wherein n is from 2 to about 200, preferably from about 5 to about 100, R1 is a divalent aliphatic hydrocarbon group, and X is an active hydrogen containing group such as --SH, --NOH, --NHR, or --O--(C2 H4)(CH2 CH2 O)a --H wherein R is hydrogen or an alkyl group and a is 0 to 100.