Thermoplastic polyurethane elastomers prodn. with improved hydrolysis and wear resistance - by adding further di:isocyanate during thermoplastic processing, followed by heating

High-mol. wt. thermoplastic polyurethane (TPU) elastomers (I) are prepd. by adding 0.05-5 wt.% organic di-isocyanate (II) to a conventional TPU elastomer (III) during thermoplastic processing, and conditioning the moulding material obtd. for at least 1 hr. at 50-150 deg.C. Specifically amt. of (II) is 0.2-3 wt.%. (III) is a polyester- or polyether-urethane derived from long-chain OH cpds. with mol.wt. 500-3000, short-chain aliphatic and/or aromatic diols with mol.wt. below 600, aromatic cyclic and/or aliphatic di-isocyanates and opt. stabilisers, additives etc. (II) is an aliphatic and/or aromatic ring-contg. di-isocyanate and/or a di-isocyanate-producing cpd. and/or a NCO-terminated prepolymer with mol.wt. below 5000; (II) is added to the polymer melt as a solid or liq., via the feed opening or feed zone or at another suitable point in the extruder or injection moulding machine, or (II) is premixed with (III) outside the processing machine, and the wetted granules are then processed as usual. After processing or final moulding, the material is conditioned for at least 1 (pref. 24) hrs. at 50-150 (pref. 100) deg.C. USE/ADVANTAGE - Addn. of (II) increases the mol.wt. of the TPU, giving TPU elastomers with improved hydrolytic stability and wear resistance (for prodn. of coatings, tubes, profiles, wearing parts etc.).