CA1141061A - Ductile and solvent resistant polycarbonate compositions having improved flame retardance - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Ductile and solvent resistant aromatic polycarbonate compositions are obtained comprising an admixture of a high molecular weight aromatic polycarbonate and a block copolymer consisting of alternating segments of an aromatic polycarbonate and a polyorganosiloxane.
The polycarbonate compositions also exhibit improved flame retardance.

Description

~ 8CH-3077 This invention relates to ductile and solvent resistant aromatic polycarbonate compositions that also have improved flame retardance.
Polycarbonate polymers are known as being excellent molding materials since products made therefrom exhibit such properties as high impact strength, toughness, high transparency, wide temperature limits (high impact resistance below -60C and a UL thermal endurance rating of 115C with impact), good dimensional stability, good creep resistance, good flame retardance, and the like. It would be desirable to add to this list of properties those of ductility and solvent resistance enabling these poly-carbonate compositions to be employed to form molded articles that can be used in such applications as aircraft tray tables and seat backs, aircraft ducting, ski boots, wire coatings, films, and the like wherein the articles will be required to exhibit high tensile properties and resistance to the corrosive effects of commercial cleaning compounds and other organic chemicals.
It has now been found that ductility and solvent resistance as well as improved flame retardance can be imparted to high molecular weight, aromatic polycarbonate resins by mixing the polycarbonate resin with block copolymers consisting of alternating segments of polybisphenol carbonates and polyorganosiloxane in amounts of up to about 50% by weight, preferably abGut 1-30% by weight, of the base polycarbonate resin.
In the practice of this invention, any of the aromatic polycarbonates can be employed that are prepared by reacting a diphenol with a carbonate precursor. Typical of some of the diphenols that can be employed are bisphenol-A
(2,2-bis(4-hydroxyphenyl)propane), bis(4-hydroxyphenyl) 8-C~-3077 methane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 4,4-bis(4-hydroxyphenyl)heptane, 2~2-(3,5-3',5'-tetrachloro-4,4'-dihydroxydiphenyl)propane, 2,2-(3,5,3',5'-tetrabromo-4,4l-dihydroxydiphenyl)propane, (3,3'-dichloro-4, 4'-dihydroxyphenyl)methane. Other halogenated and non-halogenated diphenols of the bisphenol type can also be used such as are disclosed in U.S. Patent 2,999,835 - Goldberg -dated September 12, 1961; U.S. Patent 3,028,365 - Schnell et al - dated April 3, 1962; U.S. Patent 3,334,154 - Kim -dated August 1, 1967.
It is possible to employ two or more different diphenols or a copolymer 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 preparing the aromatic polycarbonate. Blends of any of these materials can also be used to obtain the aromatic polycarbonates.
These diphenols can then be employed to obtain the high molecular weight aromatic polycarbonates of the invention which can be linear or branched homopolymers or copolymers as well as mixtures thereof or polymeric blends and which generally have an intrinsic viscosity (IV) of about 0.40-1.0 dl/g as measured in methylene chloride at The carbonate precursor used can be either a carbonyl halide, a carbonate ester or a haloformate. The carbonyl halides can be carbonyl bromide, carbonyl chloride and mixtures thereof. The carbonate esters can be diphenyl carbonate, di-(halophenyl) carbonates such as di-(chlorophenyl) carbonate, di-(bromophenyl) carbonate, di-(trichlorophenyl) carbonate, di-(tribromophenyl) carbonate, etc., di-(alkylphenyl) carbonate such as di(tolyl) ~ CH-3077 carbonate, etc., di-(naphthyl) carbonate, di-(chloronaphthyl) carbonate, phenyl tolyl carbonate, chlorophenyl chloronaphthyl carbonate, etc., or mixtures thereof. The holoformates that can be used include bis-haloformates of dihydric phenols (bischloroformates of hydroquinone, etc.) or glycols (bishaloformates of ethylene glycol, neopentyl glycol, polyethylene glycol, etc.). 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 3,169,212 - Walters - dated February 9, 1965 which are particularly preferred. This class of compounds is generally referred to as copolyestercarbonates.
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-l, paratertiarybutylphenol, 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, tributylamine, 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 émployed are those that typically aid the polymerization of the diphenol with phosgene. Suitable catalysts include tertiary amines such ~ 6~ ~-CH-3077 as triethylamine, tripropylamine, N,N-dimethylaniline, quaternary ammonium compounds such as, for example, tetraethylammonium bromide, cetyl triethyl ammonium bromide, tetra-n-heptylammonium iodide, tetra-n-propyl ammonium bromide, tetramethylammonium chloride, tetramethyl ammonium hydroxide, tetra-n-butyl ammonium iodide, benzyltrimethyl ammonium chloride and quaternary phosphonium compounds such as, for example, n-butyltriphenyl phosphonium bromide and methyltriphenyi phosphonium bromide.
Also included herein axe branched polycarbonates wherein a polyfunctional aromatic compound is reacted with the diphenol and carbonate precursor to provide a theroplastic randomly branched polycarbonate. These polyfunctional aromatic compounds contain at least three functional groups which are carboxyl, carboxylic anhydride, haloformyl, or mixtures thereof. Illustrative of polyfunctional aromatic compounds which can be employed include trimellitic anhydride, trimellitic acid, trimellityl trichloride, 4-chloroformyl phthalic anhydride, pyromellitic acid, pyromellitic dianhydride, mellitic acid, mellitic anhydride, trimesic acid, benzophenonetetracarboxylic - acid, benzophenonetetracarboxylic anhydride, and the like.
The preferred polyfunctional aromatic compounds are trimellitic anhydride and trimellitic acid or their acid halide derivatives.
Blends of linear and branched aromatic polycarbonates are also included within the scope of this invention and further reference to the aromatic polycarbonate portion of the composition of the invention is intended to and should be understood as including such blends.
The block copolymers that can be employed in the practice of this invention can be prepared by methods known to those skilled in the art, such as are disclosed in ~ 6~ 8CH-3077 U.S. Paten-ts 3,189,622, Beaton, dated June 15, 1965; and 3,189,634, r~eeler et al, dated June 15, 1965; and 3,821,325, Merritt et al, dated June 28, 1974.
These block copolymers typically comprise alternating segments of polycarbonate and polyorganosiloxane blocks, as represented by one of the general formulae:

