Patent Publication Number: US-6037424-A

Title: Clear blends of polycarbonates and polyesters

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. provisional application Serial No. 60/034,995, filed Dec. 28, 1996, and the 60/034,995 application is herein incorporated by this reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to clear blends of polycarbonates and polyesters. More particularly, the present invention relates to clear blends of polycarbonates of dihydroxydiphenyl cycloalkanes and optionally bisphenol A with polyesters from terephthalic acid, isophthalic acid, ethylene glycol and 2,2,4,4-tetramethyl-1,3-cyclobutanediol. 
     BACKGROUND OF THE INVENTION 
     The polycarbonate of 4,4&#39;-isopropylidenediphenol (bisphenol A polycarbonate) is a well known engineering molding plastic. Bisphenol A polycarbonate is a clear high-performance plastic having good physical properties such as dimensional stability, high heat resistance, and good impact strength. Although bisphenol A polycarbonate has many good physical properties, its relatively high melt viscosity leads to poor melt processability and the polycarbonate exhibits poor chemical resistance. 
     Blends of the polycarbonates of bisphenol A and various dihydroxydiphenyl cycloalkanes have been used in making plastic films, molded articles, and extruded articles. These polycarbonate blends are especially useful in the performance plastics industry because they tend to have good heat resistance, high melt viscosities suitable for injection molding and extrusion, toughness, and good chemical resistance. 
     U.S. Pat. No. 5,034,457 discloses blends of dihydroxydiphenyl cycloalkane polycarbonates with a mixture of amorphous thermoplastics, party crystalline thermoplastics, and rubber used for injection molding. U.S. Pat. No. 5,104,723 discloses blends of dihydroxydiphenyl cycloalkane polycarbonates with amorphous thermoplastics, partially crystalline thermoplastics, and elastomers for the production of films. 
     However, there has been no disclosure of miscible blends of dihydroxydiphenyl cycloalkane polycarbonates with other materials. Immiscible blend compositions are inadequate for many uses because they are opaque, and generally result in an unacceptable reduction in impact strength and tensile strength. 
     Clear, miscible blends of any two polymers are rare. The term &#34;miscible&#34; refers to blends that are a mixture on a molecular level wherein intimate polymer-polymer interaction is achieved. Miscible blends are clear, not translucent or opaque. In addition, differential scanning calorimetry testing detects only a single glass transition temperature (Tg) for miscible blends composed of two or more components. 
     There have been very few clear polycarbonate/polyester blends developed. U.S. Pat. Nos. 4,619,975 and 4,645,802 disclose clear blends based on bisphenol A polycarbonate with polyesters of poly(1,4-tetramethylene terephthalate), poly(1,4-cyclohexylenedimethylene terephthalate) and selected copolyesters and copoly(ester-imides) of poly(1,4-cyclohexylenedimethylene terephthalate). U.S. Pat. No. 4,786,692 discloses clear blends of bisphenol A polycarbonate and polyesters of terephthalic acid, isophthalic acid, ethylene glycol, and 1,4-cyclohexanedimethanol. U.S. Pat. Nos. 4,188,314 and 4,391,954 disclose clear blends of bisphenol A polycarbonate with poly(1,4-cyclohexylenedimethylene terephthalate-co-isophthalate). These polyester blends do have improved chemical resistance and melt processability, when compared to unblended bisphenol A polycarbonate. However, the good heat resistance and impact strength of bisphenol A polycarbonate blends based on these compositions is reduced significantly. 
     In light of the above, it would be desirable to be able to form clear polyester blends of dihydroxydiphenyl cycloalkane polycarbonates having good melt processability suitable for injection molding. Such blend would be especially suitable for the manufacture of clear molded articles, fibers, sheeting, and film. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the blend composition according to the present invention comprises: 
     (A) from 1 to 99 percent by weight of a polycarbonate comprising a diol component comprising from 5 to 100 mol percent units of a diphenol or mixture of diphenols having the formula ##STR1## wherein R 0 , R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , and R 7  are independently selected from the group consisting of hydrogen, halogen, C 1  -C 8  alkyl, C 5  -C 12  cycloalkyl, C 5  -C 12  aryl, and C 6  -C 12  aralkyl, 
     X represents carbon, 
     m is an integer of from 4 to 7, and 
     R 8  and R 9  are independently selected for each X and independently selected of each other from the group consisting of hydrogen and C 1  -C 8  alkyl; and 
     from 0 to 95 mol percent 4,4&#39;-isopropylidenediphenol units; and from 0 to 10 mol percent modifying glycol units having 2 to 16 carbons, wherein the total mol percent of diol units is equal to 100 mol percent; and 
     (B) from 1 to 99 percent by weight of a polyester comprising 
     (a) a dicarboxylic acid component comprising from 80 to 100 mol percent dicarboxylic acid units selected from the group consisting of terephthalic acid units, isophthalic acid units, and mixtures thereof; and from 0 to 20 mol percent modifying dicarboxylic acid units having from 2 to 20 carbons, wherein the total mol percent of dicarboxylic acid units is equal to 100 mol percent; and 
     (b) a glycol component comprising from 20 to 99 mol percent 2,2,4,4-tetramethyl-1,3-cyclobutanediol units, from 1 to 80 mol percent ethylene glycol units, and from 0 to about 10 mol percent modifying glycol units having 3 to 16 carbons, wherein the total mol percent of glycol units is equal to 100 mol percent; 
     wherein the total units of said polyester is equal to 200 mol percent; 
     wherein said blend is clear and the total weight percent of said polycarbonate (A) and said polyester (B) is equal to 100 weight percent. 
