Molecular weight of polyvinylpyrrolidone
Polyvinylpyrrolidone (PVP) is a fine chemical downstream of acetylene. PVP is a moisturizing and detoxifying agent for cosmetics, which can effectively remove the irritation of cosmetics on the skin and help to soften and lubricate the skin. For hair cosmetics, PVP and its copolymers have the functions of styling, hair care, increasing the luster and smoothness of hair, and are indispensable raw materials for styling hair lotion, mousse and hair spray. As a bonding excipient, thickener, solubilizer, dispersant, stabilizer, film forming agent and disintegrator in medicine, it is considered to be one of the most important medicinal synthetic new excipients in the world. Povidone iodine (PVP-I) with PVP as the main raw material is a new type of non-toxic, non-irritating and highly efficient germicidal disinfectant, and can also be directly used as medicine. Cross-linked PVP(PVPP) can be used as a clarifying agent and stabilizer for beer, wine and juice. In addition, PVP is increasingly widely used in textile printing and dyeing, paper making, adhesives, coatings, detergents, energy, lithium batteries, polymer polymerization, electronics, separation membranes, medical polymer materials, nanomaterials, graphene, catalysts, agriculture and animal husbandry.
The average molecular weight of PVP can be characterized in three different ways, including the weight average, number average and viscosity-average molecular weight. The weight average molecular weight Mw was determined by light scattering, ultracentrifugation or gel permeation chromatography. The average molecular weight of Mn was measured by osmotic pressure or membrane filtration. The viscosity average molecular weight Mv was determined by the viscosity method. For convenience, the specification and molecular weight of the product are usually expressed by the K value, such as PVP K12, PVP K15, PVP K17, PVPK30, PVP K60, PVP K90, and PVP K120.
The molecular weight determination of PVP has been extensively reported in the literature, but recent results do not always agree with earlier results because the instrumentation has been significantly improved over the years. Table 1 lists the weight average molecular weight and number average molecular weight of PVP with different K values. At present, the results of PVP weight average molecular weight determination are very different from the earlier studies, which is something that needs attention in this field.
Table 1 Weight average molecular weight and number average molecular weight of PVP
| PVP specifications | weight-average molecular weight | Weight average molecular weight reported in early literature | number-average molar mass |
| PVP K 12 | 2 000-3 000 | 2 500 | 1 300 |
| PVP K 17 | 7 000-11 000 | 9 000 | 2 500 |
| PVP K 25 | 28 000-34 000 | 25 000 | 6 000 |
| PVP K 30 | 44 000-54 000 | 40 000 | 12 000 |
| PVP K 90 | 1 000 000-1 500 000 | 700 000 | 360 000 |
Table 2 Viscosity-average molecular weight of PVP
| PVP specifications | Viscosity-average molecular weight of nominal K value | Viscosity-average molecular weight within the allowable K value range |
| PVP K 12 | 3 900 | 2 600～5 500 |
| PVP K 17 | 9 300 | 7 100～11 000 |
| PVP K 25 | 25 700 | 19 300～31 100 |
| PVP K 30 | 43 500 | 31 700～51 400 |
| PVP K 90 | 1 100 000 | 790 000～1 350 000 |
Table 2 shows the viscosity-average molecular weight of PVP with different K values. It should be noted that the results of the current study on the viscous-average molecular weight of PVP are also different from those reported in the earlier literature. Marking a certain K value specification of PVP products, allowing its actual K value or molecular weight in a certain range on both sides of its nominal value (when the nominal K value is less than 15, the actual K value range is 85.0% ~ 115.0% of the nominal K value; When the nominal K value is greater than 15, the actual K value ranges from 90.0% to 108.0% of the nominal K value).
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