Flame Retardant Polycarbonate Compositions

This invention relates to thermoplastic, amorphous, halogen-free aromatic, high molecular weight polycarbonate compositions having improved flame retardance.

BACKGROUND OF THE INVENTION

The increasing concern for safety has resulted in increased e forts towards providing safer materials for commercial and household use. One particular area of need is that of providing flame retardant plastic products, many of which are now required to meet certain flame retardant criteria established by local and federal governments as well as by the manufacturers of such prod¬ ucts. One particular set of conditions commonly accepted and used as a standard for flame retardancy is that which is set forth in Underwriters' Laboratories, Inc. Bulletin 94 which proscribes cer¬ tain conditions by which materials are rated for self-extinguish¬ ing characteristics.

It is known that various halogen-containing, flame retardant additives can be employed to render plastic products self-extinq- uishing or flame retardant. Such flame retardant additives are typically employed in amounts sufficient to be effective for their intended purpose? generally, on the order of about 5-20% by weight based upon the weight of the plastic composition. In many ins¬ tances, use of these flame retardants in such amounts can have a degrading affect upon the plastic compositions to be rendered flame retardant often resulting in the deterioration of valuable physical properties of the base polymer. This is particularly so when known flame retardant additives are employed with polycarbon¬ ate resins since many of these additives have a degrading affect upon the base polymer typically resulting in discoloration and a loss of impact strength.

It is also known that blends and/or copαiymers of halogen-con¬ taining copolycarbonates and aromatic thiodipheπols can be employed

to obtain flame retardant compositions. For example, U.S. Patent 4,043,980 discloses polycarbonate compositions obtained as the reaction product of an aromatic diol, a halogenated phenol, and a carbonic acid coreacted with an aromatic thiodiphenol (TDP) , which compositions exhibit flame rεtardancy stated to be the result of the synergism between the sulfur and the halogen present in the composition. It is also disclosed that such, compositions overcome the detrimental critical thickness effect; i.e., that thickness at which notched Izod impact values of a test sample began to decrease, due to the presence of sulfur in the compositions.

In U.S. Patent 4,174,359, flame retardant polycarbonate comp¬ ositions are disclosed which are obtained as blends of a polycarb¬ onate - TDP copolymer and a halogen-containing compound- The comp¬ ositions can optionally include small amounts of a s l onic or car- boxylic acid salt which are preferably perfluαrinated.

Other sulfur-containing polycarbonate compositions are also known such as crystalline copolycarbonates obtained as the rea¬ ction of polycarbonate and TDP as disclosed in "Polycarbonates and Mixed Polycarbonates based on Bis (4-hydroxyphenyl)sulfide", O.V. Smirnova, G.S. Kolesnikov, A.X. Mikitaeo and T.G. richevskaya (Mosk. Khi -Teckhnol. Inst. im Mendeleeva, Moscow) , Vysokomol Soldin, Ser. 4 10(1), 96 101 (1968) (Russ), also reported in "Chem. Abstracts:, 6j3_, 1968.

In addition, U.S. Patent 3,398,212 discloses copolymers and blends of copolycarbonates and copolyesters prepared from halo¬ genated or non-halogenated polycyclic bisphenols and TDP.

Further, in an article entitled "Linear Aromatic Polyesters of Carbonic Acid", H. Schnell (Ind. Chem. Eng. , 1959) there is dis¬ closed crystallizable polycarbonates which can contain TDP.

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DESCRIPTION OF THE INVENTION It has now been found that the flammability of halogen-free, conventional, aromatic polycarbonate compositions can be dramat¬ ically improved by the incorporation therein of sulfur-containing polycarbonates derived from sulfur-containing diphenols. The e- ffect is truly remarkable in that high degrees of flame retardancy are achieved without the presence of any halogen additives and/or halogen-containing polycarbonates.

