Alkyds also unsaturated

Phthalic anhydride (phthalic-acid anhydride) n. C6H4(C0)20. a white, odorless, crystalline compound derived by oxidation of naphthalene or o-xylene, shipped in flake or molten form. It major use is in the production of phthalate esters for plasticizing vinyl and cellulosic resins. It is also an important intermediate in the manufacture of alkyd and unsaturated polyester resins, and is a curing agent for epoxy resins. Bp, 284°C mp, 130°C Sp gr, 1.53 acid value, 758.0 See image). 

Polyols. Several important polyhydric alcohols or polyols are made from formaldehyde. The principal ones include pentaerythritol, made from acetaldehyde and formaldehyde trimethylolpropane, made from -butyraldehyde and formaldehyde and neopentyl glycol, made from isobutyraldehyde and formaldehyde. These polyols find use in the alkyd resin (qv) and synthetic lubricants markets. Pentaerythritol [115-77-5] is also used to produce rosin/tall oil esters and explosives (pentaerythritol tetranitrate). Trimethylolpropane [77-99-6] is also used in urethane coatings, polyurethane foams, and multiftmctional monomers. Neopentyl glycol [126-30-7] finds use in plastics produced from unsaturated polyester resins and in coatings based on saturated polyesters. 

Oxidation of n-hutane to maleic anhydride is becoming a major source for this important chemical. Maleic anhydride could also be produced by the catalytic oxidation of n-butenes (Chapter 9) and benzene (Chapter 10). The principal use of maleic anhydride is in the synthesis of unsaturated polyester resins. These resins are used to fabricate glass-fiber reinforced materials. Other uses include fumaric acid, alkyd resins, and pesticides. Maleic acid esters are important plasticizers and lubricants. Maleic anhydride could also be a precursor for 1,4-butanediol (Chapter 9). 

Polyester-based networks are typically prepared from polyester prepolymers bearing unsaturations which can be crosslinked. The crosslinking process is either an autoxidation in the presence of air oxygen (alkyd resins) or a copolymerization with unsaturated comonomers in the presence of radical initiators (unsaturated polyester resins). It should also be mentioned that hydroxy-terminated saturated polyesters are one of the basis prepolymers used in polyurethane network preparation (see Chapter 5). 

The initial drying of currently applied alkyd paints is accomplished by evaporation of solvent (physical drying). Subsequently, the eventual curing of the alkyd paint is completed by the formation of a polymer network, which is mainly formed by chemical crosslinks (oxidative drying) but in some cases also physical interactions between the fatty acid side chains occur, such as crystallization or proton-bridge formation [129]. Efficient network formation is crucial in the formation of dry films with good mechanical properties. Due to the presence of unsaturated units in the investigated LOFA- and TOFA-PHA bin-... 

Applications. Phthalic anhydride is used largely to make plasticizer for polyvinyl chloride. It is also a feed for alkyd resins and. for unsaturated polyesters that are widely used in construction, rharine, and synthetic marble applications. Other minor applications are dyes, esters, drying oil modifiers and pharmaceutical intermediates. 

Simple polyesters of the type described by Eq. 2-170 are too limited to be of commercial interest. Almost all crosslinked polyesters are either unsaturated polyesters or alkyd polyesters. These offer a greater ability to vary the final product properties to suit a targeted market. Also, they offer greater process control since different chemical reactions are involved in the polymerization and crosslinking reactions. A typical unsaturated polyester... 

From an industrial point of view, not only the high-molecular-weight linear polyesters are of interest. Also, a series of low-molecular-weight linear or branched polyesters (Example 4-1) find application in surface coating systems (alkyd resins), as coreactants in unsaturated polyester resins (Example 4-8), or in polyurethane foams (Examples 5-28 and 5-29). 

Alkyd resins are also polyesters containing unsaturation that can be cross-linked in the presence of an initiator known traditionally as a drier. A common example is the alkyd formed from phthalic anhydride and a glyceride of linolenic acid obtained from various plants. Cross-linking of the multiple bonds in the long unsaturated chain produces the thermoset polymer. 

The processing equipment (reaction kettle and blending tank) used for unsaturated polyesters can also be used for manufacturing alkyd resins. 

Phthalic anhydride is made by air oxidation of ortho-xylene. About half of phthalic anhydride is used to make plasticizers, especially the compound dioctyl phthalate, for softening polyvinyl chloride plastic. Phthalic anhydride is also used to make unsaturated polyester resins and alkyd paints. 

Alkyds. Alkyd resins consist of a combination of unsaturated polyester resins, a monomer, and fillers. Alkyd compounds generally contain glass fiber filler, but they may also include clay, calcium carbonate, alumina, and other fillers. Alkyds have good heat, chemical, and water resistance, and they have good arc resistance and electrical properties. Alkyds are easy to mold and economical to use. Postmolding shrinkage is small. Then-greatest limitation is extremes of temperature (above 175°C) and humidity. 

Maleic Anhydride. Maleic anhydride is one of the fastest-growing chemical end-uses for butane. The demand in the United States was about 500 million lb in 2000. About 60 percent of the maleic anhydride produced goes into the manufacture of unsaturated polyester resins, used primarily in fiber-reinforced plastics for construction, marine, and transportation industries. It is also used to make lube oil additives, alkyd resins, fumaric and malic acids, copolymers, and agricultural chemicals. 

Isophthalic Acid. Although m-xylene is an abundant material, it has limited demand as a chemical raw material. The only major outlet is in the manufacture of isophthalic acid. More than 220 million pounds were produced in the United States in 1992, primarily for use in preparing alkyd resins and unsaturated polyester resins. Small amounts also are used in PET bottle applications. 

Phenolic resins are well known for their contribution in improving hardness, gloss, and water and chemical resistance in oleoresinous varnishes. Those based on p-alkyl-substituted phenols and with heat-reactive methylol groups have also been incorporated into alkyd resins. The reaction has not been well smdied. Presumably, the methylol group would react with the unsaturation functionality on the fatty acid chain to form the chroman stmcture, similar to what is believed to have occurred in the varnish. Etherification between the methylol group and free hydroxyl of the alkyd resin, catalyzed by the residual acidity in the resin, would be another possible reaction. 

This product is an ultraviolet light absorber for use in polystyrene, unsaturated polyesters, coatings, varnishes, lacquers, and coatings based on epoxy or phenolic alkyds. It is also used in pressure sensitive adhesives, polymethylacrylate (fdm or sheeting), thermoplastic rubbers, polyisoprene latex and alcohol based cosmetics. 

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