Two step production of polycarbonates

Details Two step production of polycarbonates Two step production of polycarbonates

2002-11-05

2004-05-11

Boykin, Terressa (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

06734279

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to polycarbonates and methods of producing these polycarbonates. More particularly, it relates to production and use of high molecular weight polycarbonates.
BACKGROUND
Polycarbonates are amorphous thermoplastic materials that typically exhibit extremely high impact strength coupled with excellent clarity, as well as relatively high continuous use temperatures (250° F.). Polycarbonates have been used in a wide range of applications (e.g., the production of membrane filters), and in many of these application it is preferable to use high molecular weight polycarbonates.
Polycarbonates are typically produced by phosgenation of bisphenols. (See, e.g., U.S. Pat. No. 3,912,687; and U.S. Pat. Nos. 2,970,131; 4,262,113; 4,286,086; and 4,291,151). In some synthetic methods, substituted and/or activated pyridine catalysts have been used to produce polycarbonates from bisphenol A. (See, e.g., U.S. Pat. No. 4,286,085; U.S. Pat. No. 4,794,156 and U.S. Pat. No. 3,530,094). Additionally, U.S. Pat. No. 5,804,525 discloses the production of polycarbonates from certain bisphenols using TEA catalysts.
However, none of these processes reliably and efficiently produce high molecular weight polycarbonates, particularly when synthesizing polycarbonates from bulky (or sterically hindered) bisphenols or bisphenols that are poor nucleophiles. Even polymerization accomplished in the presence of an activated pyridine catalyst, yield polycarbonates having lower than desired molecular weights. (See, U.S. Pat. No. 4,794,156).
Thus, there remains a need for methods of producing high molecular weight polycarbonates from polyhalobisphenols and compositions comprising these polycarbonates.
SUMMARY OF THE INVENTION
The present invention provides novel methods of synthesizing high molecular weight polycarbonates, wherein the polycarbonates have a high weight average molecular weight and, preferably, relatively low polydispersity. The methods comprise reacting bisphenol with at least two different catalysts. The first catalyst comprises at least one phase transfer catalyst (PTC) and the second catalyst comprises at least one activated pyridine.
Thus, in one aspect, the invention relates to a method for synthesizing polycarbonates, the method comprising the steps of:
(a) mixing a bisphenol with at least one phase transfer catalyst;
(b) adding phosgene to the mixture of step(a);
(c) adding a catalytic amount of an activated pyridine, thereby producing said polycarbonate; and
(d) recovering said high molecular weight polycarbonate.
In another aspect, the invention relates to a method for synthesizing a polycarbonate having a molecular weight over 150,000, the method comprising the steps of:
(a) mixing a bisphenol with a phase transfer catalyst and with sufficient caustic solution to maintain an alkaline pH in the range of about 7.5 to 11;
(b) adding phosgene to said mixture and maintaining the pH in the range of about 7.5 to 11;
(c) adding a catalytic amount of an activated pyridine catalyst, thereby producing said high molecular weight polycarbonate; and
(d) recovering said polycarbonate.
In another aspect, the invention relates to a method for synthesizing a polycarbonate having a molecular weight over 150,000, the method comprising the steps of:
(a) mixing a bisphenol with a phase transfer catalyst and a molecular weight modifier;
(b) adjusting the pH of the mixture of step(a) to an alkaline pH in the range of about 7.5 to 11;
(c) adding phosgene to said mixture, while maintaining the pH in the range of about 8.0 to 10;
(d) adding a catalytically effective amount of an activated pyridine catalyst;
(e) adjusting the pH of the solution to about 7.0; and
(e) recovering said high molecular weight polycarbonate.
In any of the methods described herein, the bisphenol preferably comprises a halobisphenol (e.g., 9,9-bis-(3,5-dibromo-4-hydroxyphenyl)fluorene); the weight average molecular weight of the resulting polycarbonate is preferably greater than about 150,000; and the polydispersity of the polycarbonate is preferably less than about 12. Furthermore, in any of these methods, the solvent is preferably a halogenated solvent, such as methylene chloride. In certain embodiments, one phase transfer catalyst (e.g., benzyltriethylammonium chloride, tetrabutylammonium hydroxide, etc.) is mixed with bisphenol, while in other embodiments, two or more PTCs are mixed with bisphenol. Preferably, the ratio of bisphenol to each PTC is between about 90:1 and 200:1. Similarly, in preferred embodiments, the mole ratio of bisphenol to phosgene is between about 0.30 and 0.40.
In any of the methods described herein, a molecular weight modifier can be used, for example, a phenol such as para-tertiary butyl phenol can be added to the bisphenol-PTC mixture. In preferred embodiments, between about 0.10 to 8 mole % of molecular weight modifier based on the total moles of bisphenol is added.
In certain embodiments, the activated pyridine comprises dimethylamino pyridine. Preferably, the catalyst ratio of PTC to activated pyridine is between about 2.5:1 and about 15:1 (or any value therebetween), even more preferably between about 3:1 and 11:1 and even more preferably between about 4:1 and 5:1
In still further aspects of the invention, high weight average molecular weight polycarbonates produced by any of the methods described herein are provided.
These and other embodiments of the subject invention will readily occur to those of skill in the art in light of the disclosure herein.
DESCRIPTION OF THE INVENTION
Methods of preparing high molecular weight polycarbonates using two or more catalysts during the polymerization process are described. In particular, one catalyst, the phase transfer catalyst (PTC), facilitates the growth of monobischloroformate to a chloroformate terminated multimer. The second catalyst, dimethylaminopyridine (DMAP) facilitates the final coupling and allows for formation of higher weight average molecular weight products. Compositions comprising polycarbonates produced by these methods as well as methods of using these compositions also form aspects of this invention.
The practice of the present invention will employ, unless otherwise indicated, conventional techniques of chemistry and engineering which are within the skill of the art. Such techniques are explained fully in the literature. See, e.g., Kesting, R. E.,
Synthetic Polymeric Membranes
, John Wiley & Sons, 2
nd
Ed. (1985); Hwang, Sun-Tak and Kammermeyer, Karl,
Membranes in Separation
, Robert E. Kriegar Publishing Co., Inc., (1984). Although a number of compositions and methods similar or equivalent to those described herein can be used in the practice of the present invention, the preferred materials and methods are described.
All publications, patents and patent applications cited herein, whether above or below, are hereby incorporated by reference in their entirety.
It must be noted that, as used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to “a polycarbonate” includes a mixture of two or more such polycarbonates and the like.
The present invention provides a method for preparing high weight average molecular weight polycarbonates. The methods described herein can be used to synthesize polycarbonate from virtually any bisphenol, including, for the first time, hindered bisphenols. Polyhalobisphenols are described, for the example in U.S. Pat. No. 3,912,687. Suitable bisphenols are known and are commercially available, for example, from Dow Chemical Company; Great Lakes Chemical Company. However, unlike previous methods, the processes described herein are also useful with bulky bisphenols, for example 9,9-bis-(3,5-dibromo-4-hydroxyphenyl)fluorene (TBBHPF).
Polycarbonates produced by these methods are useful in a variety of applications. For instance, polycarbonate gas separation membranes exhibit improved flux and selectivity as well as stability when the polycarbon

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