Photoinduced free radical Polymerasation of unsaterated polyesters in presence of multicrylate reacting diluents

The polymerisation of coatings and printing inks using ultraviolet light (UV) or electron beam energy sources (EB) is constantly challenged to improve performances, to increase durability, to reduce costs and to satisfy environmental and safety regulations. In particular, UV curing had success in several applications as clear top coating, for the protection of paper, wood and metallized automotive and thermoplastic manufactured articles 2]. The commercially available unsaturated oligomers are mainly formed by epoxy-acrylates, acrylourethanes and polyesters containing acrylic polymerisable groups at the chain ends. The most acrylated oligomers are usually constituted from two acrylated groups per chains and have a molecular weight ranging from 600 to 20,000 g/mol. The acrylated oligomers provide good film-forming properties, suitable viscosity and flexibilty to UV cured materials. There are aromatic oligomers after UV curing that form hard rigid polymer films with high tensile strength and modulus, while those aliphatic generate soft, extensible coatings with high tensile elongations. Another class of oligomers often used in several applicative formulations for wood and composites are unsaturated polyesters (UP). Unsaturated polyester (UP) resins are linear polycondensated oligomers based both on unsaturated and saturated acids/anhydrides and aliphatic diols. These oligomers may be viscous liquids or brittle solids with a low degree of polymerization with a molecular weight ranging from 1200 to 5000 g/mol. These unsaturations into the polymer backbone provide reactive sites for the copolymerization with vinylic or acrylic monomers by using free-radical initiators. The copolymerization reactions thereby lead to the formation of a threedimensional network. The UP, diluted by vinyl or acrylated monomers (reactive diluents) are often known as UP resins. The diluted UP resins with a reacting diluents show a viscosity in a range of 250 — 5000 can be usually processed over a wide temperature range. Glass-fiber-reinforced UP resins are extensively used in building, construction, transportation, electronic industries and domestic applications for their possibility of thermal curing at room temperature and atmospheric conditions (Le. ambient conditions). UP resins may be classified on the basis of their structure into the following groups: ortho, isoresins and chlorendics resins.