The optimum temperature and concentration of initiator for the synthesis of high molecular weight polyacrylonitrile PAN from acrylonitrile monomer depend on the specific initiator used and the desired properties of the polymer. However, I can provide some general guidelines for these parameters and their effects on the yield and properties of PAN.Temperature:The polymerization of acrylonitrile is an exothermic process, and the reaction rate increases with temperature. However, at higher temperatures, the rate of chain termination reactions also increases, which can lead to lower molecular weight polymers. Therefore, a balance must be struck between reaction rate and molecular weight. Typically, the polymerization of acrylonitrile is carried out at temperatures between 40C and 70C. Lower temperatures e.g., 40-50C favor the formation of high molecular weight PAN, while higher temperatures e.g., 60-70C can lead to faster reaction rates but may result in lower molecular weight polymers.Initiator concentration:The concentration of the initiator affects the number of active sites available for initiating the polymerization reaction. A higher initiator concentration will lead to a higher number of active sites, which can increase the reaction rate. However, this can also result in a higher number of shorter polymer chains, leading to lower molecular weight PAN. Conversely, a lower initiator concentration will result in fewer active sites and a slower reaction rate, but may favor the formation of higher molecular weight PAN. The optimum initiator concentration depends on the specific initiator used and the desired properties of the polymer. For example, for a common initiator like ammonium persulfate, a concentration of 0.1-1.0 wt% based on the weight of acrylonitrile monomer is typically used.Effect of temperature and initiator concentration on yield and properties:1. Yield: Higher temperatures and initiator concentrations generally lead to higher yields, as they increase the reaction rate. However, this must be balanced against the potential for lower molecular weight polymers and other undesirable side reactions that can occur at higher temperatures.2. Molecular weight: As mentioned earlier, lower temperatures and initiator concentrations favor the formation of high molecular weight PAN. High molecular weight PAN generally has better mechanical properties, such as tensile strength and modulus, compared to lower molecular weight PAN.3. Polymer properties: The temperature and initiator concentration can also affect other properties of PAN, such as its glass transition temperature Tg , thermal stability, and crystallinity. For example, higher molecular weight PAN typically has a higher Tg and better thermal stability. Additionally, the polymerization conditions can influence the tacticity i.e., the arrangement of side groups along the polymer chain of PAN, which can affect its crystallinity and other properties.In summary, the optimum temperature and initiator concentration for the synthesis of high molecular weight PAN depend on the specific initiator used and the desired properties of the polymer. Lower temperatures and initiator concentrations generally favor the formation of high molecular weight PAN, but may result in slower reaction rates. The choice of these parameters should be based on a balance between the desired molecular weight, yield, and other properties of the polymer.