of a salt occurring as a by product and the separation and purification of the polymer the method relying on the phase transfer reaction as hereinabove described is generally simpler and more advantageous the invention will now be described with reference to examples which are merely illustrative and do in no way limit the scope of this invention 125 millimols of sodium hydroxide were dissolved in 70 ml of water and 50 millimols of bisphenol s were added thereinto to form a homogeneous solution added further into the solution were 7 5 millimols of p xylylene dichloride 134 6 millimols of methylene bromide and 2 millimols of trioctylmethylammonium chloride the solution thus obtained was heated at 40 u00b0 c for one hour and after its temperature had been raised to 90 u00b0 c the reaction was continued at 90 u00b0 c for three hours whereby a solid polymer was precipitated the polymer was crushed washed with methanol and water and dried at a reduced pressure whereby it was purified it had a melting point of 227 u00b0 c to 230 u00b0 c if further purification is required it is possible to conduct reprecipitation by pouring a dimethylacetamide solution of the polymer into.