Thermal and photopolymerization of divinyl ethers using an iodonium initiator: the effect of temperature

Differential scanning calorimetry was employed to monitor the thermal polymerization and the photopolymerization kinetics of divinyl ethers by temperature‐ramping and isothermal modes, respectively, with a diphenyl iodonium salt photoinitiator and a thioxanthenone photosensitizer. For thermal polymerization of triethylene glycol divinyl ether (TEGDVE), the peak temperature (i.e. the temperature at the maximum rate) decreased with increased photoinitiator concentration and reduced scanning rate, but the final conversions were all very high (>90%). The exotherm was extremely narrow, suggesting that the reaction was inhibited by a cation scavenger until it was all consumed. The activation energy, determined by the Ozawa method, was 108 ± 7 kJ mol^?1. With isothermal photopolymerization of the flexible divinyl ether TEGDVE, the final conversion rose from 30 to 70% with an increase in temperature from 40 to 80 °C. A similar trend but with much lower conversions was observed for a more rigid divinyl ether (bis4‐(vinyloxy)butyl] terephthalate, BVEBT). For TEGDVE, the activation energy determined from the maximum photocuring rate was 43 ± 4 kJ mol^?1, but the activation energy measured at a fixed conversion increased as the conversion rose. A similar value for the activation energy was found for the photocuring of BVEBT. The changes in the dynamic rheology were measured for TEGDVE during its photocuring and the gel point identified. Dynamic mechanical thermal analysis of the cured TEGDVE polymer showed it was a highly crosslinked network with T_g of 23 °C. The vinyl ethers could also be thermally cured by free radicals, but the extent of conversion was less than 33%. Copyright © 2007 Society of Chemical Industry