CA1162688A - Polycarbonate blends having improved flow and critical thickness characteristics - Google Patents

Abstract

Mo-2077 PC-014 POLYCARBONATE BLENDS HAVING IMPROVED FLOW AND CRITICAL THICKNESS CHARACTERISTICS ABSTRACT OF THE DISCLOSURE A polycarbonate is comprised of a blend of polycarbonate resins. One polycarbonate resin is based upon an aromatic diphenol and the second polycarbonate is a copolycarbonate resin based upon an aromatic diphenol and an aromatic thiodiphenol. The copolycarbonate resin is incorporated into the blend in an effective amount to improve the critical thickness of the polycarbonate.

Description

- i 162688 Mo-2077 POLYCARBONATE BLENDS HAVING IMPROVED FLOW AND
CRITICAL THICKNESS C~ARACTERISTICS
.. . . .. _ . _ _ . .. .
BACKGROUND OF THE INVENTION
. .
1. Field of the Invention This invention relates to polycarbonate resin blends and more particularly to polycarbonate resin blends having improved critical thickness values and melt ~low rates.

2. Description of_the Prior Art Polycarbonate~ derived from reactions involving organic dihydroxy compounds and carbonic acid derivatives have found extensive commercial application because of their excellent mechanical and physical properties. These thermoplastic polymers are particularly suited for the manufacture of molded articles requiring impact strength, rigidity, toughness, thermal and dimensional stability as well as excellent electrical properties. However, one deficiency of polycarbonate when used in molded articles is the low critical thickness values of the polycarbonate polymer.
It is kno~n that polycarbonate plastics exhibit high notched Izod (ASTM D-256) impact values. These values, however, are dependent upon the thickness of the test specimens. Typical notched Izod impact values of a 1/8" specimen are about 16 ft.-lbs/inch.
These high Izod values result because a specimen of a 1/8" thickness is thinner than the critical thickness of the polymer and therefore upon impact a hinged or ductile break occurs. On the other hand, a I/4"
specimen exhibits a clean or brittle break and gives notched Izod impact values of only about 2.5 ft.-lbs/inch.
Mo-2077 '~h ~ 162688 The 1/4" specimens are said to be above the critical thickness of the polymer. "Critical thickness" has been defined as the thickness at which a discontinuity in Izod impact values occurs. In other words, it is the thickness at which a transition from a brittle to a ductile break or vice versa occurs. Thus, a standard impact specimen of polycarbonate polymer thicker than the critical thickness exhibits brittle breaks and those thinner than the critical thickness exhibit hinyed or ductile breaks. Further, the critical thickness of a polycarbonate based on bisphenol A with a melt flow of

3 to 6 grams/10 minutes at 300C (ASTM D-1238) has a critical thickness of 225 mils.
One approach to solving the critical thickness problem has been to incorporate polyolefin polymers into the polycarbonate which has substantially improved critical thickness (see U.S. Patent No. 3,437,631).
But along with this improvement has come detrimental effects such as colorant dispersion problems, lack of transparency, poor weld line strength, and worsened flammability.
Another approach to solving the critical thickness problem has been to prepare polycarbonate resins incor-porating thiodiphenols which exhibit improved critical thickness. Further, these polycarbonate resins based upon thiodiphenol and particularly bisphenol A exhibit high melt flows along with the improved critical thickness. Such copolymers of thiodiphenol and bis-phenol A are more fully disclosed in U.S. Patent No.
3,250,774. One disadvantage of such a system Mo-2077 ~\
-is that the single copolymer must be prepared at the desired level of thiodiphenol content for each particu-lar use~
These aromatic diphenol-aromatic thiodiphenol copolycarbonates have been shown to have superior toler-ance for the presence of halogen. In particular, U.S.
Patent 4,174,359 discloses that these copolycarbonates maintain high critical thickness values, e.g., more than 20~ mils in many cases, upon the incorporation of flame retardin~ amounts o~ halogen. The halogen can be carried by either monomeric compounds or polymers such as the homopolycarbonate of 2,2-bis-(3,5-dibromo-4-hydroxyphenyl) propane or copolycarbonates of this monomer and 2,2-bis-(4-hydroxyphenyl~ propane, i.e., tetrabromo BPA~BPA copolymers.
In accordance with the invention a polycar-bonate is provided which has improved critical thickness ~alues, is highly transparent, exhibits excellent weld line strength, and exhibits acceptable flammability ratings.
The composition of the polycarbonate of the invention comprises an intimate mixture of an aromatic polycarbonate resin which is the reaction product of an aromatic diphenol and a carbonate precursor on the one hand and an effective amount of an aromatic copolycar-bonate which is the reaction product of an aromatic diphenol, an aromatic thiodiphenol and a carbonate pre-cursor, ~hich copolycarbonateischaracterized in that it contains from about 2 to 50% of an aromatic thio-diphenol, relative to the total moles of diphenol andaromatic thiodiphenol, DET~I$ED DESCRTPTION OF THE INVENTION
~ hen used herein "polycarbonate resin" or "resins" means the neat resin or resins without addi-tives; "polycarbonate" means the polycarbonate resinor resins with additives therein Mo-2077 ~ 16268~

