CA1161987A - Process for preparing polycarbonates using substituted pyridine catalysts - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An interfacial polymerization process for preparing a high molecular weight aromatic carbonate polymer by reacting A dihydric phenol with a carbonate precursor in the presence of a catalytic amount of a substituted pyridine or a salt of a substituted pyridine.

Description

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This invention is di.rected to an interfacial polymerizatio~
process for preparing high molecular ~7eight aromatic polycarbon-ates which comprises reacting under interfacial polycarbonate-forming conditions a dihydric phenol and a carbonate precursor in the presence of a catalytic amount of a substituted py~idine or a salt of a substituted pyridine.
BACKGROUND OF THE INVENTION
Polycarbonates are well known thermoplastic materials finding a wide range of uses, particularly for injection molding applications and as glazing sheet for replacement of window glass. The interfacial polymerization technique, which is one of the methods employed in preparing a polycarbonate, involves reactin~ a dihydric phenol and a carbonate precursor in the presence of an aqueous caustic solution containing an alkali or alkaline earth-metal hydroxide, and an inert organic solvent medlum which is a solvent for the polycarbonate as it is formed.
While the interfacial polymerization process is generally effec-tive in producing polycarbonates, it does, in general, suffer from two disadvantages. Firstly, the rate of reaction is relatively slow. Secondly, there is a general difficulty in pro-ducing high molecular weight aromatic polycarbonates, i.e., those having a weight average molecular weight of about 15,000 to greater. Many techniques, such as those employing ultrasonic waves during the reaction, have been employed to remedy these two disadvantages. These techniques have not always proved to be entirely effective and involve the use of cumbersome and expen-sive equipment. It is advantageous economically to speed up the reaction and to produce high molecular weigilt aromatic polycarbon-ates without having to employ extra equipment or more severe reaction conditions. One such method is the use o~ catalysts in ' ~CL-~14 ~L~6~ 3~
the interfacial polymerization process.
However, there is generally rela~ively little known about effective catalysis of polycarbonate reactions. The prior art discloses that certain compounds such as tertiary and quaternary 5 amines and their salts (U.S. Pat. 3,275,601), guanidine compounds (U.S. Pat. 3,763,099), and ammonia and ammonium compounds (U.S.
Pat. 4,055,544) are effective catalysts for the interfacial poly-merization process for producing polycarbonates. However, the prior art also teaches that certain organic nitrogen compounds function as molecular weight regulators or chain terminators in the polycarbonate reactions. Thus, the afore-mentioned U.S. Pat.
3,275,601 discloses that aniline and methyl aniline function as chain terminators in the polycarbonate reaction, while U~S. Pat.
4,001,184 discloses that primary and secondary amines are effective molecular weight regulators. Furthermore, U.S. Pat.
4,111,910 teaches that ammonia, ammonium compounds, primary amines, and secondary amines function as chain terminators in -the formation of polycarbonates via the interfacial polymerization process, and U.S. Pat 3,223,678 teaches that monoethanolamine and morpholine act to break the polycarbonate chain thereby re-sulting in lower molecu~ar weight polycarbonates.
DESCRIPTION OF THE INVENTION
This invention is directed to an interfacial pol~merization process ~or producing high molecular weight aromatic carbonate polymers wherein a dihydric phenol is reacted with a carbonate precursor in the presence of an aqueous caustic solution con-taining an alkali metal or alkaline earth metal hydroxide and a catalyst which is a substltuted pyridine or a salt of a substi-tuted pyridine.

