Isothermal and non-isothermal polymerization of methyl methacrylate in presence of multiple initiators

Methyl methacrylate (MMA) polymerization is a diffusion-controlled reaction, characterized by a strong gel effect, which may cause uncontrolled heat generation and the thermal runaway of the process. For applications to industrial polymerization, kinetic control is particularly important and difficult to achieve due to the interplay between heat development and diffusional control occurring during polymerization. Sustaining the polymerization reaction (i.e. enhancing heat exchange) is a promising strategy to control MMA polymerization kinetics. In particular, different initiators triggering polymerization at different times can be used, thus reducing the possibility of thermal runaway by engineering temperature history and initiator nature/concentrations. There are few models accounting for the presence of multiple initiators and non-isothermal conditions. Therefore, a new, simple semi-empirical model, relating degree of conversion and polymerization rate to time and temperature, was developed. To validate the model, DSC tests were performed in isothermal and non-isothermal conditions, thus deriving the heat developed during polymerization. Model parameters were calculated from isothermal DSC experiments, and the model was predictive of monomer conversion in non-isothermal conditions in presence of single initiators and the mixture of them. Results indicate that, by varying formulation parameters (temperature history and initiator concentrations), polymerization kinetics may be optimized.