Catalytically curing compounds

Catalytic-curing agents (Lewis bases and Lewis acids). Both Lewis bases and Lewis acids in catalytic quantities (2-4 phr) cure epoxy resins rapidly without requiring heat. Lewis bases are compounds that have a free pair of electrons such as tertiary amines while Lewis acids are compounds that can accept a pair of electrons suchasboron trifluoride. Lewis acids such as boron trifluoride are so reactive that, in addition to their being highly... 

Catalytic curing agents are a group of compounds which promote epoxy to epoxy reactions without being consumed in the process. A typical epoxy homopolymerization using a tertiary amine is shown below ... 

The catalytic effect has been explained in terms of the activation of the anhydride by interaction with the amine to give a zwitterionic intermediate (47 Scheme 10) (B-68MI11501). Imidazoles have also been suggested as accelerators for anhydride cures (68USP3394105). A review of the patent literature (B-77MI11502) shows that several heterocyclic compounds are of interest as curatives for epoxy resins. 

An identical mathematical description of the kinetics of curing of reactants different in chemical nature and that obtained on the basis of fundamentally different experimental methods allows us to assume that this apparent selfacceleration course of some rheokinetic parameters is common to the processes of formation of materials with a crosslinked structure. It should be emphasized once more that the self-acceleration" effect must not be identified with the self-catalysis of the reaction of interaction between epoxy monomers and diamines which is studied in detail on model compounds [116, 117]. For each particular curing process the self-acceleration effect is influenced by the mechanism of network formatic, namely, chemical self catalysis [118], the appearance of local inhomogeneities [120], the manifestation of gel eff t [78], parallel course of catalytic and noncatalytic reactions [68]. It is probably true that the phenomena listed above may in one form or another show up in specific processes and make their contribution into self-acceleration of a curing reaction. 

On the other hand, there is a need to use inhibitors of the platinum catalysts temporarily to reduce their catalytic activity in the presence of hydro- and vinyl-polysiloxanes in order to stop the curing process at room temperature, but to allow the platinum catalyst to be activated at elevated temperature. Among the principal types of compounds reported are alkenyl derivatives, esters of unsaturated acids, crown ethers, organic nitrogen compounds, phosphines, linear and cyclic vinyl-siloxanes, and poly(vinyl)siloxanes [2], and recently fumarate [44] and maleinate [33]. New co-activators of the catalysts (precursors) have been revealed in the 1990s to reduce to ppm the levels of platinum required to effect hydrosilylation curing [45, 46]. 

The use of polystannoxane catalysts with improved cure performance over dibutyltin or other stan-noxane compounds has been claimed with a range of blocked isocyanates iron, zinc, zirconium, nickel, and bismuth salts are claimed as cocatalysts. The improved catalytic activity appears, to some extent, related to increased solubility of the polystannoxanes. 

Shibahara et al. [89] used CPMAS and solution-state NMR to study the cure of BMI resins catalyzed with triphenylphosphine. The chain extender in this case was diallylbisphenol-A. The presence of the allyl was shown to result in the formation of trimers of A-phenyl maleimide by solution-state NMR. The solid-state spectra of the resin cured at 393 K also showed evidence of the formation of trimers in the Zjw-maleimides. The diallyl compound did not appear to participate in the polymerization, and could be extracted with acetone after completion of reaction of the BMI. Nonetheless, the rate of reaction determined from the ratio of the peak in the CPMAS spectra at 175 ppm, due to reacted BMI with that at 170 ppm because of unreacted BMI, was increased in the presence of the diallyldiol. The catalytic effect of the hydroxy group on the dially compound was confirmed by studying the reaction of p-hydroxy-A-phenyl maleimide. 

In a typical formulation, an ethylene-n-butyl-acrylate-carbon monoxide (60/30/10) terpolymer (60 wt%) is melt compounded with plasticized PVC (40 wt%) in a twin-screw extruder and the ethylene terpolymer dispersion cured in situ during the mixing by catalytic amounts of a suitable peroxide (0.3%) and a bismaleimide crosslink promoter (0.2%). The extruded pellets of the elastomeric blend can be used in conventional melt fabrication processes such as profile extrusion, extrusion coating, milling and calendering of sheets, injection and/or compression molding. 

Both Lewis bases and Lewis acids in catalytic quantities (2-4 phr) cure epoxy resins rapidly without requiring heat. Lewis bases are compounds that have a free pair of... 

Hexamethylenetetramine (Hexamine) - te-tr9- inen [ISV hexa- + methylene + tetra-+ amine] (1888) (HMT, methenamine, and urotropine) n. (CH2)6-N4. A bicyclic compound, the reaction product of ammonia and formaldehyde. It is used as a basic catalyst and accelerator for phenolic and urea resins, and a solid, catalytic-type curing agent (hardener) for epoxies See image). 

The solid resins in powder paints are produced in two different ways. In the conventional method, the resin is produced in isobutyl methyl ketone. In the fusion method, bisphenol-A is condensed catalytically without solvents to give a liquid epoxy resin. In this study, the powders were cured in a device permitting precise control of temperature, type of atmosphere, rate of gas flow, and the collection of the volatile compounds. The compounds were studied with a high-resolution GC and a GC-MS. The mass loss of the powders during curing was studied by thermogravimetry. 

The polysulfide polymers react slowly with the epoxies when used alone. One to three parts of an active catalytic amine, or amine salt are used to accelerate cure. Triphenyl phosphite reduces viscosity and somewhat reduces the ultimate cost of a compound. Although reactive with the epoxy, it is not effective as a curing agent by itself. A polyfunctional amine is necessary to effect a satisfactory cure. 

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