EFFECT OF CO-POLYMERIZATION AND HEAT-TREATMENT ON THE STRUCTURE AND X-RAY-DIFFRACTION OF POLYACRYLONITRILE

Wide-angle x-ray diffraction studies are reported on polyacrylonitrile (PAN) (homopolymer powder and fiber samples) and its random copolymers with methyl methacrylate (MMA) and methacrylonitrile (MAN). A new method of determination of degree of order which involves resolution of the individual maxima in the diffraction pattern is described and compared with the methods used in the literature. Comparison of the results on untreated fibers with those on untreated homopolymer powder samples, and the effect of heat treatment, suggest the molecular rod conformation of the PAN molecules in the amorphous phase. Heat treatment or the orientation induces a parallel alignment of the molecular rods in the amorphous phase, similar to the crystalline structure of PAN. Copolymerization with both the comonomers MMA and MAN produces qualitatively similar effect on the structure of PAN, which depends on the comonomer content. Below a critical comonomer content c*(c* equals 12 mol% for MMA and 25 mol% for MAN comonomer), the crystalline lattice remains that characteristic of PAN, whereas above the critical comonomer content some modification in the crystalline lattice is apparent.