The synthesis of polyvinyl alcohol PVA from vinyl acetate monomer VAM involves two main steps: the polymerization of VAM to polyvinyl acetate PVAc and the hydrolysis of PVAc to PVA.1. Polymerization of VAM to PVAc:The polymerization of VAM is typically carried out via a free radical mechanism, using initiators like azo compounds or peroxides. The optimum reaction conditions for this step are:- Temperature: 60-80C. Higher temperatures lead to faster reaction rates but can also cause side reactions and degradation of the polymer.- Initiator concentration: 0.1-1 wt% based on VAM. Higher initiator concentrations increase the reaction rate but can also result in lower molecular weight polymers.- Solvent: The reaction can be carried out in bulk or in a solvent like water or an organic solvent. The choice of solvent can affect the reaction rate and the molecular weight of the resulting PVAc.2. Hydrolysis of PVAc to PVA:The hydrolysis of PVAc to PVA is typically carried out using an alkaline catalyst like sodium hydroxide NaOH or potassium hydroxide KOH . The optimum reaction conditions for this step are:- Temperature: 60-90C. Higher temperatures lead to faster hydrolysis rates but can also cause side reactions and degradation of the polymer.- Catalyst concentration: 1-5 wt% based on PVAc. Higher catalyst concentrations increase the hydrolysis rate but can also result in over-hydrolysis and lower molecular weight polymers.- Reaction time: The hydrolysis reaction can take several hours to complete, depending on the desired degree of hydrolysis. Longer reaction times result in higher degrees of hydrolysis and more hydrophilic PVA.The yield and properties of the final PVA product are affected by the reaction conditions in the following ways:- Molecular weight: The molecular weight of PVA depends on the polymerization and hydrolysis conditions. Higher initiator concentrations and faster reaction rates can result in lower molecular weight polymers. Lower molecular weight PVA has lower viscosity, tensile strength, and film-forming properties.- Degree of hydrolysis: The degree of hydrolysis affects the hydrophilicity and solubility of PVA. Higher degrees of hydrolysis result in more hydrophilic and water-soluble PVA. This can affect the swelling behavior, mechanical properties, and biodegradability of PVA.- Crystallinity: The crystallinity of PVA depends on the degree of hydrolysis and the reaction conditions. Higher degrees of hydrolysis and slower cooling rates during the synthesis can result in more crystalline PVA. Crystalline PVA has higher tensile strength, thermal stability, and resistance to solvents.By optimizing the reaction conditions, it is possible to tailor the properties of PVA for specific applications, such as films, fibers, hydrogels, and adhesives.