Polycarbonate Compositions Having Improved Barrier Properties

This invention relates to high molecular- weight aromatic polycarbonate compositions having improved barrier properties; i.e., low water vapor transmission and low gas permeability. Background Art

Polycarbonate polymers are known as being excellent molding materials since products made there¬ from exhibit such properties as high impact strength, toughness, high transparency, wide temperature, limits (high impact resistance below -60°C and a UL thermal endurance rating of 115°C with impact)-, good dimensional stability, good creep resistance, and the like.

Dimethylated aromatic polycarbonates are known as disclosed in U.S. Patent 3,028,365. Tetra- methylated aromatic polycarbonates are also known and their high heat distortion properties have been recognized as disclosed in U.S. Patent 3,879,384. It would be desirable to add to this list of properties those of low water vapor transmission and low gas permeability to enable the aromatic poly- carbonates to be used to form containers and film wraps for foods, beverages, cosmetics, and the like. In particular, food and beverage containers made from aromatic polycarbonates having these added barrier properties would be more economical as they would be capable of reuse and would thus also help reduce the impact of environmental waste occasioned by broken glass and discarded, non-reuseable containers.

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Summary of the Invention

It has now been found that mono- and di-alkyl substituted, high molecular weight aromatic poly¬ carbonates can be obtained that exhibit improved wa 5 vapor transmission and gas barrier properties, as compared to non-alkylated aromatic polycarbonates.

It has been further surprisingly found that mono- and dialkylated aromatic polycarbonates exhib far superior barrier properties than either non- 10 alkylated or tetramethylated aromatic polycarbonate

The alkylated aromatic polycarbonates of this invention can be prepared by known techniques using appropriate monomers. The monomers that can be employed can be represented by the following genera 15 formula:

25

wherein X and Y can each independently be selected from the group consisting of hydrogen, an alkyl of ^c l"* ^c 10' ^an< ^ .mixtures thereof with the proviso that 30 at least either X or Y is a C-^-C-^ _Q alkyl; and, is a member selected from the following group:

fy

(a) — ir-CH ₂ — _r wherein r is 0 or an integer from 2-10 ;

!

(b) -C- wherein R is a member selected from

I

H the group consisting of cycloalkyl and C ₆ -C ₁₄ aryl;

and R' can each independently be the same as R in (b) above with the proviso that, when both R and R' are each CH3, X and Y are not both symmetrically substituting CH3;

an integer of 4-20;

q can each independently

Typical of some of the monomers that can be employed in this invention are bis (4-hydroxy-3-methyl- phenyl)methane, 1,6-bis (4-hydroxy-3-ethylphenyl) hexane, 2,2- (4-hydroxyphenyl) (4-hydroxy-3-methyl- phenyl)propane, 1,1-bis (4-hydroxy-3-methylphenyl) propane, 1,1-bis (4-hydroxy-3-methylphenyl)cyclohexane, bis (4-hydroxy-3-ethylphenyl) sulfbne, bis (4-hydroxy-3- isopropylphenyl) ether and the like.

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_4- Of course, it is possible to .employ two or mo different monomers or a copolymer with a glycol or with hydroxy or acid terminated polyester, or with a dibasic acid in the event a carbonate copolymer 5 or interpolymer rather than a homopolymer is desir for use in preparing the aromatic polycarbonate. Blends of any of these materials can also be used obtain the aromatic polycarbonates.

These high molecular weight aromatic polycar-

10 bonates can be linear or branched homopolymers or copolymers as well as mixtures thereof or polymeri blends and generally have an intrinsic viscosity C of about Q,40—1,0 dl/g as measured in met ylene chlororide at 25°C, These high molecular weight

15 aromatic polycarbonates can be typically prepared by reacting a monomer with a carbonate precursor.

The carbonate precursor used can be either a carbonyl halide, a carbonate ester or a halo- formate. The carbonyl halides can be carbonyl

20 bromide, carbonyl chloride and mixtures thereof. The carbonate esters can be diphenyl carbonate, di-(halophenyl) carbonates such as di-(chlorophenγ carbonate, di-(.bromophenyl) carbonate, di-(trichlo rophenyl) carbonate, di-(.tribromophenyl) carbonate

25 etc., di-(alk lphenyl) carbonates such as di(tolyl carbonate, etc., di-(naphthyl) carbonate, di-(chlo ronaphthyl) carbonate, phenyl tolyl carbonate, chlorophenyl chloronaphthayl carbonate, etc., or mixtures thereof. The haloformates that can be

30 used include bis-haloformates of dihydric phenols (bischloroformates of hydroquinone , etc.) or glycols (bishaloformates of ethylene glycol,

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neopentyl glycol, polyethylene glycol, etc) as well as haloformates of the monomers described above in formula I. While other carbonate precursors will occur to those skilled in the art, carbonyl chloride, also known as phosgene, is preferred.

