Thermoplastic molding composition and process for preparing the same

Abstract: Environmental stress failure resistant and impact resistant polycarbonates are prepared from an aromatic polycarboante and a copolymer of ethylene and carbon monoxide. These polycarbonates exhibit high impact resistance, chemical resistance, temperature stability and excellent thermoplastic engineering properties, making them suitable for producing molded plastic components for the automotive and electrical housing manufacturing industries.

Description: This invention relates generally to polycarbonates and, more particularly, to environmental stress failure resistant and impact resistant polymer blends comprising a polycarbonate and an olefin-based copolymer. Polycarbonates are well-known commercially available resinous materials having a variety of applications. They are typically prepared by the reaction of dihydroxy compounds with a carbonate precursor, such as phosgene, in the presence of a catalyst. Methods of direct phosgenation, interfacial condensation and transesterification, for the preparation of polycarbonates, are described in detail in "The Chemistry and Physics of Polycarbonates", by H. Schnell, John Wiley & Co., N.Y., 1964. Polycarbonates are high temperature, high performance engineering thermoplastics having a combination of good thermal and mechanical properties, especially when prepared from one or more aromatic diols. The blending with polycarbonates of additional compounds such as, for example, other thermoplastic resins and copolymer rubber compounds, is commonly practiced in order to improve one or more properties of the homopolymer polycarbonate. The applications for polycarbonates as engineering materials are limited because they generally exhibit severe environmental stress failure. By environmental stress failure is meant surface crazing or cracking, or disintegration of the molded piece resulting from its contact with organic solvents while under stress, such as may occur for example when solvents are used to clean or degrease stressed parts fabricated from polycarbonates or polycarbonate blends. For example, U.S. Patent No. 3,431,224 discloses a blend of a polycarbonate and a polyolefin such as polyethylene or an olefin copolymer such as ethylene/propylene, in order to improve the environmental stress failure resistance of the homopolycarbonate. U.S. Patent No. 3,780,140 discloses a terpolymer of ethylene, carbon monoxide and a third component such as vinyl acetate, for blending with a polycarbonate to improve impact resistance. U.S. Patent No. 3,248,359 discloses the use of an ethylene/carbon monoxide copolymer for improving the environmental stress failure resistance of polyolefins such as polyethylene. Finally, U.S. Patent No. 2,541,987 discloses a copolymer of ethylene and carbon monoxide as a plasticizer in chlorinated vinyl polymers such as polyvinyl chloride. It can be seen from the foregoing that the prior art does not suggest that an ethylene/carbon monoxide copolymer would be an effective blend component for increasing the environmental stress failure resistance and impact resistance of polycarbonates. The present invention is directed toward a novel polymer blend, comprising an aromatic polycarbonate and a copolymer of an olefin and carbon monoxide. The blend surprisingly is highly impact resistant, and is likewise resistant to environmental stress failure. The polymer blends of the present invention exhibit high impact resistance, chemical resistance, temperature stability, and excellent thermoplastic engineering properties, making them particularly suitable for producing molded plastic components for the automotive and electrical housing manufacturing industries. The aromatic polycarbonates suitable for use in the present invention are produced by any of the conventional processes known in the art for the manufacture of polycarbonates. Generally, aromatic polycarbonates are prepared by reacting an aromatic dihydric phenol with a carbonate precursor such as, for example, phosgene, a haloformate or a carbonate ester. A preferred method for preparing the aromatic polycarbonates suitable for use in the present invention involves the use of a carbonyl halide, such as phosgene, as the carbonate precursor. This method involves passing phosgene gas into a reaction mixture containing an activated dihydric phenol, or a nonactivated dihydric phenol and an acid acceptor such as, for example, pyridine, dimethyl aniline and quinoline. The acid acceptor may be used undiluted or diluted with inert organic solvents, such as methylene chloride, chlorobenzene or 1,2-dichloroethane. Tertiary amines are advantageous since they are good solvents as well as acid acceptors during the reaction. The temperature at which the carbonyl halide reaction proceeds may vary from below 0°C to 100°C. The reaction proceeds satisfactorily at temperatures from room temperature to 