Abstract
Coatings based on a hybrid organic–inorganic epoxy system were prepared by a dual‐curing mechanism, via cationic photopolymerization in the first step at room temperature and a subsequent hydrolysis/condensation reaction of a trialkoxy‐silane compound (sol–gel process) at high temperature. To this end, a high T~g~ epoxy resin (3,4‐epoxycyclohexylmethyl‐3′‐cyclohexenyl‐methyl adipate, UVR 6128) was added in increasing amounts to a precursor for the inorganic‐like phase (3,4‐epoxycyclohexylethyltrimethoxysilane, EETMOS). The mixture contained triphenylsulfoniumhexafluoroantimonate as a cationic photoinitiator. By this method, the strongly acid environment generated by the photolysis of the triarylsolfunium salt in the first step induces the hydrolysis of EETMOS alkoxy‐silane groups. The films produced in the first step of the process were thermal treated to promote the condensation reactions of the siloxane moieties. The kinetics of the reactions of photopolymerization and condensation was investigated. It was found that the presence of EETMOS increases both the polymerization rate and the final consumption of epoxy groups. Thermogravimetric analyses performed in air have revealed an increased stability of the hybrid coatings with respect to the films produced from formulations without EETMOS. A significant increase in surface hardness was also observed for the hybrid coatings. The thermo‐mechanical properties were found to be strongly affected by the temperature used in the thermally induced reactions in the second step. The hybrid coatings on a low‐density polyethylene substrate were found to decrease the diffusivity of oxygen and to increase the oxygen solubility within the coating. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:77–85, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20149