Monitoring the kinetics of UV curing using in situ rheology and real-time fourier transform infrared spectroscopy

摘要

An in situ dynamic rheology technique and real-time Fourier transform infrared (FTIR) spectroscopy were used to characterize the UV cross-liniing of a thiol-ene system consisting of trimethylolpropane tris(2-mercaptoacetate) and trimethylolpropane diallyl ether. In order to compare the changes in rheological properties and chemistry of the thiolene system during UV curing, the evolving elastic modulus was correlated with the thiol coversion. The thiol conversion increased the fastest during the initial stages of the reaction while the elastic mdulus did not have an appreciable value until the thiol conversion reached 0.65. From the Flory-Stockmayer theory of gelation, the critical thiol conversion at the gel point was determined to be 0.71, suggesting that the elastic modulus did not have an appreciable value until the sample is near its gel point. This indicated that large enough cross-linked clusters, with relaxation times comparable to the time scales of the imposed deformation, have to be formed in order for the elastic modulus to have an appreciable value.