-3a-The copolycarbonate resins of the invention may be prepared by conventional methods for polycarbonate resins, and may have an average molecular weight of 10,000 to 200,000, and preferably a melt flow rate of 1 to 24 grams/10 minutes at 300C (ASTM 1238).
Any suitable process, reactant catalyst, solvent, reaction condition and the like for the production of the polycarbonate and copolycarbonate resins of this inven-tion which are customarily employed in polycarbonate resin syntheses may be used such as disclosed in Mo-2~77.
PC-014.

~ 162688

-4-German Patent Nos. 962,274 and 1,046,311; and U.S.
Patent Nos. 2,964,794; 2,970,131; 2,991,273; 2,999,835;
2,999,846; 3,028,365; 3,153,008; 3,187,065; 3,215,668;
and 3,248,414. The preferred process is the interfacial polycondensation process.
According to the inter~acial polycondensation process, polycarbonate and copolycarbonate resins are obtained by reacting the aromatic dihydroxy compounds with an alkali metal hydroxide or alkaline earth metal oxide or hydroxide to form the salt of the hydroxy compounds. The salt mixture is present in an aqueous solution or suspension and is reacted with pnosgene, carbonyl bromide, or bischloroformic esters of the aromatic dihydroxy compounds. An organicsolvent i5 provided in the reaction admixture which is a solvent for the polymer but not for the aromatic dihydroxy salts.
Thus, chlorinated and non-chlorinated aliphatic hydro-carbons or chlorinated and non-chlorinated aromatic hydrocarbons are used as the organic solvent which dissolves the condensation product. Suitable solvents include cyclohexane, methylcyclohexane, benzene, toluene, xylene, methylene chloride, chloroform, carbon tetra-chloride and chlorobenzene.
In order to limit the molecular weight, one may use monofunctional reactants such as monophenols, for example the propyl-, isopropyl- and butyl-phenols~
especially p-tert.-butyl-phenol and phenol itself. In order to accelerate the reaction, catalysts such as tertiary amines, quaternary ammonium, phosphonium or arsonium salts and the like may be used. The reaction temperature Mo-2077 i 162688

-5-should be about -20 to ~150C, preferably about 0C
to 100~C.
According to the polycondensation process in a homogeneous phase, the dissolved reaction components are polycondensed in an inert solvent in the presence of an equivalent amount of a tertiary amine base required for absorption of the generated HCl, such as N,N-dimethyl-aniline; N,N-dimethyl-cyclohexylamine or preferably pyridine and the like.
In still another process, diaryl carbonate can be transesterified with the aromatic dihydroxy compounds to form the polycarbonate resin.
It is to be understood that it is possible to combine in a chemically meaningful way in the processes described above both the aromatic dihydroxy compounds and the monohydroxy compounds in the form of the alkali metal salts and~or bis-haloformic acid esters, and the amount of phosgene or carbonyl bromide then still required in order to obtain high molecular weight products. Other methods of synthesis in forming the polycarbonate and copolycarbonate resins of the invention such as dis-closed in U.S. Patent No. 3,912,688, may also be used.
"Aromatic diphenol" as used herein means those aromatic diphenols which do not include thiodiphenols.
The aromatic diphenols useful in the practice of the present invention include the following compounds:
hydroquinone, resorcinol, dihydroxydiphenyls, bis-(hydroxy-phenyl)-alkanes, bis-(hydroxyphenyl)-cycloalkanes, bis-(hydroxyphenyl)-ethers, bis-(hydroxyphenyl)-ketones, bis-(hydroxyphenyl)-sulphoxides, bis-(hydroxyphenyl)-sulphones and a,~-bis-(hydroxyphenyl)-diisopropylbenzenes, as well as their nuclear-alkylated and nuclear-halogenated Mo-2077 ~ 162~88 compounds. These and ~urther suitable aromatic dihydroxy compounds are described, for example, in U.S. Patent Nos. 3,028,365; 2l999l835; 3,148,172; 3,271,368; 2,991,273;
3,271,367; 3,280,078; 3~014,891; and 2,9~9,846; in German Offenlegun~sschriften (German Published Specifications) 1,570,703; 2,063,050; 2,063,052; 2,211,956; and 2,211,957;
in French Patent Specification 1,561,518; and in the monograph "H. Schnell, Chemistry and Physics of Poly-carbonates, Interscience Publishers, New York, 1964".
Preferred bisphenols are those of the formula:
R R

