Polyvinyl resins

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Polymeric materials generally considered to include polymers derived from monomers having the structure

in which R₁ and R₂ represent hydrogen, alkyl, halogen, or other groups. This article refers to polymers whose names include the term vinyl. For discussions of other vinyl-type polymers See also Polyacrylonitrile resins; Polyfluoroolefin resins; Polyolefin resins; Polystyrene resin.

Many of the monomers can be prepared by addition of the appropriate compound to acetylene. For example, vinyl chloride, vinyl fluoride, vinyl acetate, and vinyl methyl ether may be formed by the reactions of acetylene with HCl, HF, CH₃OOH, and CH₃OH, respectively. Processes based on ethylene as a raw material have also become common for the preparation of vinyl chloride and vinyl acetate.

The polyvinyl resins may be characterized as a group of thermoplastics which, in many cases, are inexpensive and capable of being handled by solution, dispersion, injection molding, and extrusion techniques. The properties vary with chemical structure, crystallinity, and molecular weight.

Poly(vinyl acetals) are relatively soft, water-insoluble thermoplastic products obtained by the reaction of poly(vinyl alcohol) with aldehydes. Properties depend on the extent to which alcohol groups are reacted. Poly(vinyl butyral) is rubbery and tough and is used primarily in plasticized form as the inner layer and binder for safety glass. Poly(vinyl formal) is the hardest of the group; it is used mainly in adhesive, primer, and wire-coating formulations, especially when blended with a phenolic resin.

Poly(vinyl acetate) is a leathery, colorless thermoplastic material which softens at relatively low temperatures and which is relatively stable to light and oxygen. The polymers are clear and noncrystalline. The chief applications are as adhesives and binders for water-based or emulsion paints.

Poly(vinyl alcohol) is a tough, whitish polymer which can be formed into strong films, tubes and fibers that are highly resistant to hydrocarbon solvents. Although poly(vinyl alcohol) is one of the few water-soluble polymers, it can be rendered insoluble in water by drawing or by the use of cross-linking agents. Two groups of products are available, those formed by the essentially complete hydrolysis of poly(vinyl acetate), and those formed by incomplete hydrolysis.

The former may be plasticized with water or glycols and molded or extruded into films, tubes, and filaments which are resistant to hydrocarbons. These products are used for liners in gasoline hoses, for grease-resistant coating and paper adhesives, for treating paper and textiles, and as emulsifiers and thickeners.

Poly(vinyl carbazole) is a tough, glassy thermoplastic with excellent electrical properties and a relatively high softening temperature. Uses of the product has been limited to small-scale electrical applications requiring resistance to high temperatures.

Poly(vinyl chloride) [PVC] is a tough, strong thermoplastic material which has an excellent combination of physical and electrical properties. The products are usually characterized as plasticized or rigid types. Poly(vinyl chloride)[and copolymers] is the second most commonly used polyvinyl resin and one of the most versatile plastics. The plasticized types are somewhat elastic materials which are familiar in the form of shower curtains, floor coverings, raincoats, dishpans, dolls, bottle-top sealers, prosthetic forms, wire insulation, and films. Rigid products, which may consist of the homopolymer, copolymer, or polyblends, are commonly used in the manufacture of phonograph records, pipe, chemically resistant liners for chemical reaction vessels, and siding and window sashes.

Poly(vinylidene chloride) is a tough, hornlike thermoplastic with properties generally similar to those of poly(vinyl chloride). Because of its relatively low solubility and decomposition temperature, the material is most widely used in the form of copolymers with other vinyl monomers, such as vinyl chloride. The copolymers are employed as packaging film, rigid pipe, and as filaments for upholstery and window screens.

Poly(vinyl ethers) exist in several forms varying from soft, balsamlike semisolids to tough, rubbery masses, all of which are readily soluble in organic solvents. Polymers of the alkyl vinyl ethers are used in adhesive formulations and as softening or flexibilizing agents for other polymers.

Poly(vinyl fluoride) is a tough, partially crystalline thermoplastic material which has a higher softening temperature than poly(vinyl chloride). Films and sheets are characterized by high resistance to impact and cracking caused by flexing and temperature and by resistance to weathering.

Poly(vinyl pyrrolidone) is a water-soluble polymer of basic nature which has film-forming properties, strong absorptive or complexing qualities for various reagents, and the ability to form water-solubles salts which are polyelectrolytes. The main uses are as a water-solubilizing agent for medicinal agents such as iodine, and as a semipermanent setting agent in hair sprays. Certain synthetic textile fibers containing small amounts of vinylpyrrolidone as a copolymer have improved affinity for dyes. See also Plastics processing; Polymer; Polymerization.

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