During the normal operation of plastic sheet polymerization reactors, large monomer conversion and average molecular weight should be achieved. However, improving any one of these two operating objectives would result in worsening the remaining one, and vise versa. Because of physical constraints, it would not be possible to meet both operating objectives in similar extent. Therefore, trade-off solutions must be obtained from which the designer can pick up the one that best suits her/his design objectives. In this work we compute the whole set of trade-off solutions by solving a set of multiobjective optimization problems. In this work we select as the best trade-off solution, the point on the trade-off curve closest to the utopia region. We demonstrate that dynamic optimal warming temperature profiles improve the control on the weight-average molecular weight and monomer conversion simultaneously, and lead to a polymer sheet with better homogeneity characteristics, when trade-off solutions based on multiobjective optimization are used.