The preferred macromonomer includes a Z group which has the general formula ##STR2## wherein R2 is a hydrogen atom or a lower alkyl group (typically C1 to C4), R3 is a lower alkyl group (typically C1 to C4), 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 group (typically C1 to