Research Progress And Classification Of Polyvinylpyrrolidone

Research progress and classification of polyvinylpyrrolidone

Polyvinylpyrrolidone (PVP) is a very important water-soluble polymer. It is polymerized by N-vinylpyrrolidonc (NVP) under certain conditions. Since 1938, when German chemist Reppe first used acetylene as a raw material to synthesize NVP and its polymer PVP, PVP has developed into three categories: homopolymer, copolymer and cross-linked product. PVP products have also developed into three specifications: industrial grade, pharmaceutical grade and food grade.

PVP has been increasingly widely used due to its unique properties. It not only has excellent solubility, chemical stability, film-forming property, physiological inertness, bonding ability and protective adhesive effect, but also can be combined with many inorganic and organic compounds. Therefore, PVP has been widely used in medicine, cosmetics, food, brewing, coatings, adhesives, printing and dyeing auxiliaries, separation membranes, photosensitive materials and other fields since its launch. With the development of science and technology, the application field of PVP is becoming more and more extensive. It has also been applied in high-tech fields such as photocurable resins, optical fibers, laser video discs, and drag reduction materials. It can be said that PVP has penetrated into all areas of the national economy and people's lives.

China started late in researching the production technology of PVP. In 1987, Henan Boai Chemical Plant and Zhejiang Chemical Plant Research Institute jointly built a pilot plant with an annual output of 50 tons of NVP. In 1996, Guangdong University of Technology cooperated with Luoding Pesticide Factory in Guangdong Province to build a production plant with an annual output of 500 tons of PVP. However, my country's PVP products still mainly rely on imports, and there is a big gap in research and development and application fields compared with foreign countries. In recent years, with the development of my country's economy and the progress of science and technology, research on the production and application of PVP has also been carried out in many aspects. Its demand is also increasing. Therefore, research on the development and application of PVP has very important theoretical significance and practical value.

Properties and Synthesis of Vinylpyrrolidone

Physical Properties of NVP

NVP is the abbreviation of vinylpyrrolidone, which is a monomer for synthesizing PVP. NVP is a colorless or light yellow transparent liquid with a slight odor at room temperature. It is easily soluble in water, with a relative density of 1.04 and a boiling point of 148°C. In addition to being soluble in water, NVP is also soluble in many organic solvents, such as methanol, ethanol, propanol, isopropanol, chloroform, glycerol, tetrahydrofuran, vinyl acetate, toluene, etc., and has excellent solution properties.

Chemical Properties of NVP

The molecule of NVP is a five-membered ring containing a N atom, which belongs to the lactam compound. There is a vinyl group attached to the atom. This group provides special properties for the polymerization and application of NVP. The molecular formula of NVP is C6H0NO.

NVP has two important properties, namely, easy polymerization and hydrolysis.

NVP can undergo polymerization reaction to obtain polyvinyl pyrrolidone in the presence of appropriate initiators or under light conditions. Even in the absence of initiators, NVP will undergo self-polymerization due to reasons such as long storage time. Therefore, commercially available NVP generally contains inhibitors, and we need to remove the inhibitors during polymerization. There are two treatment methods: one is to add activated carbon and use its adsorption effect to remove the inhibitors; the other is to use the method of vacuum distillation to obtain pure NVP at a pressure of about 133.32Pa and a temperature of about 50°C.

Another important chemical property of NVP is that it is easy to undergo hydrolysis reaction in the presence of acid or salt conditions to produce pyrrolidone and acetaldehyde. Through research, we can obtain the hydrolysis mechanism of NVP under acidic conditions.

The vinyl charge in the NVP molecule is unbalanced, that is, the charge density on the two carbon atoms connected by the double bond is different. When under acidic conditions, isomerization occurs in the NVP molecule, forming a series of transition states, and finally generating pyrrolidone and acetaldehyde. The generated pyrrolidone reacts with the NVP molecule and decomposes into pyrrolidone and acetaldehyde with the participation of water. Therefore, we should pay attention to two points in the synthesis and application of NVP: 1. Water should be completely removed during the synthesis of NVP, and 2. During storage and transportation, 0.1% of alkali (such as sodium oxide, ammonia, etc.) should be appropriately added.

Synthesis method of NVP

The main synthesis methods of NVP include acetylene method, pyrrolidone method, butyrolactone method, maleic anhydride method (maleic anhydride method for short), etc. Among them, acetylene method is the main method.

The acetylene method was first invented by German chemist W. Reppe in the 1930s. It uses acetylene and formaldehyde as starting materials, and undergoes acetylene aldehyde addition, catalytic hydrogenation, catalytic decomposition, amination, alkyne addition and other reactions to obtain monomer NVP.

The acetylene method has strict requirements on operating conditions due to the main raw material acetylene used. The process needs to be carried out under high pressure and high temperature conditions. It has high requirements on equipment, long process flow, and equipment investment. It is only suitable for large-scale production and not suitable for the construction of medium and small manufacturers.

The pyrrolidone method directly uses pyrrolidone as the main raw material, and obtains NVP through intramolecular addition reaction and then heating to eliminate one molecule. Generally, pyrrolidone and vinyl carboxylate, vinyl ether, ethylene oxide, etc. are reacted under the condition of a catalyst, and then heated to remove molecular substances such as carboxylic acid, alcohol, and water to obtain N-vinyl pyrrolidone; while the γ-butyrolactone method is a method in which -butyrolactone reacts with ethanolamine to generate hydroxyethyl pyrrolidone (NHP), and then NHP is directly dehydrated in the presence of a dehydration catalyst to generate the monomer NVP.

Compared with the acetylene method, the γ-butyrolactone method and the pyrrolidone method have the advantages of short process flow, small equipment investment, short plant construction cycle, and mild operating conditions, but they also have the disadvantages of high raw material prices and high production costs. Therefore, whether it is the acetylene method, the γ-butyrolactone method or the pyrrolidone method, there are shortcomings, and further improved methods still need to be studied.