Experimental studies on optimal molecular weight distribution control in a batch-free radical polymerization process

An experimental study on the control of polymer weight chain length distribution is presented for batch-free radical solution polymerization of methyl methacrylate. The weight chain length distribution is calculated using the method of finite molecular weight moments in which the weight fraction of polymers over a number of finite chain length intervals covering the theoretically infinite chain length domain is calculated. Control of a target polymer chain length distribution is achieved by first computing a discrete sequence of reactor temperature setpoints which lead to the best match of a given target weight chain length distribution at a final desired monomer conversion. During the polymerization, an on-line extended Kalman filter is used to incorporate infrequent and delayed off-line molecular weight measurements. The piecewise constant reactor temperature setpoints are taken as the decision variables in a nonlinear programming problem. They are recomputed and updated at each sampling point during the course of polymerization to match the final desired molecular weight distribution. It is demonstrated through simulations and experimentation that it is feasible to control the entire polymer chain length distribution in a batch polymerization process. (C) 1998 Elsevier Science Ltd. All rights reserved.