Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2001-10-10
2002-12-31
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
06500914
ABSTRACT:
BACKGROUND OF INVENTION
This application relates to a method for end-capping polycarbonate resins and to end-capping compositions useful in such a method.
Polycarbonates prepared by the reaction of a dihydric phenol (such as bisphenol A, “BPA”) and a diaryl carbonate (such as diphenyl carbonate, “DPC”) in a melt transesterification process generally contain significant levels of uncapped chains (7-50%) as compared to interfacially prepared polycarbonates. These uncapped chains can have a significant impact on the resulting properties of polycarbonate, and it is therefore desirable in many instances to include an end-capping agent with a higher capping efficiency than DPC during or after the polymerization reaction which terminates the uncapped chains.
Known end-capping reagents are frequently carbonate or ester derivatives of phenol. U.S. Pat. No. 4,680,372 discloses the use of phenyl benzoate as an end-capping reagent to terminate polymers formed by melt polymerization of a bisphenol and an aromatic dicarboxylic acid such as terephthalic acid and/or isophthalic acid. U.S. Pat. No. 4,886,875 describes preparation of polyarylate compositions using diaryl carbonates, polyarylcarbonate oligomers or polyarylcarbonate polymers as end-capping agents. In particular, the Examples of the ″875 patent teach the use of diphenyl carbonate or highly endcapped polycarbonate oligomers as end-capping agents. Unfortunately these end-capping reagents all yield the byproduct phenol, which then rapidly re-equilibrates with the polycarbonate to limit the achievable molar mass and end-cap level. Long reaction and devolatization times are required to counteract this effect.
Therefore known end-capping reagents are frequently also carbonate or ester derivatives of electronegatively-ortho-substituted phenols which are more reactive than DPC. U.S. Pat. No. 4,310,656 describes the transesterification of of bis (ortho-haloaryl)carbonates, haloaryl aryl carbonates, and a dihydric phenol, and indicates that controlled aryl end-capping is achieved. U.S. Pat. No. 4,363,905 describes the transesterification of of bis(ortho-nitroaryl)carbonates, nitro aryl aryl carbonates and a dihydric phenol, and indicates that controlled aryl end-capping is achieved. It should be noted though that both bis(ortho-haloaryl)carbonates and bis(ortho-nitroaryl)carbonates have quite different properties than DPC. Thus the replacement of DPC by these compounds requires considerably different equipment and operating conditions than typically found in melt polycarbonate production. In addition 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 carbonates that are free from chlorine and nitro-activating groups. U.S. Pat. No. 4,661,567 describes the use of vinylene carbonate derivatives as end-capping agents which are added to preformed polycarbonates to terminate the polymers.
U.S. Pat. No. 5,696,222 describes a process for production of a terminally-blocked polycarbonate by melt transesterification of a dihydric phenol and a diaryl carbonate in the presence of an asymmetric substituted phenol ester or carbonate as an end-capping agent, and in particular end-capping agents which are salicylic acid derivatives. European Patent Publication No. 0 980 861 discloses an improved method for making such derivatives. These end-capping agents are derived from one salicylate (activated) and one non-activated phenol. While such end-capping agents are effective, they are not without their drawbacks. Specifically, such asymmetric carbonates require two separate steps for their preparation (generation of a chloroformate from one of the phenols, followed by condensation with the second phenol). This two step process adds significantly to the cost of the end-capping agent. An additional deficiency of this method is that the asymmetric mixed carbonates prepared in this way are often contaminated with traces of nitrogen- and halogen-containing impurities and with symmetrical carbonates derived from one or both of the phenols used in the reaction. As a consequence, in order to obtain materials of suitable quality for polymerization, purification is often both essential and difficult.
The ″222 patent also describes the use of di-activated carbonates, for example derived from two salicylates to either couple polycarbonate chains to increase molecular weight, or to cap phenolic hydroxyl end groups. This method suffers from the fact that only salicylate (activated) end groups can be incorporated. These salicylate end groups are different from the conventional phenol or alkyl-substituted phenol end groups typically found in commercial polycarbonate resins. In addition, capping is accompanied by coupling so that it is difficult to only cap without increasing molecular weight, or to systematically vary the endcap level without varying also the polycarbonate molecular weight. Indeed, while increasing levels of conventional end-capping agents tend to decrease molecular weight, in the case of the di-activated species there are opposing tendencies where the end-capping function reduces molecular weight while the coupling function tends to increase molecular weight, making the characteristics of the product difficult to predict or control.
SUMMARY OF INVENTION
It has now been found that end-capping reagents which comprise a mixture of different species, including at least: (a) a symmetrical activated aromatic carbonate, and (b) a symmetrical non-activated aromatic carbonateprovide effective end-capping of polycarbonate resins and can avoid the deficiencies described above. Thus, the present invention provides an end-capping reagent, and a method for preparing an end-capped polycarbonate resin using the reagent. In accordance with an embodiment of the method of the invention a mixture comprising a polycarbonate having free hydroxyl-end groups and an end-capping reagent is processed in a melt transesterification reaction to produce a polycarbonate resin.
The carbonates of the end-capping reagent reacts with at least some of the free hydroxyl end-groups of the polycarbonate to produce an end-capped polycarbonate resin.
DETAILED DESCRIPTION
End-Capping Reagent: This application relates to an end-capping composition comprising a mixture of different species, including at least: (a) one species of symmetrical activated aromatic carbonate, and (b) one species of symmetrical non-activated aromatic carbonate.
This invention further relates to a method of making polycarbonate resin which uses an end-capping reagent of this type.
As used in the specification and claims of this application, the term “symmetrical activated aromatic carbonate” refers to compounds containing two phenolic groups linked through a carbonate bridge, with each phenol group being substituted with the same electronegative and therefore activating substituent at the ortho position. Many of these symmetrical activated aromatic carbonates can be represented by the general formula:
wherein R is the electronegative substituent. Preferred electronegative substituents are carbonyl-containing groups, nitro groups, and halo groups. Symmetrical activated aromatic carbonates of this type may be synthesized by the reaction of an appropriate ortho-substituted phenol with phosgene.
Symmetrical activated aromatic carbonates for use in compositions and methods in accordance with the invention may also be made either by reaction of two equivalents of an appropriate “activated” or ortho-substituted phenyl chloroformate with a bisphenol, such as bisphenol A, or by reaction of a bis-chloroformate with two equivalents of an “activated” or appropriate ortho-substituted phenol. Where bisphenol A is used, the resulting composition has the following general formula,
wherein R is as defined above.
Specific examples of symmetrical activated aromatic carbonates which may
Brack Hans Peter
Cella James Anthony
Karlik Dennis
Smigelski, Jr. Paul Michael
Boykin Terressa M.
General Electric Company
Oppedahl & Larson LLP
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