PVP is obtained from the monomer vinyl pyrrolidone (NVP) through bulk polymerization, solution polymerization and other methods. During the preparation process of bulk polymerization, the viscosity of the reaction system is high, the polymer is not easy to diffuse, and the heat of the polymerization reaction is not easily removed, leading to local overheating. Therefore, the obtained product has low molecular weight, high residual monomer content, and more Yellow, not much practical value. The industry generally uses solution polymerization to synthesize PVP. There are two main routes for PVP production and polymerization. The first is solution polymerization of NVP in an organic solvent, followed by steam stripping. The second route is aqueous solution polymerization of NVP monomer and water-soluble cationic, anionic or nonionic monomer. Heat the NVP monomer directly above 140℃, or add an initiator to the NVP solution for heating, or add an initiator to the NVP solution (the solvent can be water, ethanol, benzene, etc.) to polymerize by free radical solution, or use it directly PVP homopolymers can be obtained by light irradiating NVP monomers or their solutions. Different polymerization methods result in different polymer structures and properties. Among them, the polymer composition and structure obtained by free radical solution polymerization are relatively uniform. The performance is also relatively stable. It is the most commonly used method for NVP homopolymerization. By adjusting the reaction conditions such as monomer concentration, polymerization temperature, and initiator dosage, PVP homopolymers with different molecular weights and different water solubility can be obtained.
Process 1: Configure 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°C under the action of azobisisobutyronitrile, so that almost all NVP is converted into PVP. Then add ammonia water to the polymer to decompose the remaining azobisisobutyronitrile, the monomer polymerization conversion rate is nearly 100%, and the solid content is 50%.
Process 2: Add 0.4g dispersant P (NVP-co-VAc) and 80g dispersing medium ethyl acetate into a 250 mL four-necked flask. After stirring and dissolving in a 70℃ constant temperature water bath, add 20g monomer NVP and 0.15g initiator AIBN , React for 6h under a nitrogen atmosphere, cool and filter, place the insoluble matter in a vacuum drying box and vacuum dry for 24h to obtain a white PVP solid powder.
Most of the PVP polymerization uses AIBN as the initiator. There is no literature on the use of water-soluble azo initiators to initiate the synthesis of PVP, but some people are doing work in this area. Since both NVP monomer and PVP are soluble in water, water-soluble azo initiators can be used to initiate polymerization to form linear PVP polymers. Moreover, AIBN contains cyano groups that are harmful to humans, while water-soluble azo Most of the initiators do not contain cyano groups, and PVP is mostly used for products that are in direct contact with the human body, so water-soluble azo initiators have more advantages than AIBN.