HO ~ ~ - X ~ OH

R R
in which R is identical or different and denotes H, Cl to C4 alkyl, Cl or Br; and in which X is Cl to C8 alkylene, C2 to C8 alkylidene, C5 to C15 cycloalkylene, C5 to C15 cycloalkylidene, -SO2-, -SO-, -CO- or:
CH3 ~ CH3 Examples of these bisphenols are: 4,4'-dihydroxy-diphenyl; 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol ~); 2,4-bis-(4-hydro~yphenyl)-2-methylbutane; l,l-bis-(4-hydroxyphenyl)-cyclohexane; ~,~-bis-(4-hydroxyphenyl)-p-diisopropyl-benzene; 2,2-bis-(3-methyl-4-hydroxyphenyl)-propane; 2,2-bis-(3-chloro-4-hydroxylphenyl)-propane bis-(3,5-dimethyl-4-hydroxyphenyl)-methane; 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane; bis-(3,5-dimethyl-Mo-2077 ,~, 1 ~62688 4-hydroxyphenyl)-sulphone; 2,4-bis-(3,5-dimethyl-4-hydroxyphenyl)~2-methylbutane; 1,1-bis-(3,5-dimethyl-4-hydroxyphenyl)-cyclohexane; ~,~-bis-(3,5~dimethyl-4-hydroxyphenyl)-p-diisopropyl-benzene; 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane; and 2,2-bis-(3,5-dibromo-4-hydroxyphenyl)-propane (te~rabromobisphenol A) propane.
Examples of particularly preferred bisphenols are:
2,2-bis-(4-hydroxyphenyl)-propane, 2l2-bis~(3,5-dimethyl-4-hydroxyphenyl~-propane; 2,2-bis-(3l5-dichloro-4- -hydroxyphenyl)-propane; 2,2-bis-(3~5-dibromo-4-hydroxy-phenyl)-propane; and l,l-bis-(4-hydroxyphenyl)-cyclo~
hexane.
The most preferred bisphenol is 2,2-bis-(4-hydroxy-phenyl)-propane (bisphenol A).
The aromatic thiodiphenols useful in the practice of the invention are those representedby the structural formula:
(Rl)n (R2)n HO ~S ~OH

wherein Rl and R2, which may be the same or different, are H, Cl to C4 alkyl, Cl or Br, preferably H or Cl to C4 alkyl; and n is equal to 0, 1 or 2.
The aromatic copolycarbonates of the present inven-tion preferably contain from about 6 to 50 mole percent, preferably fro~ about 10 to 40 mole percent, of the aromatic thiodiphenol, based on the total mole percent of diphenols. Suitable aromatic copolycarbonates are described in U.S. Patent No. 3,250,774.

Mo-2077 ~ .

