Study Of Zero-valent Iron Catalyzed CRP

Controlled radical polymerization (CRP) has been one of the hottest topics in theresearch field of polymer science in the past two decades, because of its powerfulcapability of precise control of molecular weights and architectures of the obtainedpolymers, wide range of available monomers and mild polymerization conditions. Up tonow, scientists have developed various CRP techniques, and they never stop seeking fornew CRP techniques being environment friendly, energy efficient and facilely operated.Fe(0) had been introduced to RAFT polymerization system successfully in our previouswork, the polymerization system has obvious advantages compared with common RAFTpolymerization: room temperature, no need of thermal initiator, excellent polymerizationcontrollability and high end group fidelity. Compared with the transition metal catalyzedCRP (such as typical copper-mediated atom transfer radical polymerization), Fe(0) is alsofavorable due to its low toxicity, biocompatibility and readily abundance. Herein, in thisthesis we focuse on exploring the methodology of Fe(0)-catalyzed CRP, including thefollowing two part of work:(1) ATRP of St catalyzed by elemental Fe(0) and Br2Zero-valent iron (Fe(0))(powder or wire) and elemental bromine (Br2) were used asthe catalysts for atom transfer radical polymerization (ATRP) of styrene (St) without anyadditional initiator at110oC. The polymerizations happened with controlled evidence atappropriate molar ratio of Fe(0) to Br2: a remarkable increase of molecular weights with Stconversions, the narrow molecular weight distributions and living polymer chainsend-capped by Br. More Br2or less Fe(0) led to a slow polymerization rate but animproved control over molecular weights. After examining the polymer chain ends bymatrix-assisted laser desorption/ionization time-of-light mass spectrometry, it wasconcluded that the polymerization was initiated by thermal self-initiation, and regulated bythe in situ generated FeIIIBr3. The results suggested that the Fe(0)/Br2catalyzingpolymerization was a classical ATRP process with easier operation and more economicalcomponents.(2) Fe(0)/Cu(0)-mediated CRP of MMA in the presence of typical RAFT agent. Our group has ever reported that Fe(0)/CPDN mediated polymerization undergoes aRAFT process at room temperature. While, Cu(0)/CPDN mediated polymerization wasdemonstrated to be performed under a manner of typical metal catalyzed CRP in a similarcondition. Therefore, in this work, the feasibility of the bimetallic Fe(0)/Cu(0)-mediatedCRP in the presence of CPDN was investigated. The polymerizations proceed smoothlywith characters of CRP. The polymerization profiles were studied in detailed. Based onexperimental results, a hybrid mechansim, i.e., RAFT dominating the initial stage of thepolymerization and ATRP regulating the latter stage, was proposed.