Polycarbonate membranes and production thereof

Claim 1

A process for producing a polyether-polycarbonate block copolymer having a molecular weight within the range of from about 50,000 to about 750,000 as determined by the intrinsic viscosity measurement and containing from about 5 to about 35 percent by weight of repeating alkylene ether units and correspondingly from about 95 to about 65 percent by weight of repeating bisphenol A-carbonate units for use in forming membranes comprising: dissolving a polyether glycol compound, bisphenol A, and pyridine in a solvent to give a total solids content of about 5 percent to about 16 percent, by weight, reacting the dissolved bisphenol A, polyether glycol compound, and pyridine with phosgene by adding phosgene, at an initial feed rate, to said solution with vigorous stirring while maintaining the solution in the temperature range of about 20° C. to about 43° C. until crystals of pyridine hydrochloride begin to form; thereafter adding a chain terminator to the reacted solution and reducing the phosgene feed rate to about one-fiftieth of initial phosgene rate until the reaction solution undergoes a permanent color change, thereafter precipitating said polyether-polycarbonate block copolymer by mixing the reaction solution with an acidified liquid chosen from the group consisting of isopropyl alcohol, hexane and a 80:20 by volume mixture of acetone and water, and separating the precipitated polymer from the liquid.