In Situ Reduction/Activation Generated Copper(0)Catalyzed SET-LRP

Significant progress has been made in the precise synthesis of polymers, most notably via living polymerization. Controlled/"living" radical polymerization (LRP) witnessed vast developments for the synthesis of well-defined polymer with predetermined molecular weights, tailored architectures and functionalities. Living polymerization has since been elaborated into several classes of powerful techniques, including living anionic polymerization, living cationic polymerization, atom transfer radical polymerization (ATRP), reversible chain transfer catalyzed polymerization (RAFT), and single electron-transfer living radical polymerization (SET-LRP). Among them, SET-LRP has shown distinct advantages over other LRPs since its emergence in2006by Percec et al., including mild reaction conditions (room temperature or below), a catalytic amount of catalyst, ultrafast polymerization and resultant of high molecular weight polymers with low polydispersity. The thesis was based on the study of the mechamism of SET-LRP with the utilization of high-valent copper compound in the presence of reducing agent including:(1) Single-electron transfer-living radical polymerization (SET-LRP) was catalyzed by in situ Cu(0) generated from copper(Ⅱ) sulfate pentahydrate (CuSO4·5H2O) and hydrazine hydrate (N2H4·H2O). The polymerization occurred smoothly with moderate controllability:the polymerization rates increased by the increases of N2H4·H2O, and the initiator concentration had an optimal value on the polymerization rate; the number-average molecular weights (Mn,GPC) increased with monomer conversions and polydispersities were low; This polymerization can be conducted in unfavorable solvents, such as toluene and tetrahydrofuran in a typical SET-LRP owing to the H2O contained in CuSO4·5H2O and N2H4·H2O. On account of the utilization of CuSO4·5H2O, a non-active Cu(Ⅱ) compounds in LRP area, this work confirmed from experimental level that it was Cu(0) which activated and mediated the SET-LRP. Despited of the not so good control over the polymerization, this work provided a first example with in situ Cu(0) catalyzing SET-LRP with CuSO·5H2O as copper source. Many efforts are under way in our lab by the selection of proper reducing agents with the balacence of adequate reduction ability and minimimal side reactions.(2) Copper oxides (CuO and Cu2O) was used as the catalyst for the single electron transfer-reversible addition-fragmentation chain transfer (SET-RAFT) polymerization of methyl methacrylate (MMA) in the presence of ascorbic acid at25℃.2-Cyanoprop-2-yl-l-dithionaphthalate (CPDN) was used as the RAFT agent. The polymerization occurred smoothly after an induction period arising from the slow activation of CuO (or Cu2O) and the "initialization" process in RAFT polymerization. The polymerizations conveyed features of "living"/controlled radical polymerizations: linear evolution of number-average molecular weight with monomer conversion, narrow molecular weight distribution and high retention of chain end fidelity. From the polymerization profile, it was deduced that the polymerization proceeded via a conjunct mechanism of SET-LRP and RAFT polymerization, wherein CPDN acting as the initiator for SET-LRP and chain transfer agent for RAFT polymerization.(3) Single-electron transfer-living radical polymerization (SET-LRP) was catalyzed by in situ Cu(0) generated from copper(Ⅱ) sulfate pentahydrate (CuSO·5H2O) and glucose (C6H12O6) at25℃. The polymerization occurred smoothly with moderate controllability:the polymerization rates increased by the increases of glucose, and polydispersities were low; The polymer have chain-end fidelities. The poly(methyl acrylate) and poly(styrene) occurred smoothly after the induction time and the conversion reached95%in short tiome. This work provided a new way to product high conversion of poly(styrene) at room temperature.