This polymer has the general formula: ##STR1## wherein R1 is hydrogen, methyl or ethyl, R2 is an alkyl group of from 1 to 6 carbon atoms, R3 is the diisocyanate moiety and can be alicyclic, aryl, alkyl or arylalkyl in structure and R4 is alkyl, alkylene, aryl or alkyl or hydroxy substituted aryl, and (PE)x is a polyester and/or polyether chain extender unit where X is an integer of from 2 to 50.