METHOD OF STABILIZATION OF DIHYDRIC PHENOLS
A method of producing a polycarbonate, the method comprising: polymerizing a dihydric phenol and a carbonate precursor in the presence of a stabilizer to provide a polycarbonate with a yellowness index of less than or equal to 10 measured in accordance with ASTM E313 test method on molded samples having a thickness of about 2.5 millimeters; wherein the stabilizer is selected from the group consisting of ascorbic acid, salts of ascorbic acid, esters of ascorbic acid and a mixture of two or more of the foregoing; wherein the dihydric phenol is represented by Formula (I): wherein R is a hydrogen atom or an aliphatic functionality having 1 to 6 carbon atoms; and n is an integer having a value of 1 to 4.
1 . A method of producing a polycarbonate, the method comprising:
polymerizing a dihydric phenol and a carbonate precursor in the presence of a stabilizer to provide a polycarbonate with a yellowness index of less than or equal to 10 measured in accordance with ASTM E313 test method on molded samples having a thickness of about 2.5 millimeters;
wherein the stabilizer is selected from the group consisting of ascorbic acid, salts of ascorbic acid, esters of ascorbic acid and a mixture of two or more of the foregoing; wherein the dihydric phenol is represented by Formula (I):
wherein R is a hydrogen atom or an aliphatic functionality having 1 to 6 carbon atoms; and n is an integer having a value of 1 to 4.
2 . The method of claim 1 , wherein the stabilizer is present in an amount of about 20 parts per million to about 500 parts per million, relative to an amount of the dihydric phenol.
3 . The method of claim 1 , wherein the dihydric phenol has less than or equal to about 10 parts per million of oxalic acid, relative to the amount of the dihydric phenol.
4 . The method of claim 1 , wherein the step of polymerizing the dihydric phenol in the presence of a stabilizer comprises:
mixing the dihydric phenol with a stabilizer to obtain a stabilized dihydric phenol; and polymerizing the stabilized dihydric phenol in the presence of a carbonate precursor and a catalyst.
5 . The method of claim 4 , wherein the mixing is effected at a temperature higher than the melting point of the dihydric phenol.
6 . The method of claim 4 , wherein the mixing is effected under atmospheric pressure or under a reduced pressure.
7 . The method of claim 1 , wherein the carbonate precursor comprises a carbonyl halide, a haloformate, a carbonate ester or an activated carbonate.
8 . The method of claim 1 , wherein the carbonate precursor comprises bis(methylsalicyl)carbonate.
9 . The method of claim 4 , wherein the catalyst comprises:
a. an alpha catalyst selected from the group consisting of alkali metal salts and alkaline earth metal salt; and
b. a beta catalyst selected from the group consisting of a quaternary ammonium compound and a quaternary phosphonium compound.
10 . A polycarbonate produced by the method of claim 1 .
11 . The method of claim 1 , wherein the dihydric phenol comprises methyl hydroquinone or hydroquinone.
12 . A method of producing a polycarbonate, the method comprising:
polymerizing a dihydric phenol and a carbonate precursor in the presence of a catalyst and a stabilizer to provide a polycarbonate with a yellowness index of less than or equal to 10 measured in accordance with ASTM E313 test method on molded samples having a thickness of about 2.5 millimeters;
wherein the stabilizer is selected from the group consisting of ascorbic acid, salts of ascorbic acid, esters of ascorbic acid and a mixture of two or more of the foregoing; wherein the dihydric phenol is represented by Formula (II):
wherein R is a hydrogen atom or a methyl group.
13 . The method of claim 12 , wherein the catalyst comprises:
a. an alpha catalyst selected from the group consisting of alkali metal salts and alkaline earth metal salt; and
b. a beta catalyst selected from the group consisting of a quaternary ammonium compound and a quaternary phosphonium compound.
14 . A method of producing a polycarbonate, the method comprising:
polymerizing a dihydric phenol and an activated carbonate in the presence of a catalyst and a stabilizer to provide a polycarbonate with a yellowness index of less than or equal to 10 measured in accordance with ASTM E313 test method on molded samples having a thickness of about 2.5 millimeters;
wherein the stabilizer is selected from the group consisting of ascorbic acid, salts of ascorbic acid, esters of ascorbic acid and a mixture of two or more of the foregoing; wherein the dihydric phenol is represented by Formula (II):
wherein R is a hydrogen atom or a methyl group.
15 . The method of claim 14 , wherein the activated carbonate comprises bis(methylsalicyl)carbonate.
16 . The method of claim 14 , wherein the catalyst comprises:
a. an alpha catalyst selected from the group consisting of alkali metal salts and alkaline earth metal salt; and
b. a beta catalyst selected from the group consisting of a quaternary ammonium compound and a quaternary phosphonium compound.