Methyl Acrylate and Tertiary-butyl acrylamide Solution Radical Polymerization Kinetics

Abstract

Acrylate-acrylamide copolymers are used in a variety of applications, including for wastewater treatment and in pharmaceuticals, cosmetics, and hair-care products. These materials are synthesized by radical copolymerization in polar media, with an increased emphasis on conducting reactions in water or alcohol/water mixtures. Under these reaction conditions, both the monomer to solvent ratio and the solvent composition are known to influence the polymerization kinetics. In this study, the copolymerization propagation kinetics of tertiary butyl acrylamide (tBuAAm) and methyl acrylate (MA), a system of commercial interest, are systematically studied using the pulsed laser polymerization-size exclusion chromatography (PLP-SEC) technique. The Mark-Houwink(M-H) calibration parameters required for molecular weight analysis of poly(tBuAAm) in THF are determined using both triple detector and dual detector SEC setups, as no values have been reported previously in the literature. The influence of temperature (30-60 oC), monomer weight fraction (5-50 %) and ethanol/water solvent composition (varying from 100% EtOH to 100% H2O) on the propagation kinetics of MA and tBuAAm was determined. The homopropagation (kp) values for 10 wt% monomer in a 75/25 EtOH/H2O mixture at 30 oC are 41,900 L·mol-1·s-1 and 13,800 L·mol-1·s-1 for MA and tBuAAm, respectively. The rate coefficients were found to increase substantially as the fraction of water in the solvent mixtures is increased, and as the monomer to solvent ratio is decreased, such that the value for 5 wt% MA in water (close to its miscibility limits) is 16 times higher than its bulk value. Experimental measurement of copolymer kp values indicate that while the terminal model predictions are successful in describing the kinetics for solvent mixtures with low water content, it fails to describe the kinetics for mixtures with 50 wt% water or greater. The large influence of solvent choice and composition on the chain-growth rates of these two monomers must be considered for both product and process design.