~ 18~688 The aromatic polycarbonate and copolycarbonate resins can be hranched due to the. incorporation of small amounts, preferably o~ betwe.en about 0.05 and 2.0 mole percent ~relative to diphenols employed~, of trifunc-tional or more than trifunctional compounds, espe~iallycompQ.unds with three or more phenolic hydroxyl ~roups.
Polycarbonates of this type are described, for example, in German Offenlegungsschriften (German Pub-lished Speci~ications) 1,570,533; 1~595l762; 2,116,974;
and 2,113,347; British Patent Specification 1,079,821 and U.S. Paten-t Specification 3,544,514.
Some examples of compounds with three or more than three phenolic hydroxyl groups which can be used are phIoroglucinol; 4,6-dimethyl-2,4,6-tri-(4-hydroxy-phenyl)-heptane-2,4,6-dimethyl-2r4,6-tri-(4-hydroxy-phenyl)-heptane; 1,4,5-tri-(4-hydroxyphenyl)-benzene;
1,1,1-tri-(4-hydroxyphenyl)-ethane; tri-(4-hydroxy-phenyl)-phenylmethane; 2,2-bis-[4,4-bis-(4-hydroxyphenyl)-cyclohexyl]-propane; 2,4-bis-(4-hydroxyphenyl -isopropyl)-20.phenol; 2,6-bis-(2-hydroxy-5'-methyl-benzyl)-4-methyl-phenol; 2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)-propane; hexa-(4-(4-hydroxyphenylisopropyl)phenyl) ortho-terephthalic acid ester; tetra-(4-hydroxyphenyl)-methane; tetra-(4-(4-hydroxyphenylisopropyl)-phenoxy)-methane; and 1,4-bis-((4l,4"-dihydroxytriphenyl)-methyl)-benzene. Some of the other trifunctional compounds are 2,4-dihydroxybenzoic acid, trimes.ic acid, cyanuric chlo~ide and 3,3-bis~(4-h.ydroxyphenyl)-2-oxo-2,3-dihydro-indole.
3Q Th~e aromatic copqlycarbonates. of the present inven-tion are intimately blended ~ith the aromatic polycar-bonate resins in an ef~ective amount, ~ased on the Mo-2077 ..
.,,,~

1 1628~B

total weight of the blend~ to improve the critical thick-ness properties o~ the aromatic polycarbonate resins.
Preferably, the aromatic c4polycarbonates are present in from about 1 to 50 weight percent, most preferably from about 10 to 50 weight percent, based on the total weight of the blend.
Furthermore, the aromatic copolycarbonate-aromatic polycarbonate blend of the present invention preferably has an aromatic thiodiphenol content of about 5 to 10 20 weight percent, mQst preferably about 10 to 15 weight percent, based ~n the total diphenol content.
The blends of the present invention may also contain conventional resin additives such as glass fibers~ pigments, dyes, UV stabilizers~ mold release agents and fillers.
The copolycarbonates and any additives, including glass fibers~ may be intimatel~ blended with the aromatic polycarbonate in known mixing devices such as kneaders, single-screw extruders, twin-screw extruders, mills and the like.
Although copolymers of bisphenols and thiodiphenols are known, (see U.S. Patent No. 3,250,744)l the contem-plated use of these polymers of the prior art was as coatings and moldings having good anchorage. The copolymers of the prior art have from 20 to 100 mole percent of the repeating structural unit:
[ ~:

Mo-2077 ,~

1 1~2688 to obtain good anchorage, but the prior art did not recognize the improved critical thickness values obtained if such copolymers are intimately blended with an aromatic polycarbonate.
The invention will be further illustrated, but is not intended to be limited by the fcllowing examples.

A copolycarbonate was prepared by reacting a mixture of the disodium salts of bis-2-(4-hydroxyphenyl) propane (bisphenol A) and 4,4'-thiodiphenol with phosgene in accordance with the interfacial polycondensation synthesis hereinbefore discussed. The weight ratio of bisphenol ~ to 4,4'-thiodiphenol was 9 to 1. The copolycarbonate prepared was tested for physical, mecha~ical and rheological proper~ies and the t~st resul~s are reported on Table 1. The copolycarbonate was found to be highly transparent.

Example 1 was repeated except that the ratio of 20 4,4'-thiodiphenol:bisphenol A was 30:70. Test results of the copolycarbonate prepared in accordance with Example 2 are shown on Table 1. The copolycarbonate of Example 2 was found to be highly transparent.

The polycarbonate prepared according to Example 2 was intimately blended with a bisphenol A homopoly-carbonate having a melt index of 3.3 grams/10 minutes in the ratio of 1 part by weight copolycarbonate resin to 2 parts by weight homopolycarbonate resin. The test results of the polycarbonate of Example 3 are shown on Table 1. The blend was found to be highly transparent.

Mo-2077 Example 3 was repeated except that the ratio of homopolycarbonate resin to copolycarbonate resin was 1:1. The test results of the blend are reported in Table 1. The blend was highly transparent.

Example 3 was repeated except that the ratio of copolycarbonate resin to homopolycarbonate resin was 1:5.
The test results of the blend are reported in Table 1.
The blend was found to be highly transparent.

Example 1 was repeated except that the ratio of thiodiphenol:bisphenol A was 40:60 on a weight basis.
Test results of the polycarbonate of Example 6 are reported in Table 1. The polycarbonate was highly transparent.

The polycarbonate resin of Example 6 was blended at various levels with bisphenol A homopolycarbonate resin having a melt index of 3.3. The test results along with the composition of the polycarbonates are reported in Table 1. All of the polycarbonates were highly transparent.

