English name: Poly (vinyl alcohol)
CAS number: 9002-89-5
Molecular formula: (CH 2 CHOH) n
Storage conditions: sealed in a cool place
White to slightly yellow powder or translucent particles, odorless, tasteless, non-toxic, non-corrosive. Easily soluble in water, also soluble in solvents containing hydroxyl groups, such as glycerol, ethylene glycol, acetic acid, acetaldehyde, phenolic acid, etc., insoluble in general non-polar organic solvents and inorganic acids.
Polyvinyl alcohol (PVA) is made of vinyl acetate through polymerization and alcoholysis, and the molecular formula is (C 2 H 2 CHOH) m (C 2 H 2 CHOCOCH 3 ) n , is a stable, non-toxic water-soluble polymer.
The polyvinyl alcohol series contains a variety of product types. Different types of polyvinyl alcohol are usually distinguished by four digits, where the first two digits multiplied by 100 represent the degree of polymerization, and the last two digits represent the degree of alcoholization.
The properties of polyvinyl alcohol are mainly determined by the degree of polymerization and alcoholysis. The characteristics of basically completely alcoholyzed polyvinyl alcohol are that there are very few hydrophobic acetates remaining in the molecule, the molecules are neatly arranged, and there are a large number of hydroxyl groups, forming strong hydrogen bonds. It is a crystalline polymer with high strength. Incomplete alcoholyzed polyvinyl alcohol can be regarded as a macromolecule formed by the copolymerization of vinyl alcohol and vinyl acetate. Vinyl alcohol has strong hydrophilicity, while vinyl acetate is lipophilic. This amphiphilic structure determines that low alcoholysis PVA macromolecules have the properties of increasing water viscosity and reducing surface tension in the oil-water boundary.
The viscosity of PVA that is completely alcoholized increases with time, and gradually gels, and can be restored after reheating. Gel can be produced by adding sodium sulfate, potassium sulfate, ammonium sulfate and borax. Partial alcoholized PVA solutions do not produce gel.
In addition, the presence of a large number of hydrogen bonds and weak non-covalent bond forces such as van der Waals forces in the PVA system will significantly affect its water solubility. The residual acetate of partially alcoholized PVA macromolecules can weaken the hydrogen bonds between adjacent macromolecules and within macromolecules, improving the water solubility of PVA. However, the increase of acetate makes the critical temperature of phase separation drop, and the water solubility gradually decreases at high temperatures. For example, PVA with an alcoholysis of less than 60% has insolubility in water above 40 ° C.
PVA1799 is a polyvinyl alcohol polymer with a degree of polymerization of 1700 and a degree of alcoholysis of 99%. It is soluble in hot water above 95 ° C. The aqueous solution has good adhesion and film-forming properties. Aqueous solutions with a concentration greater than 10% will gel and freeze at room temperature, and will become thinner and restore fluidity at high temperature.
Under the action of the outside world, PVA can be physically and chemically crosslinked. PVA prepared by cyclic freezing and thawing method can exhibit rubber-like elasticity, and its mechanical properties are unmatched by most current hydrogels. PVA's strong tensile and compressive properties, good flexibility and ductility make it an ideal candidate for flexible substrates, laying a good foundation for the development of wearable and implantable medical devices. In addition, PVA can also be used as a hydrogel substrate to composite hydrogel materials with different kinds of polymers and nanoparticles, thereby obtaining superior mechanical properties and biological properties matched with many biological tissues to meet application requirements.
