Development and Characterization of Poly(phenylacetylene) Copolymers as Contemporary Carbon Fiber Precursors

Carbon fibers offer a high temperature resistance which allows them to also be used in the hydrogen storage industry. Polyacrylonitrile (PAN) is the most common precursor because of its superior physical properties to rayon-based fibers and higher strain and tensile strength than mesophase pitch. Due to the low carbon yield (50%) and high manufacturing cost, PAN may not be the best solution for carbon fibers. The low yield is caused by the removal of oxygen and nitrogen heteroatoms that are also accompanied with organic volatiles in the released gases. This paper studies poly(phenylacetylene) and its copolymer derivatives because of their conjugated nature. Poly(phenylacetylene) (PPA) and poly(1-ethynyl-4-(phenylethynyl) benzene) (PPP) have carbon yields of 10% and 80%, respectively, in a one-step thermal conversion process under N2 atmosphere. PPA and PPP have carbon yields of 40% and 34%, respectively, in a multi-step thermal conversion procedure in air. Their copolymers derivatives vary in between the extremes of the homopolymers. Even without the use of oxygen, we were able to achieve a carbon yield higher than PAN because of the polyaromatic moieties formed on the polymer chain. With increasing temperature hydrogen atoms were removed, which promoted cyclization and ring fusion. Due to their solubility in organic solvents (THF, Toluene), the electrospinning process was used to produce microfibers with a diameter under 10 microns for PPP and under 20 microns for PPA.