WO1998038249A1

WO1998038249A1 - Waterborne dispersions of polyurethane and ethylenic polymers

Info

Publication number: WO1998038249A1
Application number: PCT/US1998/003440
Authority: WO
Inventors: Rodney M. Weston; Konstantinos A. Arvanitis
Original assignee: Witco Corporation
Priority date: 1997-02-28
Filing date: 1998-02-23
Publication date: 1998-09-03
Also published as: AU6180698A

Abstract

Homogeneous dispersions of polyurethane and polyethylenic polymers are made by dispersing an isocyanate prepolymer into an aqueous dispersion of the polyethylenic polymer, and then chain extending the prepolymer. The resulting dispersion exhibits a single glass transition temperature.

Description

WATERBORNE DISPERSIONS OF POLYURETHA E AND ETHYLENIC POLYMERS

The present invention relates to aqueous dispersions containing both polyurethane polymers, and ethylenic polymers. Polyurethanes find use in a variety of applications, including coatings, paints, adhesives, and the manufacture of fibers and solid articles. Polyurethanes are typically soluble in organic solvents, and exhibit little if any solubility in aqueous solvents or in systems in which water and a second water-soluble solvent are employed. Organic solvent-based resin solutions have thus typically been the vehicle of choice for use in forming coatings and the like of polyurethanes. However, many organic solvents commonly used in conjunction with such resins present environmental problems associated with their toxicity. There has been a growing concern based on the effects of such organic solvents on the environment, as well as on the long-term health of individuals who come into contact with such solvents. There has, therefore, been a growing interest in the use of aqueous resin compositions as a means of eliminating toxicity problems associated with organic solvents, and as a means of complying with governmental edicts with respect to the use of such solvents .

For many applications, it would be desirable to incorporate several types of polymer into a given dispersion, to obtain the benefits of each polymer's desirable properties. Doing so is not at all straightforward, because of incompatibilities between the polymers and/or the vehicles in which they are solubilized or dispersed.

Various processes have been proposed for forming dispersions of polyurethane and acrylates or other ethylenic polymers. These however do not uniformly provide satisfactory approaches.

U.S. Patent No. 4,318,833 discloses that a urethane/acrylic dispersion could be made by adding an ethylenic monomer to a fully reacted polyurethane dispersion and then polymerizing the monomer by free radical initiation.

U.S. Patents No. 4,644,030 and No. 5,169,895 describe a process in which a urethane prepolymer is prepared as a solution in an ethylenic monomer. This mixture is dispersed in water, the prepolymer is chain extended and the monomer is then polymerized by free radical initiation.

European Patent Application No. 0 510 572 A2 discloses the preparation of urethane/vinyl polymer dispersions by the addition of ethylenic monomers to a completely reacted urethane prepolymer to give a solution which is dispersed in water. The monomer is then polymerized by free radical initiation and the prepolymer is chain extended. The present invention is thus directed to an improved technique for forming aqueous dispersions containing both polyurethane, which technique affords improved ease of operation, more satisfactory yields, and offers a greater variety in the selection of reactants and in the range of properties of the products that can be obtained.

More specifically, the present invention is directed to a process for producing an aqueous dispersion of polyurethane and polyethylenic polymers, comprising

(a) providing a urethane prepolymer substituted with an average of at least 2 isocyanate groups, per molecule;

(b) providing an aqueous dispersion of a polyethylenic polymer;

(c) combining said prepolymer and said aqueous dispersion to form a combined dispersion which is homogeneous; and

(d) chain extending said prepolymer in said combined dispersion.

