Branched melt polycarbonate with low content of defective structures

1. An aromatic branched polycarbonate, produced via melt transesterification of a bisphenol with a diaryl carbonate in the presence of a branching agent, wherein the aromatic branched polycarbonate comprises branching point structures and structures of formula (D)

wherein X is a single bond, C1- to C6-alkylene, C2- to C5-alkylidene or C5- to C6-cycloalkylidene, optionally substituted by C1- to C6-alkyl;

wherein the amount of D in the aromatic branched polycarbonate is in the range of from 5 to 450 mg per kg of the aromatic branched polycarbonate; and

wherein the ratio of the total branching point structures to the total structures of the formula D in the aromatic branched polycarbonate is in the range of from 8 to 200.

2. A composition comprising at least one polycarbonate according to claim 1 and at least one organic phosphorus compound selected from the group consisting of phosphines, phosphites, diphosphites, phosphates and mixtures thereof.

3. The composition according to claim 2 , wherein the at least one organic phosphorus compound is a phosphite and is tris(2,4-tert-butylphenyl) phosphite.

4. The composition according to claim 2 , wherein the composition further comprises an aliphatic carboxylic ester of formula (III)

(R 4 —CO—O) o —R 5 —(OH) p   (III)

where o is an integer from 1 to 4, p is an integer from 0 to 3, R 4 is an aliphatic, saturated or unsaturated, linear, cyclic or branched alkyl moiety, and R 5 is an alkylene moiety of a mono- to tetravalent aliphatic alcohol of the formula R 5 —(OH) o+p .

5. The composition according to claim 2 , wherein the composition further comprises a UV absorber selected from the group consisting of benzotriazoles, triazines, cyanoacrylates and malonic esters.

6. The composition according to claim 2 , wherein the at least one organic phosphorus compound is a phosphine and the phosphine has the following structure:

wherein Ar 1 and Ar 2 are, independently of one another, optionally substituted aryl moieties; and

R′ is an optionally substituted aryl moiety or at least one moiety selected from the group consisting of

wherein R represents an unsubstituted or substituted C 6 -C 14 -aryl moiety; and

n and m are independently of one another, an integer from 1 to 7,

wherein the H atoms of the moieties (Ia) to (Ic) can also be replaced by substituents; and

wherein R′ can also be 4-phenylphenyl or α-naphthyl, if Ar 1 and Ar 2 in formula (I) are respectively likewise 4-phenylphenyl or α-naphthyl and wherein the 4-phenylphenyl moieties and the α-naphthyl moieties can have substitution.

7. The composition according to claim 6 , wherein the phosphine is triphenylphosphine.

8. The composition according to claim 2 , wherein the composition further comprises an aromatic antioxidant.

9. The composition according to claim 8 , wherein the aromatic antioxidant is n-octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

10. A process for producing polycarbonates according to claim 1 , wherein said process comprises reacting a bisphenol with a diaryl carbonate in the presence of a branching agent in a melt transesterification process; and purifying the branching agents prior to using the branching agents in the melt transesterification process.

11. The process according to claim 10 , further comprising pretreating the branching agents with a cation exchanger in solution before using the branching agents in the melt transesterification process.

12. The process according to claim 10 , wherein the branching agent is 1,1,1-tris(4-hydroxyphenyl)ethane (THPE).

13. The process according to claim 10 wherein the melt transesterification process further comprises a catalyst of formula (VII)

wherein

R 9 , R 10 , R 11 and R 12 represent, independently of one another, a compound selected from the group consisting of C 1 - to C 18 -alkylene moieties, C 6 to C 10 -aryl moieties, and C 5 to C 6 -cycloalkyl moieties; and

X − represents an anion, wherein the corresponding acid-base pair H + +X − →HX has a pK b of less than 11.