Specific examples of suitable B groups include ##STR111## wherein X is an alkyl group (including cyclic alkyl groups and substituted alkyl groups), preferably having from 1 to about 50 carbon atoms, an aryl group (including substituted aryl groups), preferably having from 6 to about 50 carbon atoms, an arylalkyl group (including substituted arylalkyl groups), preferably having from 7 to about 50