| Controlled/"living" radical polymerizations based on the RAFT (reversible addition-fragmentation chain transfer) process have been extensively studied in the past ten years. The living feature of the RAFT-based polymerization is achieved through the reversible chain transfer of propagating radicals towards thiocarbonylthio compounds such as dithioesters and trithiocarbonates. When xanthates are used as chain transfer agent, the reaction is independently nominated as macromolecular design via the interchange of xanthates (MADIX) processes, which is a very efficient approach in the synthesis of narrow disperse vinyl alkanoate polymers. Usually, the studies of the RAFT and MADIX polymerizations require the synthesis of thiocarbonylthio compounds in a laboratory scale, while an alternative way is to form RAFT agent in situ by the reaction of radical initiator and disulfide. In the present work, we use (DIP), a conventional rubber vulcanization accelerator, to mediate the RAFT/MADIX polymerization of vinyl acetate and vinyl neo-decanoate (VNDc).DIP is a bifunctional xanthogenic derivative and vinyl neo-decanoate (VNDc) is a functional monomer with bulky branched alkyl group.The present work demonstrates that:1)DIP is rather a precursor of RAFT agent than an iniferter during the polymerization of vinyl alkanoates, thereby 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. An induction period of up to 5 hours is observed for both systems. At the end of the induction period, molecular weight starts to increase linearly with monomer conversion. Nevertheless, the molecular weight increases abruptly when it starts to grow, exhibiting a "hybrid" behavior of conventional and controlled radical polymerization during the initial stage.2) The formation of induction period and the reaction mechanism are 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 three main products derived from DIP, including two kinds of RAFT agents, i.e., 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. The formation route of these two agents and the cyclic 1,3-dithiol-2-one compound is proposed. Although diisopropyl dithiocarbonate is a main product as indicated by chromatography, chain species derived from diisopropyl dithiocarbonate constitutes only a minor fraction in the polymer products. Instead, the major part of living chains is initiated by 2-cyano-isopropyl radical, either from S-(cyano)isopropyl O-isopropyl xanthate or from continuous initiation of AIBN. This may be a consequence of poor leaving and reinitiating abilities of isopropyl in relative to cyanoisopropyl group.3)Block copolymers are successfully synthesized by sequential polymerization of VAc and VNDc. High efficiency of the cross initiation is achieved. The length of blocks can be tuned by changing the molar ratio of the second monomer, VNDc, to the first block PVAc. Taking advantage of alkaline resistance of VNDc units, the block copolymer is selectively hydrolyzed to prepare well-defined PVOH-b-PVNDc possessing semicrystalline PVOH segment. The block copolymer before hydrolysis aggregates into micelles in acetone, a selective solvent of PVAc, and undergoes microphase separation in bulk state.A series of instruments, such as DLS,XRD,TEM and DSC, are introduced to investigate the properties of block polymers. For the hydrolyzed block copolymer, the melting temperature is observed at 215℃for PVOH domain.
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