This study investigated the suitability of chaotic mixers as polymerization reactors by taking chain extension of thermoplastic polyurethanes as an example. The performance of chaotic mixers was analyzed in terms of the effects of mixer designs and mixer operating conditions on polymer molecular weight and properties. Specifically, the analysis involved computation of time scales of mixing and chemical reactions and finding their relationship to mixing torque, polymer molecular weight, and mechanical and thermal properties. It was found that the time scale of mixing has a strong dependence on the Liapunov exponent, a parameter used to characterize the degree of chaotic mixing. The results showed that the highest polymer molecular weight is obtained when the mixer operates under globally chaotic conditions and when the magnitudes of the time scales of mixing and chemical reactions are made comparable to each other. The study also showed that hard segment phase separation can reduce the value of the reaction rate constant and hence hinder the progress of polymerization.