Structure-property-relationship of sustainable thermosets using photoinitiated cationic ring-opening polymerization of epoxy and oxetane

Abstract

Because of the high viscosity of ELO (?? = 2,100 cp) at room temperature, the UV curing kinetics of ELO is limited by the slow diffusion of monomers. Extensive characterization techniques, such as optical pyrometry, DSC, real-time ATR-FTIR, Confocal Raman spectroscopy and DMA, were employed to study and control the mechanical and thermal properties of the UV-cured ELO films using thermal postcuring and the copolymerization of reactive low-viscosity comonomers. While the DOX monomer has a low viscosity (?? = 13 cp) and the ring strain energy of oxetane is comparable to that of epoxide, DOX shows a long induction time (typically ~ 60 sec) before the onset of autoaccelerated cationic polymerization. We found that the prolonged induction period is due to the resonance-stabilized secondary oxonium ion intermediate formed during photoinitiation.