Styrene (S)/acrylonitrile [AN; initial acrylonitrile molar feed compositions (fAN,0's) = 0.10–0.86) and tert-butyl methacrylate (tBMA)/AN (fAN,0 = 0.10–0.80) copolymers were synthesized at 90°C in 50 wt % 1,4-dioxane solutions with a unimolecular initiator, N-(2-methylpropyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-O-(2-carboxylprop-2-yl) hydroxylamine [BlocBuilder (BB)]. In the tBMA/AN copolymerizations, 8.0–8.5 mol % N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) free nitroxide relative to BB was added. The S/AN copolymers exhibited narrow, monomodal molecular weight distributions (MWDs) with low polydispersities [weight-average molecular weight (Mw)/number-average molecular weight (Mn) = 1.14–1.26], and the Mn versus monomer conversion (X) plots were relatively linear (Mn = 18.1 kg/mol, X ≈ 0.7); this suggested that pseudo-living behavior was approached. AN proved to be an effective controlling comonomer for tBMA because the tBMA/AN copolymers exhibited narrow monomodal MWDs with Mw/Mn = 1.17–1.50 and relatively linear Mn versus X plots to reasonably high X values (Mn = 15.6 kg/mol, X ≈ 0.6). The AN and S monomer reactivity ratios were rAN = 0.07 ± 0.01 and rS = 0.27 ± 0.02 (Fineman–Ross) and rAN = 0.10 ± 0.01 and rS = 0.28 ± 0.02 (Kelen–Tüdos), respectively; these values were in good agreement with conventional free-radical polymerization. Error-in-variables model (EVM) analysis indicated that the use of cumulative composition S/AN data was more effective than typical approaches using low-X data with the Mayo–Lewis model. The AN and tBMA reactivity ratios [rAN = 0.07 ± 0.01 and rtBMA = 1.24 ± 0.20 (Fineman–Ross) and rAN = 0.14 ± 0.01 and rtBMA = 0.89 ± 0.19 (Kelen–Tüdos)] were similar to those reported for related alkyl methacrylate/AN conventional radical copolymerizations. EVM analysis suggested significant experimental error was associated with the tBMA/AN system, and this warrants further investigation. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
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