Radical copolymerization kinetics of N-tert -butyl acrylamide and methyl acrylate in polar media

The effect of solvent on the radical copolymerization propagation kinetics of methyl acrylate (MA) with N-tert -butyl acrylamide ( t BuAAm) is studied using the pulsed laser polymerization size exclusion chromatography technique (PLP-SEC), with SEC calibration for poly( t BuAAm) in tetrahydrofuran (THF) established using two different methodologies. A solid at room temperature, t BuAAm has limited solubility in both ethanol (EtOH) and water that restricts the range of conditions for measurement of the homopropagation rate coefficients, k p . For 10 wt% t BuAAm in solution at 30 °C, k p, t BuAAm = 12.7 × 10 3 L mol −1 s −1 and 13.8 × 10 3 L mol −1 s −1 in EtOH and in a 75/25 w/w EtOH/H 2 O mixture, respectively. These k p, t BuAAm values are a factor of 2.5–3.0 times lower than the value of k p,MA at equivalent conditions. This study, the first of copolymerization propagation kinetics in polar solutions, demonstrates that the composition-averaged copolymerization k p,cop values increase systematically with increasing MA content in the comonomer mixture. The experimental data are well-represented by the terminal model provided that the solvent influence on the two homopropagation values are accounted for in the EtOH-rich systems. However, the representation fails to represent the data when the polymerization is conducted with elevated (50% or greater) water content in the EtOH/H 2 O mixture.