Styrene/tert-Butyl Acrylate Random Copolymers Synthesized by Nitroxide-Mediated Polymerization: Effect of Free Nitroxide on Kinetics and Copolymer Composition

Styrene/ tert -butyl acrylate (S/ t -BuA) mixtures were copolymerized using nitroxide-mediated polymerization in bulk at 115 °C using an alkoxyamine unimolecular initiator, 2-[ N - tert -butyl-2,2-(dimethylpropyl)aminooxy]propionic acid (BlocBuilder) to observe the effect of additional N - tert -butyl- N -[1-diethylphosphono-(2,2-dimethylpropyl)] nitroxide (SG1) on kinetics and copolymer composition. Polymerizations with 4.5 mol % SG1 relative to BlocBuilder were more controlled with lower polydispersities (from 1.14 to 1.22), and the number-average molecular weight M̄ n exhibited linear behavior with conversion up to ∼50%. In contrast, without SG1, apparent rate constants were greater but higher polydispersities were observed, and M̄ n vs conversion deviated from the ideal linear relationship at low conversions ∼20%. The value of k p K ( k p = propagation rate constant, K = equilibrium constant) for t -BuA at 115 °C was 3.0 × 10 -6 s -1 and is lower than other acrylic monomers. The copolymers were richer in t -BuA than the feed composition at low initial t -BuA feed compositions f t -BuA,0 (20 mol %) but became richer in styrene when f t -BuA,0 > 40 mol %. Copolymer reactivity ratios ranged from r t -BuA = 0.09 to 0.12 and r S = 0.40 to 0.49 using Fineman−Ross, Kelen−Tüdos, and nonlinear least-squares fitting methods.