Traditionally, molecular weight averages and polydispersity have been used as polymer property indices in controlling the polymer molecular weight properties. In this paper, a new method is presented for the control of weight chain length distribution of polymer in a batch free radical polymerization process. The weight chain length distribution is directly calculated using the method of finite molecular weight moments in which the weight fraction of polymers is computed over a number of finite chain length intervals covering the theoretically infinite chain length domain. Task level control of chain length distribution is achieved using nonlinear programming to compute a suboptimal sequence of reactor temperature set points which lead to the best match of a given target weight chain length distribution.