Synthesis Of Narrow And Bimodal MWD Polymers Via Living Radical Polymerization

In this thesis, a new method, atom transfer radical polymerization using activatorsgenerated by electron transfer （AGET ATRP） mediated by Fe^Ⅲcatalyst, was developedusing Fe⁰powder as a reducing agent. The Fe^Ⅲ/Fe⁰catalyst system presents higher catalyticactivity and controllability as compared with the reported AGET ATRP of MMA catalyzedby iron catalyst. Subsequently, we synthesized a pair of RAFT agents: mono-functionalRAFT agent–{2-bromo-2-methyl-propionic acid4-[2-（carbazole-9-carbodithioate）-2-methyl-propionyloxy] phenyl ester}（BMCCDP）, RAFT-1, and difunctional RAFT agent–{1,4-[2-（carbazole-9-carbodithioate）-2-methyl-propionic acid] phenyl ester}（BCCDP）,RAFT-2. Bimodal molecule weight distribution （MWD） polymers were successfullyprepared with this pair of RAFT agents in the same polymerization system. The details wereshown as follows:（1） Fe⁰powder was firstly used as a reducing agent in iron-mediated AGET ATRPpolymerization. The polymerization system used ethyl2-bromoisobutyrate （EBiB） as theATRP initiator, FeCl₃·6H₂O as the catalyst, triphenylphosphine as the ligand, Fe⁰powderas the reducing agent, and anisole or toluene as the solvent. The kinetics of MMA in thepresence or absence of a limited amount of air were studied in detail. The effects oftemperature and the concentration of Fe^Ⅲon the polymerization were also investigated inthis work. The results showed that the molecular weight (M_n,GPC) values of the polymersincreased linearly with conversion while the polydispersity index （Mw/Mn） values of theobtained PMMAs remained narrow （less than1.37）. Moreover, the M_n,GPC values wereconsistent with the corresponding theoretical values （Mn,th）, which indicated a highcatalytic activity, almostly100%(I_eff=M_n,th/M_n,GPC). The polymerization can be carriedout in a wide range of temperature （25-90oC） and a wide range of molar ratio of Fe^Ⅲ/Fe⁰（10/1-1/1）. （2） We used a pair of RAFT agents (mono-functional RAFT agent–{2-bromo-2-methyl-propionic acid4-[2-（carbazole-9-carbodithioate）-2-methyl-propionyloxy] phenyl ester}（BMCCDP）, RAFT-1, and difunctional RAFT agent–{1,4-[2-（carbazole-9-carbodithioate）-2-methyl-propionic acid] phenyl ester}（BCCDP）, RAFT-2, with similar structure in the samepolymerization system. RAFT polymerization method has been developed to establish a novelstrategy for synthesizing bimodal MWD polymers by one-step/one pot method. The systemshowed excellent controllability and “living” characteristics toward both higher and lowermolecular weight fractions in molecular weight （MW） and MWD. It is vital that bimodalmolecular weight distribution polymers and block copolymers with both well-controlled MWand MWD be prepared easily due to the “living” features of RAFT polymerization. Thestrategy utilized the mixture of higher/lower molecular weight polymers in molecular level andmade sense for effectively balance the processing performance （Lower MW component） andmechanical performance （Higher MW component） of materials.