~A ~ ~ ~ ~ g ~ R~

Rlo Rlo R12 _ R3 R4 R7 R8 R3 R4 R7 R8 n P

( 9~

R3 R4 R7 R8 m wherein Rl-R8 can each be independently selected from the group consisting of hydrogen, halogen, alkyl having l to 6 carbon atoms and aryl; Rg and Rlo can each be independently selected from the group consisting of hydrogen, alkyl lOhaving l to 6 carbon atoms and aryl; Rll and R12 can each be independently selected from the group consisting of alkyl having l to 6 carbon atoms and aryl wherein the aryl can also form a ring memberi m is an integer of about 1-10, n is an integer of about 5-100; and, p has a value of at least 1.
Blends and mixtures of aromatic polycarbonates as well as blends and mixtures of polyorganosiloxanes forming the block copolyrner segments are also within the scope of the invention and further reference to the polycar-bonate and polyorganosiloxane segments of the block copolymer is intended to include and should be understood as including such blends and mixtures.
Preferably, however, the polycarbonate segment of the block copolymer is derived from the same diphenol as is the polycarbonate resin with which the block copolymer is to be blended. For example, if the ~J

~4~6~ ~C~-3077 polycarbonate resin is derived from the diphenol, bisphenol-A;
i.e., (2,2-bis(4-hydroxyphenyl)propane), then the polycarbonate segment of the block copolymer is preferably also derived ~rom bisphenol-A. As a further example, if the polycarbonate resin is derived from the diphenol 2,2-bis(4-hydroxy-3-methyl-phenyl)propane, then the polycarbonate segment of the block copolymer is preferably also derived from 2,2-bis(4-h~droxy-3-methylphenyl)propane, and so forth.
While the same applies to the polyorganosiloxane segment of the block copolymer, this segment is preferably polydimethyl-siloxane (PDMS).
The following examples are set forth to more 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.

One hundred (100) parts of an aromatic polycarbonate was prepared by reacting BPA (2,2-bis(4-hydroxyphenyl)propane) and phosgene in the presence of an acid acceptor and a molecular weight regulator. The resultant high molecular weight aromatic polycarbonate had an intrinsic viscosity (IV) of 0.50. This aromatic polycarbonate was subsequently mixed with the various block copolymers described in the ensuing examples by tumbling the ingredients together in a laboratory tumbler. In each instance, the resulting mixture was then fed through an extruder which was operated at about 285C and the extrudate was comminuted into pellets.
The pellets were then injec-tion molded at about 315C into test bars of about 5 in. by 1/2 in. by about ~;~

~~CH-3077 1/16-1/8 in. thick and into test squares of about 2 in. by 2 in. by about 1/8 in. thick.