The present invention also includes the stable aqueous dispersions resulting from the foregoing method of this invention, the use of such dispersions for application in a film- forming amount to a substrate with subsequent drying thereon, and the resulting dried, cured and hardened films which may be permanently coated on the substrate or made self- supporting involving use of a substrate with a release surface. The dispersions of the invention may also be used in the above manner or otherwise as impregnants and sizing for paper, textiles and other foraminous materials, as pigment binders and adhesives, and for making cross -linked brittle polymeric products when the dispersion contains non-elastomeric, non-film polyurethanes . The method of this invention yields several unexpected improvements relative to the method disclosed in U.S. Patent No. 4,318,833 which produces a different type of aqueous dispersion containing polyurethanes and polymerized ethylenically unsaturated monomers. The necessity of using an organic solvent medium (with its attendant disadvantages) in the reaction for producing the fully chain-extended polyurethane is eliminated. The ethylenic polymer becomes intimately, homogeneously and/or molecularly intermixed with the polyurethane prepolymer in the reaction medium, so the subsequent chain extension of the prepolymer provides thereby a true, more thorough in situ dispersion. The resulting aqueous dispersions of this invention thereby yield films and other products with unexpectedly improved properties with respect to rapidity of curing and hardening, resistance to water, organic solvents and environmental conditions, tensile strength, modulus of elasticity, and/or elongation and the like. The products formed in accordance exhibit a single glass transition temperature (Tg) . This characteristic confirms that the products are distinct from mere mixtures of polyurethanes and polyethylenic polymers, which would exhibit at least two glass transition temperatures.

The prepolymer is terminated with preferably an average of at least two isocyanate (-NC0) groups per molecule.

NCO- terminated polyurethane prepolymers, preferably employed herein, are commonly produced by reacting organic material containing an average of at least about 2 active hydrogen atoms per molecule, usually a diol and preferably a polyester polyol, with a stoichiometric excess of an organic diisocyanate, preferably methylene bis (isocyanato cyclohexane) . Preferably a suitable proportion of the said organic material also contains anionic substituent groups for providing water dispersibility to the prepolymer, such as at least one comparatively unreactive pendant carboxylic or sulfonate group, in salt form or preferably neutralized with a suitable basic material to salt form during or after the prepolymer formation or during the formation of the dispersion. Any organic polyisocyanates may be used in the process according to the invention. It is preferred to use polyisocyanates of the formula

Q(NC0)₂ wherein Q represents an aliphatic hydrocarbon group containing from 4 to 12 carbon atoms, a cycloaliphatic hydrocarbon group containing from 6 to 15 carbon atoms, an aromatic hydrocarbon group containing from 6 to 15 carbon atoms or an araliphatic hydrocarbon group containing from 7 to 15 carbon atoms. The most preferred diisocyanate is isophorone diisocyanate. The following are examples of other preferred diisocyanates : tetramethylene- diisocyanate, hexamethylene diisocyanate, dodecamethylene- diisocyanate, 1 , 4 -diisocyanato- cyclohexane, 1- isocyanato- 3 , 3, 5 - trimethyl - 5 - isocyanatomethyl cyclohexane, 4,4' -diisocyanatodicyclohexylemethane, 4,4' - diisocyanato -dicyclohexyl -propane- (2,2); 1,4- diisocyanato-benzene, 2 , 4 -diiocyanatotoluene, 2,6- diisocyanatotoluene, 4 , 4 ' -diisocyanatodiphenylmethane, 4,4' -diisocyanatodiphenyl -propane- (2,2) , p-xylylene- diisocyanate, a, a, a ' , a ' - tetramethyl -m-or p-xylylene- diisocyanate and mixtures of these compounds. Mixtures of any of the foregoing can also be used. The mole ratio of diisocyanate to polyol is generally stoichiometric, e.g. (1.9-2.1) :1.

