Polyester initiated anionic catalyzed polymerization of lactam

A process for forming block terpolymers having the formula:

• ##EQU15## where (O-Z).sub.n is a polymeric moiety and Z is a hydrocarbon or substituted hydrocarbon group said group being alkylene, arylene, alkylene carbonyl, arylene carbonyl, and mixtures thereof;
• A and A' are acyl groups selected from ##EQU16## R is a divalent or polyvalent hydrocarbon group;
• Y is an alkylene or substituted alkylene having from about 3 to about 14 carbon atoms;
• x, x', x" and x"' are integers and the total number of x's is equal to 2w + 2;
• n, y, and w are integers equal to one or more, and b is an integer equal to zero or one;
• and R' is an aliphatic or substituted aliphatic hydrocarbon, comprising:
• contacting under anionic, catalyzed lactam polymerization conditions a polyether-polyester prepolymer formed from dialkyl esters and aliphatic polyether polyols having the formula ##EQU17## with lactams having the formula ##EQU18## where Y, Z, R, R', A, A', b, y, n, w, and b are defined above;
• resulting in the expansion of the polyether-polyester prepolymer through the reactive insertion of the lactams into the ester sites of the prepolymer, said lactams and polyether-polyester prepolymers being the sole components of the block terpolymer.