Method for producing polycarbonate

Details Method for producing polycarbonate Method for producing polycarbonate

1999-12-28

2001-07-17

Buttner, David (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From phenol, phenol ether, or inorganic phenolate

Reexamination Certificate

active

06262219

ABSTRACT:

The present invention relates to the production of thermoplastic polycarbonates, by the known transesterification method in the melt, from diphenols, carboxylic acid diaryl esters and optionally branching agents and/or monophenols, at temperatures between 80 and 400° C. and at pressures between 1000 mbar and 0.01 mbar, with the use in conjunction with catalysts, which is characterised in that N-alkyl-substituted piperidines or N-alkyl-substituted morpholines comprising C
2
-C
12
N-alkyl substituents, preferably C
2
-C
8
N-alkyl substituents, and particularly C
2
-C
5
N-alkyl substituents, are used as catalysts in amounts of 10
−2
to 10
−8
moles, preferably of 10
−2
to 10
−5
moles, per mole diphenol.
The preferred N-alkylpiperidines are N-ethylpiperidine, N-propylpiperidine and N-isopropylpiperidine. The preferred N-alkylmorpholines are N-ethylmorpholine, N-propylmorpholine and N-isopropylmorpholine.
These may be used on their own or in combination, together or in succession.
The melt transesterification method using N-containing catalysts is known from U.S. Pat. No. 5,434,227, wherein piperidine and N-methylmorpholine are cited (column 12, line 44).
Polycarbonates produced in this manner (comparative examples 1 and 2) are less thermally resistant and exhibit yellowing phenomena.
In contrast, the polycarbonates which are obtainable by the process according to the invention are distinguished by their light inherent colour and by high light transmission, even after long-term thermal loading. Moreover, they are substantially free from unwanted defects in the polycarbonate itself, and are naturally solvent-free.
In the sense of the process according to the present invention, the term “substantially free from unwanted defects in the polycarbonate” means that the content of branching agents of formula (I)
wherein
X=a C
1
-C
8
alkylidene or cycloalkylidene, S or a single bond,
R=CH
3
,Cl, or Br, and
n=0,1 or 2,
in the polycarbonate has a value after complete saponification and determination by HPLC of not more than 300 ppm, preferably not more than 100 ppm.
Diphenols which are suitable for the production of the copolycarbonates used according to the invention are those of general formula (II)
wherein
X, R and n have the same meaning as in formula (I).
Suitable diphenols are described, for example, in U.S. Pat. Nos. 3,028,365, 2,999,835, 3,062,781, 3,148,172 and 4,982,014, in DE-OS 1 570 703 and 2 063 050, and in the monograph by H. Schnell, “Chemistry and Physics of Polycarbonates”, Interscience Publishers, New York, 1964.
Preferred diphenols include
4,4′-dihydroxyphenyl,
2,2-bis-(4-hydroxyphenyl)-propane,
2,4-bis-(4-hydroxyphenyl)-2-methylbutane,
1,1 -bis-(4-hydroxyphenyl)-cyclohexane,
2,2-bis-(3-methyl-4-hydroxyphenyl)-propane,
2,2-bis-(3-chloro-4-hydroxyphenyl)-propane,
bis-(3,5-dimethyl-4-hydroxyphenyl)-methane,
2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane,
2,4-bis-(3 ,5-dimethyl-4-hydroxyphenyl)-2-methylbutane,
1,1-bis-(3,5-dimethyl-4-hydroxyphenyl)-cyclohexane,
1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane,
1,1 -bis-(4-hydroxyphenyl )-3-methylcyclohexane,
1,1 -bis-(4-hydroxyphenyl)-3,3-dimethylcyclohexane,
1,1 -bis-(4-hydroxyphenyl)-4-methylcyclohexane,
2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane, and
2,2-bis-(3,5-dibromo-4-hydroxyphenyl)-propane.
Examples of particularly preferred diphenols include:
2,2-bis-(4-hydroxyphenyl)-propane,
2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane,
1,1 -bis-(4-hydroxyphenyl)-cyclohexane,
1,1 -bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane,
1,1 -bis-(4-hydroxyphenyl)-3-methylcyclohexane.
2,2-bis-(4-hydroxyphenyl)-propane and 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethyl-cyclohexane are particularly preferred.
Any mixtures of the aforementioned diphenols can also be used.