Reaction of the diisocyanate and the polyol or polyol polymer can be carried out at moderately elevated temperatures, e.g. 50°C.-100°C. The reaction is generally carried out in an inert solvent or without a solvent. One preferred solvent is N-methyl pyrrolidone. Other suitable solvents include acetone, methyl ethyl ketone, toluene, dimethyl formamide, ethyl acetate, tetrahydro furan, and dioxane. Suitable polyol reactants preferably have a molecular weight (M.W.) of about 400 to 5000, and an average OH value of about 10 to about 1,000, preferably about 30 to about 150, as determined by ASTM E222-67, Method B. In addition to or instead of the preferred polyester polyols, other polyols or mixtures thereof may be employed such as poly-caprolactone, polycarbonate and polybutadiene resins (hydroxyl terminated homopolymers of butadiene) , polyethers based on ethylene oxide, propylene oxide and tetrahydrofuran, and the like. Use as reactants of organic material containing an average of more than 2 active hydrogen atoms per molecule, entirely or in suitable proportions with difunctional reactants, enable the production (from the aqueous dispersions of this invention) of cross -linked brittle polymeric products which are commercially useful though neither elastomeric or film- forming .

Similar considerations apply with respect to the isocyanate reactant which, in addition to or instead of the preferred organic diisocyanate may include organic materials containing an average of more than two isocyanate groups. Examples of suitable commercially available polyisocyanates include Mondur CB (adduct of 3 moles toluene diisocyanate with 1 mole trimethylol propane, Bayer) , Desmodur-N,

(trifunctional biuret of 1,6-hexane diisocyanate, Bayer) , Isonate 143L (polymeric methylene bis (phenyl isocyanate) , Upjohn) and the like. On the other hand, monofunctional isocyanate and active hydrogen containing material may also be employed, but in suitable small proportions, preferably below about 10 wt.% of the prepolymer reactants, since they yield end caps resulting in chain termination.

The NCO- terminated polyurethane prepolymers employed in this invention are preferably rendered water dispersible by including in the prepolymer chain an effective water -dispersing amount of pendant carboxylic or cationic salt groups such as sulfonate groups. Such amount is typically about 0.5 to about 10 wt.% of such groups. Alternatively, the monomer - containing prepolymer may be devoid of such groups in which case it is then dispersed in water with the aid of a dispersing agent, preferably a nonionic ethoxameric surfactant.

According to an optional feature of this invention, the polyurethane chain in known manner contains about 1 to abut 5 wt.% of units derived from melamine, thereby providing films produced from the present aqueous dispersions with improved resistance to organic solvents. According to another optional feature of invention, the polyurethane is provided in known manner with cross - linking, curable, hardening groups activated to self condensation and cross - linking upon drying of the film on a substrate under ambient conditions, such groups comprising about 2 to about 10 wt.% of N-methylol hydrazide terminii or end caps.

B. THE POLYETHYLENIC POLYMER DISPERSION

By "polyethylenic polymer" is meant herein a polymer obtained by polymerization of monomers having polymerizable ethylenic (that is, C=C) unsaturation . Homopolymers are contemplated as are copolymers of two (or more) different ethylenically unsaturated monomers .

Examples of such monomers include butadiene, isoprene, styrene, alpha-methyl styrene and the like; substituted styrenes such as chlorostyrene, dichlorostyrene, bromostyrene, p-vinylphenyl phenyl oxide and the like; the acrylic and substituted acrylic monomers such as acrylic acid, methacrylic acid, cyclohexyl acrylate and methacrylate, benzyl acrylate and methacrylate, the C^._g alkyl acrylates and methacrylates such as methyl , ethyl and butyl acrylate and methacrylate, phenyl acrylate, phenyl methacrylate, alphachloroacrylonitrile and the like; the vinyl esters and vinyl ethers such as vinyl acetate, vinyl acrylate, vinyl methacrylate, vinyl propyl ethers, vinyl butyl ethers and the like; other water soluble monomers, especially hydroxy -C₁-C₆- alkyl esters such as hydroxy ethyl acrylate or methacrylate, hydroxy propyl acrylate or methacrylate and the like. Any of the known polymerizable monomers can be used and the compounds listed above are illustrative and not restrictive of the monomers suitable for use in this invention.