A block copolymer consisting of a polycarbonate segment derived from BPA and polydimethylsiloxane (PDMS) in the polyorganosiloxane segment was prepared in accordance with the method disclosed in U.S. Patent 3,189,622 - Beaton -dated ~une 15, 1965. That is, the block copolymer was prepared by forming a mixture of BPA and PDMS at a temperature of about 25-100C in the presence of an acid acceptor and phosgenating the mixture until the mass achieved a maximum viscosity. The resultant block copolymer consisted of 50% by weight polycarbonate segments and 50% by weight PDMS segments.

The block copolymer of Example 2 was mixed with the aromatic polycarbonate of Example 1 at the weight percentages shown below and each of the mixtures was then extruded into pellets which were then molded into test bars and test squares following the procedure described in Example 1.

Example 2 Example 1 Block CopolymerAromatic Polycarbonate Example (Wt. %) (Wt. ~) 6 10 ~0 EX~MPLE 7 Following the proced~lre of Example 2, a block ~ copolymer was obtained consisting of 35~ by weight polycarbonate segments and 65% by weight PDMS segments.

~ 7 --~L g-CH-3077 EXA~PLE 8 Following the procedure of Example 1, 5% by weight of the block copolymer of Example 7 was mixed with ; 95~ by weight of the aromatic polycarbonate of Example 1 whereupon the mixture was extruded into pellets and the pellets molded into test bars and test squares as described in Example 1.

.
The procedure of Example 2 was used to prepare a block copolymer consisting of 95% by weight polycarbona~e segments and 5~ by weight PDMS segments. This block copolymer was then extruded into pellets and the pellets molded into test bars and test squares as described in Example 1.

A mixture of 97% by weight of the polycarbonate of Example 1 and 3% by weight PDMS was prepared, which was then extruded into pellets and the pellets molded into test bars and test squares following the procedure of Example 1. In contrast to the smooth, homogeneous appearance of test bars and test squares obtained from mixtures of the aromatic polycarbonate of Example 1 with the block copolymers of Examples 3-6 and 8, the test bars and test squares obtained from the aromatic polycarbonate-PDMS mixture of this example had a mottled, laminar appearance which could not be used as a commercially acceptable product.
The test bars and test squares of Examples 1, 3-6 and 8-10 were subject to various tests to determine various properties of the compositions. The test results wherein 5 test bars and 5 test squares were used for each test are set forth in Tables I and II below wherein the various tests were determined in accordance with the following methods.

Flame retardancy was determined according to Underwriters' Laboratories, Inc. Bulletin UL-94, Burning Test for Classifying Materials. In accordance with this test procedure, materials so investigated are rated either V-0, V-I or V-II based on the results of 5 specimens. The iteria for each V (for vertical) rating per UL-94 is briefly as follows:
"V-0": Average flaming and/or glowing after removal of the igniting flame shall not exceed 5 seconds and none of the specimens shall drip flaming particles 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 flame 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 instant invention, as "burns".
Flexural modulus was determined in accordance with ASTM D-790; flexural yield was determined in accordance with ASTM D-790; unnotched and notched Izod impact strengths were determined in accordance with ASTM D-256; flammability oxygen ration (Fenimore/Martin) was determined in accordance with ASTM D-2863; solvent resistance was evaluated by 8-C~I-3077 by measuring the percent strain necessary to cause crazing in test samples exposed to one drop of solvent for a period of 3 minutes; and RDT (Retention of Ductility Time) denotes the maximum number of hours for which a test bar can be aged at a temperature before the mode of failure in the notched Izod impact test (ASTM~256) changes from ductile to brittle. Unless otherwise specified, the RDT

refers to heat aging at 125C of test bars 1/8" thick.
/11~ f~
A In Table I, "Skydrol" identifies a commercially obtained hydraulic fluid particularly deleterious to - polycarbonates.

