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

BACKGROUND: 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 k p K ( k p = propagation rate constant, K = equilibrium constant) was not significantly different for styrene/acrylic acid and styrene/sodium acrylate compositions at 110 °C ( k p K = 2.4 × 10 −6 –4.6 × 10 −6 s −1 ) and agreed closely with that for styrene homopolymerization at the same conditions ( k p K = 2.7 × 10 −6 –3.0 × 10 −6 s −1 ). All random copolymers had monomodal, narrow molecular weight distributions (polydispersity index M̄ w / M̄ n = 1.10–1.22) with similar number‐average molecular weights M̄ n = 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 ( M̄ w / M̄ n = 1.37–2.04) compared to chains re‐initiated by styrene/sodium acrylate random copolymers ( M̄ w / M̄ n = 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