     In another embodiment, the blend composition of the instant invention comprises: 
     (A) from 1 to 99 percent by weight of a polycarbonate comprising a diol component comprising from 5 to 100 mol percent units of a diphenol or mixture of diphenols having the formula ##STR2## wherein R 0 , R 1 , R 3 , R 4 , R 5 , R 6 , and R 7  are independently selected from the group consisting of hydrogen, halogen, C 1  -C 8  alkyl, C 5  -C 12  cycloalkyl, C 5  -C 12  aryl, and C 6  -C 12  aralkyl, 
     X represents carbon, 
     m is an integer of from 4 to 7, and 
     R 8  and R 9  are independently selected for each X and independently of one another from the group consisting of hydrogen and C 1  -C 8  alkyl; 
     from 0 to 95 mol percent 4,4&#39;-isopropylidenediphenol units; and from 0 to 10 mol percent modifying glycol units having 2 to 16 carbons, wherein the total mol percent of diol units is equal to 100 mol percent; and 
     (B) from 1 to 99 percent by weight of a polyester comprising 
     (a) a dicarboxylic acid component comprising from 80 to 100 mol percent dicarboxylic acid units selected from the group consisting of terephthalic acid units, isophthalic acid units, and mixtures thereof; and from 0 to 20 mol percent modifying dicarboxylic acid units having from 2 to 20 carbons, wherein the total mol percent of dicarboxylic acid units is equal to 100 mol percent; and 
     (b) a glycol component comprising from 20 to 100 mol percent 2,2,4,4-tetramethyl-1,3-cyclobutanediol units, 0 to about 80 mol percent ethylene glycol units, and 0 to about 10 mol percent modifying glycol units having 3 to 16 carbons, wherein the total mol percent of glycol units is equal to 100 mol percent; 
     wherein the total units of said polyester is equal to 200 mol percent; 
     wherein said blend is clear and the total weight percent of said polycarbonate (A) and said polyester (B) is equal to 100 weight percent. 
     The invention also covers a method of using the blend compositions to produce a clear article of manufacture. The method of using the clear blend composition to produce a clear article of manufacture comprises the steps of: 
     (a) blending polycarbonate (A) and polyester (B); 
     (b) before, during, or after the blending, melting polycarbonate (A) and polyester (B) to form, after the blending and melting, a melt blend; 
     (c) then cooling the melt blend to form a clear blend composition. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention may be understood more readily by reference to the following detailed description of preferred embodiments of the invention and the Examples included therein. 
     Before the present compositions of matter are disclosed and described, it is to be understood that this invention is not limited to specific synthetic methods or to particular formulations, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. 
     In this specification, the singular forms &#34;a,&#34; &#34;an&#34; and &#34;the&#34; include plural referents unless the context clearly dictates otherwise. 
     The applicants have unexpectedly discovered clear blends of the polycarbonate of the diphenol of formula (I) with particular polyesters from terephthalic acid, isophthalic acid, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, and ethylene glycol. The applicants were also surprised to discover clear blends of copolycarbonates of the diphenol of formula (I) and bisphenol A with particular polyesters from terephthalic acid, isophthalic acid, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, and ethylene glycol. 
     This discovery was surprising since there are no teachings of clear polycarbonate/polyester blends based on the polycarbonate of a dihydroxydiphenyl cycloalkane. This discovery was particularly surprising since there are no teachings of a polycarbonate/polyester blend having a 2,2,4,4-tetramethyl- 1,1,3-cyclobutanediol based glycol component in the polyester. Nor are there any teachings suggesting that such a blend may be clear. Although U.S. Pat. No. 3,301,777 discloses polyesters containing 2,2,4,4-tetramethyl-1,3-cyclobutanediol, there is no suggestion of the benefit of blending a 2,2,4,4-tetramethyl-1,3-cyclobutanediol based polyester with a polycarbonate. 
     In addition to the unexpected clarity of the blend, the applicants were also surprised to find that the polyester portion of the present invention provides an unexpected amount of impact strength, hardness and heat resistance to the polymer blend. 
     The term &#34;polycarbonate&#34; is herein defined as the condensation product of a carbonate source and a diol source, having a carbonate component containing 100 mol percent carbonate units and a diol component containing 100 mol percent diol units, for a total of 200 mol percent monomeric units. The term &#34;diol&#34; as used herein, includes both aliphatic and aromatic compounds having two hydroxyl groups, while the term &#34;glycol&#34; refers to aliphatic and aromatic/aliphatic compounds having two hydroxyl groups. 