50°C. Since the reaction is exothermic, the rate of phosgene addition may be used to control the temperature of the reaction. The amount of phosgene required will generally depend upon the amount of dihydric phenols present. Generally speaking, one mole of phosgene will react with one mole of dihydric phenol to form the polycarbonate and two moles of HCl. The HCl is in turn taken up by the acid acceptor. Another method for preparing the aromatic polycarbonates useful in the present invention comprises adding phosgene to an alkaline aqueous suspension of dihydric phenols. This is preferably done in the presence of inert solvents such as, for example, methylene chloride and 1,2-dichloroethane. Quaternary ammonium compounds may be employed to catalyze the reaction. Yet another method for preparing such aromatic polycarbonates involves the phosgenation of an agitated suspension of an anhydrous alkali salt of an aryl diol in a nonaqueous medium such as benzene, chlorobenzene or toluene. The reaction is illustrated by the addition of phosgene to a slurry of the sodium salt of, for example, Bisphenol A in an inert polymer solvent such as chlorobenzene. Generally speaking, a haloformate such as the bis-haloformate of Bisphenol A may be used in place of phosgene as the carbonate precursor in any of the methods described above. When a carbonate ester is used as the carbonate precursor in the polycarbonate forming reaction, the materials are reacted at temperatures in excess of 100°C, for times varying from 1 to 15 hours. Under such conditions, ester interchange occurs between the carbonate ester and the dihydric phenol used. The ester interchange is advantageously consummated at reduced pressures on the order of from (10 to 100 millimeters of mercury) 1.3 to 13 kPa, preferably in an inert atmosphere such as nitrogen or argon. Although the polymer forming reaction may be conducted in the absence of a catalyst, one may, if desired, employ a typical ester exchange catalyst, such as metallic lithium, potassium, calcium or magnesium. The amount of such catalyst, if used, is usually small, ranging from 0.001 percent to 0.1 percent, based on the weight of the dihydric phenols employed. In the solution methods of preparation, the aromatic polycarbonate emerges from the reaction in either a true or pseudo solution depending on whether an aqueous base or pyridine is used as an acid acceptor. The copolymer may be precipitated from the solution by adding a polymer nonsolvent, such as heptane or isopropanol. Alternatively, the polymer solution may be heated, typically under reduced pressure, to evaporate the solvent. A preferred aromatic polycarbonate is characterized by repeated units corresponding to the general formula: wherein X is a divalent C₁-C₁₅ hydrocarbon radical, a single bond, -O-, -S-, -S₂-, -SO-, -SO₂-, or -CO-. Each aromatic ring may additionally contain 1 or 2 substituents such as C₁-C₄ alkyl hydrocarbon radicals or halo radicals. A most preferred aromatic polycarbonate is prepared from 2,2-bis-(4-hydroxyphenyl)-propane (Bisphenol A). The aforementioned methods of preparing aromatic polycarbonates are more fully set forth in U.S. Patents 2,999,846, 3,028,365, 3,148,172, 3,153,008, 3,248,414, 3,271,367, and 4,452,968. Also included in the term aromatic polycarbonate are the polycarbonate/polyester copolymers of the types disclosed in U.S. Patents Nos. 3,169,121, 4,105,633, 4,156,069, 4,260,731 and 4,287,787, as well as mixtures of polycarbonates and polycarbonate/polyester copolymers. The carbonate polymers employed in the present invention also include aromatic carbonate polymers such as the trityl diol carbonates described in U.S. Patent Nos. 3,036,036, 3,036,037, 3,036,038 and 3,036,039; polycarbonates of bis (ar-hydroxyphenyl)-alkylidenes (often called Bisphenol-A type diols), including their aromatically and aliphatically substituted derivatives such as disclosed in U.S. Patent Nos. 2,999,835, 3,028,365, 3,334,154 and 4,299,928; the ester/carbonate copolymers of the types described in U.S. Patent Nos. 4,287,787, 4,156,069, 4,260,731 and 4,105,633; carbonate polymers derived from other aromatic diols such as described in U.S. Patent No. 3,169,121; and carbonate polymers based on dihydroxy benzenes such as pyrocatechol, resorcinol and hydroquinone (and their halo- and alkyl-substituted derivatives), and on dihydroxy naphthalenes and anthracenes. Although the polycarbonates mentioned above, such as those derived from Bisphenol-A or from 1,1-bis(4-hydroxyphenyl)-1-phenyl ethane ("Bisphenol-A-P" or "Bis-A-P"), can each be employed in this invention as a homopolymer ( i.e. the product obtained when only one dihydroxy compound is used to prepare the polycarbonate), the polycarbonate used herein can also be derived from two or more different dihydroxy compounds, or mixtures thereof, in the event a carbonate copolymer or interpolymer rather than a homopolymer is desired. For