Curing aromatic diamines

Bismaleimides are best defined as low molecular weight, at least diftinctional monomers or prepolymers, or mixtures thereof, that carry maleimide terminations (Eig. 3). Such maleimide end groups can undergo homopolymerization and a wide range of copolymerizations to form a highly cross-linked network. These cure reactions can be effected by the appHcation of heat and, if required, ia the presence of a suitable catalyst. The first patent for cross-linked resias obtained through the homopolymerization or copolymerization of BMI was granted to Rhc ne Poulenc, Erance, ia 1968 (13). Shordy after, a series of patents was issued on poly(amino bismaleimides) (14), which are synthesized from bismaleimide and aromatic diamines. 

Bismaleimides - Bismaleimides resins were first introduced into the market in the early 1970 s. As with other resin systems, there are many variations of bismaleimides. The Kermid and Kinel bismaleimide products as marketed in the U. S. by Rhodia are representative examples. Bismaleimide chemistry is represented in Eq. 3 where curing can be accomplished thermally through the unsaturation in the maleimide or by way of the Michael Reaction where an appropriate curing agent such as aromatic diamine adds across the activated double bond. In most instances, a combination of curing thermally through the double bond and via an aromatic diamine is used in actual practice. Bismaleimides are frequently formulated... 

Although this change in crosslinking chemistry holds promise for increased use temperatures, a tougher product is desirable. Experiments were therefore designed to decrease the crosslink density by the addition of a monofunctional reactant (Structure IV in Table I). For these experiments, an aromatic diamine co-reactant was used to accelerate the cure (8). 

A great variety of aromatic diamines and aliphatic di- and poly-amines are used as epoxy resin curing agents, and tert-amines can act as catalysts for anionic epoxide homopolymerisation. 

Figure 5.7 shows the superposition of Tg vs lnt data for the diepoxide (DGEBA)-aromatic diamine (TMAB) system, to form a master curve at 140°C (Wisanrakkit and Gillham, 1990). Vitrification times, defined as the time at which Tg equals the cure temperature, are marked by arrows (Tg was defined as the midpoint of the baseline change during a DSC scan). 

Some aromatic diamines used as curing agents, such as 4,4 diaminodi-phenyl derivatives or 3,3 Dichloro 4,4 diaminodiphenylmethane (MOCA), have been investigated and have been declared to have suspect carcinogenic properties. All local rules and regulations must be adhered to if these materials are used. 

Amino and functional aromatic phosphates, phosphonates, and phosphine oxides have also been used as reactive components to impart flame retardancy to cured epoxy resins. Phosphine oxides are particularly hydrolytically stable and several studies have been reported, for example, of the curing of epoxy resins with bis(aminophenyl) alkyl and aryl phosphine oxides65-67 (Structure 5.19). The relative performances of epoxies cured with aromatic diamine hardeners containing phosphine oxide, phosphinate, phosphonate, or phosphate units have recently been assessed.68 Aromatic phosphine oxides have been functionalized also with maleimide and hydroxyl groups for use as epoxy resin hardeners.69,70... 

Other latent curing agents that are used in solid adhesives are dihydrazides and BF3-MEA complexes. These compositions are also stable at room temperature but cure when heated. Solid anhydrides can be used in one-component powder blends (e.g., 10 pph of trimellitic anhydride accelerated with 0.5 pph of 2-methylimidazole). Solid systems with aromatic diamines are prepared by comelting the solid epoxy with the amine. Typically 30 pph of curing agent is used.1... 

Poly(amic acids) were prepared by the ambient temperature condensation of 1,2,3,4-cyclobutane tetracarboxylic dianhydride with selected aromatic diamines. When the poly(amic acids) and liquid crystal alignment agents y-butyrolactone and A-methyl-pyrrolidone were spin-coated and cured onto an inert surface, the polyimide was effective as a liquid crystal aligner. 

Covers a two-part epoxy-resin system in the form of a bisphenol "A" epoxy resin filled with fumed silica and carbon microspheres and a separate aromatic diamine curing agent. 

Other special aliphatic imide forming compounds claimed in patents, like 2-oxazolidone [85] or epsilon-caprolactame, lead to polymers having aliphatic chains. These chains are responsible for the lower Tg of the cured films in comparison with the polymers having aromatic diamines. No commercial polyfes-ter-imide) wire enamel in western Europe contains them. 

Seven polyurethane adhesives have been developed at Lawrence Livermore National Laboratory (LLNL). These adhesives, designated Halthanes were synthesized because of OSHA restrictions on the use of the curing agent methylene bis(2-chloroani1ine). Four of the Halthanes were made fromLLNL-developed 4,4 -methylene bis(phenylisocyanate) terminated prepolymers cured with a blend of polyols three were made from an LLNL-developed prepolymer terminated with Hylene W and cured with aromatic diamines. In this paper we report the dynamic mechanical and thermal behavior of these seven segmented polyurethanes. 

MBOCA is an aromatic diamine that is used as a curing agent for polyurethane and epoxy resins. It has some of the general toxicity characteristics of aromatic amines. However, methemoglobinemia and the resulting cyanosis, hallmark symptoms of exposure to aromatic amines, are reported with much less frequency after exposure to MBOCA (Linch et al. 1971). 

The cured or fully imidized polyimide, unlike the poly(amic acid), is insoluble and infusible with high thermooxidative stability and good electrical-insulation properties. Thermoplastic polyimides that can be melt processed at high temperatures or cast in solution are now also available. Through an appropriate choice of the aromatic diamine, phenyl or alkyl pendant groups or main-chain aromatic polyether linkages can be introduced into the polymer. The resulting polyimides are soluble in relatively nonpolar solvents. 

Iij lijima, T., Suzuki, N., Fukuda, W., Tomoi, M. Toughening of aromatic diamine-cured epoxy resins by modification with hybrid modifiers composed of N-phenylmaleimide-styrene copolymers and N-phenylmaleimide-styrene-p-hydroxystyrene terpolymers. Polym. Intern. 38 (1995) 343-352. 

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