The polycarbonate resin of Example 6 was blended at various levels with bisphenol A homopolycarbonate resin having a melt index of 7.4 grams/10 minutes. The test results along with the composition of the polycar-bonates are reported in Table 1. All of the polycarbonates were highly transparent.

Example 1 was repeated except that the ratio of thiodiphenol:bisphenol A was 25:75 on a weight basis.
Test results of the polycarbonates of Example 13 are reported in Table 1. The polycarbonate was highly transparent.
Mo-2077 i 162688 The polycarbonate resin of Example 13 was blended at various levels with bisphenol A homopolycarbonate resins having melt indices of 3.3 and 7.4. The test results along with the compositions are reported in Table 1. All of the polycarbonates were highly trans-parent.

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~n ~n dP 1-~ ~ ~C ~ w Mo-2077 ~ 162~88 As can be seen from Table 1, blending of a copoly-carbonate resin having the aromatic thiodiphenol therein with a homopolycarbonate resin improve~ the critical thickne~
over a polycarbonate fabricated solely from the homopoly-carbonate.
Polycarbonates of 1/4" thickness (250 mils) are usefulin many applications, and therefore, it is desirable to provide polycarbonates havin~ a critical thickness of 250 mils or greater.
The results presented in Table 1 indicate that critical thickness values equivalent to a BPA/TDP copoly-carbonate with a 10 weight percent TDP level can be achieved from a polyblend (in a 1:1 weight ratio) of a BPA/TDP copolycarbonate having a 30 weight percent TDP
level and a melt index of 6.6 grams/10 minutes with a BPA polycarbonate having a melt index of 3.3 grams/10 minutes. Thus, a 15 weight percent TDP le~el is required in a polyblend to achieve impact and critical thickness values equivalent to those of a BPA/TDP copolycarbonate having a 10 weight percent TDP level.
- The exact compositions of the blend will also be a function of the melt flow properties of the aromatic diphenol-aromatic thiodiphenol copolycarbonate and the aromatic diphenol polycarbonate. For example, a polyblend of a BPA/TDP copolycarbonate (30 weight percent TDP
level and melt index of about 3-4) and a BPA polycarbonate ~melt index of about 3-4) in a weight ratio of 1:2 will lower the TDP content of the polyblend to about 10 weight percent required to achieve the critical thickness comparable to the copolycarbonate cited in Example 1.

Mo-2077 ~ 162688 The data from Table 1 demonstrates that there is a correlation between melt index of the polycarbonate resin blend and critical thickness values of 250 mils or greater.
Table 2 demonstrates this correlation.

Weight Percent TDP* Melt Index g/10 Critical Thickness in Blend min. of Blend Value > 250 Mils 2.9 255 4.8 >250 18.75 7.1 >250 11.3 >255 *TDP is thiodiphenol.
Upon linear regression analysis, a critical thickness 15 of >250 mils will be achieved according to the following equation:
y = 0.4239 (x) - 1.29 where y is the melt flow rate in grams/10 minutes and x is the weight percent aromatic thiodiphenol in the blend.
Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of 25 the invention except as it may be limited by the claims.

Mo-2-077

Claims (13)

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

1. A polycarbonate comprising an intimate mixture of:
(a) an aromatic polycarbonate resin comprising the reaction product of (a-i) an aromatic diphenol, and (a-ii) a member selected from the group consisting of carbonyl bromide, phosgene, bischloroformic esters of said (a-i) and diaryl carbon-ates, and (b) an effective amount of aromatic copoly-carbonate resin to improve the critical thickness value of the aromatic polyear-bonate resin, said aromatic copolycarbonate comprising the reaction product of (b-i) an aromatic diphenol, (b-ii) an aromatic thiodiphenol, and (b-iii) a member selected from the group consisting of carbonyl bromide, phosgene, bischloroformic esters of (b-i) and (b-ii) and diaryl carbonates said aromatic copolyearbonate characterized in that it contains from about 2 to 50 pereent of said (b-ii) based on the total moles of said (b-i) and said (b-ii).

2. The polycarbonate of Claim 1 wherein the aromatic diphenol is of the structural formula:
Mo-2077 wherein R is identical or different and denotes H or C1 to C4 alkyl, and X is C1 to C8 alkylene, C2 to C8 alkyli-dene, C5 to Cl5 cycloalkylene, C5 to C15 cycloalkylidene, -SO2-, -SO-, -CO- or:

3. The polycarbonate of Claim l wherein the aromatic thiodiphenol is of the structural formula:
wherein Rl and R2 are identical or different and denote H, C1 to C4 alkyl, Br or C1, and n is 0, 1 or 2.

