The preferred C macromer useful in preparing compositions according to the present inventon includes a Z group which has the general formula ##STR2## wherein R2 is a hydrogen atom or a lower alkyl group, R3 is a lower alkyl group, n is an integer from 20 to 500 and R4 is a monovalent radical selected from the group consisting of ##STR3## and --CO2 R6 wherein R5 is a hydrogen atom or a lower alkyl