Through further research, the hydrolysis mechanism of NVP in the presence of acrylic acid or KSO is obtained. The charge imbalance of the vinyl group in the NVP molecule, that is, the charge density on the two carbon atoms connected by the double bond is different. This charge imbalance provides the hydrolysis of NVP In the presence of acidic or alkali metal ions, isomerization occurs in the NVP molecule, forming a series of transition states, and finally pyrrolidone and acetaldehyde are formed. This is the first step of NVP hydrolysis. The second step of NVP hydrolysis The pyrrolidone produced in one step undergoes an addition reaction with NVP molecules, and then is further decomposed into pyrrolidone and acetaldehyde with the participation of water. From the perspective of the hydrolysis mechanism of NVP, whether NVP can be hydrolyzed mainly depends on whether a series of transition states can occur in one step. It can be formed, or whether the intramolecular isomerization reaction of NVP can occur is the key to whether the hydrolysis of NVP occurs.
The presence of H* or alkali metal cations in the solution just enables the intramolecular isomerization of NVP to be realized, so the hydrolysis of NVP can proceed. The hydrolysis rate of NVP mainly depends on the two steps. When K'exists, it will be generated with one step. The reaction of pyrrolidone first generates pyrrolidone potassium salt, and then it undergoes addition reaction with NVP. Obviously, pyrrolidone potassium salt is more likely to undergo addition reaction with NVP, resulting in the higher hydrolysis rate of NVP in the presence of K and SO.
Since NVP is easy to hydrolyze, two points should be paid attention to in the production and use of NVP: One is to remove water when synthesizing NVP to ensure that the product does not contain moisture:.. It is to make the product during storage and transportation. It is neutral or weakly alkaline to prevent hydrolysis and self-polymerization. The usual method is to add 0.1% alkali such as sodium hydroxide, ammonia or low molecular weight amines.
The molecular weight of PVP is usually expressed by the K value. According to the data provided by the German BASF company, when the K value is less than 30, its bulk density is 0.4~0.6g/ml, when the K value is 90, the PVP bulk density is 0.11~0.25g /ml. It can be seen that the larger the molecular weight of PVP, the lower the bulk density. This is because the larger the molecular weight of PVP, the higher the degree of grafting, the longer the molecular chain, and the greater the gap between the molecules when they are stacked. Conversely, the smaller the molecular weight, the smaller the gap between the PVP molecules when they are stacked together, and the atoms of different molecules can also fill the gaps between atoms in adjacent molecules, which will lead to an increase in the density of PVP, that is, in other molecules. The bulk density increases under the same conditions. In addition, according to the information provided by the American ISP company, the bulk density of PVP-K is about 0.3g/ml, which is quite different from the bulk density of similar products from BASF. It can be seen that the drying process is different. It has a greater impact on the bulk density of PVP products. In addition, different measurement methods will also lead to differences in PVP bulk density data. The bulk density of insoluble or cross-linked PVP is generally 0.28~0.38g/m