The ethylenically unsaturated monomers which are preferred in the practice of this invention include the (meth) acrylic and substituted (meth) acrylic monomers as well as styrene. The aqueous dispersion used in the present invention is preferably prepared by emulsion polymerization of the monomers or comonomers in an aqueous system. The reagents necessary for emulsion polymerization are those conventionally employed, including a free radical initiator (typically a peroxy compound) and a surfactant (typically an anionic surfactant, such as alkyl sulfonates, alkyl aryl sulfonates, or alkyl aryl polyalkoxy sulfonates) . The conditions for carrying out the emulsion polymerization are likewise those conventionally employed, and are familiar to those of ordinary skill in this art.

C. COMBINING THE PREPOLYMERS AND THE AQUEOUS DISPERSION

The polyurethane prepolymer, which is preferably free of ethylenically unsaturated monomeric compounds, is next combined with the aqueous dispersion of the polyethylenic polymer. The ratio by weight of the polyurethane to the polyethylenic polymer should be in the range of 10:90 to 90:10 and more preferably 70:30 to 30:70.

The polyurethane prepolymer and the polyethylenic polymer dispersion are preferably combined by dispersing the polyurethane prepolymer into the dispersion of the polyethylenic polymer. This can be accomplished by providing the polyethylenic polymer dispersion in a vessel and then adding thereto the prepolymer while the vessel contents are being subjected to high shear agitation. The presence of the surfactant (s) used in the emulsion polymerization step assists in formation of a stable aqueous dispersion of the prepolymer and the polyethylenic polymer.

D. CHAIN EXTENDING THE PREPOLYMER

The prepolymer is next reacted with a suitable chain extender, which reacts with the isocyanate groups. Satisfactory chain extenders include diamines such as hydrazine, and alkyl and aromatic polyols, especially diols, and alkyl and aromatic diamines and triamines, wherein the alkyl compounds contain a table of 2 to 12 carbon atoms or the aromatic moiety contains 6 to 10 carbon atoms. Other examples of chain extenders include ethylene diamine, diethylene triamine, 1, 2 -diaminopropane, 1,3- diaminopropane, 1 , 4 -diaminobutane, and 3,3,5- trimethyl - 5 -aminomethyl cyclohexylamine; and ethylene glycol, 1 , 2 -dihydroxypropane, 1 , 6-dihydroxyhexane, and the polyols described herein as useful reactants to make the polyester.

The product of reaction with the chain extender is a dispersion of polymeric polyurethane together with the polyethylenic polymer. This dispersion exhibits functional properties superior to those exhibited by mixtures obtained by forming the polyurethane and polyethylenic polymers separately and then mixing them together.

The aqueous dispersions of this invention are advantageously employed as coating compositions, for which purpose they may be further diluted with water and/or organic solvents, or they may be supplied in more concentrated form by evaporation of water and/or organic components of the liquid medium. As coating compositions they may be applied to any substrate including wood, metals, glass, cloth, plastics, foam and the like, by any conventional method including brushing, dipping, flow coating, spraying, and the like. The compositions may contain other conventional ingredients including organic solvents, pigments, dyes, emulsifiers, surfactants, thickeners, heat stabilizers, leveling agents, anticratering agents, fillers, sedimentation inhibitors, UV absorbers, antioxidants and the like introduced at any stage of the production process or subsequently.

These dispersions are preferably applied to substrates in effective film- forming amounts depending on the solids content, temperature and other conditions, the type of substrate, product desired, etc. The film coating on the substrate may simply be protective, decorative, and/or intelligence imparting or the like or serve as an adhesive or other function. Self-supporting thin or thick films or sheets may be produced by application to a substrate with a release surface from which the cured, hardened film can be removed. Hardening and curing on the substrate is generally accomplished by simply drying under ambient conditions, which may if desired by expedited and/or facilitated by concurrent heating, subsequent baking, etc. The dispersions of this invention have good storage storage- stability and yield films and coatings with improved properties such as resistance to water, organic solvents and environmental conditions, flexibility, elasticity and/or tensile strength, and the like.

