Epoxy quaternary phosphonium

Smith 63> has recently reported a new mechanism for the initiation by quaternary phosphonium salts. This mechanism assumes interaction of the acidic hydrogen atom of the alkyl group of phosphonium salts with epoxy oxygen as a nucleophile ... 

Quaternary Phosphonium Compound Latent Accelerators for Anhydride-Cured Epoxy Resins... 

Most of the data reported here will be concerned with bisphenol A epoxy resin systems cured with the liquid anhydride, 1-methyltetrahydrophthalic anhydride (the Union Carbide commercial designation for this material is ZZLA-0334). However, these quaternary phosphonium compounds have also been shown to be effective with other anhydrides such as hexahydrophthalic anhydride (HHPA). 

Most of the evaluation studies were made using a 1 1 stoichiometric bisphenol A epoxy-anhydride formulation. The various quaternary phosphonium compounds were added at a 0.01 to 0.25Z level (based on the combined anhydride and epoxy resin weights). With the exception of MTPP-DMP, which showed partial insolubility in the resin formulation, excellent solubilities at ambient temperature were found. 

Electrical Data. The electrical properties of cured specimens of the epoxy resin, containing various quaternary phosphonium compounds, were obtained on 2 in. diameter discs (0.125 in. to 0.25 in. thick) using standard procedures (ASTM D150-65T). In these tests, the power factor (100 x tan 6) and dielectric constant (e ) data were usually measured at 150 C (and a frequency of 60 Hz) on resin samples which had been cured for 16 h at 135 C + 5 h at 150 C. 

Comparison with Other Latent Accelerators. To illustrate the effectiveness of these quaternary phosphonium salts as accelerators for anhydride cured epoxy resins, a comparison of MTOP-DMP and TBPA with other well-known accelerators is given in Table V. The data were obtained from work done in this laboratory using the same resin systems. To make the comparison valid, the concentration given for each of these materials has been converted from phr to moles/200 g resin . Thus, the comparison is made on a molecular concentration basis instead of weight. Gel times were... 

Table IV. Electrical Properties of Cured Epoxy-Anhydride Resins Containing Various Quaternary Phosphonium Compounds ...

The Initiation Mechanism with Phosphonium Compounds. Although further experimental data are needed to give a fuller understanding of the reaction mechanisms involved in the latent acceleration effect of these quaternary phosphonium compounds in epoxyanhydride resins, there is definite indication, at this stage, that the mechanism does not involve the decomposition of the phosphonium compound to the free phosphine species (16). The initiation mechanism probably involves the formation of hydrogen-bonded phosphonium-epoxy or phosphonium-anhydride complexes which rearrange on the application of heat to form activated species resulting in polymerization of the epoxy-anhydride components ( > ... 

Quaternary phosphonium compounds have been found to be extremely effective latent accelerators for anhydride-cured epoxy resins employed in electrical insulation applications. Used at very low concentrations (0.01 to 0.25% level) in these resins, they have been found to give very fast gel times at elevated temperatures combined with very good storage stability properties at room temperature. Results show that the quaternary phosphonium compounds having non-halide anions give the best compromise of gel reactivity, storage stability and electrical properties. Comparison with other types of latent accelerators reveal that the quaternary phosphonium compounds are among the most effective additives yet discovered for epoxy-anhydride resin systems. 

Quaternary phosphonium salts such as the tetraalkyl and alkyl-triphenylphosphonium halides have been used as fast catalysts for curing of phe-nolics, carboxylic acid-terminated polyesters, or anhydrides with epoxies (126). Used in powder coatings, they showed good latency and fast cure rates at moderate temperatures. 

Quaternary Arsonium and Stibonium Compounds. More recently, experimental work in this laboratory has revealed that quaternairy arsonium compounds (18) are extremely effective as latent accelerators for epoxy-anhydride resius. Surprisingly, it has also been found that quaternary stibonium compounds are very much less effective as accelerators than quaternary arsonium, phosphonium or ammonium compounds. In fact, the order of gelation reactivity of these compounds with epoxy-anhydride resins would appear to be as follows ... 

The cyclic diether, 1,3-dioxolane, is recommended by Ferro Corporation as a more benign solvent substitute for chlorinated organic solvents, such as methylene chloride, 1,2-dichloroethane, and 1,1,1-trichloroethane, and for ketones, such as methyl ethyl ketone (MEK). This ethylene glycol-based ether is a suitable solvent under neutral and basic conditions in several major-use areas. It is a powerful solvent for softening and dissolving polymers made from polar monomers, for example, polycarbonates, acrylates, cellulosics urethanes, phenoUcs, nitriles, urea-formaldehydes, and alkyds, as well as polyesters, vinyl epoxys, and halogen-containing polymers. As a reaction solvent it is added as a component to a special quaternary ammonium or phosphonium salt solution for preparation of a vesicular phenoxy resin. Other beneficial uses for the solvent dioxolane, include ... 

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