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

Abstract

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, k_p. For 10 wt% tBuAAm in solution at 30 °C, k_p,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 k_p,tBuAAm 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/H₂O mixture.