Cycloaliphatic acid anhydrides

Curing agents account for much of the potential hazard associated with use of epoxy resins. There are several major types of curing agents aliphatic amines, aromatic amines, cycloaliphatic amines, acid anhydrides, polyamides, and catalytic curing agents. The latter two types are true catalysts, in that they do not participate in the curing process. 

Crosslinking of Aliphatic-Cycloaliphatic Epoxy Compounds with Acid Anhydrides and Amines... 

Properties of an amine and acid anhydride cured brominated epoxy compound LXIV (Scheme 79) which contains a cycloaliphatic ring are presented in... 

Acid anhydrides are more effective curing agents for cycloaliphatic epoxy resins than are the amines. In addition, the amines might also react with ester groups that are present in some of these materials and form undesirable byproducts. 

Examples of catalysts are shown on the first line, whereas all the other compounds are coreactants including dicyandiamide, ureas, imidazoles, aliphatic polyamines, cycloaliphatic polyamides, and cycloaliphatic dicarboxylic acid anhydrides. As all the corresponding reaction mechanisms have been previously disclosed in detail," the following presentation is limited to the initial reaction steps leading to the active species involved in the polymerization or polycondensation processes. These primary attacks are enlightened in Fig. 12.6, which displays only one epoxy group reacting with catalysts or coreactants. 

Other minor raw materials are used for specific needs. Fumaric acid [110-17-8], the geometric isomer of maleic acid, is selected to maximize thermal or corrosion performance and is the sole acid esterified with bisphenol A diol derivatives to obtain optimum polymer performance. Cycloaliphatics such as hydrogenated bisphenol A (HBPA) and cydohexanedimethanol (CHDM) are used in selective formulations for electrical applications. Tetrahydrophthalic anhydride [85-43-8] (THPA) can be used to improve resilience and impart useful air-drying properties to polyester resins intended for coating or lining applications. 

The components of the copolymers are cycloaliphatic monomers (norbor-nene), and vinyl ether, maleic anhydride, acrylate, and methacrylate. In addition, vinyl sulfonamides have been used as co-monomers in the synthesis of random copolymers capable of functioning as acid-amplified resists. An example is presented in Chart 9.5. A high sensitivity, S = 2mJ cm, was measured for a copolymer (Chart 9.5) with n=0.4 and m=0.6 (resist thickness d=220nm, developer aqueous tetramethylammonium hydroxide solution). Triphenylsulfonium perfluoro-1-butane sulfonate served as acid generator [33]. 

Dibasic Acid Selection. Dibasic acids used to prepare alkyds are usually aromatic. Their rigid aromatic rings increase the Tg of the resin. Cycloaliphatic anhydrides, such as hexahydrophthalic anhydride, are also used. While they are not as rigid as aromatic rings, the cycloaliphatic rings also increase Tg. 

Cured epoxy-anhydride systems exhibit excellent thermal, mechanical, and electrical properties, and are used in filament-wound epoxy pipe, PCB laminates, mineral-filled composites, and electrical casting and encapsidation applications. Anhydride-cin-ed epoxies also have better aqueous acid resistance than similar amine-cured systems. Anhydrides are the principal curing agents for cycloaliphatic and epoxidized olefin resins in electrical casting and potting. Some... 

The reactive groups attached to the molecules of an epoxy resin can react with several curing agents, such as amines, anhydrides, acids, mercaptans, imidazoles, phenols and isocyanates, to create covalent intermolecular bonds and thus to form a three-dimensional network. Among these compounds, due to the enhanced environmental stability of amine-cured epoxy resin (Dyakonov et al., 1996), primary and secondary amines are the curing agents most commonly used in particular aliphatic or cycloaliphatic amines for low-temperature epoxy systems as adhesives or coatings and aromatic amines to produce matrices for liber-reinforced composites (Pascault and Williams, 2010). In Fig. 5.14 the structures of both an aliphatic and an aromatic amine are shown. 

XU 218 is produced by the reaction of an aromatic cycloaliphatic diamine, 5[6]-amino-1(4-aminophenyl) -1,3,3-trimethylindane (DAPI) with BTDA as shown below[11]. The intermediate polyamic acid is chemically imidized by acetic anhydride/tertiary amine. ... 

For these oligomers, it is preferred that n have a value of about 1 to 6. Modified block copolymers have been synthesized by coupling the above products with difunctional isocyanates (193) and with cycloaliphatic diepoxides (194). They were also used to synthesize radiation-curable diacrylates by means of a condensation reaction with acrylic acid (195). Other modifications of the oligomeric compounds include end capping with anhydrides to form acid-terminated oligomers (196) and reaction with polyols, anhydrides, and carboxylic acids to form low-viscosity, oil-free alkyds that are useful as coating intermediates (197). 

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