Phase separation during bulk polymerization of methyl methacrylate

We report on the phase separation of methyl methacrylate (MMA) and poly(methyl methacrylate) (PMMA) during bulk free-radical polymerization. The phase separation is induced when the reaction is initiated at room temperature by the redox reaction of benzoyl peroxide in the presence of an amine. During the reaction, the ratio of MMA and PMMA changes continuously. Separation into MMA-rich and PMMA-rich phases coincides with the onset of the Trommsdorff effect. At room temperature, the interface between the two phases remains, even after drying the remaining monomer. When the sample is annealed above the glass transition temperature Tg, the interface disappears. Due to the frozen dynamics of the polymer chains, subsequent cooling below Tg does not result in further phase separation. This result provides evidence for the existence of rich, thermodynamically stable states, which are typically suppressed due to the frozen dynamics of polymers at temperatures below the Tg, after thermal processing above the Tg.