g 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 dial