Also included are the polymeric derivatives of a dihydric phenol, a dicarboxylic acid and carbonic acid such as are disclosed in U.S. Patent 3,169,121 which is incorporated herein by reference. Molecular weight regulators, acid acceptors and catalysts can also be used in obtaining the aromatic polycarbonates of this invention. The useful molecular weight regulators include monohydric phenols such as phenol, chroman-I, paratertiarybutyl-phenol, parabromophenol, primary and secondary amines, etc. Preferably, phenol is employed as the molecular weight regulator.

A suitable acid acceptor can be either an organic or an inorganic acid acceptor, A suitable organic acid acceptor is a tertiary amine such as pyridine, triethylamine, dimethylaniline, tributyl- a ine, etc. The inorganic acid acceptor can be either a hydroxide, a carbonate, a bicarbonate, or a phosphate of an alkali or alkaline earth metal, The catalysts which can be employed are those that typically aid the polymerization of the monomers with phosgene. Suitable catalysts include tertiary amines such as triethylamine, tripropylamine,

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N,N-dimethylaniline, quaternary ammonium compounds such as, for example, tetraethylammonium bromide, cetyl triethyl ammonium bromide, tetra-n-heptyl- a monium iodide, tetra-n-propy _/ 1 ammonium bromide, 5 tetramethylammonium chloride, tetramethyl ammonium hydroxide, tetra-n-butyl ammonium iodide, benzyl- trimethyl ammonium chloride and quaternary phospho nium ccmpounds such as, for exanple, n-butyltriphe phosphonium bromide and methyltriphenyl phosphoniu 10 bromide.

Also included herein are branched polycarbona wherein a polyfunctional aromatic compound is reac with the monomer and carbonate precursor to provid a thermoplastic randomly branched polycarbonate,

15 These polyfunctional aromatic compounds contain at least three functional groups which are carboxyl, carboxylic anhydride, haloformyl, or mixtures thereof. Illustrative polyfunctional aromatic compounds which can be employed include trimelliti

20 anhydride, trimellitic acid, trimellityl trichlori 4-chloroformyl phthalic anhydride, pyromellitic ac pyromellitic dianhydride, melli ic acid, meHitic anhydride, trimesic acid, benzophenonetetracarboxy acid, benzophenonetetracarboxylic anhydride, and t

25 like. The preferred polyfunctional aromatic com¬ pounds are trimellitic anhydride and trimellitic acid or their acid halide derivatives.

Accordingly, the mono- and di-alkylated, high molecular weight aromatic polycarbonates of the invention can be represented by the following general formula:

wherein X, Y and W are the same as in formula I above.

Preferred Embodiment of the Invention

The following examples are set forth to more ^r fully and clearly illustrate the present invention and are intended to be, and should be construed as being, exemplary and not limitative of the invention. Unless otherwise stated, all parts and percentages are by weight. The barrier properties for each of the ensuing examples were determined using Modern Controls, Inc, instruments. Water vapor transmission rate (WVTR) measurements were obtained on an I D-2C instrument pursuant to ASTM F-372-73; carbon dioxide data (C0 ₂ TR) were obtained using a Permatran-C instrument; and, oxygen transmission rates 0 ₂ TR) were determined using an OX-TRAN 100 instrument. The methods used to obtain WVTR and C0 ₂ TR data are based on infrared analysis whereas the 0 ₂ TR measurements are based on a coulometric method.

The WVTR measurements are expressed in grams/24 hrs./lOO in, ² /mil at 100°F and 90% relative humidity (RH) whereas those of C0 ₂ TR and 0 ₂ TR are expressed in cc/24 hrs./lOO in. /mil/atmosphere.

Preparation of 4,4'-cyclohexylidenedi-o-cresol(CDC)

To a 22 1, three-necked flask, equipped with stirrer, subsurface gas inlet tube, thermometer and reflux condenser was charged 2180 g (22.2 moles) of cyclohexanone and 12000 g (111 moles) of o-cresol and to the resulting solution was introduced sub- - surface HC1 gas with good stirring. A mildly exothermic reaction ensued; by external cooling, the temperature was not allowed to exceed 55°-60°C. The introduction of HC1 was continued until blow- through was observed, when it was stopped. The progress of the reaction was followed by ir (infrared) spectroscopy) , which indicated that in ca. 1,5—2 hrs, all of the cyclohexanone was consumed, by the disappearance of the carbonyl band at 1710 cm .

Crystals started to come out of the warm solution in an additional 1—2 hours, which was facilitated and completed by cooling and stirring.

