Gel time prediction of multifunctional acrylates using a kinetics model

A kinetics model for prediction of double-bond conversion and gel time in the photopolymerization of multifunctional acrylates is presented. The system consisting of a trifunctional acrylate, trimethylolpropane triacrylate (TMPTA), and a photoinitiator, 2,2-dimethoxy-1,2-diphenylethan-1-one (DMPA), was studied using Fourier-transform infrared spectroscopy (FTIR) measurements to monitor double-bond conversion and microrheology techniques to quantify the gel time for this system. Rate constants for the kinetics model were first estimated by fitting the model only to the FTIR double-bond conversion data, and later to both the FTIR and microrheology data. The measured gel time correlated with both the calculated initial rate of radical generation and a constant value of the predicted double-bond conversion, over a broad range of conditions. The model allows for materials formulation and exposure source intensity variables to be included in stereolithography inverse problem solutions, and could be applied to other cross-linking based photopolymerization systems.