| abstract |
Halogenated aromatic polycarbonate for making halogen-free aromatic polycarbonates flame resistant is produced from 50-100 mole % bisphenol of formula I: (where R is Cl or Br; andX is alkylene, alkylidene, cycloalkylene, cycloalkylidene, O.S. SO2, SO, CO, or a gp. of formula (II) e.g. tetrahomobisphenol A, by (a) reacting a basic aqs. soln. of (I) with phosgene at pH 7-9 in the presence of 2-20 mole % t-amine catalyst, pref. triethylamine, to give oligocarbonates having an end group ratio chlorocarbonic esters: OH>1.1; and (b) polycondensing at pH >13, and an OH concn. of 0.20-0.40 wt. %, based on aqs. phase, opt. with addn. of 2-20 mole % fresh t-amine catalyst. |