Study On Radical Polymerization In The Presence Of Cyclic Trithiocarbonate

In recent years, considerable efforts have been expanded to develop free radical processes that display the characteristics of living polymerization. Several controlled/living radical polymerization methods have been developed. In general, they are nitroxide-mediated polymerization (NMP), metal catalyzed atom transfer radical polymerization (ATRP), and reversible addition-fragmentation chain transfer radical polymerization (RAFT). Polymers with predetermined molecular weight and narrow molecular weight distribution can be prepared by living polymerization methods. RAFT polymerization has several advantages compared with NMP or ATRP processes, since it can be easily adapted to a wide range of monomers under mild conditions. The most effective reagents for RAFT polymerization are dithioesters and trithiocarbonates. Up to now, no cyclic trithiocarbonate has been reported as RAFT agent.In this paper, the cyclic trithiocarbonate,o-xylenyl-l,3-dithiolane-2-thione(XDTT), was synthesized by two different methods, dialkylation of trithiocarbonate anion with alkyl halides in a two-phase system using an onium salt as a phase-transfer agent and reaction between carbon disulfide and alkyl halides using a commercially available hydroxide form of an anion-exchange resin. The structure of the new compound has been proved by NMR, EA, MS and FT-IR measurements.Homopolymerization of styrene and n-butyl acrylate were carried out in the presence of cyclic trithiocarbonate. The molecular weights of polymers were much higher than the calculated ones. After treatment with diamine, the molecular weight of polymer declined rapidly and was close to calculated one. It is proposed that polymer prepared in the presence of the cyclic trithiocarbonate have multiblock structure with more than one trithiocarbonate function per chain, compared with polymers prepared in the presence of linear trithiocarbonate, which have only one trithiocarbonate function per chain.Bulk polymerizations of styrene in the presence of different concentration ofXDTT were carried out. With the increase of the concentration of XDTT, the number of trithiocarbonate unit in one polymer chain increased, while the conversion of monomer and molecular weights of resulting polymers before and after treatment with diamine decreased. Under certain conditions, polymers with controlled molecular weight and narrow molecular weight distribution were obtained. Kinetic study of styrene polymerization in the presence of XDTT was carried out. It is found that the mechanism of polymerization in the presence of cyclic trithiocarbonate is different from reported mechanism. At the early stage of polymerization, XDTT functions as comonomer in normal radical polymerization. After it is incorporated into the polymer chain, the trithiocarbonate keeps its merits as RAFT agent. Therefore ln[Mo/M] increases linearly with the reaction time and the molecular weight of polymer before and after treatment with diamine grow linearly with conversion of monomer.The homopolymers containing trithiocarbonate units were used as macro-RAFT agent for copolymerization. The molecular weights of copolymers before and after treatment with diamine increased compared with their parent polymers. It is proposed that copolymers with structure of (BAB)n have been prepared by the copolymerization.In conclusions, two new types of block polymers have been synthesized in the presence of novel cyclic trithiocarbonate. It is the first time that block copolymer with the structure of (BAB)n has been prepared by two-step polymerization.