nk carrier, said carrier comprising at least one radically curable monomer compound and a compound of the formula wherein R1 and R1??? each, independently of the other, is an alkyl group having at least one ethylenic unsaturation, an arylalkyl group having at least one ethylenic unsaturation, or an alkylaryl group having at least one ethylenic unsaturation, R2, R2???, and R3 each, independently of