Polyvinyl chloride PVC is synthesized through the polymerization of vinyl chloride monomer VCM . The key chemical reaction involved in this process is the free radical polymerization of VCM. The reaction can be summarized in three main steps: initiation, propagation, and termination.1. Initiation: In this step, a free radical initiator, such as an organic peroxide or azo compound, is used to generate free radicals by breaking a covalent bond. The initiator reacts with the vinyl chloride monomer, forming a reactive free radical.Initiator 2 R free radicals R + CH2=CHCl VCM R-CH2-CHCl initiated VCM radical 2. Propagation: The initiated VCM radical reacts with another vinyl chloride monomer, forming a new free radical. This process continues, leading to the formation of a growing polymer chain.R-CH2-CHCl + CH2=CHCl R-CH2-CHCl-CH2-CHCl propagation 3. Termination: The polymerization reaction is terminated when two free radicals react with each other, forming a covalent bond and ending the growth of the polymer chain.R-CH2-CHCl + CH2-CHCl-R R-CH2-CHCl-CH2-CHCl-R termination To optimize the reaction conditions and increase the yield and purity of PVC, several factors should be considered:1. Temperature: The reaction temperature should be carefully controlled, as it affects the rate of polymerization and the molecular weight of the PVC. Higher temperatures increase the rate of polymerization but may lead to lower molecular weight PVC. A temperature range of 40-60C is typically used for PVC synthesis.2. Pressure: The polymerization of VCM is an exothermic reaction, and controlling the pressure can help manage the heat generated during the process. The reaction is usually carried out at moderately high pressures 10-20 atm to maintain a suitable reaction rate and control the heat.3. Initiator concentration: The concentration of the initiator affects the rate of polymerization and the molecular weight of the PVC. Higher initiator concentrations lead to a faster reaction rate but may result in lower molecular weight PVC. The optimal initiator concentration should be determined based on the desired properties of the final product.4. Reaction time: The reaction time should be optimized to achieve the desired degree of polymerization and molecular weight of the PVC. Longer reaction times may lead to higher molecular weight PVC, but the reaction should be stopped before the PVC becomes too viscous or crosslinked.5. Purity of the monomer: The purity of the vinyl chloride monomer is crucial for the synthesis of high-quality PVC. Impurities in the monomer can lead to defects in the final product or cause undesirable side reactions. The VCM should be purified before use in the polymerization reaction.6. Inhibitors: In some cases, inhibitors may be added to the reaction mixture to control the rate of polymerization and prevent undesired side reactions. However, the use of inhibitors should be carefully balanced, as they can also reduce the yield of the final product.By optimizing these factors, the yield and purity of the synthesized PVC can be increased, resulting in a high-quality final product with the desired properties.