     The polycarbonate portion of the blend of the present invention is based upon the polycarbonate of the diphenol or mixture of diphenols of formula (I) ##STR3## in which R 0 , R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , and R 7  independently of one another are hydrogen, halogen, C 1  -C 8  alkyl, and C 5  -C 12  cycloalkyl, C 5  -C 12  aryl or C 6  -C 12  aralkyl, X represents carbon, m is an integer from 4 to 7, and R 8  and R 9  are, independently for each X and independently of one another, hydrogen or C 1  -C 8  alkyl. 
     Suitable halogen substituents of the diphenol of formula (I) include, but are not limited to, chlorine, bromine and fluorine. Examples of suitable alkyl substituent groups are methyl, ethyl, propyl, isopropyl, t-butyl, pentyl, hexyl, heptyl and octyl groups. Examples of suitable cycloalkyl substituent groups include, but are not limited to, the cyclohexyl, and the methyl-, ethyl-, propyl-, and t-butyl-cyclohexyl moieties. Examples of suitable aryl substituent groups include, but are not limited to, phenyl, benzyl, substituted alkyl phenyl, substituted halophenyl and naphthyl. 
     The preferred diphenol of formula (I) is a cyclohexyl diphenol shown by formula (II) below, wherein R 0  through R 7  are selected as described above. The most preferred diphenol of formula (I) is the condensation product of isophorone and phenol known as 3,3,5-trimethylcyclohexane bisphenol, the cyclohexyl diphenol of formula (II) in which R 0  through and R 7 , are substituted with hydrogen. ##STR4## 
     The polycarbonate portion of the blend of the present invention is preferably a copolycarbonate of the diphenol of formula (I) and 4,4&#39;-isopropylidenediphenol, commonly known as bisphenol A, shown below in formula (III). ##STR5## 
     Suitable polycarbonates are those having a diol component containing about 5 to 100 mol percent formula (I) diphenol units and 0 to about 95 mol percent bisphenol A units, preferably about 20 to 50 mol percent formula (I) diphenol units and about 50 to 80 mol percent bisphenol A units, more preferably about 30 to 35 mol percent formula (I) diphenol units and about 65 to 70 mol percent bisphenol A units. One especially suitable commercial copolycarbonate is APEC HT copolycarbonate from Miles, Inc. The approximate diol component structure of APEC HT, as determined by nuclear magnetic resonance spectroscopy (NMR), is 68 mol percent bisphenol A units and 32 mol percent 3,3,5-trimethylcyclohexane bisphenol units. 
     For the polycarbonates of the invention, suitable carbonate sources for the carbonate units are preferably phosgene, dialkyl carbonate, such as preferably dibutyl carbonate; or diaryl carbonate, such as preferably diphenyl carbonate. 
     Up to 10 mol percent of the diol component of the polycarbonate portion can be substituted with units of other modifying aromatic diols, besides bisphenol A and formula (I) diphenol, having from 2 to 16 carbons. It is preferable to have no more than 5 mol percent of other modifying polycarbonate present in the polycarbonate portion of the blend, more preferably 0 mol percent. The modifying polycarbonates are preferably polycarbonates of aromatic diols. Suitable examples of other modifying diols include the aromatic diols of U.S. Pat. Nos. 3,030,335 and 3,317,466. 
     The inherent viscosity of the polycarbonate portion of the blends according to the present invention is preferably at least about 0.3 dL/g, more preferably at least 0.5 dL/g, determined at 25° C. in 60/40 wt/wt phenol tetrachloroethane. 
     &#34;Polyester,&#34; as used herein, refers to any unit-type of polyester falling within the scope of the polyester portion of the present blend, including but not limited to homopolyesters, copolyesters, and terpolyesters. The polyester portion of the blend of the present invention comprises a dicarboxylic acid component of about 80 to 100 mol percent terephthalic acid and/or isophthalic acid units, and 0 to about 20 mol percent modifying dicarboxylic acid units, and a glycol component of about 20 to 100 mol percent 2,2,4,4-tetramethyl-2,3-cyclobutanediol units, 0 to 80 mol percent ethylene glycol units, and 0 to about 10 mol percent modifying glycol units, wherein the total dicarboxylic acid units is equal to 100 mol percent, the total glycol units is equal to 100 mol percent, with a total polyester units equal to 200 mol percent. 
     Terephthalic acid and isophthalic acid have been found to be the preferred primary dicarboxylic acids for providing a polyester that forms a clear blend with a copolycarbonate of bisphenol A and the diphenol of formula (I). A higher concentration of terephthalic acid in the polyester than isophthalic acid is preferred because terephthalic acid produces a polyester that provides greater impact strength to the blend. Therefore, it is preferred that the dicarboxylic acid component of the polyester portion be 50 to 100 mol percent terephthalic acid and 0 to 50 mol percent isophthalic acid, more preferably 70 to 100 mol percent terephthalic acid and 0 to 30 mol percent isophthalic acid, with about 100 mol percent terephthalic acid being most preferred. 