-~ 8CL-3~14 The reaction of a dihydric phenol such as 2,2-bis~4-hydro~y-phenyl)propane with a carbonate precursor such as phosgene results in a high molecular weight aromatic polycarbonate polymer consist-ing of dihydric phenol derived units bonded ~o one another through carbonate linkages. The reaction is carried out in the presence of an aqueous caustic solution containing the alkali and alkaline earth metal hydroxide as acid acceptors and an inert organic sol-vent medium which is a solvent for the polycarbonate as it is formed. Generally, a molecular weight regulator is also present to control the molecular ~eight of the polycarbonate polymer. In the process of the present invention, a substituted pyridine is present and acts as an effective catalyst to-speed up the reaction between the carbonate precursor and the dihydric phenol.
The high molecular weight aromatic carbonate polymers pro-duced in accordance with the practice of this invention include carbonate homopolymers of dihydric phenols or carbonate copoly-mers of two or more different dihydric phenols. Additionally, the production of high molecular weight thermoplastic randomly branched polycarbonates and copolyester-polycarbonates are in-cluded within the scope of this invention. The randomly branchedpolycarbonates are prepared by coreacting a polyfunctional or-ganic compound with the afore-described dihydric phenol and car-bonate precursor.
The dihydric phenols employed in the practice of this inven-tion are known dihydric phenols in which the sole reactive groups are the two phenolic hydroxyl groups. Some of these are repre-sented by the general formul,a ~ X
HO ~ A)n ~ ~ ~ ~ OH
~X `~

wherein A is a divalent hydrocarbon radical conkaining 1-15 carbon O O p atoms, -S-, -S-S-, -S-, -S-, -o-, or -C-~ X is independently o hydrogen, halogen, or a monovalent hydrocarbon radical such as an alkyl group of 1-4 carbons, an aryl group of 6-10 carbons such as phenyl, tolyl, xylyl, naphthyl, an oxyalkyl group of 1-4 carbons or an oxyaryl group of 6-10 carbons and n is O or 1.
Typical of some of the dihydric phenols that can be employed in the practice of the present invention are bisphenols such as bis(4-hydroxyph-enyl) methane, 2,2-bis(4-hydroxyphenyl) propane (also known as bis-phenol-A), 2,2-bis(4-hydroxy-3-methylphenyl)propane, 4-4-bis(4-hydroxy-phenyl)heptane, 2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane, 2,2-bis (4-hydroxy-3,5-dibromophenyl)propange, etc., dihydric phenol ethers such as bis(4-hydroxyphenyl) ether, bis(3,5-dichloro-4-hydroxyphenyl) ether, etc., dihydroxydiphenyls such as p,p'-dihydroxydiphenyl, 3,3'-dichloro-4,4'-dihydroxydiphenyl, etc.; dihydroxyaryl sulfones such as bis(4-hydroxyphenyl) sulfone, bis(3,5-dimethyl-4-hydroxyphenyl) sulfone, etc., dihydroxy benzenes, resorcinol, hydroquinone, halo- and alkyl-substituted dihydroxy benzenes such as 1,4-dihydroxy-2,5-dichlorobenzene, 1,4-dihydroxy-3-methylbenzene, etc., and dihydroxy diphenyl sulfides and sulfoxides such as bis(4-hydroxyphenyl) sulfide and bis (4-hydroxyphenyl) sulfoxides, bis-(3,5-dibromo-4-hydroxyphenyl)sulfoxide, etc. A
variety of additional dihydric phenols are also available and are disclosed in U.S. Patent Nos. 2,999,835 to Goldberg dated September 12, 1961, 3,028,365 to Schnell et al dated April 3, 1962 and 3,153,008 to ox dated October 13, 1964. It is, of course, possible to employ two or more different dihydric phenols or a copolymer of a dlhydric phenol with glycol or with hydroxy or acid-terminated polye~t~r, or with a dibasic acid in the event a polycarbonate copolymer or interpolymer rather than a homopolymer i.s desired Eor use Ln the preparation of the polycarbonate polymers of this invention.

