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

Abstract

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 °C. While short-chain branching for poly(t-BuAAm) samples could not be detected by 13 C 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.

Measurement and Modeling of Semi-Batch Solution Radical Copolymerization of N-tert-Butyl Acrylamide with Methyl Acrylate in Ethanol/Water

“…As previously documented [ 13 , 14 ], the monomer conversion profiles and polymer MMDs obtained from the batch polymerizations conducted in the stirred reactor setup were nearly identical to those obtained using the in situ NMR technique under identical conditions. For copolymerization under semi-batch operation, the overall fraction of MA in a sample can be calculated according to Equation (3), based upon the NMR determinations of the overall monomer conversion ( and the comonomer ( ) and copolymer ( ) compositions: …”

“…The MA and t-BuAAm homo- and co-polymerization kinetic models detailed in our previous publications [ 13 , 14 ] were fitted to represent the experimental batch data, which included monomer conversion and comonomer composition drift profiles, MMDs, and branching levels. The batch experiments were conducted in ethanol-rich ( = 0.75–1) mixtures of EtOH/H 2 O at 50–70 °C, with various initial monomer and initiator levels.…”

“…The precipitated polymer was then dried again before preparation for an SEC analysis of the polymer MMDs and an 1 H NMR analysis of the copolymer composition. The analytical equipment and procedures used, the proton NMR used to determine the overall monomer conversion and instantaneous comonomer composition of the reactor aliquots diluted in CDCl 3 , and the SEC used to measure the molecular mass distributions (MMD) are explained in previous studies, including the details of SEC calibration [ 13 , 14 ].…”

“…A kinetic model that included the formation and consumption of MCRs was developed to capture the influence of solvent composition ( between 0.75 and 0.95) and initial MA content ( between 0.10 and 0.40) on monomer conversion profiles, polymer MMDs, and branching levels over a range of operating temperatures and initiator concentrations. A second publication extended the model to MA/t-BuAAm copolymerization, accounting for the backbiting of both monomers [ 14 ]. The influence of the solvent on chain-growth kinetics was determined in a PLP-SEC study of the copolymerization system [ 8 ], with reactivity ratios estimated by fitting the drift in the comonomer composition with overall monomer conversion during batch operation [ 14 ].…”

“…A second publication extended the model to MA/t-BuAAm copolymerization, accounting for the backbiting of both monomers [ 14 ]. The influence of the solvent on chain-growth kinetics was determined in a PLP-SEC study of the copolymerization system [ 8 ], with reactivity ratios estimated by fitting the drift in the comonomer composition with overall monomer conversion during batch operation [ 14 ]. The detailed model was verified by comparing predictions to the MA/t-BuAAm copolymer MMDs, comonomer compositions, and monomer conversions measured for an extensive set of batch copolymerizations [ 14 ].…”