     In addition to terephthalic acid and isophthalic acid, the dicarboxylic acid component of the polyester can be substituted with up to 20 mol percent, but preferably less than 10 mol percent of other modifying dicarboxylic acids having 2 to 20 carbon atoms. Suitable examples of modifying aromatic dicarboxylic acids include 4,4&#39;-biphenyldicarboxylic acid, 1,4-, 1,5-, 2,6-, 2,7-naphthalenedicarboxylic acid, 4,4&#39;-oxybenzoic, trans-4,4-stilbenedicarboxylic acid, or mixtures thereof. Suitable examples of modifying aliphatic dicarboxylic acids are those containing 2 to 12 carbon atoms, such as oxalic, malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, and sebacic acids, or mixtures thereof. 
     The dicarboxylic acid component of the polyester portion of the present blend can be prepared from dicarboxylic acids, their corresponding esters, or mixtures thereof. Examples of esters of the dicarboxylic acids useful in the present invention include the dimethyl, dipropyl, diisopropyl, dibutyl, and diphenyl esters, and the like. 
     The glycol component of the polyester portion of the present blend is formed from about 20 to 100 mol percent 2,2,4,4-tetramethyl-1,3-cyclobutanediol units and 0 to about 80 mol percent ethylene glycol units, and up to 10 mole percent modifying glycol units containing 3 to 16 carbon atoms. In one embodiment, the ethylene glycol units are present at from 1 to 80 mol %. Of the glycol component about 20 to 80 mol percent 2,2,4,4-tetramethyl-1,3-cyclobutanediol units and about 20 to 80 mol percent ethylene glycol units preferably form the polyester glycol component, more preferably about 30 to 80 mol percent 2,2,4,4-tetramethyl-1,3-cyclobutanediol and about 20 to 70 mol percent ethylene glycol units, with about 35 to 75 mol percent 2,2,4,4-tetramethyl-1,3-cyclobutanediol units and about 25 to 65 mol percent ethylene glycol units being most preferred. 
     The 2,2,4,4-tetramethyl- 1,3-cyclobutanediol can be cis, trans, or a mixture thereof, preferably 45-55 mol percent trans, where the total of cis and trans isomer content is equal to 100 mol percent, more preferably the isomer content is about 50/50 trans/cis. 
     The glycol component of the polyester portion of the present blend contains 0 to about 10 mol percent, but preferably less than 5 mol percent of other modifying glycol units containing 3 to 16 carbon atoms. Examples of suitable modifying glycols include, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, trans- or cis-1,4-cyclohexanedimethanol, p-xylene glycol, and mixtures thereof. The glycol component can also be modified with 0 to about 10 mol percent polyethylene glycol or polytetramethylene glycols to enhance elastomeric behavior. 
     The preferred polyester of the present invention is a copolyester formed from 100 mol percent terephthalic acid units, about 20 to 100 mol percent 2,2,4,4-tetramethyl-1,3-cyclobutanediol units, and 0 to about 80 mol percent ethylene glycol units. The more preferred polyester is formed from 100 mol percent terephthalic acid units, about 30 to 80 mol percent 2,2,4,4- tetramethyl-1,3-cyclobutanediol units, and about 20 to 70 mol percent ethylene glycol units. The most preferred polyester contains no units of other modifying dicarboxylic acids nor modifying glycols. 
     The blends of the present invention are about 1 to 99 weight percent polyester portion and about 1 to 99 weight percent polycarbonate portion, with the total weight percent of the polycarbonate portion and polyester portion preferably being equal to 100 weight percent. The preferred blend of the present invention is about 20 to 99 weight percent polycarbonate and about 1 to 80 weight percent polyester, more preferably about 40 to 99 weight percent polyester, with a weight percent of about 45 to 55 for both polycarbonate and polyester being most preferred. 
     Greater concentrations of the copolycarbonate of the blend nearer 99 weight percent produce blends having greater impact strength, heat resistance, and dimensional stability, while blends nearer 99 weight percent polyester have better chemical resistance and melt processability. The most useful blends will be those clear blends having a combination of physical properties best suited for a particular end use, as will be determined on a case by case basis. 
     The inherent viscosity of the polyester portion of the blends according to the present invention is preferably at least 0.3 dL/g, more preferably at least 0.6 dL/g, determined at 25° C. in 60/40 wt/wt phenol/tetrachloroethane. 
     The blend compositions of the present invention are clear. The term &#34;clear&#34; is defined herein as an absence of cloudiness, haziness, and muddiness, when inspected visually. The blends of the present invention also exhibit a single glass transition temperature (Tg), as determined by differential scanning calorimetry (DSC). 
     The chemical resistance and melt processability of the blends of the present invention are good. It is generally known that blending with a polyester improves the chemical resistance and melt processability of polycarbonates. See U.S. Pat. Nos. 4,188,314 and 4,267,096. 
