A phenolic group containing hyperbranched polyester (HBP) was synthesized and employed as chain transfer agent in cationic photopolymerization of a biscycloaliphatic epoxy monomer (CE). The epoxy group conversion increases by increasing the amount of HBP in the photocurable resin, due to a chain transfer reaction involving the phenolic-OH groups. HBP acts as a plasticizer inducing decrease of the T-g values together with an increase of the toughness properties. Meanwhile gel content increases together with the E' values. By increasing the amount of HBP in the photocurable resin an increase of the density is evident indicating a decrease of free volume. Therefore an improvement of the gas barrier properties might be expected; at the same time an increase of the thermal stability is evident.