This can be caprolactone itself or a substituted caprolactone wherein R' is an alkyl, alkoxy, aryl, cycloalkyl, alkaryl or aralkyl group, and R is an alkyl or alkoxy group, all as shown in U.S. Pat. No. 3,169,945, or modified caprolactones where a caprolactone polyol is reacted with (1) an anhydride of a polycarboxylic acid or (2) a polyisocyanate and an anhydride of a polycarboxylic acid or (3)