     The polycarbonate portion of the present blend can be prepared in the melt, in solution, or by interfacial polymerization techniques well known in the art. Suitable methods include the steps of reacting a carbonate source with a diol or diols at a temperature of about 0° C. to 315° C. at a pressure of about 0.1 to 760 mm Hg for a time sufficient to form a polycarbonate. Commercially available polycarbonates that are typically used in the present invention are normally made by reacting an aromatic diol with a carbonate source such as phosgene, dibutyl carbonate or diphenyl carbonate, to incorporate 100 mol percent of carbonate units, along with 100 mol percent diol units into the polycarbonate. For examples of methods of producing polycarbonates, see U.S. Pat. Nos. 5,498,688, 5,494,992, and 5,489,665, which are incorporated by this reference in their entireties for all of their teachings. 
     The polyester portion of the present invention can be made by processes known from the literature such as, for example, by processes in homogeneous solution, by transesterification processes in the melt and by two phase interfacial processes. Suitable methods include the steps of reacting one or more dicarboxylic acids with one or more glycols at a temperature of about 100° C. to 315° C. at a pressure of about 0.1 to 760 mm Hg for a time sufficient to form a polyester. See U.S. Patent 3,772,405 for methods of producing polyesters. 
     The polyester/polycarbonate blends of the present invention can be made by methods which include the steps of blending the polycarbonate and polyester portions of the present invention at a temperature of about 25° C. to 350° C. for a time sufficient to form a clear blend composition. Suitable conventional blending techniques include the melt method and the solution-prepared method. Other suitable blending techniques include dry blending and/or extrusion 
     The melt blending method includes blending the polymers at a temperature sufficient to melt the polycarbonate and polyester portions, and thereafter cooling the blend to a temperature sufficient to produce a clear blend. The term &#34;melt&#34; as used herein includes, but is not limited to, merely softening the polymers. For melt mixing methods generally known in the polymers art, see Mixing And Compounding Of Polymers (I. Manas-Zloczower &amp; Z. Tadmor eds., Carl Hanser Verlag publisher, New York 1994). 
     The solution-prepared method includes dissolving the appropriate weight/weight ratio of polyester and polycarbonate in a suitable organic solvent such as methylene chloride or a 70/30 mixture of methylene chloride and hexafluoroisopropanol, mixing the solution, and separating the blend composition from solution by precipitation of the blend or by evaporation of the solvent. Solution-prepared blending methods are generally known in the polymers art. 
     The melt blending method is the preferred method for producing the blend compositions of the present invention. The melt method is more economical and safer than the solution-prepared method which requires the use of volatile solvents. The melt method is also much more effective in providing clear blends. Any of the clear blends of the present invention that can be prepared by solution blending can also be prepared by the melt method. However, some of the blends of the present invention can be prepared by the melt method, but not by the solution method. Any blending process which provides clear blends of the present invention is suitable. One of the ordinary skill in the art will be able to determine appropriate blending methods for producing the clear blends of the present invention. 
     In addition to the polycarbonate and polyester portions disclosed above, the blend of the present invention can include at least one other modifying polymer. Suitable modifying polymers are those which form miscible blends with the polycarbonate and polyester portions disclosed above. Possible modifying polymers include other polycarbonates, other polyesters, polyamides, polystyrenes, polyurethanes, polyarylates, liquid crystalline polymers, vinyl polymers, and the like, or a mixture thereof. Suitable modifying polymers may be determined by one of ordinary skill in the polymers art by performing traditional miscibility tests with possible modifying polymers. 
     A polymer may be determined to be a suitable modifying polymer of the blend of the present invention if a clear blend is formed by: 1) blending the modifying polymer with a pre-existing blend containing the polycarbonate and polyester portions, or 2) blending the modifying polymer with the polycarbonate portion prior to the introduction of the polyester portion, or 3) blending the modifying polymer with the polyester portion prior to the introduction of the polycarbonate portion, or 4) mixing the modifying polymer, polycarbonate portion and polyester portion all together prior to blending. 
     The clear blends of the present invention can still be further modified by the incorporation of blend modifiers to produce performance blends which may not necessarily be clear. For example, polyamides such as nylon 6,6 from DuPont, poly(ether-imides) such as ULTEM poly(ether-imide) from General Electric, polyphenylene oxides such as poly(2,6-dimethylphenylene oxide) or poly(phenylene oxide)/polystyrene blends such as the NORYL resins from General Electric, polyesters, polyphenylene sulfides, polyphenylene sulfide/sulfones, poly(ester-carbonates) such as LEXAN 3250 poly(ester-carbonate) (General Electric), polycarbonates other than LEXAN polycarbonate from General Electric, polyarylates such as ARDEL D100 polyarylate (Amoco), polysulfones, polysulfone ethers, poly(ether-ketones) or aromatic dihydroxy compounds can be used as blend modifiers to modify properties or to reduce flammability. The aromatic dihydroxy compounds can be used as blend modifiers to modify properties or to reduce flammability. The aromatic dihydroxy compounds used to prepare these polymers are disclosed in U.S. Pat. No. 3,030,335 and U.S. Pat. No. 3,317,466. 
