Abstract
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 M̄n exhibited linear behavior with conversion up to ∼50%. In contrast, without SG1, apparent rate constants were greater but higher polydispersities were observed, and M̄n vs conversion deviated from the ideal linear relationship at low conversions ∼20%. The value of kpK (kp = 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 ft-BuA,0 (20 mol %) but became richer in styrene when ft-BuA,0 > 40 mol %. Copolymer reactivity ratios ranged from rt-BuA = 0.09 to 0.12 and rS = 0.40 to 0.49 using Fineman−Ross, Kelen−Tüdos, and nonlinear least-squares fitting methods.
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