Process for the production of polycarbonate

Details Process for the production of polycarbonate Process for the production of polycarbonate

2001-09-07

2003-02-25

Boykin, Terressa M. (Department: 1711)

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

Synthetic resins

From phenol, phenol ether, or inorganic phenolate

C528S198000

Reexamination Certificate

active

06525163

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for the production of polycarbonate and to the use of carbonate and ester derivatives of phenyl and benzyl salicylates, 2-hydroxybenzophenone, and benzyl 2-hydroxyphenyl ketone as end-capping agents for polycarbonate.
BACKGROUND OF THE INVENTION
Polycarbonate is excellent in mechanical properties such as impact resistance and is also excellent in heat resistance and transparency, and it is widely used in many engineering applications. It is known that a high level of end-caps, i.e., wherein most of the terminal phenolic hydroxyl groups in the polycarbonate are terminated, helps to reduce static charging, improve heat aging, and lower water absorption of polycarbonate resins. Consequently, various coupling agents and end-capping agents have been tried to enhance the end-cap levels in the production of polycarbonate.
Unexamined Japanese Patent Application H6-157739 discloses the use of certain non-activated carbonates and esters, particularly diphenyl carbonate as the most preferred, as end-capping agents.
JP-A 7-90074 discloses a method of producing a polycarbonate from a dihydric compound and a carbonic acid diester by an ester exchange method, in which a highly active diester, acid halide or acid anhydride with at least two functional groups is added after the ester exchange ratio exceeds 70% to obtain a polycarbonate having an enhanced polymerization degree. It should be noted that JP-A 7-90074 teaches the use of di-activated molecules as coupling agents or polymerization promoters, and not end-capping agents.
U.S. Pat. No. 5,696,222 and EP 0 985 696 A1 disclose a method of producing a polycarbonate having a high-end cap levels by the addition of certain activated and di-activated carbonates as end-capping agents. It is disclosed that the end-capping agents are added to the process after the polycarbonate formed having an intrinsic viscosity of at least 0.3 dl/g, to form a polycarbonate with increased end-cap levels with minimal changes in molecular weight or intrinsic viscosity, i.e., having an intrinsic viscosity that is greater or smaller than the viscosity of the polycarbonate formed before the addition of the end-capping agents by at most 0.1 dl/g. It is also disclosed that these end-capping agents are activated by a phenolic group having an ortho chlorine atom, methoxycarbonyl or ethoxycarbonyl group, with 2-methoxycarbonylphenyl-phenylcarbonate and 2-methoxycarbonylphenyl-4′-cumylphenylcarbonate being preferred. The use of chlorinated phenols results in the production of potentially toxic byproducts or ones that produce gaseous products containing chlorine upon combustion. Thus, from handling and environmental considerations, there is a demand for the use of end-capping agents that are free from chlorine groups. These end-capping agents also yield volatile byproducts having melting points considerably lower than that of the usual byproduct of the polycarbonate melt transesterfication reaction (phenol), and thus they require special low temperature coolant liquids and complicated and energy consuming apparatuses consisting of low temperature condensation vessels and distillation units for effective removal of these byproducts from the molten polycarbonate and accurate and controlled vacuum level in the batch or continuous reaction system used to prepare the polycarbonate by the melt transesterfication method.
EP 0 980 861 A1 discloses the use of certain salicylic acid ester derivatives as an end-capping agent in amounts of 0.1 to 10 times, and most preferably 0.5 to 2 times, mole per mole equivalent of terminal hydroxyl groups of the polycarbonate formed at a time of the addition, for the production of a polycarbonate having good color tone suitable for optical material use. It is disclosed that these end-capping agents are activated by a phenolic group having an ortho methoxycarbonyl or ethoxycarbonyl group. It should be noted that the examples in EP 0 980 861 A1 teach the use of 2-methoxycarbonylphenyl-phenylcarbonate as an end-capping agent in an amount that is about 1 mole per mole equivalent of terminal hydroxyl groups to form a polycarbonate with increased end-cap levels.
