The polyvinyl ester family has the general formula -[RCOOCHCH2]-. The most important member is polyvinyl acetate (PVAC). It is a completely atactic, highly branched, noncrystalline thermoplastic, prepared by conventional free-radical polymerization. The homopolymer has a glass transition temperature around room temperature (ca. 305 K). It has good resistance to UV and oxidation, but is rather brittle below the Tg and very sticky above it. For this reason, it is usually blended with plasticizers to improve the flexibility. Because of the water sensitivity of the homopolymer, (unmodified) PVAC is generally viewed as inappropriate for exterior uses.
PVACs are often used as adhesives. Water-based emulsions are, by far, the most common form in which polyvinyl acetates are used in the adhesive market. The adhesive properties are greatly affected by the molecular weight (distribution) and the compatibility of the vinyl acetate with other ingredients. The adhesive strength and moisture sensitivity also depend on the type and the amount of protective colloid (gelatin, natural gum, or cellulose derivatives) and on the functional additives, such as wetting agents and plasticizers.
PVAC emulsions are rather inexpensive and possess good adhesion to many porous substrates, such as wood and paper.
PVAC is not the only vinyl ester. Other vinyl esters have been synthesized, either by direct polymerization or by ester interchange between polyvinyl acetate and other esters/acids. Some known homologs are poly(vinyl butyrate), poly(vinyl propionate), and poly(vinyl formate). However, these vinyl ester polymers have found very little commercial use, probably due to their higher cost.
Of greater importance are the copolymers of PVAC. PVAC is a rather stiff homopolymer. For this reason, it is often copolymerized with other monomers. For example, the combination of vinyl acetate and ethylene, called ethylene vinyl acetate (EVA), yields a much softer and tougher polymer of excellent clarity, gloss and with little odor. This copolymer has excellent adhesion to many substrates, is inert, has good flex crack and puncture resistance, and good adhesion and heat-sealing properties. It finds many uses in the adhesive and coating industry.
Chemical modifications of poly(vinyl acetate) are also of great importance. Among these, its conversion to polyvinyl alcohol (PVA or PVOH) is the most important one. PVA cannot be derived from its monomer because the monomer is not stable. Instead, it is produced by hydrolyzing polyvinyl acetate to polyvinyl alcohol (PVOH). The dry polymer is a hard and crystalline thermoplastic with high tensile strength and glass transition temperature (Tg) of about 375 K. However these properties are dependent on humidity, or in other words, they depend on the amount of water absorbed by the polymer. The water acts as a plasticiser and reduces tensile strength, but increases elongation and tear strength. PVOH is fully biodegradable and water soluble and has good resistance to solvents and oils, and exceptionally good adhesion to cellulose and other hydrophilic surfaces.
Another important modification of PVAC is its derivatization with aldehydes to poly(vinyl acetal)s. The two most important derivatives are poly(vinyl formal) and poly(vinyl butyral). They are manufactured from PVA by reaction with butyraldehyde and formaldehyde. (for more information, see polyvinyl ethers).
All other polyvinyl esters are of limited use in the plastic industry. In most cases, they are copolymerized with other monomers. For example, vinyl stearate is sometimes copolymerized with vinyl chloride to reduce the melt viscosity, i.e. it acts as an internal lubricant and vinyl propionate is sometimes included in emulsion-paints, for example, it is copolymerized with vinyl acetate or vinyl acrylate to form copolymer latices for paints.
Some important manufacturers of PVAC and PVA are
Nippon-Gohsei ( Gohsenol™,
Gohsenx™ ,
Soarnol™ ),
Medtronic ( Merocel® foam products),
Kuraray ( Poval®,
Mowiol®,
Mowiflex®,
Eval™),
Dow ( VAM vinylacetate monomer),
Celanese ( Britecoat®,
Mowilith® ),
and DuPont ( Elvanol®,
Elvax® EVA)
Important brands and maufacturers of PVB are Mowital®,
Pioloform® (Kuraray),
Butvar® (Eastman).
Most of the polyvinyl acetate (PVAC) that is produced is used in the adhesive market. It is one of the main ingredients of
water based glues, commonly referred to as wood glue, carpenter's glue, Elmer's glue (USA), white glue,
or PVA glue. PVAC emulsions are used as adhesives for porous materials, particularly for wood, paper, and cloth. Major applications
are furniture and packaging bonding and book binding. PVAC glues are also used as envelope adhesives, as dry wall
primers, and for wallpaper bonding. Another major applicartion is prefab construction, like flooring and panel installation.
PVAC is not generally used as a primary fastener where great strength is needed.
PVACs find additional uses as plasticizers, thickeners for paints, textile finishes, plastic and cement additives, chewing gum.
PVA is noticeably cheaper than acrylic resins (approximately half
the cost of acrylics) and is, therefore, sometimes added to acrylic
latex paints to lower costs. However, the best exterior water-based
paints are 100 % acrylic due to elasticity and other factors.
Polyvinyl alcohol, the most important derivative, finds uses as a modifier for emulsion adhesives and as a protective colloid in emulsion polymerization. Other important applications include paper and remoistenable adhesives, textile finish, and paper surface treatment. It is also used as a binder and thickener for a variety of coatings and as emulsifier/thickener for products of the cosmetic industry. PVA is also the raw material for several other derivatives.
Other important derivatives are polyvinyl butyral (PVB) and polyvinyl formal (PVF). PVB
finds uses in paints, lacquers, and adhesives and due to its good adhesion to glass, good light resistance and excellent transparency,
as an interlayer for fracture-resistant and shatterproof glass. It is also used as a binder for thick film pastes in electronic applications and
as a (temporary) binder for the manufacture of high performance single and multilayer ceramics.
PVF ( Vinylec®
) is mainly used as electrical insulation for magnet wires. It is often combined with other ingredients, such as phenolic
resins, to produce blends known as "wire enamels".