Effect of acrylic acid neutralization on ‘livingness’ of poly[styrene‐ran‐(acrylic acid)] macro‐initiators for nitroxide‐mediated polymerization of styrene

Abstract

AbstractBACKGROUND: The effect of acrylic acid neutralization on the degradation of alkoxyamine initiators for nitroxide‐mediated polymerization (NMP) was studied using styrene/acrylic acid and styrene/sodium acrylate random copolymers (20 mol% initial acrylate feed concentration) as macro‐initiators. The random copolymers were re‐initiated with fresh styrene in 1,4‐dioxane at 110 °C at SG1 mediator/BlocBuilder® unimolecular initiator ratios of 5 and 10 mol%.RESULTS: The value of kpK (kp = propagation rate constant, K = equilibrium constant) was not significantly different for styrene/acrylic acid and styrene/sodium acrylate compositions at 110 °C (kpK = 2.4 × 10−6–4.6 × 10−6 s−1) and agreed closely with that for styrene homopolymerization at the same conditions (kpK = 2.7 × 10−6–3.0 × 10−6 s−1). All random copolymers had monomodal, narrow molecular weight distributions (polydispersity index M̄w/M̄n = 1.10–1.22) with similar number‐average molecular weights M̄n = 19.3–22.1 kg mol−1. Re‐initiation of styrene/acrylic acid random copolymers with styrene resulted in block copolymers with broader molecular weight distributions (M̄w/M̄n = 1.37–2.04) compared to chains re‐initiated by styrene/sodium acrylate random copolymers (M̄w/M̄n = 1.33).CONCLUSIONS: Acrylic acid degradation of the alkoxyamines was prevented by neutralization of acrylic acid and allowed more SG1‐terminated chains to re‐initiate the polymerization of a second styrenic block by NMP. Copyright © 2008 Society of Chemical Industry