The following examples are illustrative of the present invention and are not intended to limit its scope. EXAMPLE 1

Aqueous dispersion of polyurethane (based on neopentyl adipate polyester) /poly (methyl methacrylate- methacrylic acid)

A. Prepolymer preparation.

A four-necked resin flask equipped with a stirrer, condenser, thermometer and gas inlet tube was charged with 1, 2, 3, 4 and 5 below

1. Neopentyl adipate (OH No . = 112) 365.70 g

2. Dimethylol propionic acid 49.50 g

3. Trimethylol propane 14.50 g 4. Methylene bis (isocyanato cyclohexane) 363.00 g

5. N-methyl pyrrolidone 170.00 g

6. Triethylamine 37.30 g

The mixture in the flask was heated under dry air for 4 hours at 80°C-85°C, until the residual isocyanate content was 4.1% (theoretical isocyanate content was 4.1%) , then 6. was added and mixed for 30 minutes. The result was a NCO- terminated prepolymer.

B. Acrylic dispersion preparation

A four necked flask was equipped with a stirrer, condenser, thermometer and nitrogen inlet tube. A redox initiated polymerization of the methyl methacrylate and methacrylic acid monomers was carried out using the following formula -

1. Deionized Water 1480.00

2. Triton X-200 (alkyl aryl EO sulfonate) 96.00 3. Methyl methacrylate 792.00

4. Methacrylic acid 8.00

5. Ferrous sulfate solution 16 mL

6. Ammonium persulfate 4.00

7. Sodium metabisulfite (in 20 mL of water) 4.00 8. t- Butyl hydroperoxide solution (70%) 20 drops

1 and 2 were added to the flask with stirring. When the emulsifier had dispersed, 3, 4, 5 and 6 were added and the nitrogen flow was started. The nitrogen was bubbled through the mixture for 15 minutes while stirring and cooling to 20°C, then 7 and 8 were added and the polymerization began after a short induction period. The exotherm temperature rose to 60°C in 10 minutes and then fell slowly to 35°C over 40 minutes. At this stage the dispersion was filtered and had the following properties:

Total solids content, % 34.2

Particle charge anionic Particle size (μm) 0.08

T_g, °C (calculated) 105.2

Acid number (calculated) 6.5 pH (before neutralization with ammonia) 1.9 pH (after adjustment) 8.1 C. Urethane/acrylic dispersion preparation.

1038 g of deionized water and 1008 g of the poly (methyl methacrylate-methacrylic acid) dispersion from step B were added to a mixing vessel equipped with a high speed stirrer. 1000 g of the NCO- terminated prepolymer from step A, at a temperature of 75°C-80°C, was added to this with vigorous stirring to produce a colloidal dispersion. 40.1 g of 35% hydrazine solution was then added with rapid stirring, to chain extend the NCO- terminated prepolymer. The resulting polyurethane/polymethyl methacrylate dispersion had a pH of 8.25 and a viscosity of 45 cps at 37.5 solids .

A film cast from the above dispersion after drying for 1 day at room temperature and then 2 hour at 130°C, had the following tensile properties:

Ultimate tensile strength, psi 6325 Elongation, % 75

T_g, °C 64

As a comparison, a purely physical blend of the polyurethane and the acrylic dispersion was prepared by making a water-borne polyurethane dispersion by the method shown below and blending this with the acrylic dispersion described earlier.

(Comparative) Polyurethane dispersion preparation 1256 g of deionized water was added to a mixing vessel equipped with a high speed stirrer.

1000 g of the -NCO terminated prepolymer from step A (at a temperature of 75°C-80°C) was added, with vigorous stirring, to produce a colloidal dispersion. 40.10 g of a 35% hydrazine solution was then added to chain extend the -NCO terminated prepolymer. The resulting polyurethane dispersion had a pH of 8.38 and a viscosity of 35 cps at a TSC of 35%.

