an acetal of polyvinyl alcohol; a polymer of the general formula (I).
Polyvinyl acetate is hydrolyzed to form polyvinyl alcohol. An aldehyde is then added to obtain polyvinyl acetal. Thus, in addition to the acetal groups (x), polyvinyl acetals contain hydroxyl groups (y) and acetyl groups(z):
Polyvinyl acetals are hard, amorphous, and colorless substances that are soluble in aromatic hydrocarbons and in mixtures of aromatic hydrocarbons with alcohols. The hydroxyl groups of polyvinyl acetals react with acids, isocyanates, and epoxides; these reactions improve the heat resistance of items made from polyvinyl acetals and make them resistant to organic solvents and water. Polyvinyl acetals are highly adhesive to various materials, including metal and glass, and are good electrical insulators.
The most widely used polyvinyl acetals are polyvinyl formal (R = H) and polyvinyl butyral (R = C3H7). Polyvinyl formal is used mainly in the manufacture of electrical insulating varnishes (brand VL-941) and adhesives for the bonding of metals, fiberglass laminates, and wood and rubber. Polyvinyl butyral is used as a plastic film (brands PP, PSh-1, and PSh-2) and in the production of shatterproof triplex glass used in automobile and airplane construction. Polyvinyl butyral is also used in alcohol solutions in the production of butvar-phenolic adhesives (brands KA and KB) and varnishes (brands LA and LB). Anticorrosive and decorative coatings on metal items are obtained from polyvinyl butyral (brand NK) by flame spraying.
Outside the USSR, polyvinyl acetals are known by various trade names. Polyvinyl butyrals include Butvar (Canada, USA, and Great Britain), Mowital B (Federal Republic of Germany), Revyl B and Rhovinal B (France), and S-lec B (Japan). Polyvinyl formais include Formvar (USA), Formadur, Mowital F and Pioloform F (Federal Republic of Germany), and Revyl F and Rhovinal F (France).
REFERENCESSee references under .
M. E. ROZENBERG