The sulfur-containing aromatic polycarbonates can be present as copolycarbonates derived from mixtures of non-polycyclic, sulfur- free and sulfur-containing diphenols or as blends of conventional polycarbonates and sulfur-containing polycarbonates. The term "conventional" as used throughout this application is intended to encompass and should be understood as encompassing polycarbonates derived from diphenols that are non-polycyclic and that are free of sulfur and halogen substituents in their molecular structure.

The flame retardant polycarbonate compositions of the inven¬ tion comprise the sulfur-free and sulfur-containing diphenols either as a chemical mixture or a physical mixture, or both. When pre- sent as a chemical mixture, the sulfur-free polycarbonate and the sulfur-containing polycarbonate are linked together by chemical bonds, such as in copolycarbonates. Thus, copolycarbonates of two, or more, components can be coreacted to form alternating or random or block copolycarbonates as well as chemical mixtures thereof. Represented symbolically by A and B for the two diphenol-derived moieties, an alternating copolycarbonate structure would be as follows:

O O 0 0 II II u II

-0-A-O-C-O-S-O-C-O-A-O-C-O-B-C-O-, etc. I.

while a random copolycarbonate would have the structure:

O 0 00 00 0o o II II II II II

-A-O-C-O-A-O-C-O-A-O-C-B-O-C-O-A-O-C-O-A-O-C- O O ll II

O-B-O-C-O-B-O-C-O-, etc. II. and a block copolycarbonate would have the structure:

where n m and n are greater than -and p is at least 1. Chemical mixtures of such copolycarbonates would be repre- sentated by structures in which the structures shown in formulae I and/or II and/or III are joined together by chemical bonds.

The non-polycyclic, sulfur-free polycarbonate and the sulfur- containing polycarbonate can also be present as a physical mixture or blend, of two or more components wherein no chemical interact¬ ion occurs and, thus, no chemical bonds are present linking the components together. Represented symbolically, a physical mixture of the two polycarbonates, in its simplest form, ould be as shown below:

0 0 0 0 0

II ll, II II

-0-CJ-O-A-O-Cj-O-A-O-C- . plus -O-Cτb-B-0-CJ-O- IV m *- n

IVa IVb wherin m and n have the same value as above, or as physical ix- tures of IVa with I and/or II and/or III, or as physical mixtures of IVb with I and/or II and/or III, or as physical mixtures of I and II, or I and III, or II and III.

In addition, the polycarbonate composition can comprise both chemical and physical mixtures.

Accordingly, in the practice of this invention, the conven-

tional non-polycyclic aromatic polycarbonates that can be employed are homopolymers and copolymers that can be prepared by reacting a halogen-free and sulfur-free diphenol with a carbonate precursor. Typical of some of the diphenols that can be employed are 2,2-bis (4-hydroxyphenyl) ropane, (also known as bisphenol-A or 3PA) , bis (4-hydroxyphenyl)methane, 2,2-bis (4-hydroxy-3-methylphenyl)propane, 4,4-bis (4-hydroxyphenyl)heptane, 1,1-bis (4-hydroxyphenyl)ethane, 1,1-bis (4-hydroxyphenyl)cyclohexane, 1,1-bis (4-hydroxyphenyl) ro¬ pane, 3,3-bis (4-hydroxyphenylJpentane. Other diphenols of the bisphenol type are also available such as are disclosed in U.S.

Patents 2,999,835; 3,028,365; and 3,334,154 incorporated herein by reference.

These non-polycyclic, halogen-free and sulfur-free diphenols can be represented by the structural formula:

wherein each X can independently be selected from the group consis¬ ting of H or Cj - C ₅ alkyl, and W can be a chemical bond, Ci - C _β alkylene, C ₂ - C _β alkylidene, Cs - C _{l 2} cycloalkylene or cycloalky- lidene.

