Abstract
To produce a photocurable thiolโene system, unsaturated polyester was prepared from the condensation reaction of ethylene glycol, diethylene glycol, and fumaric acid. Diallyl groups were introduced into the ends of the unsaturated polyester by a sequential condensation reaction. The coating formulation studied contained an equimolar ratio of thiol and vinyl groups of the prepared unsaturated polyester, including 1 wt % Irgacure 184. The curing behaviors of the unsaturated polyester with multifunctional thiols were investigated using realโtime FTIR spectroscopy. The rates of disappearance of thiol and vinyl groups of the unsaturated polyester were similar, demonstrating that there was little freeโradical homopolymerization of the internal fumaric group or the endโcapped vinyl ether group during the photocuring process and that the thiolโene reaction is the dominant process. The kinetics of the model compounds demonstrated that the reaction of the terminal allyl double bond with the thiyl radical is faster than that of the internal fumaric double bond in the UV curing of the unsaturated polyester. The storage stability of the thiolโene system based on unsaturated polyester was effectively increased by the addition of NโPAL. The Raman spectra revealed that the presence of a multifunctional thiol (penta 3โMP4) in the coating formulation increased the degree of surface curing due to the chainโtransfer ability of the thiyl radical. ยฉ 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 342โ350, 2005