Electron paramagnetic resonance and electron–nuclear double resonance characterization of radicals in photopolymerized multifunctional methacrylates

Abstract

Propagation radicals generated during the photopolymerization and photo-cross-linking of a trimethacrylate and a vinylmethacrylate monomer have been characterized by EPR and ENDOR spectroscopy at different temperatures. Also, radical decay has been investigated at 363–423 K. The EPR spectral shape reflects a fast exchange process between two radical conformations and is sensitive to the mobility of the polymeric structure surrounding radicals. ENDOR spectra show ¹H-matrix lines and a band around 45 MHz, which has been attributed to the interaction of the unpaired electron with the hydrogen nuclei of a freely rotating methyl group. Radical decay and dynamic phenomena involving radicals have been interpreted in the light of a dispersive kinetic model, which allows the evaluation of useful parameters for polymer characterization.