The sulfur-containing diphenols from which the sulfur-contain¬ ing pol carbonates can be obtained, can be represented by the fol- lowing structural formula:

wherein R and R ¹ can each independently be H or Ci to C-. alkyl, and n is 1 or 2. Typical of some of these sulfur-containing diphenols

are 4,4-'-thiodiphenol; 2-methyl-4,4'-thiodiphenol; 2,2'-dimethyl- 4,4'-thiodiphenol, 2,2'-di-tertiary-butyl-4,4'-thiodiphenol, and the like, all of which are collectively referred to as "thiodiph¬ enol" or "TDP" . Such thiodiphenols can be prepared by known meth- ods such as that disclosed in U.S. Patent 3,931,335 incorporated herein by reference.

It is, of course, possible to employ two or more different diphenols in either or both the sulfur-free and sulfur-containing components or a copolymer of a. diphenol with a ^' glycol or with hy- droxy or acid terminated polyester, or with a dibasic acid in the event a carbonate copolymer or interpolymer rather than a homopol- y er is desired for use in the preparation of the aromatic carbon¬ ate polymers of this invention. Also, blends of any of the above materials can be employed to provide the aromatic polycarbonate. The carbonate precursor can be either a carbonyl halide, a carbonate ester or a haloformate. The carbonyl halidεs which can be employed are carbonyl bromide, carbonyl chloride and mixtures thereof. Typical of the carbonate esters which can be employed are diphenyl carbonate, di-(halophenyl)carbonates such as di- (chloro- phenyl) carbonate, di-(bromophenyl) carbonate, di-(trichlorophenylj carbonate, di- (tribromophenyl) carbonate, etc., di-(alkylphenyl) carbonates such as di(tolyl) carbonate, etc., di-(naphthyl)carbonate , di-(chloronaphthyl)carbonate, phenyl tolyl carbonate, chlorophenyl chloronaphthyl carbonate, etc., or mixtures thereof. The haloform- ates which can be used include bis-haloformates of the diphenols employed, including both the sulfur-free and sulfur-containing bisphenols, such as BPA-bis (chloroformate) and thiodiphenol bis- (chlorofor ate) and their congeners. While other carbonate pre¬ cursors will occur to those skilled in the art, carbonyl chloride, also known as phosgene, is preferred.

The aromatic carbonate polymers of this invention can be pie- pared by employing a molecular weight regulator, an acid acceptor and a catalyst. The molecular weight regulators which can be em¬ ployed include monohydric phenols such as phenol, chroman-I, para- tertiarybutylphenol, parabromophenol, and the like. Preferably, phenol is employed as. the molecular weight regulator.

The acid acceptor can be either an organic or an inorganic acid- acceptor. A suitable organic acid acceptor is a tertiary amine and includes such materials as pyridine, triethylamine, dimethylan- iline, tributyla ine, etc. The inorganic acid acceptor can be one which 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 any of the catalysts that aid the polymerization of the diphenol such as bisphenol-A with phosgene. Suitable catalysts include tertiary amines such as for example, triethylamine, tripropylamine, N,N-dimethylaniline, quaternary ^" ammonium compounds such as, for example, tetraethylam¬ monium bromide, cεtyl triethylammonium bromide, tetra-n-heptylam- monium iodide, tetra-n-propylammonium bromide, tetramethylammon- ium chloride, tetramethylammonium hydroxide, tetra-n-butylammonium iodide, benzyltrimethylammoniu chloride and quaternary phosponiuπ compounds such as, for example, n-butyltriphenyl phosphonium bro¬ mide and ethyltriphenyl phosphonium bromide.

Also, included herein are branched polycarbonates wherein a polyfunctional aromatic compound is reacted with the diphenol and carbonate precursor to provide a thermoplastic randomly branched polycarbonate.

