Prodn. of polycarbonate with little branching by ester exchange in melt

摘要

Prodn. of polycarbonate (I) with little branching by ester exchange in the melt is carried out in two separate stages.Stage (1) comprises producing a catalyst-free oligocarbonate (II) by (1a) melting the reactants over up to 5 hr. at 80-180 deg C and atmos. pressure; (1b) adding 10-4 to 10-8 mole volatile N and/or phosphonium catalyst per mole diphenol; (1c) applying a vacuum (from atmos. pressure to 1 mbar) and heating (to up to 290 deg C) to remove monophenols by distn.; and (1d) isolating (II).Stage (2) comprises polycondensation to (1) at 240-320 deg C and pressure of under 500 mbar to 0.01 mbar in short times (less than 3 hr.) with addn. of 10-4 to 10-8 mole alkali(ne earth) metal salts per mole diphenol.