The optimum temperature and reaction time for synthesizing high molecular weight polyacrylonitrile PAN from acrylonitrile monomer using a free radical polymerization method can vary depending on the specific conditions and catalysts used. However, generally speaking, the following conditions are considered optimal:Temperature: The polymerization of acrylonitrile is typically carried out at temperatures between 40C and 70C. Lower temperatures can result in slower reaction rates, while higher temperatures can lead to premature termination of the polymer chains and lower molecular weights.Reaction time: The reaction time required to achieve high molecular weight PAN can range from several hours to a few days, depending on the reaction conditions and the desired degree of polymerization. Typically, longer reaction times will result in higher molecular weights, but this must be balanced against the risk of side reactions and degradation at extended reaction times.It is important to note that the specific temperature and reaction time required for optimal synthesis of high molecular weight PAN can be influenced by factors such as the choice of initiator, the concentration of monomer and initiator, and the presence of any additives or modifiers in the reaction mixture. Therefore, it is recommended to consult the relevant literature and perform experiments to determine the best conditions for a specific system.