Novel Initiation System Of Iron-Catalyzed Atom Transfer Radical Polymerization

Atom transfer radical polymerization(ATRP)is an important controlled polymerization technology and it has been widely used in the precise synthesis of functional polymers with predictable structures and molecular weights because of its widely applicable monomers,simple and easy control of the polymerization process.However,the metal complexes used in conventional ATRP are almost with high toxicity and cost,and the separation and removal of the catalyst is difficult.Hence,the development of novel ATRP initiation system with high activity,low toxicity and low cost is of great theoretical significance and practical value for the promotion of the industrialization of ATRP technology.In this thesis,we exploited the polar solvents/FeBr₃ and deep eutectic solvents/FeBr₂catalytic systems by the optimization of the reaction components in FeBr₂/FeBr₃mediated ATRP.In addition,we studied the activation effect between inorganic salts and ATRP common initiator EBr PA,and based on this,inorganic salts/FeBr₂ and inorganic salts/FeBr₃catalytic systems were further constructed.The main results are as follows:(1)The effect of silver's morphology on the polymerization rate in FeBr₃ catalyzed AGET ATRP was studied with MMA as the monomer,elemental silver as the reducing agent,and different polar solvents as the ligand.The utilization of DMF and PEG-400 as the ligand provided a well-controlled polymerization process,and the polymerization rate increased with the increasing surface area of silver.The polar solvents and silver used in this system are expected to replace the expensive,toxic ligands and the unremovable reducing agents in the traditional AGET ATRP.(2)A variety of deep eutectic solvents including amide,thiocyanate/amide and quaternary ammonium salt/polyalcohol were utilized as the ligands of FeBr₂ catalyzed ATRP.The coordination effect between FeBr₂and the deep eutectic solvents decreased the redox potential of FeBr₂,thus mediated the polymerization process,and the obtained polymers are well-controlled.The utilization of deep eutectic solvents provided the theoretical basis for the construction of“green”ATRP system.(3)The activation effect of a series of inorganic salts on the C-Br bond energy of the typical ATRP initiator,ethyl?-bromophenylacetate(EBr PA)was studied,and the density functional theory(DFT)was used to calculate the Gibbs free energy during the fracture process.The electron transfer process between inorganic salt and EBr PA significantly reduced the C-Br bond energy,thus make the polymerization take place.This system laid a foundation for the construction of inorganic salt/FeBr₂ polymerization system.(4)Based on the above-mentioned activation effect,the well-controlled FeBr₂-catalyzed ATRP system was established in the absence of additional ligands.Several elements including the content and solubility of inorganic salt were also considered for the reactivity and controllability of ATRP.The coordination effect between FeBr₂and inorganic salts generated the catalytic species[Fe^IIBr₃(MMA)]^-with high reactivity,thus make the polymerization proceed in a well-controlled way.The inorganic salt/FeBr₂ catalytic system fulfilled the construction of ligand-free ATRP process with high activity,good controllability,low cost and low toxicity.(5)In order to further improve the polymerization controllability and avoid the utilization of the water oxygen sensitive FeBr₂,FeBr₃-catalyzed ATRP process was operated based on the above inorganic salt induced FeBr₂ catalyzed ATRP.The polymerization proceeded in a new ATRP mechanism:Inorganic salts induced the cleavage of C-Br bond,and the generated free radicals can reduce FeBr₃ to FeBr₂in situ.The continuous production and accumulation of FeBr₂ enabled the occurrance of the well-controlled polymerization.This system avoided the use of water-oxygen sensitive catalyst,organic ligand and additional reducing agent in the traditional ATRP,thus reduced the content,cost and toxicity of the catalyst and provided the expectation to accelerate the industrialization of ATRP.