Synthesis Of Poly(Acrylonitrile) Via RAFT Polymerization And Investigation On Its Properties

Because of its unique and well-known properties including hardness and rigidity, chemical resistance, compatibility with certain polar substances and low gas permeability, polyacrylonitrile (PAN) is usually used as an important precursor for polymer materials especially carbon fiber. As we all know, high-quality PAN with ultra-high molecular weight and appropriate molecular weight distribution is necessary to prepare high-quality carbon fiber. In this thesis, we first synthesized PANs with controlled molecular weights and narrow molecular weight distributions via reversible addition-fragmentation chain transfer RAFT polymerization, and subsequently investigated their applications in the area of electrospinning nanofiber in detail.The work in this thesis can be summarized as follows:(1) Difunctional RAFT agent,1,4-[2-(carbazole-9-carbodithioate)-2-methyl-propionic acid] phenyl ester (BCCDP), was synthesized and used as chain-transfer agent (CTA) to carry out the polymerization of acrylonitrile (AN) in dimethyl sulphoxide (DMSO). Finally we obtained pure PANs with ultra-high molecular weights, narrow molecular weight distributions, and even improved isotacticity, which were used as precursors to prepare carbon nanofibers with high performance via electrospinning. The polymerization kinetics was studied in detail, and the effect of molecular weights and molecular weight distributions of PANs on the morphologies of the electrospun fibers was investigated.(2) An effective RAFT agent,4-Cyano-4-cpheny (phenylcarbonothicylthio) pertancic acid (CPDB-COOH), was used as CTA to carry out the copolymerization of AN and MAn. The polymerization rates and "living"/controlled features were thoroughly studied and confirmed. The reactivity ratios of AN and MAn were calculated and compared with conventional radical method. This work would first exploit the copolymerization of AN and MAn via RAFT polymerization. The thermal properties and spinnability of the prepared copolymers were investigated via differential scanning calorimetry (DSC), thermo gravimetric analyzer (TGA) and electrospinning subsequently.(3) Fe3O4magnetic nanoparticles (MNPs) were first coated with3-aminopropyltriethoxysilane. After a series of surface-modification, a great amount of amino groups was first immobilized onto the surface of the Fe3O4MNPs to obtain Fe3O4@SiO2-NH2MNPs, and then a RAFT agent CPDB-COOH was covalently grafted onto the surface of MNPs to give RAFT agent-immobilized MNPs Fe3O4@SiO2-CPDB. The Fe3O4@SiO2-CPDB was then used for the surface-initiated RAFT polymerization of acrylonitrile to give stable electrospinning solution Fe3O4@SiO2@PAN/DMF. Then we obtained magnetic nanofibers (MNFs) successfully via coaxial electrospinning. It was found that the room-temperature saturation magnetizations of the magnetic nanofibers could be adjustable with the length of the polymer chains grafted onto the surface of MNPs and the pushing speeds of syringes A and B when electrospinning. In addition, the magnetic nanofibers could be assembled into well-aligned arrays using a special magnetic collector easily.