4. The polycarbonate of Claim l wherein the aromatic copolycarbonate is present in from about l to 50 weight percent based on the total weight of the poly-carbonate.

5. The polycarbonate of Claim l wherein the aromatic thiodiphenol content is from about 5 to 20 weight percent based on the total diphenol content.

6. The polycarbonate of Claim l wherein the aromatic diphenol is bisphenol A and the aromatic thio-diphenol is of the structural formula:

7. The polycarbonate of Claim 1 wherein the critical thickness of the polycarbonate is 250 mils or greater and the melt flow rate and the percent thio-diphenol of said polycarbonate are defined by the equation:
Mo-2077 y = 0.423g (x) - 1.29 wherein y is the melt flow rate in grams/10 minutes at 300°C and x is the percent thiodiphenol in the poly-carbonate.

8. A polycarbonate comprising:
(a) an aromatic polycarbonate resin comprising the reaction product of (i) an aromatic diphenol of the structural formula:

wherein R is identical or different and denotes H, C1 to C4 alkyl, and X is C1 to C8 alkylene, C2 to C8 alkylidene, C5 to C15 cycloalkylene, C5 to C15 cycloalkylidene, -S02-, -SO-, -CO- or ,and (ii) a member selected from the group consisting of carbonyl bromide, phosgene, bischloroformic esters of (i) and diaryl carbonates, (b) intimateLy mixed with about 1 to 50 weight percent based on the total weight of the polycarbonate of an aromatic copolycar-bonate resin comprising the reaction product of Mo-2077 (i) an aromatic diphenol of the structural formula wherein R is identical or different and denotes H, C1 to C4 alkyl, and X is C1 to C8 alkylene, C2 to C8 alkylidene, C5 to C15 cycloalkylene, C5 to C15 cycloalkylidene, -S02-, -SO-, -CO- or , (ii) about 2 to 50 weight percent based on the total moles of diphenol of an aromatic thiodiphenol of the struc-tural formula wherein Rl and R2 are identical or different and denote H, C1 to C4 alkyl, Cl or Br, and n is 0, 1 or 2, and (iii) a member selected from the group consisting of carbonyl bromide, phosgene, bischloroformic esters of (i) and (ii) and diaryl carbonates.
Mo-2077

9. The polycarbonate of Claim 8 wherein the aromatic thiodiphenol content is from about 5 to 20 weight percent based on the total diphenol content.

10. The polyblend of Claim 8 wherein the aromatic diphenol is bisphenol A and the aromatic thiodiphenol is of the structural formula:

11. A process for preparing an aromatic polycar-bonate blend having improved critical thickness values comprising intimately blending (a) an aromatic polycarbonate comprising the reaction product of (i) an aromatic diphenol of the structural formula:
wherein R is identical or different and denotes H, or Cl to C4 alkyl, and X is Cl to C8 alkylene, C2 to C8 alkylidene, C5 to C15 cycloalkylidene, -SO2-, -SO-, -CO-, or , and Mo-2077 (ii) a member selected from the group con-sisting of carbonyl bromide, phosgene, bischloroformic esters of (i) and diaryl carbonates, (b) with about 1 to 50 weight percent based on the total weight of the polyblend of an aromatic copolycarbonate comprising the reaction product of (i) an aromatic diphenol of the structural formula:
wherein R is identical or different and denotes H or Cl to C4 alkyl, and X is Cl to C8 alkylene, C2 to C8 alkylidene, C5 to C15 cycloalkylene, C5 to C15 cycloalkylidene, -S02-, -SO-, -CO- or (ii) about 2 to 50 mole percent based on the total moles of diphenol of an aromatic thiodiphenol of the struc-tural formula:

wherein Rl and R2 are identical or different and denote H, Cl to C4 Mo-2077 alkyl, Cl or Br, and n is 0, 1 or 2, and (iii) a member selected from the group con-sisting of carbonyl bromide, phosgene, bischloroformic esters of (i) and (ii), and diaryl carbonates.

12. The process of Claim 11 wherein the aromatic thiodiphenol content of the aromatic polycarbonate blend is from about 5 to 20 mole percent based on the total diphenol content.

13. The process of Claim 11 wherein the aro-matic diphenol is bisphenol A and the aromatic thiodiphenol is of the structural formula: