Alkoxide cure

Proposed alkoxide cure mechanism.silicon polymer cross-linking and bonding to surface. 

After the initial screening process, it was necessary to develop model systems for both the carboxylate and alkoxide cured systems on which further experimentation could be performed. For the purposes of our testing,... 

The RTV condensation ciue system consists of four types carboxylate cure, alk-oxide cure, oxime cure, and amine cure. For electronic applications, only the alkoxide cure system is preferred because the byproduct alcohol generated during cure is non-corrosive. 

The process known as transimidization has been employed to functionalize polyimide oligomers, which were subsequentiy used to produce polyimide—titania hybrids (59). This technique resulted in the successhil synthesis of transparent hybrids composed of 18, 37, and 54% titania. The effect of metal alkoxide quantity, as well as the oligomer molecular weight and cure temperature, were evaluated using differential scanning calorimetry (dsc), thermogravimetric analysis (tga) and saxs. 

On the other hand, the alkoxide system presented several problems in formulation. The system first chosen as a model consisted of a trimethoxymethyl silane crosslinker, 8000 centistoke HEB siloxane, and a catalyst. A number of catalysts were used and each exhibited different cure rates and electrical properties. DuPont tetraalkoxytitante-Tyzor appears to he one of the better catalysts used in this type of curing system. Fillers are usually incorporated into the silicone formulation to improve mechanical properties, promote adhesion, and to serve as light screening and pigment agents. Cab-o-sil, a form of fumed silica, carbon-black, titanium dioxide and calcium carbonate are then used as RTV fillers. 

Titanates are valuable in other paint applications. Corrosion-resistant coatings have been described for tinplate, steel, and aluminum (440—444). Incorporation of phosphoric acid or polyphosphates enhances the corrosion resistance. Because titanates promote hardening of epoxy resins, they are often used in epoxy-based paint (445). Silicones (polysiloxanes) are often cured by titanates. Pigments, eg, Ti02, Si02, Al O and Zr02, are frequently pretreated with titanates before incorporation into paints (441,446). In these applications, the Ti(OR)4 compounds are often mixed with Si(OR)4, Al(OR)3, Zr(OR)4, and other metal alkoxides (12). 

A Lewis base is a compound that contains an unshared pair of electrons capable of undergoing chemical reactions. Tertiary amines are examples of Lewis bases, and often are used in epoxy curing agents. In an anionic epoxy polymerization the propagating species is the alkoxide anion generated by the reaction of the Lewis base with an epoxy ring. 

The strong base catalyzed phenolic cured epoxy reaction proceeds via the phenoxide ion which reacts with epoxide, generating the alkoxide ion. The high basicity of the alkoxide ion reacts with phenolic to regenerate the phenoxide ion and the reaction repeats itself. 

USE Friedel-Crafts catalyst- Component of Ziegler-type catalysis in the condensation of ethylene. Starting material in the synthesis of a number of organic derivs of zirconium, such as alkoxides and zircocene. The alkoxides have been shown to be of value in the curing of silicone plastic films. The alkoxyzirconium carboxylates are said to be useful in the water-repellent treatment of textiles and other fibrous materials. Review Blumenthal, J. Chem. Ed. 39, 604-610 (1962). 

In a typical formulation of epoxy resin (Epon 825, Shell) cured with aluminum alkoxide, incorporation of 30% PPE increased the elongation at break from <2% to >17%. The heat distortion temperature increased from 160 to 195°C. The dissolution of PPE in epoxy formulation-raised its viscosity at 200°C from 0.2 to 4 Pas [Anonym., 1991]. 

Mechanistic studies of 33-curing of epoxies have been undertaken in the past and concluded that curing takes place initially at both N atoms, but propagation occurs from only one center (Eqs. 24-26). These early studies did not account for several apparent anomalies, however, such as ketone formation during polymerization, the initial molecular weight distribution, and the wide differences in the activity of different imidazole derivatives. A recent mechanistic study, however, has addressed these anomalies and shown that several reactions are indeed taking place at once. It has been shown that the imidazolium ions formed early in the polymerization of epoxides are susceptible to attack by alkoxide anions and Hofmann eliminations. The first reaction, Eq. (27), caused by the... 

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