Quaternary salts having a double helix structure are prepared by the reaction of dihydroxyaromatic compound, preferably a bisphenol, with an alkali metal hydroxide and a quaternary salt, such as a tetraalkylammonium or hexaalkylguanidinium chloride. The quaternary salts and their alkaline hydrolysis products are useful as catalysts in various reactions, including imide formation from bisphenol salts and halo- or nitro-substituted phthalimides and redistribution and equilibration of polycarbonates.