Thermally stable polyurethane elastomer useful in molding flexible automobile exterior body parts

A thermally stable polyurethane elastomer which is a reaction product of:

• (a) a poly(oxypropylene)-poly(oxyethylene) glycol of molecular weight of from about 1500 to about 4000 and containing from 15% to 50% oxyethylene groups by weight;
• (b) a graft polyol of molecular weight from about 2500 to about 4500, prepared by the in situ polymerization of ethylencially unsaturated monomeric material in a glycol selected from the group consisting of (i) poly(oxypropylene) glycol, (ii) poly(oxypropylene)-poly(oxyethylene) glycol containing less than 15% by weight oxyethylene groups, and (iii) a mixture of poly(oxypropylene) glycol and poly(oxypropylene)-poly(oxyethylene) glycol containing less than 15% by weight oxyethylene groups, the amount of polymerized monomer in the graft polyol being from 5 to 50% by weight;
• (c) methylenebis(4-phenylisocyanate);
• and (d) 1,4-butanediol;
• the ratio of (a)/(b) being from about 90/10 to 10/90 by weight, the NCO/OH equivalents ratio being from 0.95 to 1.1, and the molar ratio of (d) to (a) plus (b) being from 6/1 to 12/1, said elastomer having a hardness of about 40 to 55 Shore D, an elongation of greater than 300%, an ultimate tensile strength of at least 3,000 psi and a Die C tear strength of at least 500 pli, said elastomer displaying improved thermal stability as evidenced by its ability to retain at least twice as much of its original tensile strength, after exposure to a temperature of 400.degree. F. for 20 minutes, as a similar elastomer in which (a) contains 10% or less of oxyethylene groups or in which (a) is omitted.