The polyfunctional aromatic compounds contain at least three functional groups which are carboxyl, carboxylic anhydride, halo- formyl or mixtures thereof. Examples of the polyfunctional aromatic

compounds include trimellitic anhydride, tri ellitic acid, trimel- lityl trichloride, 4-chloroformyl phthalic anhydride, pyromellitic acid, pyromellitic dianhydride, mellitic acid, mellitic anhydride, trimesic acid, benzophenonetetracarboxylic acid, benzophenonetetra- carboxylic 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. In order to impart effective flame-retardancy to the polycar¬ bonate compositions of the invention, the sulfur content thereof should be about 3 - 1 , preferably about 5 - 10, weight percent based upon the total weight of the final composition. This amount of sulfur is equivalent to a thiodiphenol content of about 23 - 98 mole percent in the broad range and about 35 - 75 mole percent in the preferred range.

The polycarbonate compositions of the invention exhibit not only excellent flame retardant characteristics, but also exhibit hitherto unknown, felicitious combinations of outstanding proper- ties such as impact strength, especially in thicker sections, and better thermal stability. Therefore, there are included in the test results shown hereinafter not only flame retardancy, but notch¬ ed Izod impact and thermal gravimetric analyses as well. PREFERRED EMBODIMENT OF THE INVENTION The following examples are presented to more fully and clearly illustrate the invention. Although the examples set forth the best mode presently known to practice the invention, they are intended to be and should be considered as being illustrative of, rather than limiting, the invention. In the examples, all parts and percent¬ ages are by weight unless otherwise specified.

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EXAMPLΞ 1 Into a mixture of 2283 grams of pure 4,4'-isopropylidenediphe- nol (BPA) (mp 156-157°C; 10.0 mole grams), 5700 grams water, 9275 grams methylene chloride, 32.0 grams phenol and 10.0 gra s triethy- 5 lamine were introduced, at ambient temperature, 1180 grams phosgene over a period of 97 minutes while maintaining the pH of the two- phase system at about 11; i.e., pH 10-12.5, by simultaneously add- 'ing a 25% aqueous sodium hydroxide solution. At the end of the ad¬ dition period, the pH of the aqueous phase was 11.7 and the BPA

10 content of this phase was less than 1 part per million (ppm) as de¬ termined by ultraviolet analysis.

The methylene chloride phase was separated from the aqueous phase, washed with an excess of dilute (0.01 N) aqueous HCl and then washed three times with deionizεd water. The polymer was pre-

15 cipiatεd by steam and dried at 95°C. The resultant, pure BPA- polycarbonate, which had an intrinsic viscosity (IV) in methylene chloride at 25°C of 0.465 dl/g. , was fed to an extruder, which ex¬ truder was operated at about 550°F, and the extrudate was comminu¬ ted into pellets.r

20 The pellets were then injection molded at about 600°F into test bars of about 5 in. by 1/2 in. by about 1/8 in. thick and into stepped test squares of about 2 in. by 2 in. by about 1/8 in. and 1/16 in. thick. The 1/8 in. test bars (5 for each test result shown in the Table) were subjected to the flame-retardancy test

25 procedure set forth in Underwriters* Laboratores, Inc. Bulletin UL- 94, Burning Test for Classifying Materials. In accordance with this test procedure, materials that pass the test are rated either V-O, V-I ^~ τ V-II based on the results of 5 specimens. The criteria for each V (for vertical) rating per UL-94 is briefly as follows:

30 "v-O": Average flaming and/or glowing after removal of

-li¬

the igniting flame shall not exceed 5 seconds and none of the specimens shall drip flaming parti¬ cles which ignite absorbent cotton. "V-I": Average flaming and/or glowing after removal of the igniting flame shall not exceed 25 seconds and the glowing does not travel vertically for more than 1/8" of the specimen after flaming ceases and glowing is incapable of igniting absorbent cotton. "V-II": Average flaming and/or glowing after removal of the igniting flame shall not exceed 25 seconds and the specimens drip flaming particles which ignite absorbent cotton. In addition, a test bar which continues to burn for more than 25 seconds after removal of the igniting flame is classified, not by UL-94, but by the standards of the invention, as "burns". Further, UL-94 requires that all test bars in each test group must meet the V-type rating to achieve the particular classification; otherwise, the 5 bars rεcεive the rating of the worst single bar. For example, if one bar is classified as V-II and the other four (4) are class- ified as V-O, then the rating for all bars is V-II.