~- 8-CH-3077 ~r ~ u~ 0 ~1 ~: H 1:: H
I ~ h H h H H

~J O
~0 ~9 ~ CO
,1 a) h Q ~
ol o I ~ ~ O ~ O O
V
~r t~ O
C~
C~ O I I
0 ~_ l o CO~rl 0 ~r~ r~ ~ In ~D I
a) ~ ~ rl t~1 ooooooo U~
h _ ~
I` ~ 0 0 0 CO
o~
tQ U~ U~ O O O ~ 1 0 ~,_ ~ /~
. ~
~ ~ Q
- ~ ~ ~
.~ 0 ~ O ~ 1- r~cr~ U~ ~ I~ ~ In ~Q O N 4~~D ~5)~) ~Lf')Lt~ ~151 ~1 Z H----1 ~Ir-l ~1~_1 ~I r-l ~1 ~ ._ H ~1 ' ~ ~ U~ .' ' ~ O ~0~
~O ~ OO OO O OO O
j_l N q-l ~~r~ ~~r~r ~ '~
5~ _ A AA A~\A AA
Q ~
.0 o ~ ~ ~ ~ s~
~ ~X a ,~ X ~ ~ rl ~ n ~ ~ ~r u~
~o a~ h u~ . . . . . . . . ~
r~~ ~rl ~ Q, ~r ~ ~ ~ ~ ~ ~1 ~ o . h ~ u~-- o P~ _ o ,~ ~
h ~ X o X ~1 o ~:5 0 ~ ~ ~ ~ ~ ~ oo ~1 0 Q, . . . . . . . . o ~ ~--~ ~ ~ ~ ~ ~ ~ ~

Q
o ~, o ~ .
~0g~ Iooooooo o Lr~ o a ~Ç ~ 9 co ~ o * #

TABLE II

Nothced Izod Impact ~trength vs O

Example Hrs. Hrs. Hrs. Hrs. r~ks. RDT
-- _ l 3.3 2.4 2.51.6 1.4 6 hrs.
3 8.2 2.7 2.81.7 - 6 hrs.
4 - - 15.8 14.15.0 2 wks.
- - - 15.114.3 2 wks.
6 14.4 - 15.1 13.613.5 2 wks.
8 - - - 14.114.4 2 wks.
9 - - - 11.44.5 2 wks.
13.6 - 14.3 12.611.3 2 wks.
In Table I, it can be seen that as little as 3%
of the Example 4 block copolymer was sufficient to improve solvent resistance against Skydrol and that 5% of the block - copolymer of Example 5 raised the resistance to 1% strain, which is about the maximum generally encountered in most practical situations.
Table I also reveals that, at higher levels of block copolymer, oxygen index and UL-94 ratings are improved (for instance Example 1 vs. Example 6).
From Table II, it can be seen that use of the block copolymers of the invention results in a larger positive ; effect on ductility and a smaller negative effect on molded properties of the test samples as shown by Examples 3-6 and 8.
For example, as little as 3% of the block copolymer was sufficient to extend the retention ductile impact behavior furing aging at 125C from 6 hours to at least 2 weeks (Example 4) and as little as 5% of the block copolymer was sufficient to eliminate any brittle impact behavior after aging for two weeks at 125C (Examples 5 and 8~.
The improvement obtained by mixing the block copolymer of the invention with the aromatic polycarbonate as opposed to using the block copolymer alone can be readily seen by comparing the results of Example 6 with Example 9 in Table II. Although each example contains 5% PDMS, Example 6 consisting of the aromatic polycarbonate-block copolymer mixture retained its impact strength and ductility after two weeks of aging at 125C whereas Example 9, consisting of only the block copolymer, did not.

The procedure of Example l was repeated except that 0.5% by weight of the sodium salt of trichlorobenzene sulfonic acid (STB) and 0.1% by weight polytetrafluorethylene (PT~E~ were mixed with the aromatic polycarbonate. The mixture was extruded into pellets as in Example l, but instead of injection molding the pellets into test bars and test squares, the pellets were extruded into sheets measuring 4 feet square by 0.125" thick.