     The blends of the present invention can also contain antioxidants, conventional flame retardants such as phosphorus or halogen compounds, or fillers such as talc or mica, or reinforcing agents such as glass fiber, KEVLAR, or carbon fiber. Additives such as pigments, dyes, stabilizers, plasticizers, etc. can also be used in the polyesters, polycarbonates, and blends of the present invention to further modify the properties of the inventive blends. 
     The blends of the present invention are useful in producing clear articles of manufacture having improved chemical resistance and melt processability while retaining excellent mechanical properties. These blends are especially useful for making molded articles, fibers, films, and sheeting. 
    
    
     The following examples are intended to illustrate the present invention but are not intended to limit the scope thereof. 
     EXAMPLES 
     The inherent viscosity of the polyesters was determined in 60/40 (wt/wt) phenol/tetrachloroethane at a concentration of 0.5 g/100 mL at 25° C. The glass transition temperatures (Tg&#39;s) were determined using a TA 2100 from Thermal Analyst System at a scan rate of 20° C./min. The glycol content of the polyester portion of these blends was determined by proton nuclear magnetic resonance spectroscopy (NMR). Clarity was determined visually. The miscibility of the blends was determined by differential scanning calorimetry and by observation of the clarity of pressed films and molded objects. 
     The blends of this invention were prepared in two ways: 
     1) The solution-prepared method of dissolving the appropriate weight/weight ratio of polyester to polycarbonate in methylene chloride or a 70/30 mixture of methylene chloride/hexafluoroisopropanol and after complete solution was obtained, precipitating the blend with methanol. 
     2) The melt mixing method of dry blending the appropriate weight/weight ratio of polyester to polycarbonate and extruding the blend on a 3/4-in Brabender extruder equipped with a screen pack and mixing screw at temperatures of 260-320° C. 
     The preparation of polycarbonates is well known in the art. The polycarbonate used in the following examples was APEC HT copolycarbonate from Miles, Inc. The bisphenol A polycarbonate used was LEXAN, available from the General Electric Company or MAKROLON 2608, available from Miles, Inc. 
     The following examples illustrate the preparation of some of the polyesters used in this invention and their miscibility with APEC HT polycarbonate. 
     Example 1 
     The blends of this example were prepared by melt mixing. Blends of APEC HT copolycarbonate with polyesters were prepared by an extruder in the melt. The blend compositions were 50 percent weight polycarbonate and 50 percent weight polyester. The pellets were first mixed by tumbling. The blends were prepared in a 3/4-in Brabender single screw extruder with a mixing screw. Injection molded parts were prepared on a Boy 22S injection molding machine. Processing temperatures used were in the range of 280° C. to 315° C. Visual inspection was used to determine clarity, and the results are presented in Table 1. Examples 1B through 1H exhibited unexpected visual clarity. Note that the clear blends of Example 2B and 2I. This difference is believed to be due to the more intensive mixing which is achieved in the melt. 
     Selected mechanical properties of some of the blends prepared in the melt are presented in Table 2. Examples 1B, 1F, and 1H, which are compositions included in the present invention, exhibit a useful combination of clarity, high heat deflection temperature, and impact strength. The improvements in chemical resistance and melt processability were not analyzed for these Examples. However, it is generally known in the polymers art that the combination of a polycarbonate with a polyester will improve the chemical resistance and melt processability of the polycarbonate. See U.S. Pat. Nos. 4,188,314 and 4,267,096. 
     As will be apparent to anyone skilled in the art, these compositions have broad applications including the fabrication of molded articles, fibers, sheeting, or films, particularly where visual clarity is important. 
     
                       TABLE 1                                                     
______________________________________                                    
Melt Blends of Polyesters of Terephthalic Acid,                           
2,2,4,4-Tetramethyl-1,3-cyclobutanediol, and                              
Ethylene Glycol with APEC HT Copolycarbonate                              
Blend Composition: 50/50 wt./wt. Polycarbonate/Polyester                  
Example  EG, Mol %   TMCD, Mol %                                          
                                Blend Clarity                             
______________________________________                                    
1A       100          0         Cloudy                                    
1B       76          24         Clear                                     
1C       66          34         Clear                                     
1D       58          42         Clear                                     
13       49          51         Clear                                     
1F       30          70         Clear                                     
1G       16          84         Clear                                     
1H        0          100        Clear                                     
______________________________________                                    
 EG = Ethylene Glycol in Polyester Composition.                           
