Curing agents, epoxy cycloaliphatic amines

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. 

The cycloaliphatic epoxides are more susceptible to electrophilic attack because of the lower electronegativity of the cycloaliphatic ring relative to the bisphe-nol A aromatic ether group in DGEBA resins. Consequently, cycloaliphatic epoxies do not react well with conventional anionic epoxy curing agents such as amines. They are commonly cured via thermal or UV-initiated cationic cures. In addition. 

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. 

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. 

Chem. Descrip. Modified cycloaliphatic amine Uses Epoxy curing agent for high-solids and solventless coatings and floors... 

Chem. Descrip. Modified cycloaliphatic amine epoxy Uses Epoxy curing agent for high solids coatings accelerator for polyamide and amidoamine curing agents Features Good chem. resist, and low temp, cure (30-35 E) exc. blush resist. 

Gonzalez, M. Cabanelas, J.C. Pozuelo, J. Baselga, J.(2011). Preparation of cycloaliphatic epoxy hybrids with non-conventional amine-curing agents. Journal of Thermal Analysis and Calorimetry, Vol.103, No.2, (February 2011), pp. 717-723, ISSN 1388-6150. 

Underfill adhesive (snap cure) Epoxy resins (high purity Bisphenol-A and cycloaliphatic resins) 45-60% Resin modifier 1—5% Curing agents (amine) 3-5% Filler (amorphous silica) 50-80% Loctite 3563, Ablebond 7811... 

Curing agents are used with epoxy resins, the most commonly used ones are aromatic amines, and two of the most common are 4,4-methylene-dianiline (MDA) and 4,4-sulfonyl-dianiline (DDS). Like the epoxies, these compounds have very low vapour pressures and in principle they should not present any airborne hazard, unless a mixture is sprayed or cured at high temperatures and certainly potential for dermal exposure is high. Several other types of curing agents to consider are aliphatic and cycloaliphatic amines, polyaminoamides, amides, and anhydrides. 

Cycloaliphatic Amines. Cycloaliphatic amines were originally developed in Europe, where their use as epoxy curing agents is well established. Compared to aliphatic amines, cycloaliphatic amines produce cured resins having improved thermal resistance and toughness. Glass-transition temperatures (Tg) approach those of aromatic amines (>150°C), while percent elongation can be doubled. 

TGA/FT-IR and DSC/FT-IR were utilized in this research to characterize an amine activated epoxy resin system. The specific system under study was a near-monomeric diglycidyl ether of Bisphenol A (2-di-[4-(2,3-epoxy-l-propoxy)-l-phenyljpropane) with an epoxy equivalent weight of 173. The curing agent was composed of a mixture of 10% tertiary amine catalyst and 90% primary cycloaliphatic diamine. Cured and uncured systems were analyzed using these hyphenated techniques. 

Figure 6 Chemical formulae of the catalysts and co-reactants used as curing agents of epoxy resins electrophilic 33 and nucleophilic 34-36 catalysts, dicyandiamide 37, ureas 38, 39, imidazoles 40-47, aliphatic amines 48, 49, polyamide 50, and cycloaliphatic...

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