Reducing the gel effect in free radical polymerization

The gel effect is a phenomenon that often takes place during a free radical polymerization at intermediate or high degrees of conversion. It consists of the autoacceleration of the rate of the polymerization and it is due to diffusion limitations that slow down the termination reaction leaving the p ropagation and the initiation reactions unaffected. This phenomenon is high ly undesired in industrial application because it causes a fast and dramati c increase of the temperature of the reacting medium, often leading to scal e-up problems, instabilities, hot spots, and erratic behavior. In this pape r, we present the results of kinetic experiments performed in a cone and pl ate rheometer with two common monomers: styrene and n-butylmethacrylate. We show that the gel effect can be significantly reduced, if not eliminated,p erforming the polymerization at high shear rate. A new experimental device, the helical barrel rheometer, has been used and some preliminary results a re presented. (C) 2001 Elsevier Science Ltd. All rights reserved.