IE49518B1 - Thermoplastic elastomeric composition - Google Patents

Description

This invention relates to a thermoplastic elastomeric composition comprising a blend of (A) a high molecular weight copolymer of ethyl or butyl acrylate or mixtures thereof with an ethylenic monomer containing an acid group and (B) a water-soluble polyvinyl lactam.

It has previously been proposed to provide chemoplastic elastomeric compositions in the form of oil extended hydrogenated block copolymers of styrene and conjugated dienes as described, for example, in U.S. Patent Specification No. 3,485,787. Such compositions are unlike ordinary elastomers in that they possess the necessary strength without vulcanization or cross-linking and, therefore, they perman ently retain their thermoplasticity. Acrylic elastomers have been made by chemically cross-liking polymers of acrylic esters such as polymers of ethyl or butyl acrylate, which'polymers without cross-linking have inadequate tensile .strength for most purposes, but such cross-linking destroys ' or greatly decreases the original thermoplasticity of the polymers. It has also been proposed to react water-soluble poly (N-vinyl lactams) with polymeric carboxylic acids (including copolymers) to form water-insoluble compositions useful for a variety of purposes as described in Stoner et al. U.S. Patent 2,904,457; and in Ono et al. U.S. ,975,570, in which it was proposed to improve the moisture permeability of conventional preasure-sensitive adhesives which are copolymers of alkyl acrylates with acrylic or methacrylic acid by blending with then hydroxyethyl cellulose, it was stated that blends of such adhesives with poly (vinyl pyrrolidone) did not exhibit improved moisture permeability. It has also been proposed to react watersoluble poly (N-vinyl lactams) with polymeric carboxylic acids (including copolymers) to form water-insoluble compositions useful for a variety of purposes, as described in Stoner et al. U.S. Patent 2,901,457· As pointed out by Stoner et al. at column 4, lines 56-73» the reaction product there described always has substantially the same properties and contains the two polymeric components in the same proportions regardless of the proportions of the two used to make the product. The compositions of the present invention, on the other hand, vary in properties and in proportions of components depending upon proportions of starting materials.

There is described in U.S. Patent Application No 956,061 filed 30 October 1978, a pressure-sensitive adhesive compostion which is a blend of a poly (N-vinyl lactam) with certain acrylic ester copolymers of relatively low molecular weight. There is also described U.S.

Patent application No. 957,885, filed 6 November 1978,a highly water-sorptive compostiion which is a blend of large pro portion of a poly( W-vinyl lactam) with certain copolymers.

It has now been found that high molecular weight copolymers of ethyl or butyl acrylate or mixtures thereof with acidic ethylenic monomers in which the acidic group is preferably sulfonic, phosphonic or carboxylic, which copolymers are thermoplastic, can be converted into nontacky, non-adhesive, strong and tough elastomeric compositions without loss of thermoplasticity by blending with the copolymers a poly( N-vinyl lactam), the total blend. containing from 2 to 15% of ‘ poly(N-vinyl lactam) hy weight.

The copolymers employed in the present invention have high molecular weights, from about 6000,000 to 1,000,000 or more, have glass transition temperatures from about -10°C to about -50°C, and-are copolymers of ethyl or butyl acrylate or mixtures thereof with ethylenic monomers containing an acid group which is preferably carboxylic, sulfonic or phosphonic, such as acrylic or methacrylic acid, crotonic acid, maleic acid, 2-sulfoethylmethacrylate, and 1-phenylvinylphosphonic acid. Host preferably, the acid group in the ethylenic monomer is carboxylic, acrylic acid being the acidic monomer of choice. The amount of copolymerizable ethylenic acid-containing monomer in the copolymer may vary from 2 to 10% by weight of the copolymer, the balance being ethyl or butyl acrylate.

The N-vinyl lactams, polymers of which can he used in. the present invention include those having, the structure in which. X represents an alkylene bridge having 5 to 5 carbon atoms, suoh as 1-vinyl-2-pyrrolidone, i-vinyl-5-methyl2-pyrrolidone , 1-vinyl-2-piperidone, and N-vinyl-epsilon5 caprolactam; the polymers may have molecular weights from 10,000 to 1,000,000 or more. Polymers of 1-vinyl-2-pyrrolidone, ie those in which X represents -CHgCI^CHj- are preferred. The amount of polymeric N-vinyl lactam in the blend can vary from 2 to 15% by weight of the total blend.

Preferably the weight percent of poly (N-vinyl lactam) based on the total weight of polymer and copolymer should total from 5 bo 15· The copolymers employed in the composition of the present invention can be prepared by conventional poly15 merization processes in emulsion, in solution, or in bulk; they may range from about 600,000 to 1,000,000 or more in molecular weight, preferably from 750,000 to 1,000,000 or more. The poly (N-vinyl lactams) which are blended with the copolymers can also be prepared by conventional procedures and are widely available commercially.

The blended compositions can be made by mixing together solutions of the copolymers and of the polymeric N-vinyl lactams in any desired vehicles or solvents which are miscible with each other, then removing the vehicle or solvent, as by evaporation. It is also possible to blend the copolymer with the polymer on conventional mixing equipment such as a two-roll mill or in an extruder.

Although different polymers and copolymers are. normally considered to he incompatible with one another when mixed, and incapable of forming a homogeneous blend having properties different from either of the components, the blends of the present invention are optically clear and transparent in the absence of any fillers or similar additives, indicating that the blends are homogeneous at least to the extent that no discrete particles of either 0 component greater than 4-,000 A in diameter are present.