After the separation of crystals was complete, the reaction mixture was filtered and the filter cake was rinsed on the funnel with methylene chloride. The crystals were then slurried up in methylene chloride _f filtered and the cake rinsed again. The crude crystals weighed 4285 g on 76.8% of theory. The cresolic mother liquor typically contained 270 g of the p,p"-product whereas the methylene chloride mother liquors contained an additional 119 g of product, bringing the total conversion of the p,p'-isomer to 83%.

Recrystallization of the 4285 g of crude filter- cake, which had an assay of 98.5% and a mp. of 184- 7°C, by dissolution in 9.5 1. or refluxing methanol and subsequent addition of 2.8 1. of water, followed

-9- by cooling, deposited colorless crystals that, after filtration and airdrying, weighed 3515 g ( _. 82% of the crude), and had an assay of 99,8-99.9%, p. 188-189°C, Example 1

Into a mixture of 74,1 parts of pure 4,4'- cyclohexylidenedi-o-cresol (CDC) (mp 188-189°C; 0.25 parts mole) , 300 parts water, 300 parts methylene chloride, 0,47 parts phenol and 0,5 parts triethyl- amine were introduced, at ambient temperature, 30 parts phosgene over a period of 30 minutes while maintaining the pH of the two-phase system at about 11; i,e, , pH 10-12,5, by simultaneously adding a 25% aqueous sodium hydroxide solution. At the end of the addition period, the pH of the aqueous phase was 11,7 and the CDC content of this phase was less than 1 part per million Cppm) as determined by ultra¬ violet analysis.

The methylene chloride phase was separated from the aqueous phase, washed with an excess of dilute (_0,01N) aqueous HCl and then washed three times with deionized water. The polymer was precipitated by adding the neutral and salt-free methylene chloride solutions to an excess of methanol and filtering off the white polymer which was dried at 95°C, The resultant, pure CDC-poly- carbonate had an intrinsic viscosity CIV) in methylene chloride at 25°C of 0.554 dl/g. Its barrier properties are set forth in the Table following the Examples.

The intrinsic viscosity values mentioned hereinafter were also measured in methylene chloride at 25 ^β C.

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-1Q- Control Example 1 The procedure of Example 1 was repeated, except that 4,4'-isopropylidenediphenol, (BPA), w substituted, in equivalent amounts, for CDC. The pure BPA-polycarbonate had an IV of 0,560 dl/g. 5lts barrier properties are lifted in the Table,

Control Example 2 Following the procedure of Example 3 of the above-mentioned U.S, Patent 3,879,384, a tetra¬ methylated polycarbonate was prepared from 2,2-bi 10(3,5-dimethyl-4-hydroxyphenyl) propane. Its barr properties are listed in the Table,

Example 2 The procedure of Example 1 was repeated, except t an equivalent amount of a 75 weight % C D C/25 15weight % BPA mixture was used in place of only CD A copolycarbonate was obtained having an IV of 0, dl/g and that yielded colorless, transparent moldings or film. Its barrier properties are listed in the Table. 20 Example 3

The procedure of Example 1 was repeated, except that an equivalent amount of a 55 weight % C D C/ weight % BPA mixture was used in place of CDC, T resultant copolycarbonate, which yielded tough, 25transparent test objects and films, had an IV of 0,54 dl/g. Its barrier properties are listed in the Table.

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Preparation of 4,4'-cyclohexylidenediphenol (CDP)

The above-described procedure for the prepara¬ tion of CDC was repeated, except that 1.0500 g (111..6 moles) of phenol was substituted for o-cresol. The 5crude crystals that separated out were rinsed with methylene chloride; after airdrying they weighed 5170 g or 87% of theoretical, Recrystallization from methanol-water yielded pure CDP, mp 188-189°C, that was 99,8% pure by gas chromatography.

I preparation of 4,4'-(1-me hylethylidene)bis-o-cresol (MEC)

The above-described procedure for the prepara¬ tion of CDC was repeated except that 645 g (11,1 moles) of acetone was substituted for the cyclo-

15hexanone and heat was applied during the introduction of HC1 to maintain the reaction temperature between 50°—70°C, The progress of the reaction was conveniently monitored by gas chromatography, which indicated that most of the 2,2'- and 2,4'-isomers 0formed at the beginning of the reaction rearranged to the 4,4'-isomer. When the concentration of this latter in the product had increased from an initial 63% to 93% (with only 7% of the 2,4'-isomer and no detectable amount of the 2,2'-isomer being present), 5 the hydrochloric acid catalyst and the excess of o-cresol were removed by heating and distillation under water aspirator vacuum. The distillation residue, after recrystallization from chlorobenzene, yielded 2333 g (9.1 mole) or 82% of MEC, mp 135-7°C, 0 that was 98.5% pure by gas chromatography.

