Thermally Stable Polycarbonate

This invention relates to thermal oxidatively stable polycarbonate compositions and more particularly to polycarbonate compositions having minor amounts of a phosphonite with or without a particular epoxy compound.

It is known to incorporate various phosphites with polymers as disclosed in U.S. Pat. No. 3,305,520 and phosphites with tetraaryl tin as shown in Canadian Pat. No. 727,700. However, these references deal solely with phosphites such as triaryl and trialkyl phosphites. Due to increase molding temperatures and use temperatures of molded shapes of polycarbonates, it is increasingly more important to prepare polycarbonates having increased stability to thermal degradation or discoloration due to elevated temperatures.

Therefore it is an object of the instant invention to provide a thermal oxidatively stable polycarbonate.

Another object of this invention is to provide a thermal oxidatively stable polycarbonate stabilized with minor amounts of a phosphonite present.

Yet another object of this invention is to provide a thermal oxidatively stable polycarbonate composition having in admixture, a polycarbonate, minor amounts of a phosphonite and an epoxy.

These and other objects of this invention will become apparent from the following detailed description thereof.

According to this invention, it has been surprisingly discovered that thermal oxidatively stable polycarbonate compositions are obtained by combining with a polycarbonate, minor amounts of a phosphonite of the formula: ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 are independently selected from the group consisting of unsubstituted and halogen substituted aryl, alkyl, cycloalkyl, aralkyl and alkaryl radicals of 1-25 carbon atoms. In addition, the above polymer may have in admixture therewith a particular epoxy compound.

The following examples are set forth to illustrate more clearly the principle and practice of this invention to those skilled in the art. Unless otherwise specified, where parts or percents are mentioned, they are parts or percents by weight.

To polycarbonate powder prepared by reacting equimolar amounts of 2,2-bis(4-hydroxyphenyl-propane (hereinafter referred to as bisphenol-A) and phosgene in an organic medium containing a molecular weight regulator, a catalyst and an acid acceptor, mix 0.02 weight percent of diphenyl benzene phosphonite and 0.08 weight percent of di-3,4-epoxy-6-methylcyclohexylmethyl adipate each based on the weight of the polycarbonate in a blender. The blend is dried overnight at 125.degree.C and extruded at about 530.degree.F into pellets using a screw extruder.

The composition is designated as I.

Example I is repeated except that dinonylphenyl benzene phosphonite is employed herein in place of diphenyl benzene phosphonite.

The composition is designated as II.

Example I is repeated except that di-isodecyl benzene phosphonite is employed herein in place of diphenyl benzene phosphonite.

The composition is designated as III.

To a reactor fitted with a reflux condenser and mechanical agitator, charge 1320 parts of methylene chloride, 113, parts of 2,2-bis(4-hydroxyphenyl) propane, 120 parts of calcium hydroxide, 2 parts of p-tertiary butylphenol, 0.05 parts of triethylamine and 0.132 part of diphenyl benzene phosphonite. The slurry is stirred and phosgene added at a rate of about 60 parts/hour. The phosgene addition is terminated after 53 minutes. The polymer is recovered in solid form by filtering and precipitation with methanol. The product is dried overnight at 125.degree.C.

The composition is designated as IV.

Example IV is repeated except that 0.245 part of dinonylphenyl benzene phosphonite is employed herein in place of 0.132 part of diphenyl benzene phosphonite.

The composition is designated as V.

Example IV is repeated except that 0.190 part of di-isodecyl benzene phosphonite is employed herein in place of the 0.132 part of diphenyl benzene phosphonite.

The composition is designated as VI.

The compositions of Examples I-III are injection molded into test specimens 3 .times. 2 .times. 1/8 inches thick at 650.degree.F and 700.degree.F separately. As a control, a polycarbonate without phosphonite and epoxy additives of the type as employed in Example I is also molded into test specimens. Separate test specimens of each are heat aged at 140.degree.C for 7 days. The test specimens are then measured for thermal stability to discoloration in accordance with ASTM Yellowness Index Test D1925-63T. The lower the number, the lower is the discoloration of the polymer and therefore the better is the thermal stability of the polymer to discoloration.

The results are as follows:

Three and a half (3.5) grams each of the compositions of Examples IV-VI, which compositions contain only the phosphonite additive and no epoxy, and a control polycarbonate containing no phosphonite are sealed in a combustion tube under a pressure of 26 inches of mercury. The tubes are heated in an aluminum block at 600.degree.F for 15 minutes. The tubes are then cooled and the contents thereof are dissolved in 25 ml. of distilled methylene chloride. The percent transmission through the solutions is measured against the percent transmission through distilled methylene chloride at 425 nanometers. The higher the transmission, the lower is the discoloration of the polymer which in turn means better thermal stability of the polymer to discoloration. The results are as follows:

The transmission is measured through a 23 mm cell in a Fischer Electrophotometer.

