Cationically polymerizable styryloxy resins having urethane linkages, represented by the formula III ##STR1## wherein R.sup.1 and R.sup.2 are H, or one of R.sup.1 and R.sup.2 is H and the other is methyl;R.sup.3 and R.sup.4 (which may be the same or different) are H, lower alkyl, or alkoxy if R.sup.2 is not methyl;R.sup.5 is a divalent hydrocarbon radical;G.sup.1 is an n-valent hydrocarbon radical free of amino, aliphatic thiol, aliphatic hydroxyl or other groups which interfere with cationic polymerization;and n is an integer of 2 or more.G.sup.1 is a hydrocarbon backbone which is not interrupted by a hetero atom. Preferably G.sup.1 is a residue of a diene homopolymer or copolymer, in which case the resins produce flexible polymers. The resins are polymerized with a cationic polymerization initiator or latent acid catalyst. The resins have utility in the field of electronics.