Heat Cure Cationic Catalysts

As discussed earlier, the use of unmodified Lewis acid catalysts as epoxy curatives has been restricted due to the extremely rapid rate of cure of such systems, and the poor physical properties of the cured resins. Lewis acids are frequently modified by the formation of heat-activatable complexes with amines or glycols. Such complexes display moderate room temperature 

In certain cases, the Lewis acidity of transition metal complexes, e.g., those of aluminum, is so low that they are relatively inactive toward epoxy resins, even at elevated temperatures. A series of patents issued to Toshiba Corp. describe the activation of organoaluminum compounds, such as jS-diketones (64), j8-ketoesters (65), and salicylate esters (66), by the addition of organosilane compounds with hydrolyzable groups as epoxy curatives. Excellent room temperature latency with rapid heat cures are claimed. 

Cationic iodonium and sulfonium salts of strong acids are well known as UV-activatable strong acid sources, but they have also found use as heat-activatable acid sources in epoxy resins. Diaryliodonium salts, such as diphenyliodonium tetrafluoroborate (67), have found use with activators, e.g., benzopinacol, in epoxy adhesive and coating formulations. Cure times of several minutes at 160 C were claimed, with good room temperature latency. In a series of patents issued to Asahi Denka Kogyo K.K., several strong acid salts of aliphatic sulfonium compounds have been described as catalysts in heat curing epoxy compositions (68). The counteranions 

Various phosphate salts have been described as useful heat cure catalysts for epoxy resins. Calcium glycerolphosphate salts (69) have been 

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Eor instance, exhaust appHcation is possible with cationic finishes which have an affinity for the anionic groups in polymeric materials. After appHcation, the textile is dried. Durable antistatic finishes require cross-linking of the resin. Cross-linking is usually achieved by subjecting the treated, dried material to heat curing. A catalyst is often incorporated to accelerate insolubilization. 

A number of curing agents and catalysts used in epoxies are complex metal salts that are added to cure at room temperature or with heat. Curing agents or catalysts such as cationic dinonato (acetylacetone, etc.) complexes of Si, B, Ge, and P behave as hydrolytic activated Bronsted acid precursors, e.g. ... 

Toxicology LD50 (subcut., mouse) 2500 mg/kg mod. toxic by subcut. route TSCA listed Precaution Combustible Hazardous Decomp. Prods. Heated to decomp., emits toxic vapors of NOx Uses Curing agent, catalyst for polyurethane foams intermediate for cationic surfactants Manuf./Distn b. Aldrich http //www.sigma-aldrich.com... 

The polysiloxanes are applied by padding followed by drying and heating for a few minutes at 120-150°C to cure the finish, or by exhaust procedures [70b]. Because most textile fabrics have a negative surface potential in water, cationic surfactants are used for emulsifying polysiloxanes for exhaust application. The padding or exhaust application should deposit about 1-2% polysiloxane onto the fabric the amount can be smaller in coapplication with a zirconium or titanium catalyst. ... 

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