FREMGANGSMADE TIL RENSNING AF POLYCARBONATER

1479389 Purifying polycarbonates SOC NATIONALE DES POUDRES ET EXPLOSIFS 18 Nov 1975 [11 Dec 1974] 47471/75 Heading C3R Oligocarbonates (O) which have been formed by transesterification between a diol and a diphenyl carbonate are purified by: (1) introducing liquid water into liquid (O) which is at elevated temperature (T) and under reduced pressure (P); and (2) flushing the liquid mixture with an inert gas, while maintaining the temperature and further reducing the pressure to effect degassing. (T) may be 150-200‹ C., and (P) may be # 250 mmHg. The water may contain, e.g. HCl, H 3 PO 4 , or H 2 SO 4 , e.g. in amount slightly greater than that required to neutralize the transesterification catalyst. The water may be introduced continuously and may be dissolved-oxygen-free distilled water. The purification is performed to remove the byproduct phenol, in both the free form and bonded as alkyl phenyl ether or alkyl phenyl carbonate. The water vaporizes immediately, entraining the byproducts.