Study Of Zero-valent Iron (0) Co-Mediated LRP At Ambient Temperature

During the past decades, because of the powerful capability of designing andfabricating well-defined macromolecules,“living”/controlled radical polymerization （LRP）has attracted more and more attentions. Among those well-developed LRP techniques,metal-catalyzed living radical polymerizations have been widely employed for polymersynthesis. Since1995, atom transfer radical polymerization （ATRP）, a metal-catalyzedliving controlled radical polymerization, has achieved huge advancements and becamewidely used “living”/controlled radical polymerization （LRP） methods.2006, Percec et al.proposed a new metal-catalyzed LRP technique, named single-electron transfer mediatedLRP （SET-LRP）, using the zero-valent copper （Cu（0））（powder or wire） as catalyst.Compared with copper, iron is a preferential metal catalyst for its particularly attractiveproperties, such as biocompatibility, easy separation and low cost， which has beenreceived more and more attentions in LRP area. It was demonstrated that the Fe（0） canreact with alkyl halide to generate alkyl radical, which can initiate the polymerization,however, the simply combination of Fe（0）/alkyl halide gave a uncontrolled polymerization.The article was to realize the Fe（0） mediated living”/controlled radical polymerization.The work can be summarized as follows:（1） Zero-valent Bimetallic Iron/Copper CatalyzedSET-LRP;（2） Fe（0） Powder/CuBr₂Mediated “Living”/Controlled Radical Polymerizationof Methyl Methacrylate and Styrene at Ambient Temperature.（3） Fe（0） powder/CuSO₄.5H₂O Mediated “Living”/Controlled Radical Polymerization of MethylMethacrylate （MMA）, Methyl Acrylate （MA） and Styrene （St） at25oC.The detailed work of this thesis was summarized as the following:（1） Bimetallic zero-valent metal （Fe（0） powder and Cu（0） powder） was used tomediate the single-electron transfer-living radical polymerization （SET-LRP） of methylmethacrylate at25oC in dimethyl sulfoxide. Different feed ratios of [Fe（0）]0/[Cu（0）]0（0/1.5,0.5/1,0.75/0.75,1/0.5and1.3/0.2） were explored. With the increase of Fe（0） feed, the polymerization rate was mildly depressed with a prolonged induction period. While,the control over the molecular weights was improved upon the increase of Fe（0）. A bestcontrol （initiation efficiency=91%） was achieved at [Fe（0）]0/[Cu（0）]0=1/0.5. A furtherincrease of Fe（0） to the feed ratio of [Fe（0）]0:[Cu（0）]0=1.3:0.2led to a uncontrolledpolymerization. Explorations of available solvents and ligands for this polymerizationconfirmed the SET-LRP mechanism. It was suggested that Fe（0） might act as a dual role inthis process: one was the activation agent for Cu（0）, which favored a better control over themolecular weights; The other was an alternative catalyst for the activation of R-X or Pn-Xto generate radicals, which assured a comparable polymerization rate as that of Cu（0）. Thiswork provided an alternative and economical catalyst for SET-LRP, and would eventuallyreinforce the SET-LRP technique.（2） The combination of zero-valent iron （Fe（0） powder） and copper（II） bromide wasused to mediate the polymerization of methyl methacrylate （MMA） and styrene （St） at25oC. The polymerizations in different solvents were explored. The results demonstrated thatthe solvent played an important role on the polymerization rate and molecular-weightcontrol. The polymerization in toluene displayed a poorly controlled process, and thepolymerization rate was remarkably low. With DMSO as solvent, the polymerization wasmuch faster with well-controlled manner, considering the number-average molecularweights evolution and relatively narrow molecular weight polydispersities （M_w/M_n<1.20）.In respect of St as monomer, high conversions （80%） could be got with narrow molecularweight distributions in DMSO at25oC. The polymerization was via a ATRP mechanism.The Fe（0） may act as the activator for the generation of active radical as well as thereducing agent for CuBr₂, and then mediate the polymerization was via a ATRPmechanism.（3） The combination of zero-valent iron （Fe（0） powder） and CuSO₄·5H₂O was used tomediate the polymerization of methyl methacrylate （MMA）, methyl acrylate （MA） andstyrene （St） at25oC. It was found that the ratio of [Fe（0）]0/[CuSO₄·5H₂O]0played animportant role on the polymerization rate and molecular-weight control. Thepolymerization might be via a SET-LRP mechanism. The Fe（0） was suggested to act as theactivator for the generation of active radical as well as the reduce the CuSO₄·5H₂O to Cu（0）. The in situ generated Cu（0） may mediate the polymerization via a SET-LRPmechanism.