Curing agents phthalic anhydride

Cyclic acid anhydrides such as maleic, dodecylsuccinic, hexahydrophthalic, phthalic, phyromellitic, etc. are widely employed as curing agents for epoxy resins. They form esters with epoxy resins. These resins have better thermal stability and good electrical insulation and chemical resistance expect to alkalis. 

Figure 2. Solid-state spectra of four different epoxies (hosed on the resin diglycidyl ether of bisphenol-A) are compared with the liquid-state spectra of their respective unreacted components, The chemical compositions are in Table I. Here the epoxies are identified by their main curing agent (a) PIP—piperidine (b) MPDA—metaphenylene diamine (c) HHPA—hexahydro-phthalic anhydride (d) NMA—nadic methyl anhydride.

Crosslinking of epoxy plastics through the hydroxyl groups of the repeat unit is used for prepolymers with low epoxide group contents. The most common curing agent is phthalic anhydride although other acid anhydrides such as tetrahydrophthalic, nadic methyl, and chloroendic anhydrides are used in specialty applications ... 

After the primary amines, acid anhydrides are the next most important class of epoxy curing agents, although these are not used as often in adhesive systems as they are in casting compounds, encapsulants, molding compounds, etc. The most common types of anhydrides are hexahydrophthalic anhydride (HHPA), phthalic anhydride (PA), nadic methyl anhydride (NMA), and pyromellitic dianhydride (PMDA), although there are several others. Chemical structures of several anhydrides are illustrated in Fig. 5.6. 

Phthalic anhydride (PA) and its derivatives are among the most common anhydride curing agents. Table 12.6 describes an anhydride cured epoxy adhesive that is accelerated with... 

SAFETY PROFILE Most cured resins have little or no toxicity. If curing is incomplete there may be residues of highly toxic curing agents such as the organic amines m-phenylene diamine, diethylene triamine, tetraethylene pentamine, and hexamethylene tetramine, as well as phthalic anhydride and related compounds. When heated to decomposition they emit highly toxic fumes. See also various epoxy hardeners and POLYMERS, INSOLUBLE. 

Polymer concretes show excellent mechanical properties and chemical resistance compared with conventional cement concretes. Polymer concretes can be cured quickly by the use of curing agents. Thus, the applications of polymer concretes are being increased. One of the popular polymers for polymer concretes is unsaturated polyester (UPE) resin. The properties of UPE resin can be modified by changing its molecular features. For the synthesis of the resin, phthalic anhydride or isophthalic acid as well as maleic anhydride can be employed to modify the mechanical properties or hydrothermal resistance. Terephthalic acid which is also used for the synthesis of poly ethylene terephthalate (PET) enhances the thermal resistance of the cured UPE resin. However, the synthesis of unsaturated polyester resin from terephthalic acid is difficult. One method to synthesize unsaturated polyester from terephthalic acid is the use of recycled PET. 

There are two options for the other component of an epoxy resin system. Use of mono- or di-anhydrides as curing agents, usually catalyzed by a tertiary amine, causes reactions with the residual secondary hydroxyls in the repeating unit of the prepolymer forming esters and free carboxylic acids. The carboxylic acids formed also react with the epoxide end groups forming cross-links and further free secondary hydroxyl groups. Maleic anhydride, phthalic anhydride, or pyromellitic dianhydride are suitable for this process (Eq. 21.27). 

Acid anhydrides. These are the second most commonly used curing agents after polyamines. In general, acid anhydrides require curing at elevated temperatures, but offer the advantages of longer pot lives and better electrical properties than aromatic amines. Illustrative of some of the more commonly used acid anhydrides are phthalic, trimellitic, hexahydrophthalic, and methylnadic anhydride. 

Phthalic anhydride is the cheapest anhydride curing agent, but it has the disadvantage of being rather difhcult to mix with the resin. Liquid anhydrides (e.g., dodecenylsuccinic anhydride and nadic methyl anhydride), low-melting anhydrides (e.g., hexahydrophthalic anhydride), and eutectic mixtures are more easily incorporated into the resin. Since maleic anhydride produces brittle products, it is seldom used by itself and is used as a secondary hardener in admixture with other anhydrides. Dodecenylsuccinic anhydride imparts flexibility into the casting, whereas chlorendic anhydride confers flame resistance. 

Asthma due to exposure to ethylene amines in manufacture has been reported by Dernehl (1951), and after exposure to aliphatic polyamine or epoxy resin curing agents (Dernehl 1963). Phthalic anhydride, often used in hot curing systems, is a recognised irritant of the respiratory tract and asthma has been reported (American Industrial Hygiene Association Journal 1967 Malten and Zielhuis 1964 Petit et al. 1961). 

Common curing agents in such products include anhydrides (e.g., phthalic anhydride, hexahydro-phthahc anhydride, pyromellitic dianhydride), and also polyamine and polyamide-based hardeners. 

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). 

Acid anhydride curing agents, especially the liquid anhydrides, are particularly important for epoxy resins. They cure at elevated temperatures but offer long pot life, good electrical properties, and heat resistance. Typical of these agents are phthalic anhydride and nadic methyl anhydride. The high-temperature properties of resin systans cured with these materials are better than those of resin systems cured with... 

Phthalic anhydride is used in the manufacture of unsaturated polyesters and as a curing agent for epoxy resins. When used as a pigment, it can be responsible for sensitization in ceramic workers. 

The hardener portion (Part B) may also be mixed with fillers, diluents, solvents, and other additives. Fillers may be mixed in the resin portion alone or partly in the resin and partly in the hardener portion. Adhesion promoters such as Dow Coming A-180 silane may also be added to enhance the adhesion of the filler particles to the resin or hardener. Examples include several electrically conductive epoxy formulations that were usedto evaluate their electrical stability onnon-noble metal surfaces.t The base epoxy resin was the diglycidylether of bisphenol-F (DGEBF, equivalent wt. = 170 g). Methylhexahydrophthalic anhydride, hexahydro-phthalic anhydride, and 4-methylphthalic anhydride were evaluated as curing agents with 4-methylimidazole as a catalyst. The manufacturing procedure was ... 

An acid anhydride as curing agent is bifunctional (f=2) and crosslinking occurs primarily through the hydroxyl groups. In this reaction, the prepolymer acts as a structopendant prepolymer. Maleic anhydride introduces C-C- double bonds into the resin. Mostly phthalic anhydride and pyromellitic anhydride are used. 

Cyclic acid anhydrides are widely employed as curing agents for epoxy resins. Both mono- and dianhydrides are used. Examples of anhydrides which find application are maleic anhydride (MA) (XIX), dodecenylsuccinic anhydride (DDSA) (XX), hexahydrophthalic anhydride (HPA) (XXI), phthalic anhydride (PA) (30(11), pyromellitic dianhydride MDA) (XXIII), nadic methyl anhydride (NMA) (a mixture of maleic anhydride adducts of methylcyclopentadienes cf.. Section 10.2.2.3) (XXIV) and chlorendic (HET) anhydride (XXV see also Section 102.2.3). 

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