The copolymers may be expressed by the idealized formula ##STR1## where the molar ratio of ACN to Ester, i.e. x to y is from about 10:1 to 1:10, such as from about 8:1 to 1:5, for example from about 6:1 to 1:5, but preferably from about 5:1 to 1:1; the R1 's which may be the same or different are hydrogen or lower alkyl such as methyl and R is an alkyl group having from about 1 to 20 or more carbo