Quaternary phosphonium salts, epoxy

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 ... 

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... 

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. 

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 ... 

---