Injection moldable polyurethanes

#Thermoplastic polyurethanes are known and for some years small injection molded parts and articles have been made from thermoplastic polyurethanes. Because of the good physical properties of polyurethanes, larger parts and articles are desired which have a sufficient balance of desirable physical properties, particularly including stiffness as well as high and low temperatures resistance for a variety of applications. For example, molded thermoplastic polyurethanes find use in automobile parts, which parts are subjected to temperature extremes requiring that such materials have low temperature impact and elevated temperature resistance. Low temperature impact properties are particularly desirable when a part has been painted, and the high elevated temperature resistance, because of exposure to heat effects from sunlight and the high temperature generated in the engine and by friction. While a number of polyurethanes have been used, generally one or another physical properties has to be sacrificed. With most polyurethanes available, to achieve low temperature impact, the elevated temperature resistance to distortion generally is sacrificed; and to obtain high temperature distortion resistance, the low temperature impact is often sacrificed. Therefore, it is an objective of those skilled in the art to obtain thermoplastic polyurethanes that may be injection molded to form parts and articles weighing several pounds which have the required degree of stiffness and strength, and especially, both low temperature impact and high temperature resistance.

#Improved thermoplastic polyurethanes which are injection molded to form articles weighing several pounds which exhibit significantly improved stiffness, low temperature impact resistance and high heat distortion properties, as well as the necessary balance of other desirable physical properties are obtained by reacting a hydroxylterminated polyester or polylactone having molecular weights in the range of greater than about 2800, more preferably about 3000 to about 5000 and an aliphatic diol used in amounts so that a mixture of the hydroxyl polyether glycol or polyester and diol have a blend molecular weight, determined by hydroxyl analysis, of greater than 450 to about 650, more preferably about 500 to 600, and with an excess of cyclic diisocyanate, reacted whereby the reaction between the reactants is initiated at a temperature greater than about 50.degree. C. and allowed to continue to a temperature less than about 160.degree. C. Large articles can be injection molded from these novel polyurethanes that, even when painted, have excellent low temperature impact.

#The polyurethanes are readily prepared from a variety of compounds having terminal functional groups reactive with organic diisocyanates. Normally used are hydroxyl-terminated compounds. The hydroxyl-terminated compounds or macroglycols usually have molecular weights greater than about 2800. The macroglycols are hydroxyl-terminated polyesters and polylactones. The hydroxyl polyester macroglycols are linear hydroxyl-terminated polyesters having molecular weights between about 2800 and 5000 and acid numbers usually less than about 10. The polyesters utilized include those prepared by the polyesterification of aliphatic dicarboxylic acids including for example, adipic, succinic, pimelic, suberic, azelaic, sebacic and the like or their anhydrides. Aromatic dicarboxylic acids may also be used, or mixtures of aliphatic and aromatic dicarboxylic acids. Useful acids include aliphatic dicarboxylic acids of the formula HOOC--R--COOH where R is an alkylidene radical containing 2 to 8 carbon atoms. The glycols used in the preparation of the polyesters by reaction with the dicarboxylic acids are aliphatic glycols containing 2, preferably greater than 2, as 4 to about 10 carbon atoms such as butanediol, hexamethylene glycol, octamethylene glycol, 2-ethylhexanediol-1,6, neopentyl glycol, and the like. Polyesteramides also are contemplated usually be substitution of a diamine or amino alcohol for at least part of the glycol. Especially outstanding results are obtained with hydroxyl poly(tetramethylene) adipate.

#To demonstrate the criticality of the nature of the polyester, molecular weight and aliphatic diol, a series of polyurethanes were prepared by heating one mol of the polyester having the molecular weight shown in the table, mixed with sufficient aliphatic diol to give a blend molecular weight of 550, which mixture was mixed with 106% p,p'-diphenylmethane diisocyanate, heated initially to about 60.degree. to 80.degree. C. and then to 130.degree. to 150.degree. C. to complete the reaction. The reaction was controlled by discharging the mixed reactants after heating has begun while at low viscosity at about a 1/2 inch thick layer and maintaining the exotherm temperature between 130.degree. and 150.degree. C., after which the polyurethane is cooled and ground into granules.

#The polymers were prepared into test specimens by injection molding into 3 inches .times. 6 inches .times. 0.125 inch plaques which were then tested.

#Samples of injection molded plaques were painted with an automotive metal paint and tested for cold impact resistance at -20.degree. F. and -40.degree. F. using a weight dropped upon the panels from different heights. The painted panels were considered satisfactory from a cold impact resistance if there was no failure of the paint substrate at the 10 inch drop level.