A block copolymer consisting of a polycarbonate segment derived from BPA and PDMS in the polyorganosiloxane segment was prepared in accordance with the method disclosed in U.S. Patent 3,821,325 - Merritt Jr. et al - dated June 28, 197~. That is, the block copolymer was prepared by reacting a mixture of ~PA and PDMS at a temperature of about 20-50~ and thereafter phosgenating the reaction mixture in the presence of additional dihydric phenol using alkali~metal hydroxide as an acid acceptor while maintalning the 3Q phosgenation reaction mixture at a pH of about 6-12 until the resulting mass achieved a maximum viscosity. The resulting block copolymer consisted of 57% by weight ~ 8-CH-3~77 polycarbonate segments and 43% by weight PDMS.
E ~PLE 13 The procedure of Example 11 was repeated except that 4~ by weight of the block copolymer of Example 12 was mixed with the other ingredients of Example 11 to obtain the aromatic polycarbonate sheets.
The sheets obtained from Examples 11 and 13 were then subjected to solvent exposure to determine the stress levels necessary to induce stress crazing during given time periods. The resul-ts obtained are set forth in Tables III
a r~
and IV below wherein "Spray Nine", "Lexsol" and "Royalite S-22" identify commercially obtained cleaning fluids.
TABLE III
Stress Level After One Hour Exposure . .
Stress Level (psi) SolventExample 11 Example 13 Carbon Tetrachloride 500 1000 Toluene 500 1000 Benzene 500 1000 Bu-tyl Cellosolve 1500 2000 Isopropyl Alcohol ~ 2500 ~ 2500 Methyl Alcohol> 2500 > 2500 Royalite S-22 500 1000 Spray Nine 2000 > 2500 Lexsol ~ 2500 > 2500 TABLE IV
Time to Stress Crack at 1500 PDI Stress _ _ ~ . . _ _ ,, ........... ... _ _ With Continuous Wetting . _ Solvent Example 11 Example 13 Carbon Tetrachloride 1 min. 38 min.
Gasoline immediate ~Jl min.

8-CH-3~77 The results in Tables III and IV above reveal that Example 13, containing the additional 4% by weight of the block copolymer, required higher stress levels to induce stress-cracking than did Example 11. Example 13 was also more durable than Example 11 when exposed to carbon tetrachloride as shown in Table IV. In general, the results in Tables III and IV lndicate that improved solvent resistance is obtained when the aromatic polycarbonate is further modified with the block copolymer.

The procedure of Example 1 was followed to prepare aromatic polycarbonate test bars and test squares comprising 70% by weight of the polycarbonate of Example 1 and 30% by weight of the block copolymer of Example 12. The properties of Example 1 were compared with those of this example (14 and the results are set forth in Table V b~low wherein tensile strength (psi), elongation (%), and modulus (psi) - results were determined in accordance with ASTM D-638.
TAsLE V
_mparative Properties of Example 14 and Example 1 Properties Example 14 Example 1 Tensile Strength (psi) 6700 9500 Elongation (~) 155 110 Modulus (psi) 150 x 103 350 x 10 UL-94 Rating V-O V-II
Time to Stress Crack @ 1500 psi No crack with carbon tetrachloride > 1 hr. <1 min.
with gasoline ~ 1 hr. <1 min.
Stress level to crack after 1 hr.
continuous exposure (psi) with carbon tetrachloride * No crack 1100 with butyl cellosolve * No crack 1800-2000 with Royalite C * No crack 500 ~ 8~C~-3077 * Surface etch was noted after 500, 2500 and 5000 psi, respectively, but test bars remained completely ductile upon bending.
The results in Table V above reveal the dramatic improvement in solvent resistance obtained with the aromatic polycarbonate-block copolymer mixture (Example 14) as opposed to the unmodified aromatic polycarbonate (Example 1).

The block copolymer of Example 12 was mixed with the aromatic polycarbonate of Example 1 and the aromatic polycarbonate-PDMS mixture of Example 11 at the weight percentages shown below and test sheets of these mixtures were prepared as described in Example 11.