The polycarbonates can be deliberately branched in a controlled manner by the use of small amounts of branching agents. Some suitable branching agents are: phloroglucin,
4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-heptene-2,
4,6-dimethyl-2,4,5-tri-(4-hydroxyphenyl)-heptane,
1,3,5-tri-(4-hydroxyphenyl)-benzene,
1,1,1-tri-(4-hydroxyphenyl)-ethane,
tri-(4-hydroxyphenyl)-phenylmethane,
2,2-bis[4,4-bis-(4-hydroxyphenyl)-cyclohexyl-propane,
2,4-bis-(4-hydroxyphenyl-isopropyl)-phenol,
2,6-bis-(2-hydroxy-5′-methyl-benzyl)-4-methylphenol,
2-(4-hydroxyphenyl)-2-(2,4-dihydroxypbenyl)-propane,
hexa-(4-(4-hydroxyphenyl-isopropyl)-phenyl)-ortho-terephthalic acid ester,
tetra-(4-hydroxyphenyl)-methane,
tetra-(4-(4-hydroxyphenyl-isopropyl)phenoxy)-methane,
1,4-bis-((4′,4″-dihydroxytriphenyl)-methyl)-benzene, and particularly
&agr;,&agr;′,&agr;″-tris-(4-hydroxyphenyl)-1,3,5-triisopropylbenzene.
Other possible branching agents are:
2,-4-dihydroxybenzoic acid,
trimesic acid,
trimesic acid trichloride,
cyanuric chloride, and
3,3 -bis-(3 -methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole.
The 0.05 to 2 mole %, with respect to the diphenols used, of branching agents which are optionally used in conjunction can be used together with the diphenols.
Carboxylic acid esters in the sense of the present invention are di-C
6
-C
12
aryl esters, preferably the diesters of phenol or alkyl-substituted phenols, namely diphenyl carbonate or dicresyl carbonate for example. The carboxylic acid diesters are used in an amount of 1.01 to 1.30 moles, preferably 1.02 to 1.15 moles, with respect to 1 mole of bisphenol.
It should be ensured that the reaction components, namely the diphenols and the carboxylic acid diaryl esters, are as free as possible from alkali metal and alkaline earth metal ions. Pure carboxylic acid diaryl esters or diphenols of this type can be obtained by recrystallising, washing or distilling the carboxylic acid diaryl esters or diphenols. In the process according to the invention, the content of alkali metal and alkaline earth metal ions, both in the diphenol and in the carboxylic acid diaryl ester, should have a value of <0.01 ppm.
The production of the polycarbonate can be carried out in one step. The aromatic dihydroxy compounds and the carboxylic acid diesters are then reacted under the usual condensation polymerisation conditions known from the literature.
For example, these conditions comprise the melting of the aromatic dihydroxy compound and of the carboxylic acid diester at temperatures of 80° C. to 250° C., preferably 100 to 230° C., most preferably 120 to 190° C., under normal pressure, within 0.1 to 5 hours, preferably 0.25 to 3 hours. The catalysts according to the invention or combinations of the catalysts according to the invention can be added before melting or to the molten starting materials. An oligocarbonate is then produced from the aromatic dihydroxy compound and the carboxylic acid diester by distilling off the monophenol, by applying a vacuum and increasing the temperature. Following this, the polycarbonate is produced during the condensation polymerisation step by further increasing the temperature to 240 to 400° C. and by reducing the pressure to 0.01 mbar.
It may also be advantageous, however, to conduct the condensation polymerisation in two or more steps.
The oligocarbonates produced as the intermediate step in the course of this procedure have average molecular weights M
w
of 3000 to 24,000, preferably from 5000 to 20,000, as determined by measuring the relative solution viscosity in dichloromethane or in mixtures of equal amounts by weight of phenol/o-dichlorobenzene, which are calibrated by light scattering. The temperature for the production of these oligocarbonates is between 100 and 290° C., preferably between 150 and 280° C. The monophenols formed during the transesterification to produce the oligocarbonate are removed by applying a vacuum of 1 bar to 0.5 mbar, preferably <500 mbar to 1 mbar.
The polycarbonate is produced by condensation polymerisation of the oligocarbonate, optionally with a further addition of the catalysts according to the invention to the oligocarbonate, by further increasing the temperature to 230 to 400° C., preferably to 250 to 320

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