Impact measurements by the notched Izod test were determined pursuant to ASTM D-256 on 1/8 in. thick test bars.

Thermal gravimetric measurements were carried out on a Per in Elmer TGS1 instrument pursuant to ASTM D-1238, condition 0. EXAMPLE 2

The procedure of Example 1 was exactly repeated, except that half of the BPA (1141.5g) was replaced with 1091.5g of 4,4'-thiodi¬ phenol (TDP) (5 moles; i.e., 50 mole % TDP, or about 6.6 wt. % sulfur) and only 19.8g of phenol was employed.

-12- EXAMPLΞ 3

The procedure of Example 1 was exactly repeated, except that a mixture of 570.7g(2.5 mole) of BPA and 1637.Ig of TDP (7.5 moles; i.e., 75 mole % TDP, or 9.8 wt. % sulfur) was used and only 16.9g 5 of phenol was employed.

EXAMPLE 4 Repeating the procedure of Example 1 with a mixture of 1712.5g (7.5 moles) of BPA and 545.7g of TDP (2.5 moles; i.e., 25 mole % TDP, or 3.3 wt. % sulfur) yielded a polycarbonate having an IV of 10 0.478 dl/g.

The flame retardancy, notched Izod impact and thermal gravi¬ metric results of the copolycarbonate test samples obtained from foregoing Examples are set forth in the Table herein below wherein the sample of Example 1, from which a conventional polycarbonate 15 was obtained, is identified as the "Control".

EXAMPLE 5 The procedure of Example 2 was exactly repeated, except that BPA was replaced with 1342g of 4,4 '-cyclohexylidenediphenol. The copolycarbonate obtained was found to be V-O pursuant to UL-94. 20 EXAMPLE 6

The procedure of Example 2 was repeated except that 1482g of 4,4'-cyclohexlidenebis (2-meth lphenol) was employed in place of BPA. The copolycarbonate obtained was found to be V-O pursuant to UL-94. 25 EXAMPLE 7

A physical mixture consisting of 2560g of the polycarbonate of Example 1 and 244Og of a polycarbonate preparεd from TDP and phos¬ gene following the procedure of Example 1 was fed to an extruder operating at about 550°F and the pellets obtained therefrom were 30 molded into test samples as described in Example 1. The clear,

colorless test bars obtained had a sulfur content of -6.0 wt. % and were found to be V-O per UL-94.

EXAMPLE 8 Following the procedure of Example 7, additional test bars were obtained from a physical mixture consisting of 128g of the polycarbonate of Example 1 and 2318g of a TDP-polycarbonate. The clear, colorless test bars had a sulfur content of 12.4 wt. % and were found to be V-O per UL-94.

TABLE

TEST AKX Γ OF SAMPLE DIPHENOL SULFUR INTRINSIC THERMAL GRAVIMETTRY ³ UL-94

FROM DPΛ TDP MDL. RATIO FOUND. VISCOSITY N. IZOD 5% wt. loss 50% wt. loss Flame-Out Drips EXAMPUΞ (g) (g) (DPA:TDP) ( t %) (di/g) (ft. lb.) (°C) Time, (sec.) (per 5 bars) Rating

Control 2283 0 1:0 0.0 0.465 16.2 338 380 26 13 Burns

2 1141.5 1091.5 1:1 6.4 0.462 13.4 362 401 3.8 0 V-O

3 570.7 1637.1 1:3 9.7 0.524 ^b 13. β 370 414 3.2 0 V-O

4 1712.2 545.7 3:1 3.1 0.478 16.5 350 393 4.6 0 V-O I

a) Analyses carried out in air b) Determined in s-tetra ύoicoethane instead of methylene chloride