Cationic photopolymerizations of thick polymer systems: Active center lifetime and mobility

摘要: Abstract Cationic photopolymerizations are essentially non-terminating and the long-lived active centers may lead to “dark cure” long after illumination has ceased. In this contribution, it is shown that cationic center lifetimes known be responsible for dark cure can also “shadow of unilluminated regions thick systems. “Shadow occurs when migrate out illuminated region, leading polymerization unexposed monomer. Photopolymerizations a cycloaliphatic diepoxide monomer were performed in which produced first 0.7 mm system by illuminating one end sample, shadow was monitored up 8 h. A front (with highly crosslinked polymer matrix on side unreacted other) observed move from region into at rate proportional square root time. The effective diffusion coefficient 50 °C found 1 × 10−5 cm2/s, temperature dependence well described Arrhenius relationship with an activation energy 89 kJ/mol. Studies based upon photoinitiator counter-ions differing size revealed larger counter-ion (and therefore correspondingly higher propagation constant) exhibited significantly coefficient. All experimental observations consistent hypothesis mobility arises largely reactive diffusion.