Physical blend of polyurethane dispersion/acrylic dispersion. (70/30 by weight solids)

The dispersions were blended as per the formula

Polyurethane dispersion 700.00

Acrylic dispersion 300.00

10% Fluorad FC-129 solution 0.70

Water 80.00 Butyl Propasol 40.00

Dowanol DPM 40.00

Films were prepared from this blend. These were air -dried overnight and annealed in an oven at 130°C for 2 hours. The films had the following properties :

Tensile strength, psi 5210 Elongation, % 50

T , °C -12,46,117

The physical properties of the film prepared from the blended dispersions were inferior to those of the film prepared from urethane/acrylic dispersion of the present invention. The film from the blend also exhibited three T_g values, unlike the dispersion of the present invention; which showed a single T . A comparison of the chemical resistance tests carried out on the blend and the dispersion of the present invention also showed the inferiority of the physical blend (see table below) :

Chemical Resistance Tests

(three coats over red oak test pieces^'

(0 = best, 5 = worst)

EXAMPLE 2 Aqueous dispersion of polyethylene adipate based polyurethane/poly (methyl methacrylate - methacrylic acid)

A. Prepolymer preparation

A 3000 mL resin reactor equipped with a stirrer, heating mantle, thermometer and nitrogen inlet was charged with Polyethylene adipate (M.W. 2000) 1249 g

Trimethylol propane 21 g

Dimethylol propionic acid 124 g

N-methyl -2 -pyrrolidinone 244 g

Bis- (cyclohexyl) methane diisocyanate 768 g

This mixture was stirred and heated to 80°C for 3 hours after which it was cooled to 70°C, and then 94 g of triethylamine was added.

B. Acrylic dispersion preparation.

The poly (methyl methacrylate- methacrylic acid) copolymer as described in Example 1, step B, was also used in this example.

c Dispersion Preparation

2517 g of water and 2692 g of the above acrylic dispersion were placed in a mixing vessel and 2500 g of the NCO- terminated prepolymer was added to this mixture with high speed stirring. A water temperature of 25° - 35°C was maintained during the addition of the prepolymer. After 5 minutes of high speed mixing 98 g of 35% hydrazine solution was added. This resulted in a 5° - 10°C exotherm.

The resulting dispersion had the following physical properties:

Total solids content, % 40.7 pH @ 25°C 8.39 Viscosity (Brookfield LVF) , cps 65

EXAMPLE 3

Aqueous dispersion of poly (ethylene adipate) based urethane with a poly (butyl acrylate-methacrylic acid)

A. Prepolymer preparation

The prepolymer was prepared using the same ingredients and same procedure as in Example 2.

B. Acrylic dispersion

This was prepared by substituting butyl acrylate for methacrylate in the formula used in Examples 1. and 2.

C. Dispersion preparation

The NCO- terminated prepolymer as described in Example 2. was dispersed in 2692 g of the poly (butyl acrylate- methacrylic acid) dispersion and chain extended as in Example 2. The physical properties of the resulting dispersion were:

Total solids content, % 40.17 pH @ 25°C 8.17 Viscosity (Brookfield LVF, cps 9

EXAMPLE 4

Aqueous dispersion of a poly (1,6 hexane adipate/isophthalate) based polyurethane/poly (butyl acrylate-methacrylic acid)

A. Prepolymer preparation

A 2000 mL resin reactor equipped with a stirrer, heating mantle, thermometer and nitrogen inlet was charged with -

Poly (1,6 hexane adipate/isophthalate) diol (M.W. 1600) 594.0 g

Dimethyl propionic acid 10.4 g

Bis- (cyclohexyl) methane diisocyanate 189.6 g

and the mixture was stirred and heated to 100°C for three hours. The resulting NCO- terminated prepolymer had a theoretical % NCO of 2.88.

B. Acrylic dispersion preparation The poly (butyl acrylate-methacrylic acid) dispersion prepared as described in Example 3 was used.

