The synthesis of polyacrylonitrile PAN from acrylonitrile AN monomer is typically carried out through a process called free radical polymerization. Here's an overview of the mechanism and the key parameters for optimizing the process:Mechanism:1. Initiation: The process begins with the formation of free radicals, which can be generated using various initiators, such as azo compounds e.g., AIBN or peroxides e.g., benzoyl peroxide . The initiator decomposes upon heating, producing free radicals that can react with the acrylonitrile monomer.2. Propagation: The free radical reacts with the acrylonitrile monomer, forming a new radical at the end of the growing polymer chain. This new radical can then react with another acrylonitrile monomer, and the process continues, leading to the formation of a long polymer chain.3. Termination: The polymerization process eventually stops when two free radicals react with each other, resulting in the termination of the polymer chain growth. This can occur through various mechanisms, such as combination two radicals joining together or disproportionation one radical abstracting a hydrogen atom from another, forming a double bond .Key parameters for optimizing the process:1. Temperature: The reaction temperature plays a crucial role in controlling the rate of polymerization and the molecular weight of the resulting PAN. Higher temperatures lead to faster initiator decomposition and a higher rate of polymerization, but may also result in shorter polymer chains due to increased termination reactions. The optimal temperature depends on the specific initiator used and the desired properties of the PAN.2. Monomer concentration: The concentration of acrylonitrile monomer in the reaction mixture affects the rate of polymerization and the molecular weight of the PAN. Higher monomer concentrations generally lead to higher molecular weights, but may also increase the viscosity of the reaction mixture, making it more difficult to mix and control the reaction.3. Initiator concentration: The concentration of the initiator affects the number of free radicals generated and, consequently, the rate of polymerization. Higher initiator concentrations can lead to faster polymerization rates, but may also result in shorter polymer chains due to increased termination reactions.4. Solvent: In some cases, a solvent may be used to control the viscosity of the reaction mixture and improve the processability of the resulting PAN. The choice of solvent can also affect the rate of polymerization and the molecular weight of the PAN.5. Inhibitors: Polymerization inhibitors, such as hydroquinone or monomethyl ether hydroquinone, can be added to the reaction mixture to control the rate of polymerization and prevent premature gelation or crosslinking.6. Reaction time: The duration of the polymerization reaction affects the molecular weight of the resulting PAN, with longer reaction times generally leading to higher molecular weights. However, excessively long reaction times may result in unwanted side reactions or degradation of the polymer.By carefully controlling these key parameters, it is possible to optimize the synthesis of polyacrylonitrile from acrylonitrile monomer to achieve the desired properties and performance characteristics for specific applications.