~CL-:3414 Also employed in the practice of khis invention are blends of any of the above dihydric phenols, the preferred dihydric phenol is bisphenol-A. The polyfunctional organic compounds which may be included within the scope of this invention are set forth in U.S. Patents 3,635,895 to Kramer dated January 18, 1972 and 4,001,184 to Scott dated January 4, 1977.
These polyfunctional aromatic compounds contain at least three functional groups which are carboxyl, carboxylic anhydride, haloformyl or mixtures thereof. Examples of these polyfunctional aromatic compounds include trimellitic anhydride, trimellitic acid, trimellityl trichloride, 4-chloroformyl phthalic anhydride, pyromellitic acid, pyro-mellitic dianhydride, mellitic acid, mellitic anhydride, trimesic acid, benzophenonettracarboxylic acid, benzophe-nonetetracarboxylic anhydride, and the like. The preferred polyfunctional aromatic compounds are trimellitic anhydride or trimellitic acid or their haloformyl derivatives. Also included herein are blends of a linear polycarbonate and a branched polycarbonate.
The carbonate precursor can be either a carbonyl halide or a bishaloformate. The carbonyl halides include car-bonyl bromide, carbonyl chloride, and mixtures thereof.
The bishaloformates suitable for use include the bishalo-formates of dihydric phenols such as bischloroformates of

2,2-bis(4-hydroxyphenyl) propange, 2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane, hydroquinone, and the like, or bishaloformates of glycols such as bishaloformates of ethylene glycol, and the like. While all of the above carbonate precursors are useful, carbonyl chloride, also known as phosgene, is preferred.
By adding monofunctional compounds which are capable of reacting with phosgene or with the end groups of the polycarbon-ates consisting of the chlorocarbonic acid ester group and which ~6~ CL-3~1~

terminate the chains, such as the phenols, e.g., phenol, tert-butylphenyl, cyclohexylphenol, and 2,2-(4,~-hydxoxyphenylene-4'-methoxyphenylene)propane, aniline and methylaniline, it is possible to reyulate the molecular weight of the polycarbonates.
S As mentioned hereinabove, the acid acceptor is an alkali or alkaline earth metal hydroxide. Illustrative of these acid acceptors are sodium hydroxide, lithium hydroxide, potassium hydroxlde, calcium hydroxide, and the like. The amount of said acid acceptor present should be sufficient to maintain the pH of the aqueous caustie solution above about 9.
Illustrative of the inert organic solvents which are present during the reaction and which dissolve the polycarbonate as i~ is formed are aromatic hydrocarbons and halogenated hydrocarbons such as benzene, toluene, xylene, chlorobenzene, orthodichlorobenzene, chloroform, methylene ch-oride, carbon tetrachloride, trichloro-ethylene and dichloroethane. The solvent is present in an amount effective to solubilize or dissolve substantially all of the polycarbonate as it is formed.
The catalytic compounds within the scope of the instant invention are the substituted pyridlnes and the.ir salts. The substituted pyridines are represented by the general formula Rn I.
N

wherein each R is independently selected from alkyl, substituted alkyl, alkenyl, substituted alkenyl, cycloaliphatic, preferably cycloalkyl, substituted cycloaliphatic, preferably substituted cycloalkyl, alkoxy, aryl, substituted aryl, alkaryl, aralkyl, alkylamino, and dialkylamino radicals; and n is an inteyer having a value of from 1 to 5, inclusive.

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Preferred alkyl radicals represented by ~ are those con-taining from 1 to about 20 carbon atoms. Illustrative of -these preferred alkyl groups are methyl, ethyl, n-propyl, isopropyL, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, and the various positional isomers thereof, and likewise the straight and branched chain positlonal isomers of hexyl, heptyl, octyl, nonyl, decyl, and the like.
Preferred alkenyl radicals represented by R are those containing from 2 to about 20 carbon atoms. Illustrative of these preferred alkenyl radicals are vinyl, allyl, propenyl, butenyl, 2-methylpropenyl, methallyl, 3-octenyl, an~ the llke.
Preferred cycloalkyl radicals represented by R are those con-taining from 3 to about 12 carbon atorns. Illustrative of these cycloalkyl radicals are cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclononyl, dimethylcyclohexyl, propyl-cyclohexyl, and the like.
Pre~erred aryl radicals represented by R are those containing from 6 to 18 carbon atoms, such as phenyl, naphthyl, and anthracyl radicals.
Preferred aralkyl radicals represented by R are those con-taining from 7 to about 20 carbon atoms. Illustrative of these aralkyl radicals are benzyl, 2-phenylethyl, 2-phenylpropyl, cumyl, phenylbutyl, naphthylmethyl, and the like.
Preferred alkaryl radicals represented by R are those con-taining from 7 to about 20 carbon atoms. Illustrative of these alkaryl radicals are tolyl, 2,6-xylyl, 2,~-xylyl, 2-methyl-1-naphthyl, and the like.
- Preferred alkoxy radicals represented by R are those con-taining from 1 to 18 carbon atoms. Illustrative of these alkoxy radicals are methoxy, ethoxy, isopropoxy, L~entoxy, dodecyloxy, octadecyloxy, and the like.

