact with the flat surface of the rod. The band and the ring attached to it remain suspended on the pole as the wearer continues to descend. The carrier then changes direction of movement and returns to pick up the ring, whereby the band is removed from the rod's surface. Separation begins after one second of contact between the stick and the adhesive. The force exerted to separate the tape from the rod is recorded by the force meter. The specified value is the "probe-tack" value. The weight of the ring is such that it gives a contact pressure between the rod and the adhesive surface of 0.0703 kg/cm^.

When performing the "Instron" test, a strip of adhesive tape is held flat in a perforated tape holder. The adhesive surface is exposed through the perforation. The holder and band are attached to the crosshead of an "Instron" machine. A machined and polished brass rod of 7.15 mm diameter is held in the jaws of the "Instron" machine and brought into contact with the exposed surface of the adhesive tape with a pressure of 0.0703 kg above the contact surface. After two seconds of contact between the rod and the adhesive, the rod is removed,

and the force needed to remove the rod is recorded by

The "Instron" machine. The recorded force is the "Instron" adhesive value.

The table's "adhesion" refers to the force needed

to remove the adhesive tape from a stainless steel surface after contact with it for 16 hours at a temperature of around 2l°C. The tape was torn from the surface at an angle of 180°. A 25.4 mm wide band is used for this sample.

The creep resistance test must measure the resistance of the coating

of adhesive against shear forces within the plane of the adhesive coating.

A strip of adhesive tape, 25.4 mm wide, is attached to a vertical surface

of stainless steel. The surface is heated to the desired temperature. A weight of one kilogram is suspended from the lower end of the band, which hangs freely from the metal surface. The time to failure is the time until the band falls from the stainless surface under the one kilogram weight load.

Claims (1)

Pressure-sensitive adhesive, which consists of copolymers of alkyl esters of acrylic or methacrylic acid and N-alkyl-substituted amides of ethylenically unsaturated carboxylic acids and optionally an ethylenically unsaturated compound that can be copolymerized with this, characterized in that the copolymer is a copolymer of: (A) N-alkyl-substituted amido monomers of the general formula: (B) ester monomers of the general formula where the weight ratio between monomer (A) and monomer (B) lies within the interval between 1:19 and 3:1, and where the molar ratio between monomer (A) and monomer (B) does not exceed 1:1, in which formulas (1) R and R' is hydrogen or methyl, (2) the R^ groups are alkyl groups, containing up to 28 carbon atoms, where the average number of carbon atoms of the alkyl groups is not greater than 24, and the alkyl groups containing more than 6 carbon atoms are mainly branched, being the extent of branching is increased, when the size of the alkyl groups is increased, (3) the R 2 groups are alkyl groups, containing up to 14 carbon atoms, where at least 50% of the molecules of the ester monomer have the R 2 groups bonded to the oxygen atom at non-tertiary carbon atoms, and (4) The R 3 groups are hydrogen or alkyl groups, containing up to 10 carbon atoms, where the alkyl groups containing more than 6 carbon atoms are mainly branched alkyl groups, and optionally (C) ethylenically unsaturated monomers of the following types: monocarboxylic acids or dicarboxylic acids or esters, amides, imides or anhydrides thereof, vinyl esters or ethers or alkenic hydrocarbons, which are copolymerizable with the monomers (A) and (B), in a amount up to 50% by weight of the sum of the monomers (A) and (B).