PHOTOINITIATED CURING OF MULTIFUNCTIONAL MONOMERS

This article provides an overview of the different types of photocurable systems currently used in radiation curing applications and reports the remarkable performance of some newly developed multifunctional monomers. Light-induced crosslinking polymerization has been studied by real-time infrared spectroscopy, which records directly conversion versus time profiles, thus allowing the important kinetic parameters to be evaluated for reactions occurring within a fraction of a second. Acrylate monomers bearing a carbamate or ozazolidone function exhibit an unexpectedly high reactivity. The curing reaction was shown to develop with long kinetic chains (up to 50 000 mol per initiating radical), because of a high value of the propagation rate constant and a low value of the termination rate constant. The UV-curing performances of different types of vinyl ether based systems are described, special emphasis being given to the kinetic and mechanistic aspects. Highly crosslinked polymer materials having quite different structures have ben synthesized by acting on the formulation composition and on the selected photoinitiators and co-monomers. The light-induced polymerization of a triacrylate monomer has been carried out in a polymer matrix to generate a semi-interpenetrating polymer network. In low-modulus binders, such as polyurethane or natural rubber, the UV-cured polymer combines the properties of the elastomeric polymer and of the glassy acrylate network. Dual polymer networks have been created by polymerizing photochemically a rubber bearing bath epoxy and acrylate groups in its main chain.