Hollow carbon fibers with tailored porosity and rim-thickness

The synthesis of compact and hollow carbon fibers with variable porosity and rim thickness is described. Block copolymers were prepared by anionic copolymerization of 1,3-cyclohexadiene with ε-caprolactone. By variation of the initiator, a block copolymer (P1) that contains both 1,2-cyclohex-3-enylene and 1,4-cyclohex-2-enylene repeat units (≈1:1) and a block copolymer (P2) consisting of >98% of 1,4-cyclohex-2-enylene units was prepared. Both block copolymers were melt-spun into monofilament fibers. After spinning, stabilization of the fibers was successfully accomplished by oxidation and electron beam treatment. Fibers based on >98% 1,4-cyclohex-2-enylene repeat units displayed a low but substantially higher degree of crystallinity than the P1-derived ones containing both 1,2- and 1,4-connected repeat units. Since P1-derived fibers were predominantly amorphous and had a diameter of about 20–25 μm, their thermostabilization resulted in fully compact carbon fibers. Vice versa, depending on the extent of electron beam treatment and fiber diameter, the more crystalline P2-derived fibers with a larger diameter of about 50 μm offered access to hollow and porous carbon fibers with variable rim thickness. The precursor fibers and the resulting carbon fibers were characterized by NMR- and Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, thermal analysis, nitrogen-sorption and X-ray diffraction.