the present invention provides polycarbonate compositions blended with an ortho - methyl substituted aromatic dihydroxy compound and an additional flame retardant additive to improve flame retardant properties . suitable ortho - methyl substituted aromatic dihyroxy compounds include 2 , 2 - bis ( 4 - hydroxy - 3 - methylphenyl ) propane ; 2 , 2 - bis ( 4hydroxy - 3 , 5 - dimethylphenyl ) propane ; and corresponding compounds in which only one phenol is monoor dimethyl ortho substituted . the preparation of these compounds is known . at least one of these ortho - methyl substituted aromatic dihydroxy compounds is used to prepare the polycarbonate compositions of the present invention . the polycarbonate resin used in the compositions of the present invention is an aromatic carbonate polymer which may be prepared by reacting a dihydric phenol with a carbonate precursor . the polycarbonate resin used in the blends of the present invention is an aromatic carbonate polymer which may be prepared by reacting a dihydric phenol with a carbonate precursor such as phosgene , a haloformate , or a carbonate ester . generally speaking , such aromatic carbonate polymers may be typified as possessing recurring structural units of the formula : ## str1 ## wherein a is a divalent aromatic radical of the dihydric phenol employed in the polymer producing reaction . preferably , the aromatic carbonate polymers used in the blends of the present invention have an intrinsic viscosity ( as measured in methylene chloride in deciliters per gram at 25 ° c .) ranging from about 0 . 30 to about 1 . 00 . the dihydric phenols which may be employed to produce such aromatic carbonate polymers are mononuclear or polynuclear aromatic compounds , containing as functional groups two hydroxy radicals , each of which is attached to a carbon atom of an aromatic nucleus . typical dihydric phenols are : other dihydric phenols which are also suitable for use in the preparation of the polycarbonates used in the present invention are disclosed in u . s . pat . nos . 2 , 999 , 835 ; 3 , 038 , 365 ; 3 , 334 , 154 ; and 4 , 131 , 575 . the preferred dihydric phenol is 2 , 2 - bis ( 4 - hydroxylphenyl ) propane ( bisphenol - a ). these aromatic polycarbonates can be manufactured by known processes , for example and as mentioned above , by reacting a dihydric phenol with a carbonate precursor , such as phosgene , in accordance with the methods set forth in the above - mentioned patents , and in u . s . pat . nos . 4 , 018 , 750 and 4 , 123 , 436 , or by other processes known to those skilled in the art . the ortho - methyl substituted aromatic dihydroxy compounds described above are preferably blended with an additional flame retardant additive . suitable flame retardant additives include metal salts of either monomeric or polymeric aromatic sulfonic acids , and mixtures thereof as described in u . s . pat . no . 3 , 933 , 734 , incorporated herein by reference . other flame retardant additives useful in the practice of the present invention include metal salts of either monomeric or polymeric aromatic sulfone sulfonic acids , or mixtures thereof as described in u . s . pat . no . 3 , 948 , 851 incorporated herein by reference . other flame retardant additives useful in the practice of the present invention include metal salts of a monomeric substituted aromatic sulfonic acid or mixture thereof in which the substituent is an electron withdrawing radical as described in u . s . pat . no . 3 , 940 , 366 incorporated herein by reference . other flame retardant additives useful in the practice of the present invention include metal salts of heterocyclic sulfonic acids , or mixtures thereof as described in u . s . pat . no . 3 , 919 , 167 incorporated herein by reference . other flame retardant additives useful in the practice of the present invention include metal salts of sulfonic acids of aromatic sulfides , or mixtures thereof as described in u . s . pat . no . 3 , 909 , 490 incorporated herein by reference . other flame retardant additives useful in the practice of the present invention include metal salts of either monomeric or polymeric aromatic ether sulfonic acids , or mixtures thereof as described in u . s . pat . no . 3 , 953 , 396 incorporated herein by reference . other flame retardant additives useful in the practice of the present invention include metal salts of either monomeric or polymeric phenol ester sulfonic acids , or mixtures thereof as described in u . s . pat . no . 3 , 978 , 024 incorporated herein by reference . other flame retardant additives useful in the practice of the present invention include metal salts of halocycloaliphatic aromatic sulfonic acids described in u . s . pat . no . 3 , 917 , 559 incorporated herein by reference . other flame retardant additives useful in the practice of the present invention include metal salts of either monomeric or polymeric aromatic amide sulfonic acids , or mixtures thereof as described in u . s . pat . no . 3 , 951 , 910 incorporated herein by reference . other flame retardant additives useful in the practice of the present invention include perfluoroalkane sulfonates as described in u . s . pat . no . 3 , 775 , 367 , incorporated herein by reference . preferred additional flame retardant additives include potassium diphenylsulfonesulfonate ( kss ), and sodium trichlorobenzene sulfonate . the ortho - methyl substituted aromatic dihydroxy compounds described above may be used in combination with any of the additional flame retardant additives discussed above . in addition , mixtures of the flame retardant additives discussed above may be used in combination together with an ortho - methyl substituted aromatic dihydroxy compound . the flame retardant polycarbonates of the present invention contain from about 0 . 