Thermoplastic polyurethanes having a high heat stability, based on naphthylene diisocyanate, their production and their use

A process for the preparation of a thermoplastically processible polyurethane elastomer comprising

• (i) reacting at least one substantially linear polyhydroxyl compound having a molecular weight of from about 550 to about 10,000 with a substoichiometric amount of at least one first diisocyanate to obtain an OH-prepolymer, and
• (ii) reacting said OH-prepolymer with a naphthylene-1,5-diisocyanate and a chain lengthener mixture,
• said first diisocyanate being any diisocyanate other than naphthylene-1,5-diisocyanate, said chain lengthener mixture being comprised of diols and polyols having molecular weights of from 62 to 500, said chain lengthener mixture being characterized in that between about 70 and about 92 equivalent percent of its OH groups are derived from said diols and in that between about 30 and about 8 equivalent percent of its OH groups are derived from polyols having a functionality of three and/or higher than three, said diols are being selected from the group consisting of hydroquinone-di-(.beta.-hydroxyethylether), butane diol-1,4 and hexane diol-1,6, with the proviso that in mixtures containing either butane diol-1,4 or hexane diol-1,6 such mixtures contain co-diols which provide from about 15 to about 50 equivalent percent of said OH groups which are derived from diols only, said co-diols having a molecular weight of from 62 to 500.