EFFECT OF METHYL ACRYLATE COMPOSITION ON THE MICROSTRUCTURE CHANGES OF HIGH-MOLECULAR-WEIGHT POLYACRYLONITRILE FOR HEAT-TREATMENT

The acrylate comonomer in polyacrylonitrile (PAN) precursor markedly i nfluences the microstructure of PAN fiber and its resulting carbon fib er. In this study, the change occurring during the heat treatment of P AN copolymers (acrylonitrile-co-methyl acrylate) in the presence of ai r up to 260 degrees C has been examined using both physical and chemic al techniques. Considering the effect of the methyl acrylate content o f PAN copolymers on the cyclization mechanism and fine structural chan ges in polymer chains under various heat treatment conditions, the com position of acrylonitrile and methyl acrylate = 98 : 2 to 97 : 3 mol % was suitable for the precursor preparation because the cyclization me chanism and fine structural changes in the boundary of this compositio n of copolymers were significantly different. With increasing MA conte nt, the exothermic onset and peak in the thermogram was found to shift , toward higher temperatures, and the aromaticity index decreased. Thi s evidence indicates that MA was believed not to activate at all but t o interfere with the cyclization. Additionally, by means of C-13 nucle ar magnetic resonance (C-13-NMR) analysis, the tacticities of copolyme rs were nearly same, regardless of the copolymer composition, and the cyclization occurred nonstereospecifically during the initial heat tre atment at 240 degrees C for 1 h. (C) 1998 John Wiley & Sons, Inc.