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 (tBuAAm) is studied using the pulsed laser polymerization size exclusion chromatography technique (PLP-SEC), with SEC calibration for poly(tBuAAm) in tetrahydrofuran (THF) established using two different methodologies. A solid at room temperature, tBuAAm has limited solubility in both ethanol (EtOH) and water that restricts the range of conditions for measurement of the homopropagation rate coefficients, kp. For 10 wt% tBuAAm in solution at 30 °C, kp,tBuAAm = 12.7 × 103 L mol−1 s−1 and 13.8 × 103 L mol−1 s−1 in EtOH and in a 75/25 w/w EtOH/H2O mixture, respectively. These kp,tBuAAm values are a factor of 2.5–3.0 times lower than the value of kp,MA at equivalent conditions. This study, the first of copolymerization propagation kinetics in polar solutions, demonstrates that the composition-averaged copolymerization kp,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/H2O mixture.