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Preferred alkylamino and dialkylamino radicals represented by R are those containing from 1 to about 20 carbon atoms.
Illustrative of these mono- and dialkylamino radicals are methylamino, ethylamino, butylamino, octylamino, dimethylamino, diethylamino, dibutylamino, methyloc~ylamino, me-th~vloctadecyl-amino, and the like.
T~hen substituent groups are present on the alkyl, alk.eny, cycloalkyl and aryl radicals, they are preferably those selected from the group consistin-g of alkyl and alkoxy radicals.
Illustrative substituted pyridines represented by Formula I
include 2-picoline, 3-picoline, 4-picoline, 2-ethylpyridine, 3-ethylpyridine~ 4-ethylpyridine, 2-isopropylpyridine, 3-isopropyl-pyridine, 4-isopropylpyridine, 2-butylpyridine, 4-tertiarybutyl-pyridine, 2,3-lutidine, 2,4-lutidine, 2,5-lutidine, 2,6-lutidine, -15 3,4~1utidine, 3,5-lutidine, 3,4-diethylpyridine, 3,5-diethylpyri-dine, 3-ethyl-4 methylpyridine, 2-(3-pentyl)pyridine, 4-(3-pentyl)pyridine, 2-dimethylaminopyridin0, 4-dimethylaminopyridine', 2-methoxypyridine, 2,6-dimethoxypyridine, 4-cyclohexylpyridine, 4-(5-nonyl)pyridine, 4-phenylpropylpyridine, and the like.
The salts of the substituted pyridines are represented by the ~eneral formula ~ \ -! ~ Rn\ y (m) II.

~ H /m wherein R and n are as defined above and Y is an m valent anion.
Preferred m valent anions represented by Y are sulfate, sulfite, phosphate, phosphite, halides, nitrate, nitrite, carbonate, and carboxylates.
The substituted pyridines and their salts are known com-pounds whose chemistry and preparakion are well known t:o those skilled in the art. ~hus, these compounds are described in .

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8~
_terocyclic Compounds, Volume 1, ~y R.C~ Elderfiel~, John Wiley & Sons, Inc., NY, N~.
The amount of substituted pyridine or salt of a su~stituted pyridine catalyst present during the reaction is a catalytic amount. By catalytic amount is meant an amount effective to catalyze the reaction between the dihydric phenol and the carbonate precursor to produce the high molecular weight poly-carbonate. Generally, this amount ranges from about 0.01 to about 10 weight percent based on the weiyht of the dihydric phenol present.
The process of the instant invention is carried out by reacting a dihydric phenol, such as bisphenol-A, with a carbonate precursor, such as phosgene, in a reaction medium containing an aqueous caustic solution and an inert organic solvent for the lS polycarbonate and in the presence of a catalytic amount of the substituted pyridine or substituted pyridine salt catalyst of the present invention.
The temperature at which this reaction proceeds may vary from below 0C to about 100C. The reaction proceeds satisfac-torily at temperatures ranging from about room temperature (25C)to about 50C. Since the reaction is exothermic, the rate of carbonate precursor addition may be used to control the reaction temperature. The amount of carbonate precursor, such as phosgene, required will generally depend upon the amount of dihydric phenol present. Generally, one mole of the carbonate precursor will react with one mole of dihydric phenol to provide the poly-carbonate. When a carbonyl halide, such as phosgene, is used as the carbonate precursor, two moles of hydrohalic acid such as HCl are produced by the above r~action. These two moles o~ acid are neutralized by the alkali and alkaline earth metal hydro~ide acid acceptor present. The ~oregoing are herein re~erred to as stoichiometric or theoretical amounts.

