Thermal effects on the network structure of diglycidylether of bisphenol-A polymerized by electron-beam in the presence of an iodonium salt

The cationic polymerization of diglycidylether of bisphenol A (DGEBA) initiated in the presence of a diaryliodonium salt (DAIS) by electron beam irradiation has been studied by FTIR spectroscopy and by dynamic mechanical thermal analysis (DMA). The obtained results show the gradual increase of the temperature for the network thermo-mechanical transition (T-alpha, associated with the glass transition temperature T-g) over a broad range of conversion (pi) and reveal a peculiar behavior at high conversion. In this domain (pi > 0.90), the material's T, is shown to decrease when conversion approaches unity. Moreover, the post-irradiation thermal treatment of the materials, that generally yields effective post-polymerization, appears to induce a decrease of T-g, with an amplitude correlated with the amount of DAIS in the formulation. Owing to the particular nature of the propagating centers in cationic polymerization, the thermal relaxation of ionic clusters trapped in the glassy matrix can be reasonably invoked as a possible cause for this behavior. (C) 2003 Elsevier Science Ltd. All rights reserved.