A compound of the formula wherein R1 and R1′ are the same, and wherein R1 and R1′ are each aromatic groups; and wherein R2 and R2′ and R3 each, independently of the others, are alkylene groups, arylene groups, arylalkylene groups, or alkylarylene groups; or wherein, in embodiments, R1 and R1′ can be the same or different, and wherein R1 and R1′ each, independently of the other is an alkyl group having a least one ethylenic unsaturation, an arylalkyl group having at least one ethylenic unsaturation, an alkylaryl group having at least one ethylenic unsaturation, or an aromatic group, provided that at least one of R1 and R1′ is an aromatic group; and provided that neither of R1 or R1′ is a photoinitiator group.