Nanoconfined Benzyl Methacrylate Polymerization: Kinetics, Thermodynamics, and Chain Entropy Loss

Nanoconfinement is known to affect the behavior of polymeric materials, including changes in the T_g and relaxational dynamics. However, the effect of nanoconfinement on the kinetics and thermodynamics of polymerization is less well investigated and understood. Here, the nanoconfined free radical polymerization of benzyl methacrylate is investigated using differential scanning calorimetry. Controlled pore glass (CPG) and ordered mesoporous carbon with pore sizes ranging from 3 to 8 nm are used as the confinement media. The propagation rates in CPG increase as pore size decreases and is proportional to the surface silanol concentration, whereas the rates in the carbon mesopores decrease with reciprocal pore diameter. Autoacceleration is more pronounced under nanoconfinement, and the nanoconfined polymer has higher molecular weight compared to that synthesized in bulk – both of these effects are attributed to a decrease in the nanoconfined termination rate arising from a decrease in diffusivity of the confined chains. We also explore the thermodynamics of the nanoconfined polymerization and find that the entropy loss due to confinement of chains scales with molecular weight to the first power, consistent with theoretical predictions for the weak confinement regime.