The Properites And Applications Of Composite Initiator Used In Aqueous Deposited Polymerization For Polyacrylonitrile

Polyacrylonitrile (PAN) precursors used to produce carbon fibers were polymerized by acrylonitrile and a small quantity of comonomers. In this paper, itaconic acid (IA) and acryl amide (AM) were chosen as the second and third comonomer respectively, and the polymer was synthesized by the continuous aqueous deposited polymerization using composite redox initiator. This was not identical with many researches, which employed complex initiation systems containing alkali metal ions. The effects of different composite initiator, polymerization temperature, monomer ratio, initiator ratio, the third comonomer and chain transfer agent on the copolymerization were investigated. Effects of various polymerization factors on polymerization conversion, viscosity-average molecular weight, structures and thermal properties of the PAN polymers and rheological behavior were investigated through Ukraine viscometer (UVM), Fourier transform infrared spectroscopy (FTIR), wide angle X-ray diffraction (WAXRD), differential scanning calorimeter (DSC) and rotational viscometer, the relationships with structures and the parameters of polymerization technology were also discussed.The research showed that using ammonium per sulfate (APS) and ammonium sulfite (AS) to be composite initiator, the copolymerization temperature was reduced by a third than the single initiator, which the conversion rate remains the same. Copolymers with high conversion ratio and better properties could be manufactured by controlling reactions as follows:the total monomer concentration was 22%, the temperature was between 40 to 50℃, the reaction time was 2 hours, the initiator agent concentration was 0.8% while the molar ration of APS and AS was 1:1. IA was less than 3wt%, the monomer ratio was 98:1:1. and the N-dodecyl mercaptan (SH) was used to be the chain transfer agent.The analysis of FTIR, WAXRD and DSC showed that there were little affections on the structure of different temperature, initiator ratio and monomers ratio on conversion of polymerization. With the raise of IA in the feed, the crystallinity would increase and then reduce as the ratios of IA will more than 3wt%. The exothermic rate was decreased and the concentrated exothermic was alleviated with the introduction of IA. The crystallinity of binary polymerization would reduce with the temperature decreases, when it would increase for terpolymer. The crystallinity of terpolymer would better than the binary polymerization at a lower reaction temperature, when the exothermic rate of binary polymerization was lower than the terpolymer. There were little affections on the structures, crystallinity and thermal properties with the introduction of chain transfer agent SH, but the molecular weights would increase obviously.The investigation on the PAN spinning solution rheological behavior showed that the viscosity of copolymers used composite initiator would significantly lower than the copolymer used single initiator. While the solution concentration and molecular weight became higher, the viscosity increased clearly, but the molecular weight had greater influence on rheological behavior of copolymers. It is also showed that PAN spinning solution is a shear-thinning fluid; it belongs to pseudo plastic fluid of non- Newtonian fluid.