Molecular Weight Distribution of Two Living Chains in Polystyrene Prepared by Nitroxide Mediated Polymerization
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We report on the separation and characterization of living chains in polystyrene (PS) prepared by nitroxide mediated polymerization (NMP). There are two different living chains initiated from the alkoxyamine and self-initiation of styrene when an alkoxyamine based on 2,2,6,6-tetramethyl-1-piperidinyloxy is employed in NMP of styrene. To separate the two living chains, an alkoxyamine (R-T) was designed to have one hydroxyl group in the R moiety and two hydroxyl groups in T moiety. Each living chains bears a different number of hydroxyl groups and can be fully resolved by high performance liquid chromatography. Molecular structures of the fractionated living chains were confirmed by MALDI-TOF MS and 1H NMR. Molecular weight distribution (MWD) of the two living chains are quite different. MWD of the living chains derived from the alkoxyamine is narrow while the living chains from the self-initiation have broad MWD with significant tailing toward low molecular weight.