PVP is obtained from monomer vinyl pyrrolidone (NVP) through bulk polymerization, solution polymerization, and other methods. In the process of bulk polymerization preparation, due to the high viscosity of the reaction system, the polymer is not easily diffused, and the polymerization reaction heat is not easily removed, resulting in local overheating and other problems, the resulting product has low molecular weight, high content of residual monomers, and mostly appears yellow, which has little practical value. In industry, solution polymerization is generally used to synthesize PVP. There are two main routes for PVP production polymerization. The first is solution polymerization of NVP in organic solvents, followed by steam stripping. The second route involves aqueous polymerization of NVP monomers with water-soluble cations, anions, or non-ionic monomers. Heating NVP monomers directly to above 140 ℃, or adding initiators to NVP solutions for heating, or adding initiators to NVP solutions (solvents can be water, ethanol, benzene, etc.) for free radical polymerization, or directly irradiating NVP monomers or their solutions with light, can obtain PVP homopolymers. Different polymerization methods result in different polymer structures and properties, among which the polymer composition obtained from free radical solution polymerization The structure is relatively uniform. The performance is also relatively stable, making it the most commonly used method for NVP homopolymerization. By adjusting reaction conditions such as monomer concentration, polymerization temperature, and initiator dosage, PVP homopolymers with different molecular weights and water solubility can be obtained.
Process 1: Prepare NVP into a solution with a mass fraction of 50%, use a small amount of hydrogen peroxide as a catalyst, and initiate polymerization at 50 ℃ under the action of azodiisobutyronitrile, so that almost all NVP is converted into PVP. Add ammonia water to the polymer again to decompose the remaining azodiisobutyronitrile, resulting in a monomer polymerization conversion rate of nearly 100% and a solid content of 50%.
Process 2: Add 0.4g of dispersant P (NVP co VAc) and 80g of dispersant ethyl acetate to a 250 mL four necked flask. After stirring and dissolving in a constant temperature water bath at 70 ℃, add 20g of monomer NVP and 0.15g of initiator AIBN. React under nitrogen atmosphere for 6 hours, cool and filter, and place the insoluble substance in a vacuum drying oven for 24 hours to obtain white PVP solid powder.
In the polymerization of PVP, the vast majority use AIBN as the initiator, and there is no literature on the use of water-soluble azo initiators for the synthesis of PVP. However, some people are currently working on this aspect. Due to the fact that NVP monomers and PVP are both soluble in water, water-soluble azo initiators can be used to initiate polymerization and generate linear PVP polymers. Moreover, AIBN contains harmful cyanide groups to the human body, while water-soluble azo initiators mostly do not contain cyanide groups. PVP is mostly used for products in direct contact with the human body, so water-soluble azo initiators have more advantages than AIBN.