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

摘要

Styrene/tert-butyl acrylate (SA-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 BlocBuilderwere more controlled with lower polydispersities (from 1.14 to 1.22), and the number-average molecular weight M_n exhibited linear behavior with conversion up to ～50%._In contrast, without SG1, apparent rate constants were greater but higher polydispersities were observed, and M_n vs conversion deviated from the ideal linear relationship at low conversions ～20%. The value of k_pK (k_p = propagation rate constant, K = equilibrium constant) for t-BuA at 115 °C was 3.0 x 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—Tudos, and nonlinear least-squares fitting methods.