Study On The Catalysis Systems Of Cu(O)-mediated Control Radical Polymerization

Transition metal-catalyzed controlled radical polymerization has been widely used,for its unique advantages on the precise control of molecular weights, archtectures, andchain-end functional groups. Zero-valent metal utilizated as catalyst can not only beeasily operated, but also be recycled for saving costs. The polymerization at ambienttemperature greatly optimized the polymerization conditions by reducing the sidereaction and energy consumption. In order to obtain the highly active catalytic systems ofthe metal mediated CRP, the choice of ligand is particularly important. Therefore, thedevelopment and design of efficient and green catalytic systems for synthesis of excellentperformance functional polymers with novel structure has been one of the importantassignments in polymer chemistry. Cu（O） mediated controlled radical polymerizationprovides a more cost-effective way for the synthesis of colorless and less metal residualpolymers.In this thesis, we developed a series of green, highly efficient catalytic systems, inwhich we studied the polymerization behavior and the synthesis of polymers with precisestructure in combination with the weak intermolecular interaction.The mechanisms werealso discussed deeply. The detailed researches were summarized as the following:（1） Ligand-free Cu（O）-mediated polymerization of methyl methacrylate （MMA） wasrealized by the selection of ethyl-2-bromo-2-phenylacetate （EBPA） as initiator at ambienttemperature. The conversion of the monomer can reach up to90%within5hrs withdimethyl sulfoxide （DMSO） as solvent, while keeping manners of the “living”/controlledradical polymerization. Extensive investigation of this system revealed that for awell-controlled Cu（O）-mediated polymerization of MMA, the initiator should be selected with the structure as alkyl2-bromo-2-phenylacetate, and the solvent should be DMSO orN,N-dimethylformamide （DMF）. Scanning for other monomers indicated that underequal conditions, the polymerizations of other alkyl （meth）acrylates were uncontrollable.Based on these results, plausible reasons were discussed. The ligand-free Cu（O）-mediatedpolymerization showed its superiority with economical components and needlessremoval of Cu species from the resultant products.（2） Ligand-free Cu（O）-mediated controlled radical polymerization of methylmethacrylate （MMA） was realized using ethyl-2-bromo-2-phenylacetate （EBPA）, ethyl2-bromo-2-p-tolylacetate （EBTA） and ethyl-2-bromopropionate （EBPP） as initiator atambient temperature, while keeping manners of the “living”/controlled radicalpolymerization. Cu（O）-mediated CRP of MMA and nBA was further explored in theabsence of ligand. Moreover, deep understanding of the mechanism was discussed by thecalculation of equilibrium constants (¹0^-10) to maintain a low radical concentration andminimize termination reactions, which sequentially explained the “living”/controlledcharacteristic in ligand-free Cu（O）-mediated CRP processes.（3） An iodine-based initiator,2-iodo-2-methylpropionitrile （CPI） was utilized for theCu（O）-mediated CRP of methyl methacrylate （MMA） in the absence of ligand, at ambienttemperature. The CPI-initiated ligand-free polymerizations manifested reasonable controlover molecular weights with relatively narrow distributions （Mw/Mn≤1.35）. The livingnature of the polymers was further confirmed by successful chain extension reaction and1^H NMR analysis with high chain-end fidelity （⁹6%）. Screening of the availablesolvents suggested that the controllability of this polymerization was highly depended onthe kind of solvents, wherein dimethyl sulfoxide （DMSO） was a better solvent for acontrolled molecular weight. The proposed ligand-free Cu（O）-mediated CRP initiated byCPI was intriguing since it would dramatically decreased the concentration of Cu（O） ionsboth in polymerization system and resultant polymers, and provided a more economicaland eco-friendly Cu（O）-mediated CRP technique.（4） The first example of hydrogen bonding facilitating control over polymerization of4-vinyl pyridine （4VP） was described. In the absence of ligand, well-controlled P4VPwas successfully obtained via zero-valent copper mediated radical polymerization with1,1,1,3,3,3-hexafluoro-2-propanol （HFIP）, a fuloroalcohol, as a solvent, which canstrongly interact with4VP via hydrogen bonding. With molar ratio of1/1of4VP andHFIP, the polymerizations were well regulated as illustrated by the good agreementsbetween theoretical and experimental molecular weights, narrow molecular weightdistributions （<1.30） and high chain end fidelities （⁹4%）. The hydrogen bondinginteraction between4VP and HFIP was verified by UV-Vis and1^H NMR, which alsoshed lights on the controllability, relied on molar ratio of4VP/HFIP.（5） The optimal conditions for the hydrogen bonding interaction between4-vinylpyridine （4VP） and1,1,1,3,3,3-hexafluoro-2-propanol （HFIP） were screened viaUV-Vis spectroscopy. The results demonstrated that eqivmolar4VP and HFIP, andtemperature at25oC favored a better hydrogen bonding interaction. Guided by theseprimary results, the room-temperature Cu（O）-mediated controlled radical polymerizationwas selected for the controlled polymerization of4VP in the presence of equiv. HFIP.With tris[2-（dimethylamino）ethyl] amine （Me6-TREN） as ligand, the polymerizationsproceeded much faster, producing polymers with more predictable number-averagemolecular weights （Mn,GPC） and narrower molecular weight distributions （Mw/Mn<1.25）in comparison with those without hydrogen bonding interaction. Moreover, the hydrogenbonding had profound impacts on the stereoregulation during polymerization, whichenabled P4VP with a highly syndiotactic （60.2%） and gave rise to a higher glasstransition temperature （Tg） of P4VP.（6） The Cu（O）-mediated control radical copolymerization （CRP） of4-vinylpyridine（4VP） and styrene （St） was performed using ethyl-2-chloro-2-phenylacetate （ECPA） asinitiator with Cu（O）/tris[2-（dimethylamino）ethyl] amine （Me6-TREN） as a catalystsystem in1,1,1,3,3,3-hexafluoro-2-propanol （HFIP）. The measured number-averagemolecular weight （Mn,GPC） increased with monomer conversion and the polymerizationsystem produced polymers with relatively low polydispersities （<1.25）. The copolymers of4VP and St obtained in HFIP have better controllability than that with2-propanol as solvent. The successfully obtained copolymers from4VP and St wereconfirmed by GPC traces,1^H NMR and thermal performance analysis. By this method, afacile copolymerization for4VP and St has been successfully developed through thecombination of Cu（O）-mediated CRP and HFIP as solvent.（7） The Cu（O）-mediated control radical polymerization （CRP） of2-vinylpyridine（2VP） and its copolymerization with styrene （St） was realized usingethyl-2-chloro-2-phenylacetate （ECPA） as initiator with1,1,1,3,3,3-hexafluoro-2-propanol （HFIP） as solvent in the absence of ligand. Themeasured number-average molecular weight （Mn,GPC） increased with monomerconversion and the polymerization system produced polymers with relatively controlledpolydispersities （<1.50）, as well as P2VP homopolymers with high functionality. Themaximum monomer conversion of2VP homopolymerization can reach up to95%, whilethe overall monomer conversion for the copolymerization can be achieved more than75%. The reactivity ratios of2VP （r₂VP） and St （r_St） calculated by1^H NMR were0.444and0.333, repectivly, indicating a random copolymerization. This method furtherverified the solvent effect of HFIP, and provided a new approach for the synthesis of2VPhomopolymers and its copolymers with high monomer conversion.