Reactivity and Network Structure of UV- and EB-Cured Bis-Phenol A Ethoxy Diacrylate

Theradiation-induced polymerization of acrylates is known to proceed in a very heterogeneous manner and the resulting networks often display heterogeneities at various dimension scales. In particular, the early formation of microgels produces a heterogeneous structure including highly cross-linked particles together with a gelled network, with dangling chains or loops and swelling monomer. This heterogeneous character is revealed by anomalous features in the thermo-mechanical spectrum, with the broadening and the presence of shoulders in the relaxation factor (tanö) peak, but without any possibility of straightforward quantification. In order to gain an insight into the network's heterogeneity, solid state proton 2 NMR relaxation experiments were performed on radiation-cured bis-phenol A ethoxy diacrylate samples. This method allowed us to distinguish and to quantify two phases inside the materials: one phase with low mobility, and a second one with high mobility and distinct relaxation features. The decay of transverse magnetization is fitted with two components, (short or long ), which can be assigned respectively to the highly and loosely cross-linked phases. The influence of acrylate conversion on the relaxation behavior of cured samples was examined. A comparison between relaxation behavior of networks obtained by UV- or by EB-induced polymerization does not reveal noticeable differences to be related to the initiation mechanism.