 TMCD = 2,2,4,4tetramethyl-1,3-cyclobutanediol (68/32 trans/cis) in       
 Polyester Composition.                                                   
 
    
     EG=Ethylene Glycol in Polyester Composition 
     TMCD=2,2,4,4-tetramethyl-1,3-cyclobutanediol (68/32 trans/cis) in Polyester Composition 
     
                       TABLE 2                                                     
______________________________________                                    
Selected Mechanical Properties of Melt Blends                             
of Polyesters of Terephthalic Acid,                                       
2,2,4,4-Tetramethyl-1,3-cyclobutanediol, and                              
Ethylene Glycol with APEC HT Copolycarbonate                              
50 wt % polycarbonate, 50 wt % polyester                                  
Example    1A      1B        1F     1H                                    
______________________________________                                    
TMCD/EG    0/100   24/76     70/30  100/0                                 
(mol %)                                                                   
Clarity    cloudy  clear     clear  clear                                 
Heat Deflection                                                           
           94, 71  117, 106  147, 129                                     
                                    162, 138                              
Temp, ° C.                                                         
(66 psi, 264 psi)                                                         
Strength   1.0     1.0       1.4    3.8                                   
(ft-lb/in)                                                                
Flexural   360,000 349,000   328,000                                      
                                    313,000                               
Modulus    psi     psi       psi    psi                                   
Flexural   12,450  13,780    13,690 13,660                                
Strength   psi     psi       psi    psi                                   
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     Heat deflection temperature at 66 and 264 psi loading, determined according to ASTM D648. Strength=Notched Izod Impact strength determined at 23° C. according to ASTM D256. Flexural modulus and flexural strength determined according to ASTM D790. Visual Clarity 
     Example 2 
     Examples 2A-21 illustrate the miscibility of 50/50 wt/wt solution-prepared blends of APEC HT copolycarbonate and a polyester formed from 100 mol percent terephthalic acid units and varying amounts of 2,2,4,4-tetramethyl- 1,3-cyclobutanediol and ethylene glycol. The results are presented in Table 3. 
     Example 2A (control) illustrates the immiscible blend obtained from blending APEC HT copolycarbonate with the homopolyester prepared from 100 mol percent terephthalic acid and 100 mol percent ethylene glycol (PET 7352, with Tg of 80° C., and inherent viscosity of 0.77, available from Eastman Chemical Company). 
     Example 2B illustrates the immiscible blend obtained from a copolyester containing 100 mol percent terephthalic acid, 13 mol percent 2,2,4,4-tetramethyl-1,3-cyclobutanediol (50/50 trans/cis), and 87 mol percent ethylene glycol units, having a glass transition temperature of 89° C. and inherent viscosity of 0.76 dL/g. 
     To prepare the polyester for Example 2B, a mixture of 194.0 g (1.0 mol) dimethyl terephthalate, 111.6 g (1.8 mols) ethylene glycol, 28.8 g (0.20 mol) 2,2,4,4-tetramethyl-1,3-cyclobutanediol (68% trans, 32% cis), 0.044 g zinc acetate (65 ppm Zn), and 0.24 g dibutyltin diacetate (400 ppm Sn) was placed in a 1-L flask equipped with an inlet for nitrogen, a metal stirrer, and a short distillation column. The flask was placed in a Belmont metal bath already heated to 190° C. and the contents of the flask were heated at 190° for 3 hours, 210° C. for 1.5 hours, and at 260° C. for 30 minutes. A vacuum of 0.5 mm was gradually applied over the next 3-5 minutes and after 10 minutes the temperature was raised to 280° C. Full vacuum was maintained for a total time of about 45 minutes. A high melt viscosity, amber polymer was obtained with a glass transition temperature of 89° C. and an inherent viscosity of 0.76 dL/g. 
     The polyester was then ground to pass a 3-mm screen and 0.25 g of the polyester was dissolved in a 70/30 mixture of methylene chloride/hexafluoroisopropanol with 0.25 g APEC HT copolycarbonate. After solution was complete, the polymers were precipitated by dropping the blend solution into methanol. The precipitate which formed was collected, dried in a vacuum oven for 72 hours at 50° C., and determined to have two glass transition temperatures. The blend was then melted and pressed into a thin film. The film appeared opaque to the eye. 
     Example 2C is yet another example of an immiscible blend. The polymer and blend used for this example were made in a manner similar to Example 2B, using amounts shown in Table 3. 
     Example 2D illustrates the clear blend obtained from a polyester containing 100 mol percent terephthalic acid, 34 mol percent 2,2,4,4-tetramethyl-1,3-cyclobutanediol (50/50 trans/cis), and 66 mol percent ethylene glycol units, having a glass transition temperature of 105° C. and an inherent viscosity of 0.77 dL/g. 
     To prepare the polyester, a mixture of 97.0 g (0.50 mol) dimethyl terephthalate, 36.0 g (0.25 mol) 2,2,4,4-tetramethyl-1,3-cyclobutanediol (68% trans, 23% cis), 46.5 g (0.75 mol) ethylene glycol, 0.065 g titanium tetraisopropoxide (100 ppm Ti), and 0.11 g IRGANOX 1010 was placed in a 500-mL flask equipped with an inlet for nitrogen, a metal stirrer, and a short distillation column. The flask was placed in a Belmont metal bath already heated to 190° C. The contents of the flask were heated at 190° C. for 3.25 hours, 220° C. for 0.75 hour, 240° C. for 1.0 hour and 12 minutes at 260° C. A vacuum of 0.5 was gradually applied over the next 3-5 minutes and after 20 minutes the temperature was raised to 280° C. for 35 minutes. Full vacuum was maintained for a total time of about 55 minutes. A high melt viscosity, light amber polymer was obtained with a glass transition temperature of 105° C. and an inherent viscosity of 0.77 dL/g. 