The instant invention is directed to a thermal oxidatively stable polymer composition and more particularly to a thermal oxidatively stable polycarbonate composition stabilized with a minor amount of a phosphonite of the formula: ##STR2## wherein R.sub.1, R.sub.2 and R.sub.3 are independently selected from the group consisting of unsubstituted and halogen substituted alkyl, aryl, cycloalkyl, aralkyl and alkaryl radicals of 1-25 carbon atoms. Preferably, the amount of phosphonite present is 0.005 to about 1.0 weight percent and more particularly 0.01 to about 0.1 weight percent based on the weight of the polycarbonate.

As stated previously, the phosphonite employed in the instant invention is the type set forth previously wherein R.sub.1, R.sub.2 and R.sub.3 may be alkyl such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tertiary butyl, n-amyl, isoamyl, tertiary amyl, n-hexyl, dodecyl, nonyl, etc; cycloalkyl such as cyclohexyl, 2-methylcyclohexyl, 4-methylcyclohexyl, 2-ethylcyclohexyl, 4-ethylcyclohexyl, 4-isopropylcyclohexyl, etc; aryl such as phenyl, naphthyl, 2-naphthyl, biphenyl of terphenyl, etc; aralkyl such as benzyl, phenylethyl, 2-phenylethyl, 1-phenylpropyl, 2-phenylpropyl, etc.; and alkaryl such as p-tolyl, m-tolyl, 2,6 xylyl, o-tolyl, p-cumyl, m-cumyl, o-cumyl, mesityl, p-tertiary butylphenyl; haloaryl such as 2-chlorophenyl, 2,4,6-trichlorophenyl, 2,4,6-tribromophenyl, etc; and the substituted portions thereof may be halogen atoms. The phosphonite employed herein may be added either to reaction vessel with the monomer employed to prepare the polycarbonate or it may be added after the reaction has started or it may be added at the end of the reaction or it may be blended with dry polycarbonate powder obtained from the reaction. Preferably, it has been found to blend the phosphonite with the polycarbonate powder and then extrude the molding pellets therefrom.

In addition, the invention is directed to admixing therewith an epoxy composition as represented by the following formula:

I. Derivatives of epoxy ethane represented by the following formula: ##STR3## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen, an alkyl radical of 1-24 carbon atoms, an aryl radical of 6-24 carbon atoms, --CH.sub.2 OR', --CH.sub.2 OCOR', --CH.sub.2 OCOR"COOCH.sub.2 X, CH.sub.2 OR"OCH.sub.2 X wherein R' is selected from the group consisting of an alkyl radical of 1-24 carbon atoms or an aryl radical of 6 to 24 carbon atoms and wherein R" is an alkylene radical of 1-24 carbon atoms and X is an oxirane ring.

II. Derivatives of epoxy cyclohexane represented by the following formula: ##STR4## wherein R.sub.5 through R.sub.12 are independently selected from the group consisting of hydrogen, alkyl radicals of 1-24 carbon atoms, --COOR.sub.13, --OCOR.sub.13, --COOR.sub.14 X, --OCOR.sub.14 --COOX wherein R.sub.13 is an alkyl radical of 1-24 carbon atoms and R.sub.14 therein is an alkylene radical of 1-24 carbon atoms and X is an oxirane ring.

While the actual number of hydrogen atoms employed may vary, it should be a function of the volatility of the epoxy compound. The number of hydrogen atoms should be such as to minimize the volatility of the epoxy compound since if the epoxy compound were to volatize at a low temperature, its benefit in use with a polycarbonate would be lost at the molding temperatures employed in preparing molded articles from the composition of this invention.

The amount of epoxy employed in the practice of this invention can vary from 0.01 to 0.5 weight percent based on the weight of the polymer composition and is preferably 0.03 to 0.10 weight percent. While more than 0.5 weight percent of epoxy can be employed, it has been found that higher amounts tend to degrade the physical properties of the polycarbonate and thereby reduce the usefulness of the polymer in providing tough, flexible molded articles.

