TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: A bisphenol is dissolved in an aqueous sodium hydroxide or potassium hydroxide solution to which a phase transfer agent and an acid chloride previously dissolved in organic phase are added under vigorous stirring for 0-4 hours, to form a polymer. The polymer is precipitated in a suitable non-solvent and the precipitated polymer is dried in an oven at 40-80degreesC. The polymer is purified by dissolving it in a solvent, reprecipitating the polymer in suitable non-solvent and drying it in oven at 40-80degreesC, to obtain polyarylate having intrinsic viscosity of 0.3-1 dL/g in sym-tetrachloroethane. The tetra-substituted aromatic diol is prepared by dissolving aromatic diol in aqueous alkali metal hydroxide like sodium or potassium hydroxide.Preferred Composition: The tetra-substituted aromatic diol is bisphenol of formula (I).FORMULA I, COLUMN 13R1, R2 = 1-10C alkyl, CF3, phenyl, group of formulae A, B or their mixtures; andR3, R4 = 1-5C alkyl, phenyl, fluorine, chlorine, bromine and/or iodine.SECOND AND THIRD FORMULAE, COLUMN 13 (CALLED FORMULAE (A,B))The bisphenol is preferably tetramethyl bisphenol-A, tetrachlorobisphenol-A, dimethylbisphenol-A, tetramethylhexafluorobisphenol-A, hexafluorobisphenol-A, tetrachlorohexafluorobisphenol-A, phenolphthalein, o-cresolphthalein, 4,4'-(9-fluorenylidene) bis(2,6-dimethylphenol), tetramethylphenolphthalein, tetrabromobisphenol-A, tetrabromohexafluorobisphenol-A, 4,4'-(9-fluorenylidene)bis(2,6-dibromophenol), 4,4'-(9-fluorenylidene)diphenol, 4,4'-(9-fluorenylidene di-o-cresol, bis(2-bromo-6-methylphenol), tetrabromophenolphthalein, dibromodimethylbisphenol-A, dibromodimethylhexafluorobisphenol-A, 4,4'-(9-fluorenylidene)bis(2-bromo-6-methylphenol), dibromodimethylphenolphthalein, other tetra-substituted dihydric phenols or tetra-substituted bisphenols. The phase transfer agent or non-solvent is chosen from ether quaternary ammonium salt, tetrabutyl ammonium bromide and benzyltriethyl ammonium chloride . The solvent is chloroform, methylene chloride, dioxane, tetrahydrofuran, nitrobenzene, tetrachloromethane, toluene, dimethyl formamide or dimethyl acetamide.Preferred Conditions: The polymerization is carried out at 40-80degreesC with stirring of reaction mixture at 0-5000 rpm. SPECIFIC COMPOUNDS - 20 numbers of dicarboxylic acid are claimed such as bromoisophthalic acid, tetrachloroterephthalic acid and difluoroterephthalic acid.    EXAMPLE - (In grams) Methylene chloride (15 ml), o-cresolphthalein (1.73) (o-Cp) and triethylamine (1.11), were added to flask (50 ml) equipped with nitrogen gas inlet, and stirred for 10 minutes. Nitroterephthaloyl dichloride (1.302) was dissolved separately in methylene chloride (5 ml) and the obtained solution was added dropwise to the flask with stirring for 30 minutes. Stirring was continued for 3 hours after addition was completed. The polymer was then precipitated by pouring the reaction mixture in excess of methanol, filtered under suction and dried in an oven at 50degreesC. The polymer was further purified by dissolving in chloroform, filtering the solution and reprecipitating in excess of methanol. The polymer was filtered under suction and dried in vacuum at 50degreesC to obtain pure polymer (2.58) (97% yield) having intrinsic viscosity of 0.67 dL/g in sym-tetrachloroethane at 35degreesC. The obtained polymer (0.5) was dissolved in chloroform (15 ml) with stirring, and formed solution was filtered and poured into flat-bottomed petri dish floating on mercury. The petri dish was loosely covered with aluminum foil. The solvent was evaporated for 24 hours in dry atmosphere and at 35degreesC. The formed film was peeled off and kept in vacuum oven at 50-60degreesC for 8-10 days in order to evaporate residual solvent. The obtained film (membrane) of 40-70 micron thickness was mounted in a cell and the gas permeation rates for helium, argon, nitrogen, oxygen, methane, carbon dioxide and hydrogen were measured at 35degreesC and 150 psi/ambient pressure, and found to be 8.2, 0.09, 0.05, 0.25, 0.02, 1.13 and 5.5, respectively. The film selectivity for helium/nitrogen, helium/methane, hydrogen/methane, oxygen/nitrogen and carbon dioxide/methane were measured and found to be 165, 410, 275, 5 and 59, respectively.