wherein R11 and R12 are each independently selected from a group consisting of C1 -C30 alkyl, phenyl substituted C1 -C30, C1 -C30 having a protected substituent selected from a group consisting of: ##STR7## wherein R13, R'13, R13 and R'13 are each independently C1 -C30 alkyl; Q is sulfur, nitrogen or oxygen, X is a halogen and Y is a halogen;