Polymerization Thermodynamics under Nanoconfinement

The behavior of materials confined at the nanoscale has been of considerable interest over the past several decades, especially changes in the glass transition temperature (T_g) and/or melting point (T_m). Less well studied are the effects of nanoconfinement on polymerization kinetics and thermodynamics. Our recent focus has been on understanding how nanoconfinement influences the polymer/monomer equilibrium in the free radical reaction of poly(alkyl methacrylates). We find that nanoconfinement shifts the monomer/polymer equilibrium back towards monomer, and this effect can be exploited to determine the entropy loss on confining a chain. We find that the entropy loss is as high as 10 J/mol/K, approximately 10 % of the change going from monomer to polymer. The results seem to indicate that as the n-alkyl group increases from methyl to ethyl to butyl, the entropy of confinement decreases. Interestingly, the magnitude of the T_g depression in ultrathin films of poly(n-alkyl methacrylate)s also decreases as the length of the alkyl group increases in work by Vogt et al.; whether the origin is linked to the change in chain confinement entropy is an open question.