Study On Synthesis Of High Molecular Weight Acrylonitrile-Acrylamide Copolymer For Carbon Fibers

Polyacrylonitrile(PAN)-based carbon fibers are widely used due to its excellent properties such as high strength and modulus.Up to the date,the highest strength of carbon fiber is 7.02GPa,only 4%of theoretical value.Thus,there still exists great space probability to increase the quality of carbon fibers.The monomer polymerization is the basis of carbon fibers preparation and the microstructure of PAN is closely related to the final quality of carbon fibers.But,there is still not an effective method to evaluate the influence of PAN structure on the precursor and carbon fibers.Usually,acrylonitrile homopolymer is not used for preparation of carbon fibers due to strong inter-,intra-molecule forces and sharp exothermic behavior in stabilization.The polymerization of PAN is a key step in the production of PAN based carbon fibers,which determines the structure and spinning performance of polymer directly.According to literatures,various monomers and polymerization methods have been used in the copolymerization of PAN based carbon fibers,however,it's not the final conclusion that the hightest molecular weight of the PAN couble be obtained in solution copolymerization.This article is intended to use dimethyl sulfoxide(DMSO) as the solvent,azo-bis-isobutyronitrile(AIBN) as the initiator for acrylonitrile and acrylamide free radical solution copolymerization system.The effect of total concentration of monomer,monomer ratio,AIBN concentration, reaction temperature,stirring rate and temperature on the molecular weight of PAN and conversion ratio was studied. (1) By optimization of polymerization conditions,the conversion of copolymer 90%and viscosity-average molecular weight of about 2.1×10~5 could be obtained.(2) The influence of AM on the copolymerization was studied and the structure of products was characterized.Due to the difference of the monomers in reactivity, the polymer composition is not the same with feeding ratio.With the increasement of AM content in feeding,the polymerization conversion was firstly increased and then decreased,while the molecular weight(Mη)changed reversely.(3) The copolymerization of AN with AM initiated by AIBN in DMSO at 58℃was studied.On this basis,a stepped increasing program of reaction temperature was adopted for getting prepare homogenous PAN.The results showed that the molecular weight of the PAN ould reach to 2.1×10~5 increased by nearly 1×10~5,compared with that of PAN derived at constant temperature under the following program:initiated at 58℃for 0.5h,then rose to 60℃,0.5h and 62℃31h.