(638i) Nanoconfined Benzyl Methacrylate Radical Polymerization

The behavior of materials confined at the nanoscale has been of considerable interest over the past several decades. Here, our focus is the influence of nanoconfinement on the kinetics and thermodynamics of radical benzyl methacrylate polymerization using differential scanning calorimetry. Controlled pore glass (CPG) and ordered mesoporous carbons are used as confinement media with pore sizes from 3 to 8 nm. The polymerization rate in CPG increases as the ratio of surface area to pore volume increases, consistent with the rate being proportional to the concentration of surface silanol groups, whereas the rate in the carbon mesopores decreases as pore size decreases. For both nanoconfined and bulk polymerizations, the rate is proportional to initiator concentration to the one-half power, indicating similar reaction kinetics as in the bulk, but induction times are longer for nanoconfined polymerizations. Lower conversion is required for autoacceleration under nanoconfinement, presumably due to the limited diffusivity and lower termination rate for the confined polymer chains. The molecular weight of the polymer synthesized in the nanopores is generally higher than that obtained in the bulk except at the lowest temperatures investigated. The apparent activation energy of the nanoconfined polymerization in CPG is higher than in the mesoporous carbon, but both are lower than for the bulk. In addition, based on the changes in equilibrium conversion of the nanoconfined polymerization, the entropy loss of the polymer chains due to nanoconfinement is found to be as high as 48 J·mol^-1K^-1. A new floor temperature is discovered for nanoconfined polymerization, which depends on the molecular weight of polymer synthesized and the pore size.