. . . . . . "l in this invention are preferably either:1. lactone polyesters having the formula ##STR1## end-capped with phthalic acid groups, wherein each R is hydrogen, halogen, or a monovalent hydrocarbon radical containing a maximum of 12 carbon atoms, A is an oxy group, x and y are eachintegers having values of 1 to 4 inclusive and z is an integer having a value of 0 or 1 with the provisos that(a) the tot" . .