Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2001-12-19
2003-11-25
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
06653434
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the production of polycarbonate. More specifically, it relates to a process for the production of a polycarbonate whose polymerization degree is enhanced by the use of a polymerizing promoter.
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. In a method for producing a polycarbonate, an aromatic dihydroxy compound such as bisphenol and a diaryl carbonate such as diphenyl carbonate are reacted in ester exchange in a molten state (melt-polycodensation method). It is known to enhance the polymerization degree of the polycarbonate in a melt-polycondensation method by adding polymerization promoters to the reaction system. The increase molecular weight build-up results in increased polycarbonate output through less residence time in the reactor and a lower reactor temperature, consequently facilitating simpler and less expensive reactor design.
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 highly active carbonic acid diesters based on 4-nitrophenol, 4-cyanophenol and chlorinated phenols, e.g. bis(4-nitrophenyl) carbonate, bis(4-cyanophenyl) carbonate, and bis(4-chlorophenyl) carbonate. The use of these compounds results in the production of colored or potentially toxic or explosive byproducts or ones that produce gaseous products containing chlorine upon combustion. Thus from product quality (transparency), handling, and environmental considerations there is a demand for the use of polymerization promoters that are free from chlorine, cyano-, and nitroactivating groups.
U.S. Pat. No. 5,696,222 discloses a method of producing a polycarbonate having an enhanced polymerization degree by the addition of certain polymerization promoters, e.g., carbonates and dicarboxylic acid aryl esters including bis (2-methoxyphenyl) carbonate, bis(2-ethoxyphenyl) carbonate, bis(2-chlorophenyl) carbonate, bis(2-methoxyphenyl) terphthalate and bis(2-methoxyphenyl) adipate. It should be noted that U.S. Pat. No. 5,696,222 teaches the introduction of ester linkages when esters are used as a polymerization promoter, with the results being the production of polyester carbonate copolymers (instead of homopolymers) and less hydrolytic stability.
There is still a need for an improved process for the production of a polycarbonate having an enhanced polymerization degree.
SUMMARY OF THE INVENTION
The invention relates to a process for the production of polycarbonate, the process comprising adding a polymerization promoting compound of the formula (1):
wherein R
1
and R
3
may be the same or different and are selected from the group consisting of alkoxy, phenoxy, benzoxy, aryloxy, phenyl and aryl groups.
R
2
is selected from the group consisting of alkyl, phenyl, aryl, or aralkyl groups. The phenyl, aryl or aralkyl may be optionally substituted. The alkyl groups may be any one of linear, branched, and cyclic alkyl groups.
In one embodiment, the polymerization promoter is selected from the group prepared from salicylate esters and bis-chloroformates of bisphenols.
In one embodiment, the polymerization promoter is selected from the group consisting of BPA-bis-methyl salicyl carbonate, BPA-bis-n-propyl salicyl carbonate, BPA-bis-benzyl salicyl carbonate, and mixtures thereof.
In another embodiment of the invention a large proportion of, the polymerization promoter is added to the polycarbonate oligomer after the oligomer has reached a number-average molecular weight of about 2,500 to 15,000 Dalton.
DETAILED DESCRIPTION OF THE INVENTION
Polymerization Promoter/Coupling Agent
In the process of the present invention, the compound of the following formula (1) is added to a polycarbonate oligomer to build its molecular weight:
wherein R
1
and R
3
may be the same or different and are selected from the group consisting of alkoxy, phenoxy, benzoxy, aryloxy, phenyl and aryl groups. R
2
is selected from the group consisting of alkyl, phenyl, aryl, or aralkyl groups. The phenyl, aryl or aralkyl may be optionally substituted. The alkyl groups may be any one of linear, branched, and cyclic alkyl groups. In one embodiment, R
1
and R
3
are selected from the group consisting of methoxy, ethoxy, n-propoxy, benzoxy, phenoxy, phenyl, and methoxycarbonyl. In another embodiment the polymerization promoter is selected from the group prepared from bis-chloroformates of bisphenols. In yet another embodiment, the polymerization promoter is BPA bis-methyl salicyl carbonate.
Preparation
In one embodiment of the invention, the polymerization promoter is prepared by the reaction of appropriate bis-chloroformates (e.g., BPA-bis-chloroformate) with two equivalents of an activated phenol, such as methyl salicylate, in a solvent such as methylene chloride in the presence of a base to neutralize the liberated HCl. Additional catalysts may be employed in this reaction to facilitate the condensation reaction. After completion of the condensation reaction, the product solution is washed with aqueous acid and base then with water until the washings are neutral. The organic solvent may be removed by distillation and the polymerization promoter is crystallized and recovered.
The condensation reaction to prepare the polymerization promoter of the present invention may be carried out under anhydrous conditions known in the art using one or more equivalents of a tertiary amine per equivalent of chloroformate as the base, or under interfacial conditions also well-known in the art using aqueous sodium hydroxide as the base in the presence of a condensation catalyst. In one embodiment, the condensation catalyst is triethyl amine, quaternary alkyl ammonium salt, or mixtures thereof.
Polycarbonate Production Process
The polymerization promoter of the present invention may be used to build the molecular weight of polycarbonate oligomer prepared either by the interfacial process or the melt process. It functions as a coupling agent and reacts with the terminal hydroxy group (
OH) of the polycarbonate to increase the molecular weight of the polycarbonate as shown below:
If added to a melt reactor, the ortho-substituted phenols are removed by distillation to the over-head system to expedite the terminal blocking at high yields. The phenols may be recovered and recycled/reused in preparing additional polymerization promoters.
It should be noted that the increased molecular weight polycarbonate may still contain small amounts of any unrecovered phenols, any unreacted polymerization promoters along with by-products of any side reactions to the polymerization promotion reactions, e.g. terminal 2-(alkoxycarbonyl)phenyl groups and the like. In one embodiment, the terminal-blocked polycarbonate contains about less than 500 ppm of ortho-substituted phenols and about 500 ppm of unreacted polymerization promoters of the present invention. In another embodiment, the increased molecular weight polycarbonate contains about 2,500 ppm or less of terminal 2-(alkoxycarbonyl)phenyl groups.
Melt Polycarbonate Process
In one embodiment of the present invention, the promoter is added to a melt or transesterification process. The production of polycarbonates by transesterification is well-known in the art and described, for example, in Organic Polymer Chemistry by K. J. Saunders, 1973, Chapman and Hall Ltd., as well as in a number of U.S. patents, including U.S. Pat. Nos. 3,442,854; 5,026,817; 5,097,002; 5,142,018; 5,151,491; and 5,340,905.
In the melt process, polycarbonate is produced by the melt polycondensation of aromatic dihydroxy compounds (A) and carbonic acid dieste
Brack Hans-Peter
Brunelle Daniel Joseph
Cella James Anthony
Karlik Dennis
Boykin Terressa M.
General Electric Company
Oppedahl & Larson LLP
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