05 to about 2 % flame retardant additives , preferably including an ortho - methyl substituted aromatic dihydroxy compound and an additional flame retardant additive . usually the ortho - methyl substituted aromatic dihydroxy compound and an additional flame retardant additive constitute about 1 % of the flame retardant polycarbonate composition . within the broad composition ranges specified , many resin mixtures may be prepared in accordance with the subject invention which unexpectedly improve the flame retardant properties . the compositions of the present invention may be prepared by dry blending the aromatic carbonate polymer resin component , an ortho - methyl substituted aromatic dihydroxy compound , and an additional flame retardant additive until complete dispersion of all of the ingredients is obtained . the resin mixture is then extruded and chopped to form pellets and thereafter molded in accordance with conventional methods . the flame retardant polycarbonate compositions of the present invention may be defined as intimate mixtures of a polycarbonate resin , an ortho - methyl substituted aromatic dihydroxy compound , and an additional flame retardant additive with no covalent bonds between them . in order to more fully and clearly illustrate the present invention , the following specific examples are presented . it is intended that the examples be considered as illustrative rather than limiting the invention disclosed and claimed herein . in the examples , all parts and percentages are on weight basis unless otherwise specified . the examples set forth in the tables below were prepared by blending lexan - brand polycarbonate ( pc ); 2 , 2 - bis ( 4 - hydroxy - 3 , 5 - dimethylphenyl ) propane ( tm - bpa ); and potassium diphenylsulfonesulfonate ( kss ). table i______________________________________example pc tm - bpa kss notched izod ki______________________________________control a 100 -- -- 98 . 0 53301 99 1 . 0 -- 100 . 7 47102 99 -- 1 . 0 96 . 3 52603 99 0 . 7 0 . 3 100 . 2 4740control b 100 -- -- 87 . 1 115504 99 1 . 0 -- 91 . 4 99705 99 . 5 -- 0 . 5 89 . 8 110306 99 0 . 7 0 . 3 90 . 0 9980______________________________________ table ii______________________________________ flammability ( ul 94 ) example 1 . 6 mm 3 . 2 mm______________________________________control a v2 ( 5 / 5 ) b ( 5 / 4 ) 1 v2 ( 5 / 5 ) v2 ( 1 / 5 ) 2 v2 ( 3 / 5 ) v1 ( 0 / 0 ) 3 v2 ( 0 / 5 ) v0 ( 0 / 0 ) control b v2 ( 5 / 5 ) -- 4 v2 ( 5 / 5 ) v2 ( 0 / 4 ) 5 v2 ( 0 / 4 ) v0 ( 0 / 0 ) 6 v2 ( 0 / 1 ) v0 ( 0 / 0 ) ______________________________________ in control a and examples 1 , 2 , and 3 the lexan - brand polycarbonate ( pc ) was characterized by an intrinsic viscosity of 0 . 52 to 0 . 55 . in control b and examples 4 , 5 , and 6 the lexan - brand polycarbonate was branched and was characterized by an intrinsic viscosity of 0 . 52 to 0 . 58 . intrinsic viscosity was measured at 25 ° c . in methylene chloride . the resistance to impact failure of the flame retardant polycarbonate compositions prepared in accordance with the subject invention was determined with the notched izod impact test , astm d256 on molded test specimens in the form of bars of the following size . the latter dimension being the specimen thickness . the test specimens were mounted in accordance with astm d256 procedures and were tested at room temperature . izod impact strengths were determined for all specimens according to astm d256 procedures on notched specimens and are reported in kg .- cm / cm of notch . also determined for the flame retardant polycarbonate compositions tested is the kasha index ( ki ) which is an indication or a measure of the process ability of the resin , i . e ., the lower the ki the greater the melt flow rate and , therefore , the better the processability . basically , the kasha index is a measure of the melt viscosity of the resin . the procedure for determining the kasha index is as follows : 7 grams of flame retardant polycarbonate composition pellets , dried a minimum of 90 minutes at 125 ° c ., are added to a modified tinius - olsen t3 melt indexer . the temperature of the indexer is maintained at 300 ° c . and the composition is heated at this temperature for 6 minutes . after 6 minutes the composition is forced through a 1 . 0478 mm radius orifice using a plunger of radius 4 . 7371 mm and an applied force of 8 . 04 kg . the time required for the plunger to travel 50 . 8 mm is measured in centiseconds and this is reported as the ki . the higher the ki , the higher the melt viscosity and the more viscous the composition , and therefore , the more difficult the composition is to process . the flamability of each of the compositions was tested according to underwriter &# 39 ; s laboratories bulletin ul - 94 , 3rd edition ( 1980 ). five specimens of each composition including each control composition , were tested . each specimen was exposed to two ignitions , and the number of specimens which dripped in either the first or second ignition is set forth parenthetically in table ii . as can be seen from table ii , the compositions of the present invention are especially effective in improving the self - extinguishing characteristics of thick polycarbonate sections ( 3 . 2 mm ). it should also be noted that the presence of the ortho - methyl substituted aromatic dihydroxy compound reduces the quantity of flame retardant salt necessary in the composition . it is understood that various other modifications will be apparent to and can readily be made by those skilled in the art without departing from the scope and spirit of this invention . accordingly , it is not intended that the scope of the claims appended hereto be limited to the description set forth herein , but rather that the claims be construed as encompassing all features of patentable novelty which reside in the present invention , including all features which would be treated as equivalents thereof by those skilled in the art to which this invention pertains .