Because of the thermoplasticity of the blended compositions of the present invention, they can he repeatedly formed or shaped simply hy heating to elevated tem20 peratures, e.g. 17O-2OO°G and subjecting them to pressure, as for example in a mold or in an extruder nozzle. ’«Then cooled to room temperature, the shaped articles made from the blended composition are transparent, extremely tough, and elastic in nature. They can be stretched to at least 500% of their original length, from which they rapidly regain their original length when tension is released:..

The blended compositions exhibit considerably enhanced tensile strength and modulus of elasticity, and somewhat decreased elongation as contrasted to the non5 blended acrylate copolymers. The magnitude of these properties of the blended compositions depends upon the amount of acidic comonomer, molecular weight of the copolymer, the relative proportion of poly (H-vinyl lactam) to copolymer, and the molecular weight of the poly (if-vinyl lactam). In general, an increase in the magnitude of the above variables results in increase of tensile strength of the blended composition.

In order to achieve desirable properties and service life of the blended compositions, it may be desirable to include in the composition in addition to the polymeric ΪΓ-vinyl lactam and the copolymer, conventional stabilizers, pigments, fillers and other compounding agents.

These blended compositions are especially suited for acceptable performance in an environment where there is exposure to sulfur-modified oils at elevated temperatures, under which conditions the unsaturated rubbers of commerce fail. The acrylic elastomers, as a class, are not recommended for use ia water, steam, or water soluble materials, such as methanol or ethylene glycol. An important application of these blended compositions is as seals and gaskets for auto engines and other machines.

The following specific examples are intended to illustrate more fully the nature of the present invention without acting as a limitation upon its scope.

Examples 1-6 Copolymers of ethyl acrylate with three different proportions of acrylic acid were prepared by conventional solution polymerization procedures by dissolving the desired proportions (40% solids) of monomers in ethyl acetate and by employing as the initiator of polymerization a small amount (0.1% by weight of the monomers) of a free radical generator such as benzoyl peroxide or 2-t-butylazo2-cyano propane. Polymerization was carried out at 8O-9O°C to a high degree of conversion. The peak molecular weight as determined by gel permeation chromatography and stress strain properties as determined by ASTM procedure D-412 were as follows: Ethyl Acrylate Copolymers No. Wt% Acrylic Acid Hp χ 103 Tensile Strength, PSI at Ultimate Elongation,% 100% 300% Break 1 3 923 38 50 85 1155 2 4 1076 40 71 106 1285 3 5 1076 - - 202 670 Blends of the copolymers with poly (vinyl pyrrolidone), grads K-90 (M.w. 360,000), were prepared by dissolving appropriate amounts of the respective copolymer and the polymer in chloroform and then heating the. resulting solution at 120°0 under reduced pressure to evaporate the. solvent and leave a transparent solid polymeric residue.

The dry polymeric blends were then formed into sheets 2-3 mm in thickness in a press heated at 170°C and their stressstrain characteristics determined by the same ASTM proce10 dure as above. The results were as follows: Blend of Copolymer with Poly(Vinyl pyrrolidone) Copolymer No. Wt% of Poly(vinyl pyrrolidone) Tensile Strength, PSI at Ultimate Elongation, % 100% 300% Break 1 5 63 100 323 706 1 10 76 156 508 773 2 5 67 129 508 1040 2 10 90 200 705 738 3 5 106 229 557 853 3 10 120 312 996 773 Example 7 A copolymer of 97.5% by weight of butyl acrylate and 2.5% by weight of acrylic acid was prepared by polymerizing the monomers in solution (30% solids) in refluxing ethyl acetate using the same Initiator as in the preceding Examples. The resulting copolymer was isolated by beating the solution at 12O°C under vacuum to evaporate volatile materials. A mixture of 8.57 grams of the dry copolymer and 0.95 grams of poly (H-vinyl-2-pyrrolidone) having a molecular weight of 360,000 was dissolved in 50 ml of chloroform and the solution was heated at 120°G in vacuum, to evaporate the solvent, leaving the solid transparent blended polymer composition. The blended composition «as formed into a sheet as in the preceding Examples.

The formed sheet was transparent, tough and elastic but more compliant than any of the blends of Examples 1-6.

Claims (9)

1. A thermoplastic elastomeric composition comprising an optically clear blend of (A) a high molecular weight copolymer of ethyl or butyl acrylate or mixtures thereof with from 2 to 10% hy weight, based on the weight of the copolymer, of a copolymerizahle ethylenic monomer containing an acid group and (B) a water-soluble polymer of a vinyl lactam having the structure C-0 in which X represents an alkylene bridge having three to five carbon atoms, the copolymer (A) having a molecular weight of at least 600,000 and a glass transition temperature from -10°C to -50°C, and the polymer (B) being present in an amount of 2 to 15% by weight of the blend and having a molecular weight of at least 10,000.
2. 2. A composition as claimed in Claim 1 in which X represents 5. A composition as claimed in Claim 1 or 2, in which said copolymerizahle ethylenic monomer containing an acid group is a carboxylic, sulfonic or phosphonic acid.
3. 3. 4. A composition as claimed in Claim 3 in which the copolymer (A) is a copolymer of ethyl acrylate with a copolymerizable ethylenic monomer containing a carboxyl group.
4. 4. 5 5- A composition as claimed in Claim 3 in which the copolymer (A) is a copolymer of butyl acrylate with, a copolymerizable ethylenic monomer containing a carboxyl group.
5. 5. 6. A composition as claimed in Claim 4 or 5 10 in which the ethylenic monomer is acrylic acid.
6. 6. 7- A composition as claimed in any one of the preceding claims in which the copolymer (A) has a molecular weight of at least 750,000.
7. 7. 8. A composition as claimed in any one of the 15 preceding claims in which the amount of the polymer (B) in the blend is from 5 to 15% by weight of the blend.
8. 8.
9. 9. A composition according to Claim 1 substantially as hereinbefore described.