Study On The Catalyst System And The Synthesis Of Bimodel MWD Polymers Via ATRP

"Living"/controlled radical polymerization (LRP), other than conventional radical polymerization, is an important tool to allow to design polymers with predetermined architecture and properties. This thesis focused on various catalyst systems for atom transfer radical polymerization (ATRP) to investigate how to enhance the polymerization rate significantly and how to synthesize bimodal molecular weight distribution (MWD) polymers. The work can be summarized as follows:(1) System I:Iron-mediated AGET ATRP (activators generated by electron transfer for atom transfer radical polymerization) of methyl methacrylate in the presence of catalytic amounts of base. The polymerization was carried out using FeCl3.6H2O as the catalyst, triphenylphosphine (PPh3) as the ligand, ethyl2-bromoisobutyrate (EBiB) as the initiator and vitamin C as the reducing agent. It was found that the addition of NaHCO3and Na2CO3into the polymerization system enhanced the polymerization rate significantly. The polymerization kept all the characters of "living"/controlled radical polymerization: the number-average molecular weights (Mn,GPC) increasing linearly with monomer conversion, the molecular weight distributions (Mw/Mn) being narrow. The obtained PMMA chain was end-capped by the EBiB moieties and could be reactivated for chain-extension reaction.(2) System II:Study on the catalyst system for the synthesis of bimodel MWD polymers via ATRP. A two-step polymerization strategy was designed to obtain bimodel MWD polymers using styrene as the model monomer, CuBr/CuBr2as the catalyst,2,2’-bipyridine (bpy) as the ligand and a pair of mono/difunctional such as (1-bromoethyl)benzene (PEBr) and a,a-dibromotoluene as the ATRP initiators. In the two-step ATRP polymerization, one kind of polymer was synthesized first through initiated by mono-functional initiator PEBr. In the second reaction step, a difunctional initiator α,α-dibromotoluene was added into the polymerization system to continue the polymerization to synthesize bimodel MWD polymers. The system showed successful controllability over both higher-and lower-molecular-weight fractions, which confirmed the feasibility of this strategy for synthesis bimodal MWD polymers.