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Hyperbranched polymers (HBP) belong to a group of molecules called dendritic polymers, which have peculiar and often unique properties. They are characterized by a highly branched backbone, which give access to a large number of reactive groups. Their branching pattern, Â characterized by a low amount of intermolecular or intramolecular entanglements, gives them excellent flow and processing properties 1,2]. Hyperbranched polymers are attractive because they resemble dendrimers, but they can be produced more easily on a larger scale at a reasonable cost. HBP with acrylate, vinyl ether, allyl ether or epoxy functions were studied as multifunctional crosslinker in coatings and in thermosets, using thermal as well as UV curing methods 3-8]. Considering their characteristics we were interested to employ HBP in UV curable formulations in order to improve the final properties of cured films. The UV-polymerization of multifunctional monomers is one of the more efficient methods available to generate three-dimensional polymeric networks 9]. Among the advantages of this technology are the high cure speed, the reduced energy consumption and absence of VOC emissions. It is well known that the UV curing can be performed either by a radical or a cationic mechanism. The cationic photoinduced process presents some advantages compared to the radical one 10], in particular lack of inhibition by oxygen, low shrinkage, good mechanical properties of the UV cured materials and good adhesion properties to various substrates. Moreover, the monomers employed are generally characterized by being less toxic and irritant. In the present work different functionalized hyper-branched polymers were synthesized and employed as additives in cationic photopolymerization of oxirane rings (epoxides or oxetanes). The HBP were inserted into the polymeric network either by copolymerization or through a chain transfer reaction involving the hydroxyl groups.
