This invention relates to the preparation of polyether polymers, and particularly polymers with very high molecular weight.
Various types of aromatic polyethers, particularly polyethersulfones, polyetherketones and polyetherimides, have become important as engineering resins by reason of their excellent properties. These polymers are typically prepared by the reaction of salts of dihydroxyaromatic compounds, such as bisphenol A disodium salt, with dihaloaromatic molecules such as bis(4-fluorophenyl) sulfone, bis(4-chlorophenyl) sulfone, the analogous ketones and halo- or nitro-substituted bis(phthalimides).
In particular, U.S. Pat. No. 5,229,482 describes a method for preparing polyether polymers by reactions conducted in substantially non-polar solvents such as o-dichlorobenzene, dichlorotoluene, 1,2,4-trichlorobenzene and diphenyl sulfone. Said reaction is conducted at a temperature in the range of about 125.degree.-250.degree. C. in the presence of a phase transfer catalyst which is stable at such temperatures. Various hexaalkylguanidinium salts are disclosed as being particularly useful as phase transfer catalysts under these conditions.
To maximize yield and molecular weight of the polyether polymer, it is important that the bisphenol salt be anhydrous at the time of reaction. Anhydrous bisphenol salts are typically prepared in an aqueous medium by reaction of the bisphenol with a stoichiometric amount of sodium hydroxide, followed by removal of water by azeotropic distillation in the presence of a suitable organic solvent such as toluene, xylene or chlorobenzene.
Because it is difficult to maintain precisely stoichiometric conditions, the anhydrous salt frequently contains measurable proportions of unreacted sodium hydroxide or unconverted bisphenol. These impurities may have adverse affects. For example, unreacted sodium hydroxide can absorb carbon dioxide, as can aqueous solutions of bisphenol sodium salts upon storage in prolonged contact with air.
U.S. Pat. No. 4,546,207 discloses a method for separating a bisphenol salt from an aqueous solution, frequently in the form of its hydrate. According to said patent, the hydrate is capable of use in certain displacement reactions after removal of water.