~ 9~ ~CL~3414 PREFERRED EM~ODIM~N~ ~F THE ~NVEMTION
In order ~o more fully and clearly illustrate the present invention, the following examples are presented. It is intended that the examples be considered as illustrative rather than limiting the invention disclosed and claimed herein. In the examples, all parts and percentages are on a weight basis unless otherwise specified.

This example illustrates an unsuccessful attempt to prepare a high molecular weight polycarbonate polymer via the interfacial polymerization technique without the presence of a catalyst. To a reactor Eitted with a reflux condenser and a mechanical agita-tor, charge 57 parts of 2,2-bis(4-hydroxyphenyl)propane, 57 parts of water, 325 parts of methylene chloride, and 1.2 parts of paratertiarybutylphenol. Phosgene is then added to the reaction mixture at a rate of 0.65 parts per minute for a period of 30 minutes while maintaining the pH at 9 by the addition of a 15~
aqueous sodium hydroxide solution. After 30-minutes, the pH is raised to 11.0 by the use of additional amounts of sodium hydroxide solution. Phosgenation is continued for a further 10 minutes at this pH. The material is recovered from the reaction and found to have an intrinsic viscosity of 0.12 dl./g. This indicates that a relatively low degree of polymerization is achieved.

This example illustrates an unsuccessful attempt to prepare a hlgh molecular weight polycarbonate polymer via the intexfacial polymerization technique by using pyridine, which falls outside the scope of Formula I, as catalyst. To a reactor fitted with a reflux condenser and a mechanical agitator, charye 57 parts of 2,2-bis(4-hydroxyphenyl)propane, 57 parts of 2ater, 325 parts of methylene chloride, and 0.4 parts of pyridine. Phosgene is then added to the reactio~ mi~ture at a rate of 0.~5 parts per minute for a period of 30 minutes while maintaining the pH at 9 by the addition of a 15% aqueous sodium h~droxide solution.
After 30 minutes, the pH is raised to 11.0 by the use of addi-tional amounts of sodium hydroxide solution. Phosgenation iscontinued for a further 10 minutes at this pH. The material is recovered from the reaction and found to have an intrinsic viscosity of 0.12 dl./g. This indicates no significant improve-ment over the insignificant degree of polymerization achieved in Example 1 wherein the reaction was carried out in the absence of any catalyst.
EX~MPLE 3 This example illustrates a successful attempt to prepare a high molecular weight polycarbonate polymer via the interfacial polymerization technique in the presence of an alkylpyridine catalyst. To a reactor fitted with a reflux condenser and a mechanical agitator, charge 57 parts of 2,2-bis(4-hydroxyphenyl) - propane, 57 parts of water, 325 parts of methylene chloride, and O A 54 parts of 2,4-lutidine. Phosgene is then added to the reaction mixture at a rate of 0.65 parts per minute for a period of 30 minutes while maintaining the pH at 9 by the addition of a l5% agueous sodium hydroxlde solution. After 30 minutes, the pH is raised to 11.0 bv the use of additional amounts of sodium hydroxide solution. Phosgenation is continued for a further 10 minutes at this pH. The material is recovered from the reaction and found to have an intrinsic viscosity of 0.46 dl./g. This value indicates that a high degree of pol~merization is achieved.

-Substantially the same procedure as described in Example 3 is repeated except that various other substituted pyridine . , . _ _ . . . . ... .... . . . .. ... . .. _ _ _ . _ .

` ~CL-3414 9~
catalysts are uti:Lized in place of 2,4-lu-tidine. The su~stituted pyridines used and the intrinsic viscosity o~ -the polycarbonate produced are set orth in Table I.

