Controlling the porous structures of block copolymer based carbon fibers

Block copolymer (BCP)-derived porous carbon fibers (PCFs) are emerging versatile materials that show great potential for applications ranging from energy storage to separation and to purification. To prepare PCFs from polyacrylonitrile (PAN)-based BCP, oxidative stabilization of PAN is a critical step to ensure successful carbon fiber synthesis. To investigate the effect of oxidation on the PAN-based BCP fibers, as well as the final PCFs, poly(methyl methacrylate)-block-polyacrylonitrile (PMMA-b-PAN) with varying compositions (PMMA-rich and PAN-rich) were synthesized, oxidized, and pyrolyzed. The oxidized BCP fibers exhibited improved thermal stability at ~500-800 °C compared to the as-spun BCP fibers. PCFs derived from PMMA-rich BCPs displayed mesopores within 8 h of oxidation time. The porous structures became better-defined and the pore widths and surface areas increased with oxidation time. Differently, PCFs derived from PAN-rich BCPs developed mesopores after 15 h of oxidation time and the surface area reached a plateau. The pore widths of PCFs were nearly identical when the oxidation time of BCP fibers was over 8 h. The findings highlight the importance of tuning the oxidation time to tailor the properties of BCP-derived PCFs.