     The polyester was ground to pass a 3-mm screen and 0.25 g of the polyester was dissolved in methylene chloride with 0.25 g APEC HT copolycarbonate. After solution was complete, the polymers were precipitated by dropping the blend solution into methanol. The precipitate was collected, dried in a vacuum oven for 72 hours at 50° C., and determined to have a single glass transition temperature of 128° C. The blend was melted and pressed into a thin film. The film appeared clear to the eye. 
     Examples 2E-2I shown in Table 3 further illustrate blends of APEC HT copolycarbonate and polyester. These examples were all prepared in a manner similar to Examples 2B and 2D above, using the amounts shown in Table 3. Examples 2E, 2F, 2G, and 2H illustrate unexpectedly clear, miscible blends. Example 2I was opaque. 
     Examples 2A-2I above show that clear blends of the present invention can be prepared by solution blending of the APEC HT copolycarbonate with the polyester. However, the solution prepared blends of Example 2 were not clear over as broad of a range of polyester compositions as were the blends shown in Example 1, which were prepared by the melt-mixing method. Thus, melt blending is the preferred blending method. 
     
                       TABLE 3                                                     
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Solution Prepared Blends of Polyesters of Terephthalic Acid,              
2,2,4,4-Tetramethyl-1,3-cyclobutanediol, and                              
Ethylene Glycol with APEC HT Copolycarbonate                              
Blend Composition: 50 wt. % Polycarbonate/50 wt. % Polyester              
Polyester Composition.sup.a                                               
                    Blend Visual                                          
                              DCS Number                                  
Example                                                                   
       EG, Mol % TMCD, Mol %                                              
                            Clarity of Tags                               
______________________________________                                    
2A     100        0         Opaque  Two                                   
2B     87        13         Opaque  Two                                   
2C     72        28         Opaque  Two                                   
2D     66        34         Clear   One                                   
2E     58        42         Clear   One                                   
2F     49        51         Clear   One                                   
2G     30        70         Clear   One                                   
2H     16        84         Clear   One                                   
2I      0        100        Opaque  Two                                   
______________________________________                                    
 .sup.a TMCD = 2,2,4,4tetramethyl-1,3-cyclobutanediol (68/32 trans/cis),  
 EG = ethylene glycol.                                                    
 
    
     Example 3 
     The blends in this example were prepared by the same solvent blending method used in Example 2. However, the polycarbonate used was a MAKROLON 2608, a commercially available bisphenol A polycarbonate. The results are presented in Table 4. Examples 3B and 3C show results from the same polyesters as were used in Examples 2G and 2H, respectively. However, the films which were prepared from blends with APEC HT copolyester in Examples 2G and 2H were clear, while the films which were prepared form blends with bisphenol A polycarbonate in Examples 3B and 3C were opaque. 
     These results demonstrate the importance of the polycarbonate structure in achieving visually clear films. 
     
                       TABLE 4                                                     
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Solution Prepared Blends of                                               
Polyesters with Bisphenol A Polycarbonate                                 
50/50 wt. % Polycarbonate/Polyester                                       
Example                                                                   
       EG, mol % TMCD, mol % Clarity                                      
                                   Number of Tg&#39;s                         
______________________________________                                    
3A     100        0          Opaque                                       
                                   Two                                    
3B     30        70          Opaque                                       
                                   --                                     
3C     16        84          Opaque                                       
                                   --                                     
______________________________________                                    
 TMCD = 2,2,4,4tetramethyl-1,3-cyclobutanediol (68/32 trans/cis),         
 EG = ethylene glycol.                                                    
 
    
     Example 4 
     The following example is a comparison against Example 1B. This example illustrates the effect of substituting 100 mol percent bisphenol A polycarbonate (MAKROLON 2608) for approximately 68 mol percent bisphenol A polycarbonate and 32 mol percent trimethylcyclohexane bisphenol polycarbonate (APEC HT) in the polycarbonate portion of the blend. The polyester composition (76 mol percent ethylene glycol and 24 mol percent 2,2,4,4-tetramethyl-1,3-cyclobutanediol) and polyester to polycarbonate ratio used in the present Example were the same as Example 1. The blend of Example 4 was also prepared using the same melt blending method used in Example 1. 
     The injection molded parts which were prepared from the blend of Example 1B were clear, while the injection molded parts which were prepared from the blend with a bisphenol A polycarbonate portion in the present example were cloudy. These results further demonstrate the importance of the polycarbonate structure in achieving visually clear articles of manufacture, such as molded articles, fibers, sheeting, and films. 
     The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modification can be effected within the spirit and scope of the invention. Moreover, all patents, patent application (published and unpublished, foreign or domestic), literature references or other publication noted above are incorporated herein by reference for any disclosure pertinent to the practice of this invention.