PVP is obtained from monomer vinylpyrrolidone (NVP) by bulk polymerization, solution polymerization, and other methods. In the process of bulk polymerization, due to the high viscosity of the reaction system, the polymer is not easily diffused, and the heat of polymerization is not easily removed, resulting in local overheating. Therefore, the obtained product has a low molecular weight, high residual monomer content, and is mostly Yellow, not much practical value. In industry, solution polymerization is generally used to synthesize PVP. There are two main routes for the production and polymerization of PVP. The first is the solution polymerization of N-2-pyrrolidone (NVP) in an organic solvent, followed by steam stripping. The second route is the aqueous polymerization of NVP monomers with water-soluble cationic, anionic or nonionic monomers.
Heat the NVP monomer directly to above 140 °C, 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 directly use PVP homopolymers can be obtained by irradiating NVP monomers or their solutions with light. Different polymerization methods result in different polymer structures and properties. Among them, the polymers obtained by free radical solution polymerization are more uniform in composition and structure. The performance is also relatively stable, and 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: NVP is prepared into a solution with a mass fraction of 50%, a small amount of hydrogen peroxide is used as a catalyst, and under the action of an initiator, polymerization is initiated at 50 °C, so that almost all NVP is converted into PVP. Add ammonia water to the polymer to decompose the remaining initiator, the monomer polymerization conversion rate is nearly 100%, and the solid content is 50%.
Process 2: Add 0.4 g of dispersant P(NVP-co-VAc) and 80 g of dispersion medium ethyl acetate into a 250 mL four-necked flask, and after stirring and dissolving at a constant temperature water bath at 70 °C, add 20 g of monomer NVP and 0.15 g of the initiator. agent AIBN, reacted for 6 h under nitrogen atmosphere, cooled and filtered, and the insoluble matter was vacuum dried in a vacuum drying box for 24 h to obtain a white PVP solid powder.
Most of the polymerization of PVP 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 this work. Since both NVP monomer and PVP are soluble in water, it is completely possible to use water-soluble azo initiators to initiate polymerization to form linear PVP polymers. Moreover, AIBN contains groups that are harmful to the human body. Toxic product base and most water-soluble azo initiators do not contain the highly toxic product base of banned cyanide and highly toxic products, and PVP is mostly used for products that are in direct contact with the human body, so water-soluble azo initiators are more efficient than AIBN. have more advantages.