(i) CH2???C(R1)COR2, wherein R1 is methyl and R2 is ???OZ???1, wherein Z??? is an alkyl group having from 1 to 4 carbon atoms; (ii) R3OOC???CH???CH???COOR4, wherein R3 and R4 are independently an alkyl group having from 1 to 4 carbon atoms; (iii) CH2???C(R5)OCOR6, wherein R5 is methyl and R6 is an alkyl group having from 1 to 4 carbon atoms; (iv) CH2???C(COOR7)CH2COOR8, wherein R7 and R8 are indep