| Reversible addition-fragmentation chain transfer(RAFT) process has received much attention due to its many merits such as mild reaction condition and wide monomer applicability.We have discussed some unique phenomena in RAFT process and put forward our own viewpoint based on our experiments in this paper.Moreover, model reaction has been constructed to understand the RAFT process deeply.Finally a series of amphilic tri-block polymers have been synthesized and their self-assembly behavior in water has been studied too.The main contents are as follows:Thermal decomposition of various transfer agents.The study of the mechanism and kinetics of the RAFT polymerization is still an ongoing issue.This is due to the debating interpretations on the retardation/inhibition kinetics of the RAFT polymerization.There are mainly two explanations on this phenomenon:slow fragmentation and cross-termination.In our previous work,we found that CDB underwent remarkable thermal decomposition at 90～120℃,which yields dithiobenzoic acid and related derivatives,it can affect the polymerization rate, molecular weight,and molecular weight distribution of the resulting polymers.Also polymeric dithioesters,PMMA-SCSPh underwent similar side reactions at the same temperature,which reveals that the thermal decomposition of thiocarbonylthio group is quite often encountered for different kinds of dithioesters.However,a systematic study of the decomposition behaviors of RAFT agent is still lacking.This paper studies the thermal decomposition of a number of dithioesters,trithiocarbonates and xanthates and gives their decomposition rates at various temperature and Arrhenius plots for Kd values.This paper explores the effect of the substituents R and Z of dithiobenzoate RAFT agents on the thermal stability.When Z is -Ph,the thermal stability depends strongly on R decreasing in the order where R is:-CH(CH3)Ph＞-CH(Ph)CH2OC(=O)Ph＞-PSC(CH3)2Ph＞-C(CH3)2Ph＞-C(CH3)2CN＞-PMMAC(CH3)2Ph.However,when R is -CH(CH3)Ph,Z group has a little influence on the thermal stability,which decrease in the series where Z is:- CH2Ph＞-Ph(p-OCH3)＞- Ph＞- Ph(p-NO2).Interestingly,this order is consistent with that of chain transfer coefficients of dithiobenzoate.The thermal stabilities of dithioesters, trithiocarbonates and xanthates were also compared,indicating that trithiocarbonates and xanthates are more stabile than dithioesters,while the chain transfer abilities of the latter are usually better than that of the former.So how to balance the chain transfer ability and the thermal stability of RAFT agents is a big challenge.Different RAFT polymerization behaviors between MMA and St.The other issue we found in RAFT mechanism is the fact that a different pair of monomer/RAFT agent leads to specific polymerization behavior in spite of the general regulation by the reaction in Scheme 1.Take the most widely used monomers,styrene and methyl methacrylate(MMA) as an example.This is the first report on direct observation of the RAFT polymerization process by chromatography,starting from small molecular materials.The results clearly show that styrene and MMA polymerize in different ways in the presence of CDB.The former exhibits the "initialization" kinetics in which the chain propagation occurred in a selective way,while the latter exhibits hybrid behavior of conventional and controlled chain transfer,in which CDB is consumed slowly.The remaining CDB is responsible for the discrepancy between measured and theoretical molecular weights.The chain transfer constant of CDB,Ctr, is estimated to be in a range of 40～280 by numerical fitting.The value of Ctr, although agreeing with those obtained by the CSIRO group and Fukuda group,shows unexpectedly a dependence on the ratio of CDB to MMA.The dependence is presumably ascribed to the interference of thermal decomposition of dithioester on the kinetic measurement.Finally,chromatography monitoring of the RAFT polymerization in the presence of both CDB and polymeric dithioesters allows direct comparison on their chain transfer abilities,which decrease in the order of CDB≈PMMA-SCSPh＞PS-SCSPh.The chromatography approach can serve as a useful tool in the kinetic and mechanistic study of the RAFT polymerization.Feasibility analysis of model reactions.To get more insight into the mechanism and kinetics of the RAFT process,it would be helpful to build a small molecular model reaction mimicking the RAFT process but free of a chain-propagation event. We hereby propose a model cross reaction between dithioester and alkoxyamine as a probe of the RAFT process,in which the alkoxyamine plays the role of the radical source.The generating rate of the transient alkyl radical and the nitroxyl radical can be described by the law of persistent radical effect.Thus,the advantage of the model cross reaction is that it affords a radical concentration determined by the known equation of the persistent radical effect.This feature,together with other measurable parameters,including the concentrations of the starting alkoxyamine and dithioester, as well as the counterparts in the product,will enable the evaluations of the rates of addition and fragmentation reactions in the RAFT process.As model compounds, alkoxyamine and dithioester should not undertake other side reactions under experimental condition,so finding a steady alkoxyamine and dithioester is very necessary for later model reaction study,which is the aim of this part of paper.Synthesis and self-assembly study of amphilic triblock polymer containing F. Self-assembly of amphiphilic copolymers has received tremendous interests due to novel assembled morphologies and outstanding ability to control and manipulate these morphologies by external stimuli.We prepared a serious of functional polymers with RAFT method.First we synthesize a tri-block polymer.One end is hydrophobic PMMA and the other end is hydrophilic PtAA,the middle is the functional epoxy group,which can be fluorinate by CF3COOH.The self-assembly behaviors of obtained amphilic tri-block polymer in water has been studied too.
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