In the practice of this invention, other epoxy compounds that have been employed in place of the 3,4-epoxy-cyclohexylmethyl 3,4-epoxy cyclohexanecarboxylate with essentially the same results as those set forth previously as encompassed by the formula I and II and are 3,4-epoxy-6-methylcyclohexylmethyl, 3,4-epoxy-6-methylcyclohexane carboxylate, 2,3-epoxy-cyclohexylmethyl 3,4-epoxy cyclohexane carboxylate, 4-(3,4-epoxy-5-methylcyclohexyl) butyl 3,4-epoxy cyclohexane carboxylate, 3,4-epoxy-cyclohexyl ethylene oxide, cyclohexylmethyl 3,4-epoxy-cyclohexane carboxylate, 3,4-epoxy-6-methylcyclohexylmethyl-6-methylcyclohexyl carboxylate, bisphenol-A diglycidyl ether, tetrabromobisphenol-A diglycidyl ether, diglycidyl ester of phthalic acid, diglycidyl ester of hexahydrophthalic acid, epoxidized soybean oil, epoxidized linseed oil, bis-epoxycyclohexyl adipate, butadiene diepoxide, tetraphenylethylene epoxide, octyl epoxy tallate and epoxidized polybutadiene. Also, 3,4-dimethyl-1,2-epoxy cyclohexane, 3,5-dimethyl-1,2-epoxy cyclohexane, 3-methyl-5-tert butyl-1,2-epoxy cyclohexane, octadecyl 2,2-dimethyl-3,4-epoxy cyclohexane carboxylate, N-butyl 2,2-dimethyl-3,4-epoxy cyclohexane carboxylate, N-butyl 2,2-dimethyl-3,4-epoxy cyclohexane carboxylate, cyclohexyl 2-methyl-3,4-epoxy cyclohexane carboxylate, N-butyl 2-isopropyl-3,4-epoxy-5-methyl-cyclohexane carboxylate, octadecyl-3,4-epoxy cyclohexane carboxylate, 2 ethyl hexyl 3', 4' epoxy cyclohexane carboxylate, 4,6 dimethyl 2,3 epoxy cyclohexyl 3', 4' epoxy cyclohexane carboxylate, diethyl 4,5-epoxy-cis-1,2 cyclohexane dicarboxylate, di-n-butyl 3-tert butyl-4,5-epoxy-cis-1,2 cyclohexane dicarboxylate. Specifically, any of the epoxycyclohexyl compounds meet the general formula of II and the other epoxy compounds recited herein meet the general formula of I. Preferably, the epoxy compound employed in the practice of this invention is 3,4-epoxy cyclohexylmethyl 3,4-epoxy cyclohexane carboxylate.

The dihydric phenols that can be employed herein to prepare the polycarbonates are bisphenols such as bis(4-hydroxyphenyl) methane, 2,2-bis(4-hydroxyphenyl) propane, 2,2-bis(4-hydroxy-3-methylphenyl) propane, 4,4-bis(4-hydroxyphenyl) heptane, 2,2-bis(4-hydroxy 3,5-dichlorophenyl) propane, 2,2-bis(4-hydroxy 3,5-dibromophenyl) propane, 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-chlorobenzene, 1,4-dihydroxy-2,5-dichlorobenzene, 1,4-dihydroxy-3-methylbenzene, etc.; and dihydroxy diphenyl sulfoxides such as bis(4-hydroxyphenyl) sulfoxide, bis-(3,5-dibromo-4-hydroxyphenyl) sulfoxide, etc. A variety of additional dihydric phenols are also available to provide carbonate polymers and are disclosed in U.S. Pat. Nos. 2,999,835, 3,028,365 and 3,153,008. It is, of course, possible to employ two or more different dihydric phenols or a copolymer of a dihydric phenol with a glycol or with hydroxy or acid terminated polyester, or with a dibasic acid in the event a carbonate copolymer or interpolymer rather than a homopolymer is desired for use in the preparation of aromatic carbonate polymers of this invention.

The carbonate precursors employed in the practice of this invention can be either a carbonyl halide or a bishaloformate. The carbonyl halides which can be employed herein are carbonyl chloride, carbonyl bromide and mixtures thereof. The bishaloformates of dihydric phenols (bischloroformates of hydroquinone, etc.) or glycols (bishaloformates of ethylene glycol, neopentyl glycol, polethylene glycol, etc.). While other carbonate precursors will occur to those skilled in the art, carbonyl chloride, also known as phosgene, is preferred.

As stated previously, the reaction may be carried out in the presence of an acid acceptor which may be either an organic or an inorganic compound. A suitable organic acid acceptor is a tertiary amine and includes such materials as pyridine, triethylamine, dimethylaniline, tributylamine, etc. The inorganic acid acceptor may be one which can be an hydroxide, a carbonate, a bicarbonate or a phosphate of an alkali or alkaline earth metal.

The molecular weight regulators which are also employed in carrying out the process for preparing the aromatic polycarbonate resins can be such molecular weight regulators as phenol, cyclohexanol, methanol, para-tertiarybutylphenol, para-bromophenol, etc. Preferably para-tertiarybutylphenol is employed as the molecular weight regulator.

In the broad sense of the instant invention, it is understood that other additives may be employed that are commonly used in preparing polycarbonates. These are such additives as glass fibers or filaments, sized or unsized, pigment colorants, mineral fillers such as quartz or silica, etc. Also when preparing molding compositions of the type prepared by comminuting the extrudate of a screw extruder, a vented extruder may be employed wherein the polymer may be vented to the atmosphere or to a vacuum or to a pressure in excess of atmospheric.

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 carrying out the above process and in the composition set forth without departing from the scope of this invention, it is intended that all matters contained in the above description shall be interpreted as illustrative and not in a limiting sense.