There is still a need for an improved melt process using easy to handle end-capping agents that yield volatile byproducts having melting points similar to that of phenol to produce polycarbonate having capped terminals and controlled molecular weight build-up.
SUMMARY OF THE INVENTION
The invention relates to a process for the production of polycarbonate, the process comprising adding to a polycarbonate with free terminal hydroxy groups an end-capping agent of the formula:
wherein R
1
is a phenyl, phenoxy, benzyl, or benzyloxy and R
2
is selected from the group consisting of C
1
-C
30
alkyl, C
1
-C
30
alkoxy, C
6
-C
30
aryl, C
7
-C
30
aralkyl, and C
6
-C
30
aryloxy.
Specific examples of suitable R1 groups include but are not limited to phenoxy and benzyloxy. Specific examples of suitable R2 groups include but are not limited to stearyl, phenyl, para-t-butyl-phenyl, phenoxy, para-tert-butylphenoxy, para-octylphenoxy, para-nonylphenoxy, para-dodecylphenoxy, 3-pentadecylphenoxy, para-octadecylphenoxy, para-cumylphenoxy, or mixtures thereof. R
2
aryl, aralkyl, and aryloxy groups may also be substituted with a member selected from the group consisting of a C
1
-C
24
alkyl, C
1
-C
24
alkoxy, phenylcarbonyl, phenoxycarbonyl, benzylcarbonyl, benzyloxycarbonyl, 2-(phenylcarbonyl)phenyloxycarbonyl, 2-(phenoxycarbonyl)phenyloxycarbonyl, 2-(benzylcarbonyl)phenyloxycarbonyl, 2-(benzyloxycarbonyl)phenyloxycarbonyl, 2-(phenylcarbonyl)phenyloxycarbonyloxy, 2-(phenoxycarbonyl)phenyloxycarbonyloxy, 2-(benzylcarbonyl)phenyloxycarbonyloxy, and 2-(benzyloxycarbonyl)phenyloxycarbonyloxy groups.
DETAILED DESCRIPTION OF THE INVENTION
Applicants have surprisingly found in the process of the present invention that, by adding a relatively small amount of the low melting end-capping agents of the invention, the end-capping agent rapidly caps or blocks the terminal OH groups of the melt polycarbonate.
End-capping Agent/MW Builder
In the process of the present invention, a compound of the following formula is added to a polycarbonate oligomer as an end-capping agent and to control the molecular weight of the polycarbonate oligomer:
wherein R
1
is a phenyl, phenoxy, benzyl, or benzyloxy and R
2
is selected from the group consisting of C
1
-C
30
alkyl, C
1
-C
30
alkoxy, C
6
-C
30
aryl, C
7
-C
30
aralkyl, and C
6
-C
30
aryloxy. Specific examples of suitable R
1
groups include but are not limited to phenoxy and benzyloxy. Specific examples of suitable R
2
groups include but are not limited to stearyl, phenyl, para-t-butyl-phenyl, phenoxy, para-tert-butylphenoxy, para-octylphenoxy, para-nonylphenoxy, para-dodecylphenoxy, 3-pentadecylphenoxy, para-octadecylphenoxy, para-cumylphenoxy, or mixtures thereof. R
2
aryl, aralkyl, and aryloxy groups may be substituted with a member selected from the group consisting of a C
1
-C
24
alkyl, C
1
-C
24
alkoxy, phenylcarbonyl, phenoxycarbonyl, benzylcarbonyl, benzyloxycarbonyl, 2-(phenylcarbonyl)phenyloxycarbonyl, 2-(phenoxycarbonyl)phenyloxycarbonyl, 2-(benzylcarbonyl)phenyloxycarbonyl, 2-(benzyloxycarbonyl)phenyloxycarbonyl, 2-(phenylcarbonyl)phenyloxycarbonyloxy, 2-(phenoxycarbonyl)phenyloxycarbonyloxy, 2-(benzylcarbonyl)phenyloxycarbonyloxy, and 2-(benzyloxycarbonyl)phenyloxycarbonyloxy group.
The end-capping agent used in the method of the invention may be based on derivatives of phenyl salicylate, benzyl salicylate, 2-hydroxybenzophenone, or benzyl 2-hydroxyphenyl ketone that yield by-products having melting points above 20° C. Thus, for example, phenylsalicyl phenyl carbonate, benzylsalicyl phenyl carbonate, or 2-benzoylphenyl phenyl carbonate may be used, to yield ortho-substituted by products namely benzyl salicylate or phenyl salicylate (melting points (mp) of 24 and 44-46°, respectively) or 2-hydroxybenzophenone (mp=37-39° C.).
Preparation of the End-capping Agent
The end-capping a

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