Polymerization-Induced Phase Separation: Intermediate Dynamics

When phase separation is induced by polymerizating monomers in a mixture of monomers and nonreacting molecules, the dynamics is different depending on the time scale of polymerization tau(pl) and the time scale of phase separation tau(ps) Previous studies have explored the dynamic regimes where tau(pl) \u3c\u3c tau(ps) and that where tau(pl) \u3e\u3e tau(ps). In the former, a spanning gel emerges before the phase separation and the phase separation is driven largely by activation. In the latter, phase separation occurs first between polymers and nonbonding molecules and then the polymers turn into a gel, and therefore the driving mechanism is the same as in the usual liquid-liquid demixing processes. Using Molecular Dynamics simulations, we explore in this paper the intermediate dynamic regime where the two time scales are comparable. When the polymerization is done by means of the thermal condensation reaction, we observe the expected crossover, one limit behavior at early times and then the other at late times. When the polymerization is done by means of the radical addition reaction, the results suggest that the driving mechanism changes more than once