Dielectric properties during free-radical bulk polymerization: Visible light-induced polymerization of bisphenol-A bis(2-hydroxyethyl ether) dimethacrylate

The dielectric properties of the polymerized and unpolymerized bisphenol-A bis(2-hydroxyethyl ether) dimethacrylate have been studied, and the polymerization of this monomer using visible blue light (lambda = 470 nm) and the system camphorquinone/(dimethylamino)ethyl methacrylate as a photochemical initiator has been followed in realtime. Remarkable changes in the permittivity epsilon'(omega,t,T) and the loss peak epsilon ''(omega,t,T) of the polymer have been observed and analyzed, as soon as the sample was illuminated, corresponding to a sudden fall of epsilon'(omega,t,T) for all the frequencies of measurement, a shift to low frequencies, and a large decrease of the relaxation loss peak in the frequency domain. A thermal postcuring of the acrylic polymer has been performed, leading to small changes in the chemical properties but large changes in the dielectric absorption. The present work shows how dielectric relaxation spectroscopy may be used as a very sensitive technique to follow polymerization.