Syntheses And Characterizations Of Bis-(β-ketoamine) Cobalt (Ⅱ) Complexes And Studies On Its Catalysis For Mma And St Polymerizations By Cobalt-mediated Radical Polymerization

The late-transition-metal catalysts, a very important development in polymer chemistry recently, were simple and inexpensive compounds for the controlled "living" radical polymerization leading to well-defined homopolymers and copolymers. Nowadays,Cobalt-Mediated Radical Polymerization attracts much attentions.A new-styleβ-ketoamine ligand(figure A) and Bis-(β-ketoamine) Cobalt(Ⅱ) complexes(figure B) were synthesized and characterized by the single crystal X-ray diffraction in this paper. Based on the principle of CMRP, the polymerrzations of methyl methacrylate (MMA)and styrene(ST) have been carried out by using AIBN as the initiator, bis-(β-ketoamine) Cobalt(Ⅱ) complex as the catalyst and xylene as the solvent.figure A figure BThe controlled "living" radical polymerization of ST has been studied by using the bis-(β-ketoamine) Cobalt(Ⅱ) complex (figure B) as the catalyst. The influence of reaction time, reaction temperature and catalyst concentration to the poly merization of ST were studied in this paper. As shown in the GPC Spectrum characterization, the molar mass distribution was mostly around 1.5 and below, it showed the catalyst of bis-(β-ketoamine) Cobalt(Ⅱ) complex was efficient for the polymerization of ST. With the raise of reaction temperature, the conversion and the number average molecular weigh elevates obviously, the molar mass distribution also gradually broadens. It showed the reaction was turning from in-control to out-of-control direction. With the extension of the reaction time, the conversion increased continuously, and the number average molecular weight increased to some extent. At the 70℃bulk polymerization, the molar mass distribution was wide at beginning, then it turned to narrow later, but again it turned wide gradually at last. It showed the reaction turned from out-of-control to in-control, then to out-of control again . At the 80℃solvent polymerization, the molar mass distribution becomes narrow, showing the reaction turns from out-of-control towards in-control direction gradually. With other conditions unchanged, the enhancement of catalyzer was helpful to make the molar mass distribution turn narrow. It showed the control of reaction was enhanced, but the conversion was reduced to some extent.The controlled "living" radical homopolymerization of MMA has been studied by using the bis-(β-ketoamine) Cobalt(Ⅱ) complex (figure B) as the catalyst. As shown in the GPC Spectrum characterization, the molar mass distribution was mostly around 1.5, showing the catalyst of bis-(β-ketoamine) Cobalt(Ⅱ) complex was efficient for the polymerization of ST. Therefore the experiment has basically achieved the goal of making the activeness of CMRP polymerization controllable. With the elevation of reaction temperature, the conversion and the number average molecular weigh went up obviously, the molar mass distribution gradually broadened as well. It showed the reaction was turning from in-control to out-of-control direction. At the 80℃solvent polymerization, the conversion increases continuously with the extension of the reaction time, the number average molecular weight increased to some extent and the molar mass distribution turned narrow. It showed the reaction turns from out-of-control towards in-control direction gradually. With other conditions unchanged, the enhancement of catalyzer was helpful to make the molar mass distribution turn narrow .It showed the control of reaction was enhanced, but the conversion was reduced to some extent in the mean time.