Kinetic study on UV-curing of hyperbranched polysiloxane

Ultraviolet (UV) curing kinetics of hyperbranched polysiloxane (HBP) initiated by 2-Hydroxy-2-methyl-1-[(4-isobutyl)phenyl]-1-propanone (Trade name: IHT-PI 185) was studied by using Differential Photo Calorimeter (DPC). The effects of photoinitiator concentration, UV irradiation intensity, environment temperature and atmosphere on curing behaviors were investigated. It was found that both curing rate (R) and ultimate vinyl conversion percentage (C) first increase and then tend to stabilize within 3 wt% of photoinitiator concentration. Higher UV irradiation intensity can lead to higher values of R and C. Particularly, R is proportional to the square root of irradiation intensity at initial stage. Although raising temperature could raise the values of R and C, the effect of temperature on R is not marked. Oxygen possesses a notable inhibition effect on curing, however, induction period can be reduced by enhancing irradiation intensity. Curing kinetics was studied using Ameliorated Autocatalytic Model attaching a diffusion term. It is found that the model is suitable to describe the autocatalysis effect at the initial stage and the termination stage controlled by diffusion process. The kinetic parameters including total apparent curing exponent and apparent activation energy calculated by model above are c.a. 6 and 13.15 KJ/mol, respectively.