UV curing behavior and kinetics of hyperbranched polysiloxane

Ultraviolet (UV) curing behavior and kinetics of hyperbranched polysiloxane (HBP) were studied via isothermal Differential Photo Calorimeter (DPC) technology. Firstly, the influences of the factors such as photoinitiator's concentration, light intensity, temperature and atmosphere, on UV curing behavior were investigated in detail. It is found that both curing rate (R) and ultimate vinyl conversion (C) could be raised by the increase of photoinitiator's concentration and UV light intensity as well as elevating temperature. Oxygen possessed an inhibition effect on the curing, however, it could be reduced by enhancing UV light intensity. The results could be confirmed by that induction period can be reduced by higher UV light intensity. Secondly, curing kinetics were also studied by using an autocatalytic model with a diffusion term attached. The kinetic parameters were calculated from that model, and correspondingly, the total apparent reaction exponent and apparent activation energy were obtained within the range of 6-7 and 9.95 kJ/mol, respectively. Comparative results between kinetic calculations and experimental measurements show that the autocatalytic model used was suitable to simulate the autocatalysis phenomena at the initial stage and the termination process could be controlled by diffusion. Finally, comparison of curing behavior between the HBP and two low-functionality monomers indicates that the unique hyperbranched structure and the corresponding high multifunctionality led to the gelation at the very initial stage of curing, as a result, relatively low ultimate vinyl conversion was observed.