Anionic polymerization with unequal reactivity in batch reactors is a nonlinear problem, and in order to determine the rate constants using the experimental molecular weight distribution (MWD) and conversion vs. time of polymerization, the simulation equations need to be solved repeatedly. In this work, we evolved an efficient algorithm in which the experimental MWD yields the reactivity ratio directly while conversion data give the values of all rate constants. For doing this, we proposed a series solution for the reacting species in terms of monomer conversion. A technique similar to the finite element method for boundary problems is used to divide the conversion into subdomains. The size of these steps is decided by a convergence criterion and results were determined at the end of the conversion domain through sequential computation. The scheme can be implemented on a personal computer and is considerably faster and more efficient. We used experimental data from the literature and demonstrated our technique of evaluating the rate constants.