Process for the preparation of thermoplastic aromatic polyphosphonates with improved thermal ageing resistance

Claim 1

A process for the preparation of a linear or branched-chain thermoplastic aromatic polyphosphonate having an average molecular weight number average M n in the range of from 11,000 to 200,000, which comprises solvent-free ester interchange of 97 to 100 mol of at least one diaryl phosphonate with 90 to 99 mol of at least one aromatic dihydroxy compound to obtain linear polyphosphonate, or the interchange of said diaryl phosphonate with said aromatic dihydroxy compound in the presence of from 0.01 to 3 mol %, based on 100 mol % of the diaryl phosphonate, of a triaryl phosphate or in the presence of from 0.01 to 3 mol %, based on 100 mol % of the aromatic dihydroxy compound, of an aromatic trihydroxy or tetrahydroxy compound or a mixture thereof to obtain branched polyphosphonate, provided, that the sum of branching triaryl phosphates and branching aromatic trihydroxy or tetrahydroxy compounds is not more than a total of 3 mol %, said interchange being conducted at 90°-340° C. in an oxygen-free gas atmosphere at atmospheric pressure or reduced pressure, with removal of the volatile constituents by distillation, and in the presence of a catalytic quantity of an ester interchange catalyst which comprises at least one compound taken from the group of C 1 -C 18 tetraalkyl titanates, C 2 -C 4 dialkyl tin oxides, C 2 -C 4 -dialkyl-C 1 -C 4 -dialkoxy tin compounds, C 3 -C 18 tetraalkyl zirconates and C 2 -C 18 trialkyl vanadylates, antimony or bismuth salts, C 2 -C 4 dialkyl stannic acid esters, C 2 -C 4 trialkyl stannic acid esters, or a mixture of at least one compound from the above groups and germanium dioxide and titanium dioxide.