Performance Of Polyvinyl Pyrrolidone

Physical properties of PVP

Commodity PVP is a white or milky white powder solid, a polymer composed of linear N-vinyl pyrrolidone (NVP) groups with variable polymerization degree. Its average molecular weight grade is generally expressed by K value, which is usually divided into K-15, K-30, K-60, and K-90, representing the molecular weight range of 10,000, 40,000, 160,000, and 360,000, respectively. PVP is tasteless, odorless, almost non-toxic, non-irritating to the skin and eyes, and non-allergic to the skin, and is physiologically safe.

In the structure of PVP, the methylene groups on its main chain and pyrrolidone ring are non-polar groups and are lipophilic. The lactam in the molecule is a strong polar group with hydrophilic and polar group effects. This structural feature makes PVP soluble in water and many organic solvents, such as alkanes, ethers, esters, ketones, and chlorinated hydrocarbons. PVP aqueous solution is acidic, and its melting heat is -4.81kJ/mol. Its glass transition temperature is 75℃, which is not suitable for thermoplastic molding, but it can form a film from methanol, water, dichloromethane and chloroform. The film is bright, transparent, and easy to absorb moisture. The density of the film is about 1.25, and the refractive index = 1.52. The solubilization effect of PVP can be used to increase the water solubility of certain substances that are basically insoluble in water but pharmacologically active; the dispersion effect can make the colored substances, suspensions, and emulsions in the solution dispersed evenly and maintain stability; the adsorption effect can be adsorbed on many interfaces and reduce the interfacial surface tension to a certain extent.

Chemical properties of PVP

PVP's special molecular composition and structure not only give it many excellent physical properties, but also give it some typical chemical properties.

Complexation

PVP's molecular structure has strong polarity and amide groups that can accept hydrogen bonds, which enables it to bind some polar small molecules. At the same time, the O atoms and N atoms in the PVP molecule are typical coordinating atoms, which enable it to form complexes with certain metals. These abilities enable PVP to form solid complexes with many substances, especially compounds containing hydroxyl, carboxyl, amino and other active hydrogen atoms, such as iodine, β-carotene, methylsulfonamide, phenytoin, amorphine, reserpine and a variety of sulfonamide drugs.

Chemical stability

Under normal circumstances, solid PVP is very stable. No obvious chemical changes occur when heated at 100°C for more than 15 hours. If it exceeds 150°C, or is heated to 90°C in the presence of an initiator (such as potassium persulfate, ammonium persulfate, etc.), self-crosslinking reactions may occur and it will be transformed into insoluble cross-linked PVP. On the other hand, long-term grinding will lead to PVP degradation.

Acidity and alkalinity also affect the stability of PVP, especially for PVP aqueous solution. When the PVP aqueous solution is heated under obvious acidic or alkaline conditions, some pyrrolidone rings will open and destroy the molecular structure of PVP.

Physiological safety

PVP has good physiological compatibility, does not participate in human metabolism, and does not cause any obvious irritation to the skin, mucous membranes, eyes and other parts and organs. From a biological point of view, the amide group in the PVP molecular structure is similar to the amino acid functional group similar to the simple protein model molecule, which makes some of its properties similar to those of protein, such as water solubility, complexing ability for certain small molecules, and precipitation by some protein precipitants. The property of forming precipitation when the PVP aqueous solution is heated is also similar to the denaturation of protein.

Development Status of Polyvinylpyrrolidone Styling Polymers

As the first synthetic resin for hair styling agents, PVP has many advantages: First, due to its strong polarity, PVP has excellent solubility. It is soluble in many solvents, including water, ethanol, acetone, ethyl acetate, etc., and has good compatibility with the propellant Freon, so that the formulated hair spray has an ideal cloud point; secondly, PVP has good film-forming properties and forms a shiny film on the hair. The hardness, elasticity and firmness of this film can meet the needs of hair styling agents and can be easily washed off with water; in addition, due to the presence of amide groups similar to amino acids, PVP has good biocompatibility, is safe and non-toxic, and safe to use. This is the most important reason why PVP can be used as a styling polymer. However, since the PVP molecular chain structural unit contains a five-membered heterocyclic ring, the molecular chain is rigid and has poor flexibility. In addition, the presence of polar amide groups makes PVP polymers easy to absorb water, resulting in some defects in the performance of PVP, mainly manifested in: poor climate adaptability, the film formed will absorb moisture in a humid environment, causing the film hardness to decrease and lose its gloss and styling ability; the film is brittle, and powdery substances are easily produced when combing hair. In addition, people have increasingly higher requirements for the multifunctionality of styling products. Traditional styling products with single functions and poor conditioning will gradually withdraw from the mainstream market. Therefore, the research on copolymerization modification of PVP by introducing other monomers containing hydrophobic and flexible groups has become a research hotspot in related fields at home and abroad. This copolymerization modification is of great significance to expanding the application range of PVP series products in the field of cosmetics. This significance is manifested in:

(1) Improving the moisture resistance and toughness of PVP homopolymers and improving the comprehensive performance of styling polymers.
(2) Give the styling copolymer new properties such as conditioning, gloss, UV resistance, thickening, and moisturizing, so as to achieve the multifunctional purpose of the PVP series styling polymers.
(3) Broaden the application field of PVP and open up new paths for PVP application.

Generally speaking, the research on copolymerization modification of PVP at home and abroad mainly focuses on the copolymerization of PVP with esters, acids, amides and quaternary ammonium salt monomers.