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 (20mol% initial acrylate feed concentration) as macro-initiators. The random copolymers were re-initiated with fresh styrene in 1,4-dioxane at 110 degrees C at SG1 mediator/BlocBuilder (R) 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 degrees C (k(p)K = 2.4 x 10(-6) -4.6 x 10(-6) s(-1)) and agreed closely with that for styrene homopolymerization at the same conditions (k(p)K = 2.7 x 10(-6)-3.0 x 10(-6) s(-1)). All random copolymers had monomodal, narrow molecular weight distributions (polydispersity index (M) over bar (w)/(M) over bar (n) = 1.10-1.22) with similar number-average molecular weights (M) over bar (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 ((M) over bar (w)/(M) over bar (n) = 1.37-2.04) compared to chains re-initiated by styrene/sodium acrylate random copolymers ((M) over bar (w)/(M) over bar (n) = 1.33). CONCLUSIONS: Acrylic acid degradation of the alkoxyamines was prevented by neutralization of acrylic acid and allowed more SGI-terminated chains to re-initiate the polymerization of a second styrenic block by NMP. (C) 2008 Society of Chemical Industry