Measurement and Modeling of N-tert-butyl Acrylamide Radical Homo- and Copolymerization with Methyl Acrylate in Ethanol/Water

The radical homopolymerization of N-tert-butyl acrylamide (t-BuAAm) and its copolymerization with methyl acrylate (MA) is studied in ethanol/water solutions over a range of initial monomer and initiator levels between 50 and 70 degrees C. While short-chain branching for poly(t-BuAAm) samples could not be detected by C-13 NMR, the reduced rate of monomer conversion with lowered monomer content indicates the formation of mid-chain radicals (MCR) by backbiting. Adding water as a cosolvent to ethanol significantly increases reaction rates, in agreement with recent pulsed-laser studies that quantify the influence of solvent composition on homopropagation kinetics. However, the measured drifts in comonomer composition with conversion are well represented by a single pair of reactivity ratios (r(MA) = 1.12 +/- 0.01, r(t-BuAAm) = 0.71 +/- 0.01) over the complete range of experimental conditions. A mechanistic model developed to describe t-BuAAm homopolymerization is extended to capture the impact of reaction operating conditions (monomer content and composition, solvent composition, initiator content, and temperature) on the features of t-BuAAm/MA copolymerization, thus providing a tool for product and process optimization. The model structure can be used to support the development of other acrylate/acrylamide systems as part of the continued efforts to utilize "green" solvents to reduce the environmental impacts of polymerization processes.