Construction Of Highly Efficient LRP Systems And Macromolecular Precision Synthesis

“Living”/controlled radical polymerization(LRP) combines the advantages of living polymerization and the traditional free radical polymerization, which provides a simple and efficient method to synthesize polymers with pre-designed structures and molecular weights. To date, atom transfer radical polymerization(ATRP), and reversible addition-fragmentation chain transfer(RAFT) polymerization, are the two important research topics in the field of LRP. Recent development of ATRP is mainly focused on:(1) exploring highly efficient ATRP catalytic systems to reduce the loading amount of transition metal catalyst,(2) developing highly efficient iron-mediated ATRP catalytic system,(3) highly efficient ATRP catalyst separation and recycling system,(4) developing metal free ATRP system. On the other hand, the advance of RAFT polymerization is mainly focused on:(1) developing universal RAFT agent,(2) removal of the chain-end of polymer obtained by RAFT method,(3) using RAFT polymerization method to prepare various new functional materials, and so on. The above research topics are aiming to develop efficient living “radical”/controlled polymerization systems and apply them to macromolecular precision synthesis, so as to facilitate their industrial application. Based on these purposes, this thesis is mainly focused on the construction of highly efficient transition metal catlayzed ATRP systems. However, considering inevitability of the residue of transition metal in the product via transition metal catalyzed ATRP, RAFT polymerization, a metal-free LRP, was used to constructe a strategy to synthesize controlled bimodal molecular weight distribution polymers, in order to promote the process of LRP in industrial application. The main contents and conclusions are summarized as follows:(1) In 2005, Matyjaszewski and coworkers developed the activators generated by electron transfer(AGET) ATRP system to overcome the drawbacks of normal ATRP and reverse ATRP systems, for example, to avoid using lower-oxidate transition metal catalyst, lower the loading amount of catalyst, and to save the deoxygening procedure in operation. Matyjaszewski’s group mainly studied the highly active copper-catalyzed AGET ATRP system. However, iron has attracted extensive attention owing to its biocompatibility and low cost. Based on the previous studies on iron-catalyzed AGET ATRP, in chapter III, by using metal wire(Cu(0) wire or Fe(0) wire) as the reducing agent, an iron-mediated AGET ATRP system was constructed. The polymerization rate of methyl methacrylate(MMA) can be greatly accelerated by using ethyl α-bromoisobutyrate(EBi B) as the initiator, iron(III) chloride hexahydra/tetetrabutyl ammonium bromide(Fe Cl3·6H2O/TBABr) as the catalyst, and the amount of iron catalyst can be reduced to 56 ppm. Well-defined polymers with controlled molecular weight(MW) and narrow molecular weight distribution(MWD) were obtained successfully. Chain-end analysis and chain extension reaction proved that the resultant polymers contain “living” chain-end.(2) Air-stable copper(II) acetate, as a commercially available, low cost catalyst, was widely used in organic synthetic chemistry, although there have been no reports on LRP. Iniferter, the first example of LRP, can only generate relatively poor controlled polymers with broad molecular weight distribution and some dead chains, which cannot meet the requirements of precision synthesis of polymer materials. In chapter IV, a facile and high efficient LRP system, involing iniferter agent MANDC(1-cyano-1-methylethyl diethyldithiocarbamate) and copper(II) acetate, was successfully developed using MMA as the model monomer. Meanwhile, the plausible Cu(II)/Cu(III) catalytic cycle was suggested from experimental and density functional theory(DFT) calculation results. Without any other additives, this simple polymerization system can be conducted in the presence of limted amount of air, moreover, the obtained PMMA has high chain-end functionality. At the same time, in view of the poor controllability of water-soluable monomer via transition metal catalyzed ATRP in many cases, we expand the catalytic system to the polymerization of water-soluable monomers, involing poly(ethylene glycol) monomethyl ether methacrylate(PEGMA), 2-hydroxyethyl methacrylate(HEMA), 2-(dimethylamino)ethyl methacrylate(DMAEMA) and N,N-dimethyl-acrylamid(DMA). Well-defined hydrophilic polymers can be conveniently prepared in water even with ppm level of copper(II) catalyst. Therefore, a facile and highly efficient catalytic system was constructed, which is a universal LRP system for water-soluable monomers.(3) The above-metioned copper(II) acetate/dithiocarbamate system is a highly efficient polymerization system for both water-soluble and oil-soluable monomers. Thus, based on the previous investigations, in chaper V, we still employ copper(II) acetate as the catalyst, and hydrophilic 4-cyano-4-((diethylcarbamothioyl)thio) pentanoic acid(MANDC-COOH) as the mediator, developed a soap-free method to prepare well-defined amphiphilic latexs by sequential addition of monomers. In addition, the obtained polymers have very high chain-end functionality by copper(II) acetate/dithiocarbamate system. Thus, we also prepared water-soluable deca-block homopolymer poly(potassiumsulfopropylmethacrylate)(PSPMA) and hepta-block alternating copolymer poly(potassiumsulfopropylmethacrylate)-atl-poly(Sodium methacrylate)(PSPMA-alt-PNa MA) by sequential addition of monomers.(4) Considering the processing performance of polymers maybe influenced by the residual transition metal, and the metal-free character of RAFT polymerization, at the same time, in view of bimodal polymers can optimize and balance the processing performance and mechanical performance of materials, which are useful in some occasions, however, until the theme-chosen of this dissertation, there were very few reports about the synthesis of bimodal polymers with both controlled MW and MWD. In chapter VI, based on the characteristics of the RAFT polymerization, we use a pair of mono- and difunctional trithiocarbonates dibenzyl trithiocarbonate and carbonotrithioic acid, S,S’-[1,4-phenylenebis(methylene)] S,S’-dibenzyl ester to synthesize bimodal(co)polymers in situ with both controlled MW and MWD. The obtained bimodal polymer can be used as a macro-trithiocarbonate to conduct chain-extension reaction, and generate bimodal PSt-b-PAN. Moreover, we can adjust the proportion of high and low molecular weight polymers by changing the ratio of mono- and difunctional trithiocarbonates. In addition, we also studied the polymerization mechanism of this system.