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Preparation of 4,4'-(1-methylpropylidene)bis-o- Cresol (MPC)

The above-described procedure for the prepara tion of CDC was repeated, except that 800 g (11,1 5 moles) of 2-butanone was substituted for acetone and the reaction temperature was kept at or below 50°C, Purification was effected by extracting the solid distillation residue twice with methylene chloride, which left behind the 4,4'-isomer as

10 white crystals, mp 144° - 146°C, 99.1% purity and 1840 g or 61,3% yield. This monomer, MPC, is believed to be novel.

Preparation of 4,4'—1-ethylpropylidene)bis-o-creso (EPC.)

15 The above-described procedure for the prepara tion of CEC, was repeated, except that 956 g (11.1 moles) of 3-pentanone was substituted for acetone. EPC was obtained in 99.2% purity, after recrystall zation from cyclohexane, with a melting point of

20 119° - 120°C. This monomer, EPC, is a dimethylate bisphenol-A (dimethyl BPA) and is believed to be novel.

Preparation of 2-methyl-4,4'-(1-meth/lethylidene) bisphenol (MMEP)

25 Anhydrous HC1 was introduced, with adequate cooling, into a mixture of 134 g (1.0 mole) of freshly prepared 4-isopropenyl phenol (made by thermally cracking BPA in the presence of catalytic amounts of sodium hydroxide and separating it from

30 the co-product phenol by fractional vacuum (distil¬ lation) and 540 g (5.0 moles) of o-cresol, while

aintaining the temperature of the ensuing exother¬ mic reaction below 50°C. After 4 hours, the red colored reaction mixture was stripped of HCl and excess cresol under water aspirator vacuum and the resultant straw colored melt was purified by recrystallization from cyclohexane. The 98.7% pure MMEP had a melting point of 112°-113°C. This monomer, MMEP, is a monomethyl bisphenol-A,

Example 4 - 6 The preparation of polycarbonates by the procedure of Example 1 was repeated by substituting equivalent amounts of the following diphenols for CDC:

Example 4: MEC (4,4'- l-÷ ethylethyl±deiie bis- o-cresol)

Example 5: MPC (4,4*-(1-methylpropylidene) bis- o-cresol) Example 6: EPC (4,4'-(1-ethylpropylidene)bis- o-cresol) The barrier properties of the resultant poly¬ carbonates are listed in the Table.

Examples 7 - 10 The preparation of copolycarbonates with BPA by the procedure of Example 3 was repeated by substituting equivalent amounts of the following diphenols for CDC:

Reference Example CDP (4,4'-cyclohexylidene- diphenol) Example 7: MEC (4,4'-(l-methylethylidene)bis- o-cresol)

Example 8: MPC (4,4'-(1-methylpropylidene)bis- o-cresol)

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Example 9: EPC (4,4'-1-ethylpropylidene)bis- o-cresol)

Example 10: MMEP (2-methyl-4,4'-(1-methyl- ethylidene bisphenol) The barrier properties of the resultant copoly¬ carbonates are listed in the Table wherein the Reference Example, the BPA-polycarbonate, is used as the comparative standard.

Some of the test specimens from which the barrier properties were obtained were made by extruding the polycarbonates and copolycarbonates in an extruder operated at about 265°C and, comminuting the extrudate into pellets. Thereafter, the pellets were compression molded into films having an average thickness of 10 mils. Other test specimens were obtained by film casting the polycarbonates and copolycarbonates directly from a methylene chloride solution to provide film specimens also having an average thickness of about 10 mils.

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TAB E

Barrier Properties of Polycarbonates and Copoly- carbonates

Example IV, l/g WVTR CC ₂ TR 0 ₂ TR

1 0,554 0,7 20.4 10,2 control 1 0,560 10,0 875 200 control 2 - 8,3 - —

2 0.550 1.6 148 34

3 0.540 2.7 — 56

4 0.548 2.7 - 33

5 ^" 0.526 2.0 - 34

6 0.555 1.4 - 28

Reference 0.547 6.2 - 110

7 0.542 4.8 - 122

8 0.552 5.5 - 140

9 0.538 5,2 - 132

10 0.544 5.6 — —

A comparison of the measured values of the water vapor transmission rates for the polycarbonate derived from bisphenol-A (control Example 1) and tetramethylated BPA (Control Example 2) with the values measured for the polycarbonates derived from the moncmethylated (Example 10) and dimethylated (Example 5) homologs of bisphenol-A, shows that the mono- and di-methylated polycarbonates have surprisingly superior barrier properties, as is dramatically illustrated in the following list.

WVTR _% decrease

0

BPA 10

44 monomethyl BPA 5,6 dimethyl BPA 2,0 80 17 tetramethyl BPA 8,3

* with respect to BPA polycarbonate

f f

O f _h W