C. Dispersion Preparation

The NCO- terminated prepolymer was added, with high speed stirring, to 1070 g of the poly (butyl acrylate-methacrylic acid) dispersion containing 7.9 g of triethylamine and 71 g of a nonionic nonyl phenol surfactant. The dispersion temperature was maintained below 35°C during the prepolymer addition. After stirring for 10 minutes, 21.5 g of a 35% solution of hydrazine was added and an exotherm of 5°-10°C occurred.

The physical properties of the dispersion were :

Total solids content, % 60.0 pH @ 25°C 7.72

Viscosity (Brookfield LVF) , cps 1100

Claims

WHAT IS CLAIMED IS:

1. A process for producing an aqueous dispersion of polyurethane and polyethylenic polymers, comprising

(a) providing a prepolymer substituted with an average of at least two isocyanate groups per molecule;

(b) providing an aqueous dispersion of a polyethylenic polymer;

(c) dispersing said prepolymer into said aqueous dispersion to form a combined dispersion; and

(d) chain extending said prepolymer in said combined dispersion.

2. A process according to claim 1 wherein said prepolymer is the reaction product of a polyol reactant and a polyisocyanate reactant.

3. A process according to claim 2 wherein said polyol reactant is selected from the group consisting of organic polyols having a molecular weight of 400 to 5,000 and an average OH value of 10 to 1, 000.

4. A process according to claim 2 wherein said polyisocyanate reactant has the formula Q(NCO)₂ wherein Q is alkyl containing 4 to 12 carbon atoms, cycloalkyl containing 6 to 15 carbon atoms, aromatic containing 6 to 15 carbon atoms, or alkylaromatic containing 7 to 15 carbon atoms.

5. A process according to claim 2 wherein said polyisocyanate reactant is selected from the group consisting of isophorone diisocyanate and methylene bis (isocyanate cyclohexane).

6. A process according to claim 2 wherein said polyol is selected from the group consisting of dimethylol propionic acid and trimethylol propane.

7. A process according to claim 1 wherein said polyethylenic polymer is a homopolymer or copolymer of monomers selected from the group consisting of acrylic acid, methacrylic acid, and the C_j-Cg alkyl, hydroxy-C_j-Cg- alkyl, benzyl, cyclohexyl, and phenyl esters thereof.

8. A process according to claim 1 wherein the weight ratio of said prepolymer to said polyethylenic polymer is 90:10 to 10:90.

9. A composition of matter which is a homogeneous dispersion of chain extended polyurethane and polyethylenic polymer, which composition of matter exhibits a single glass transition temperature.

10. A composition according to claim 9 wherein said prepolymer is the reaction product of a polyol reactant and a polyisocyanate reactant.

11. A composition of matter according to claim 10 wherein said polyol reactant is selected from the group consisting of organic polyols having a molecular weight of 400 to 5,000 and an average OH value of 10 to 1,000.

12. A composition of matter according to claim 10 wherein said polyisocyanate reactant has the formula Q(NCO)₂ wherein Q is alkyl containing 4 to 12 carbon atoms, cycloalkyl containing 6 to 15 carbon atoms, aromatic containing 6 to 15 carbon atoms, or alkylaromatic containing 7 to 15 carbon atoms.

13. A composition of matter according to claim 10 wherein said polyisocyanate reactant is selected from the group consisting of isophorone diisocyanate and methylene bis (isocyanate cyclohexane) .

14. A composition of matter according to claim 10 wherein said polyol is selected from the group consisting of dimethylol propionic acid and trimethylol propane.

15. A composition of matter according to claim 9 wherein said polyethylenic polymer is a homopolymer or copolymer of monomers selected from the group consisting of acrylic acid, methacrylic acid, and the C₁-C₆ alkyl, hydroxy-C₁-C₆- alkyl , benzyl, cyclohexyl, and phenyl esters thereof.

16. A composition of matter according to claim 9 wherein the weight ratio of said prepolymer to said polyethylenic polymer is 90:10 to 10:90.