More preferably, R1 and R4 are independently a linear or branched alkyl or linear or branched alkenyl group having from about 4 to about 18 carbon atoms, R2 is a linear or branched alkylene group having from about 2 to about 6 carbon atoms, R3 and R5 are each independently hydrogen or a linear or branched alkyl group having from 1 to about 6 carbon atoms, and n, y and z are 0; or R1, R2, R3 and R4