- Block copolymerization of vinyl acetate and vinyl neo -decanoate mediated by dithionodisulfide
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Block copolymerization of vinyl acetate (VAc) and vinyl neo-decanoate (VNDc) is carried out in the presence of a disulfide, isopropylxanthic disulfide (DIP), using 2,2′-azoisobutyronitrile (AIBN) as the radical initiator. The polymerization proceeds in a controlled/'living' style, as illustrated by stepwise increase in molecular weight and relatively narrow molecular weight distribution of the final product. The reaction mechanism is investigated in detail for the system of VAc homopolymerization in the presence of DIP. The results of chromatography, NMR, and mass spectra reveal that there exists two kinds of RAFT agents, that is, S-(cyano)isopropyl O-isopropyl xanthate and diisopropyl dithiocarbonate, the former coming from the reaction of 2-cyano-isopropyl radical with DIP and the latter being formed in situ during a series of radical process participated by the monomer. High efficiency of the cross initiation is achieved for the sequential polymerization. The block lengths are well controlled by the ratio of monomer to RAFT agents. The resulting block copolymer, PVAc-b-PVNDc, is hydrolyzed to prepare PVOH-b-PVNDc. These block copolymers, before and after hydrolysis, undergo self-assembly in solution and phase separation in bulk state.
- Gu, Yuankai,He, Junpo,Li, Changxi,Zhou, Changming,Song, Shijie,Yang, Yuliang
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- Free radical reaction of diisopropyl xanthogen disulfide with unsaturated systems
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1,3-Dithiol-2-ones are prepared in one pot reaction from commercially available diisopropyl xanthogen disulfide (2) and alkynes under radical conditions. The 5-membered heterocycle is formed via a ring closure of vinyl radical (7) resulting from the thio radical addition of 5 to an alkyne. The reaction worked best for alkynes conjugated with a C=C double bond. The oxygen atoms of reagent (2) could be replaced by sulfur and this new reagent furnished 1,3-dithiol-2-thiones under radical conditions.
- Gareau, Yves,Beauchemin, Andre
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p. 2003 - 2017
(2007/10/03)
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