Co-monomers were introduced at a controlled rate into the reaction vessel in order to control the distribution of composition among the polymeric chains. When acrylate co-monomer, such as methyl acrylate or 2-ethyl hexyl acrylate was slowly fed into the reactor, the reaction time required for copolymerization to reach a fixed conversion was not affected, and the cycling temperature (or the temperature at the onset of the exotherm) during oxidation for polyacrylonitrile (PAN) precursor was slightly shifted to a higher temperature. On the other hand, as itaconic acid (IA) co-monomer was slowly fed into the reactor, the reaction rate of copolymerization was increased, and the cycling temperature could be depressed to a lower temperature due to the IA co-monomer being able to initiate the cycling of the CN groups.The structures (such as crystallinity, crystal size, orientation) and mechanical properties for PAN precursor and its resulting carbon fibre were influenced by the distribution of composition among the chains.