TABLE I
Intrinsir Catalyst Viscosity Example No. Name Parts by Weight dl./g.
4 2,6-lutidine 0.54 0.31 2-picoline 0.47 0.19 6 2~ethylpyridine 0.54 0.28 7 2,5-lutidine 0.54 1.05 ~ 3,5-lutidine 0.54 0.22 9 2-propylpyridine 0.66 0.77 4-(3-phenylpropyl) 1.00 0.19 pyridine 11 2-(3-pentylpyridine) 0.75 0.22 12 4-dimethylamino- 0.61 0.79 pyridine 13 2,4,6-collidine 0.61 0.63 14 2-methoxypyridine 0.55 0.18 2 vinylpyridine 0.54 0.20 EX~MPLE~ 16-20 Substantially the same procedure as descrlbed in Ex.ample 3 is repeated except that various other substituted pyridine catal-ysts are utilized in place of 2,4-lutidine and a molecular weight regulator, i.e., phenol, used. The substituted pyridine used, the amount of molecular ~eight regulator used, and the intrinsic viscosity of the polycarbonate produced are set forth in Table II.

... . . .. . ..

~ 8~ 8CL-3414 TABL,E II

Catalyst Parts Pl.enol inIntrinsic by parts by Viscosity E~ample No. Name Weiaht weight dl /g 16 2,6-lutidine0.27 0.25 0.30 17 2,4-lutidine0.27 0.25 0.41 18 2,4-lutidine0.54 0.25 0.38 19 2,4,6-collidine 0.31 0.25 0.24 4-dlmethylamino- 0.61 0.25 0.32 pyridine As can be seen by a comparison of Example 1 with Examples

3-20, the use of the substituted pyridines of Formula I results in the production of high molecular weight aromatic polycarbonates via the interfacial polymerization technique, while in the ab-sence of the substituted pyridine catalyst, the interfacialpolymerization technique is ineffective in producing high molecu-lar weight aromatic polycarbonates under substantially identical reaction conditions.
It is further evident ~rom the composition of Examples 1 and 2 that unsubstituted pyridine is not a catalyst in the inter-facial polymerization system. But on introducing suitable sub-stituents, as shown by the numerous examples, substituted pyridine becomes an effective catalyst.
It will thus be seen that the objects set forth above, among those made apparent from -the preceding description, are efficiently attained, and since certain changes may be made in carryiny out the above process and the composition set forth without departing from the scope of the invention, it is intended that all matters contained i.n the above description shall be interpreted as illustrative and not in a limiting sense.

... ..

Claims (7)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. An interfacial polymerization process for preparing high molecular weight polycarbonates which comprises reacting, under interfacial polycarbonate-forming conditions, a dihydric phenol with a carbonate precursor in the presence of an aqueous caustic solution and a catalytic amount of a compound selected from the group consisting of substituted pyridines and substituted pyridine salts, said aqueous caustic solution containing an alkali metal or an alkaline earth metal hydroxide, and said catalytic amount being from about 0.01 to about 10 weight percent based on the weight of said dihydric phenol.

2. The process of claim 1 wherein the catalyst is a substituted pyridine.

3. The process of claim 2 wherein said substituted pyridine is represented by the formula where R is independently selected from the group consisting of alkyl, substituted alkyl, alkenyl, substituted alkenyl, cycloaliphatic, substituted cycloaliphatic, alkoxy, aryl, substituted aryl, alkaryl, aralkyl, alkylamino, and dialkylamino radicals; and wherein n is an integer having a value of from 1 to 5, inclusive.

4. The process of claim 3 wherein said dihydric phenol is bisphenol-A and said carbonate precursor is phosgene.

5. The process of claim 1 wherein the catalyst is a substituted pyridine salt.

6. The process of claim 5 wherein said substituted pyridine salt is represented by the general formula wherein R is independently selected from the group consisting of alkyl, substituted alkyl, alkenyl, substituted alkenyl, cycloaliphatic, substituted cycloaliphatic, alkoxy, aryl, sub-stituted aryl, alkaryl, aralkyl, alkylamino, and dialkylamino radicals; n is an integer having a value of from 1 to 5, inclusive, and Y is an m valent anion.

7. The process of claim 6 wherein said dihydric phenol is bisphenol-A and said carbonate precursor is phosgene.