More preferably, R1 is selected from the group consisting of secondary alkyl groups having from about 3 to about 8 carbon atoms; tertiary alkyl groups having from about 4 to about 10 carbon atoms; allylic 1-alkyl-2-alkenyl groups having 4 to 10 carbon atoms; 1-alkoxyalkyl groups --CH(OR3)R4 in which R3 is an alkyl group having from 1 to 6 carbon atoms and R4 is an alkyl group having 1 to about 6 c