A photocrosslinkable melt processible acrylonitrile terpolymer as carbon fiber precursor

A novel photocrosslinkable and melt processible terpolymer precursor for carbon fiber has been successfully synthesized and characterized. The terpolymer was synthesized by an efficient emulsion polymerization route and has a typical composition of acrylonitrile/methyl acrylate/acryloyl benzophenone in the mole ratio, 85/14/1. It has been characterized by FTIR, NMR, intrinsic viscosity and GPC molecular weights. The composition of the monomer repeat units in the terpolymer was determined by NMR, and was almost identical to the molar feed ratios of the monomers used for polymerization. The Tg of the terpolymers, were somewhat a function of molecular weight, but were in the range 77-91 °C. The fibers were spun from the terpolymer melts unlike the conventional solution spinning method. The terpolymers when stabilized with boric acid afforded a stable melt for about 30 min at 200-220 °C, which was empirically found to be sufficiently long to spin fibers. The terpolymer with the highest molecular weight (Mn, ∼48,000) was not melt processible, apparently because the melt viscosity was very high and the terpolymer degraded fast. However, terpolymers, which had an intrinsic viscosity <0.6 dL/g (NMP, 25 °C) were invariably melt processible. The initial carbon fibers produced from these terpolymer fibers upon complete carbonization exhibited good mechanical properties for proposed automotive applications; the tensile strength of the best fibers generated thus far was in the range 450-700 MPa with a strain to failure of ∼0.4%. The diameter of the carbon fibers was of the order of 7 μm.