Example 11 Example 12 Example 1 Aromatic Polycarbonate- Block Aromatic Polycarbonate STB/P~FE Mixture(Wt.%) Copolymer Example (Wt. %) BTS PTFE (Wt.%) 92.5 - - 7.5 16 95.4 0.5 0.1 4.0 17 89.4 0.5 0.1 10.0 These Examples were subjected to various tests, the results of which are set forth in Table VI below wherein tensile yield strength (psi) and ultimate streng~h (psi) were determined in accordance with ~STM D-638.
TABLE VI
Comparative Properties of Test Bars and Test Sheets Examples Properties 1 14 15 _ 11 13 16 17 Tensile:
Yield Strength (psi) 9000 - 9000 9000 9260 9200 7700 Ultimate Strength (psi) 9500 68001152Q 8500 8500 9000 6990 Elongation (%) 110 155 110 95 70 85 65 Modulus (psi x 103) 345 150 - 325 Flexural Modulus (psi) 340 - 250 325 265 250 220 ~ 6~ ~ -CH-3077 TABLE VI (Cont'd.) 1 14 15 ll 13 16 17 Solvent Resistance:
Time to crack at 1500 psi owith carbon tetrachloride (min.) ~1 >60 > 60 ~138 >60 >60 ~with gasoline (min.) ~1 >60 25<1 1 >60 >60 Stress to crack after 1 hr.
exposure (psi) o with carbon tetrachloride 110~>2500>2500 ~500 1000 2500 500-2500 with butyl cellosolve 1900>2500>2500 1500 2000 1500 500-2500 o with Royalite S-22 500>2500>2500 500 1000 2000 500-2500 with gasoline 1000 - 2500 <500<500 1000 500-2500 The results shown in Table VI above reveal that while the tensile properties of the block copolymer of the invention (Examples 13-17) compared favorably with the aromatic polycarbonate without the block copolymer additive (Examples 1 and 11), the solvent resistance and stress crack resistance were notably better.

Following the procedure of Example 1, a copolymer was obtained from spA and tetrabromo bisphenol-A wherein the amount of bromine employed was sufficient to provide a bromine content of 6~ by weight in the copolymer.

Following the procedure of Example ll, additional sheet samples were obtained employing the compounds and compositions of Examples l, 15, 16 and 18. The solvent resistance of these sheet samples was determined by subjecting the samples to various solvents for a period of 5 minutes at a temperature of 200 F and a stress of 2000 psi. The results obtained are set forth in Table VII

below wherein "X" denotes that the sample broke and failea.
"C" denotes that the sample crazed, and "S" denotes that the surface of the sample softened.
TABLE VII
Solvent Resistance of Sheet SolventsSamples from Examples Ethyl cellosolve ~ C C X
Methyl isobutyl ketone S,C S S S
Commercial Hydraulic fluid X C C
Lacquer thinner X - C C X
Butyl cellosolve X C C X
Methyl ethyl ketone S,c S S,C S,C
The results in Table VII above indicate that sheet samples containing the block copolymer of the invention (Examples 15 and 16) exhibit significantly greater chemical resistance than do sheet samples not containing the block copolymer of the invention, including the sample derived from the BPA/tetrabromo-BPA copolymer (Example 18). It is also interesting to note that the inclusion of the STB and PTFE additives (Example 16) did not impart greater chemical resistance to the sheet sample than the sheet sample obtained without these additives (Example 15).

Claims (7)

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

1. A ductile, solvent resistant aromatic polycarbonate composition having improved flame retardance, said composition comprising a mixture of a high molecular weight aromatic polycarbonate and a block copolymer in an amount of greater than 5% up to about 50% by weight of said aromatic poly-carbonate, said block copolymer having alternating segments of aromatic poly-carbonate and polyorganosiloxane represented by one of the general formulae selected from the following:

(A) (B) wherein R1-R8 can each independently be selected from the group consisting of hydrogen, halogen, alkyl having 1 to 6 carbon atoms, and aryl; R9 and R10 can each be independently selected from the group consisting of hydrogen, alkyl having 1 to 6 carbon atoms, and aryl; R11 and R12 can each be independently selected from the group consisting of alkyl having 1 to 6 carbon atoms, and aryl; m is an integer of about 1-10; n is an integer of about 5-100; and, p has a value of at least 1, the weight ratio of said polycarbonate segments to said polyorganosiloxane segments in said block copolymer being in the range of about 25:75-75:25.

2. The composition of claim 1 wherein the aromatic polycarbonate and the polycarbonate segments in said block copolymer are each derived from the same diphenol.

3. The composition of claim 2 wherein the diphenol is 2,2-bis(4-hydroxyphenyl)propane.

4. The composition of claim 1 wherein the polyorganosiloxane segments are polydimethylsiloxane.

5. The composition of claim 1 wherein the segments in said block copolymer are derived from blends and mixtures of polycarbonates and polyorganosiloxanes.

6. The composition of claim 1 which includes about 0.1-1.0 weight percent of the sodium salt of trichlorobenzene sulfonic acid and about 0.05-0.3 weight percent polytetra-fluoroethylene.

7. The composition of claim 1 wherein said composition is in the form of a shaped, molded article.