Chain Entropy and Polymerization Thermodynamics: Quantifying Nanoconfinement Effects

Polymer chains lose entropy upon nanoconfinement. Here, we exploit the changes in the limiting conversion for nanoconfined free radical polymerization compared to the bulk case in order to determine the chain confinement entropy. In particular, we investigate the free radical polymerization of butyl- and benzyl-methacrylate in bulk and in controlled pore glass using differential scanning calorimetry, as well as characterizing the molecular weight of the synthesized polymer using gel permeation chromatography. We find that the entropy loss on confined polymerization can be nearly fifty percent greater than the entropy change on bulk polymerization, leading us to conclude that the entropy loss by confining the chains is as high as 50 J/mol/K (compared to 130 J/mol/K for the entropy change on propagation). Furthermore, the chain confinement entropy is found to scale with chain length N to the first power and to scale with pore size D to a higher power. Implications and comparison to theoretical predictions will be discussed.