Segmented polyurethane resins

A process for said preparation of polyurethane resin, which may be cellular, comprising:

• reacting polyisocyanates, high molecular weight compounds having at least two isocyanate-reactive hydrogen atoms and a molecular weight of from about 500 to about 25,000 and, optionally, low molecular weight chain-lengthening agents, optionally in the presence of catalysts, blowing agents and other known additives wherein the higher molecular weight compounds having isocyanate-reactive hydrogen atoms used comprise:
• a mixture of
• (a) from about 40 to about 85% by weight based on the total weight of (a)+(b), of compounds corresponding to the following general formula:
• ##STR10## and (b) from about 15 to about 60%, by weight, based on the total weight of (a) and (b), of compounds corresponding to the following general formula:
• ##STR11## wherein X represents oxygen or sulfur;
• A represents a k-valent residue obtained by the removal of k hydroxyl groups from a polyol having n hydroxyl groups, an average molecular weight of from about 500 to about 5000 and a melting point higher than 130.degree. C.;
• B represents an h-valent residue obtained by the removal of h hydroxyl groups and/or mercapto groups from a polyol or polythiol having m hydroxyl and/or mercapto groups, an average molecular weight of from about 500 to about 25,000 and a melting point below 60.degree. C.;
• k has an average value of from 0 to n;
• h has an average value of from 0 to m;
• n represents 2 or 3;
• and
• m represents an integer of from 2 to 8;
• characterized in that a prepolymer having isocyanate end groups is prepared in a first stage from said polyisocyanate and said compound of the formula:
• ##STR12## and in a second stage, this prepolymer is reacted in the absence of a solvent with said compound of the formula:
• ##STR13## and optionally low molecular weight chain-lengthening agents and another polyisocyanate.