Photoinitiated cross-linking of a thiol-methacrylate system

The photoinitiated thiol-ene cross-linking of a dimethacrylate polyether of Bisphenol A and pentaerythritol tetrakis 2-mercaptopropionate was studied in the presence of 2,2-dimethyl-2-hydroxy acetophenone (Darocur 1173). Two complementary techniques were used: photocalorimetry and real-time infrared spectroscopy. In the first part, the kinetic reaction was characterized by a stoichiometric mixture in reactive functions. The influence of temperatu re, photoinitiator concentration and ultraviolet (UV) light intensity was i nvestigated. The results mainly show that the methacrylate homopolymerizati on is faster than the thiol-ene addition so that the reaction is usually st opped because of the complete consumption of the methacrylate double bonds. A theoretical approach has allowed us to determine a transfer constant of 0.26. Moreover, an increase in the autoacceleration rare was observed in th e presence of the thiol monomer. In the second part, the molar fraction of methacrylate double bonds and thiol functions was changed to determine the effect on the kinetic reaction and the glass transition temperature of the final material. (C) 2001 Elsevier Science Ltd. All rights reserved.