example, either 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane ("Tetrabromo Bisphenol-A" or "TBBA") or 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane ("Tetramethyl Bisphenol-A") is well suited to the formation of carbonate copolymers, a typical copolymer being that which is made from Bis-A and TBBA wherein either co-monomer can be present in a 1-99 or 99-1 molar ratio. Bis-A and Bis-A-P can also be copolymerized where either co-monomer can be present in the copolymer in a 1-99 or 99-1 molar ratio. Carbonate copolymers can also be formed when a bisphenol is reacted with a carbonic acid derivative and a polydiorganosiloxane containing α,ω-bishydroxyaryloxy terminal groups to yield a siloxane/carbonate block copolymer [as are discussed in greater detail in USP 4,569,970). Also useful in this invention are physical blends of two or more of the carbonate homo- and/or copolymers described above. The term "polycarbonate" in this invention should therefore be undestood to include carbonate homopolymers, carbonate copolymers (as described above), and/or blends of various carbonate homopolymers and/or various carbonate copolymers. The olefin/carbon monoxide copolymers of the present invention may be prepared by polymerizing ethylene, or another olefin, such as, for example, propylene, isobutylene and 1-butene, with carbon monoxide, at an elevated temperature and pressure, in the presence of a catalyst such as a peroxy compound or azo compound. Specific procedures for preparing the copolymers are more fully set forth in U.S. Patents Nos. 2,495,285, 2,541,987, 4,024,325 and 4,024,326. The amount of carbon monoxide in the copolymer may be from 0.1 percent to 50 percent of the total weight of the copolymer; preferably it is from 2 percent to 15 percent by weight. A preferred olefin/carbon monoxide is ethylene/carbon monoxide. The polymer compositions of the present invention comprises 50 percent to 95 percent, preferably from 75 percent to 95 percent, of an aromatic homopolycarbonate, copolycarbonate and/or polycarbonate blend; and from 5 percent to 50 percent, preferably from 5 percent to 25 percent, of an olefin/carbon monoxide copolymer. The recited percentages are in relation to the total weight of the composition. The components may be mixed using any conventional mixing apparatus, and can be prepared in dry-blended particulate form or as a melted admixture. The polymer blends of polycarbonate and olefin/carbon monoxide copolymer may contain, in addition, elastomeric impact modifiers such as, for example, acrylonitrile-butadiene-styrene copolymers (ABS copolymers), methylmethacrylate-butadiene-styrene copolymers (MBS rubbers), hydrogenated styrene-butadiene copolymers, functionalized EPDM copolymers, acrylic latexes, polybutadiene, polyisoprene and polybutene. The polymer blends of the present invention may furthermore contain conventional thermoplastic polymer additives such as, for example, fillers, thermal stabilizers, dyes, flame retarding agents, reinforcing agents, softeners, mold-release agents, seed-forming agents, pigments, plasticizers, antistatic agents, ultraviolet radiation absorbers and lubricants, in conventional amounts generally not exceeding 50 percent of the total weight. The invention is more easily comprehended by reference to specific embodiments which are representative of the invention. It must be understood, however, that the specific embodiments are provided only for the purposes of illustration and understanding. Examples 1-8 Dry blends comprising polycarbonate resin and ethylene/carbon monoxide copolymer were prepared in the proportions described in Table I (as were comparison compositions), and subsequently melt-mixed in a co-rotating twin screw extruder. The resulting polymer blend strands were quenched and pelletized, and the pellets injection molded into test specimens whose mechanical properties are described in Tables II and III. Table II illustrates that the environmental stress failure resistance for blends of polycarbonate and ethylene/carbon monoxide was greater than for blends of polycarbonate and other thermoplastic polyolefin materials such as polypropylene and copolymers of ethylene and acrylic acid, as evidenced by the retention of percent elongation at break values after exposure to the solvent. LDPE, when blended with polycarbonate, acted similarly to the copolymer of ethylene and carbon monoxide in that both blends retained their percent elongation at break values after exposure to the solvent. However, delamination of the polycarbonate and LDPE blends was severe, in contrast to the minimal delamination observed for polycarbonate blends containing the copolymer of ethylene and carbon monoxide. Additionally, lower initial percent elongation at break values were observed for the polycarbonate blends containing LDPE than for blends containing the copolymer of ethylene and carbon monoxide. Likewise, the initial dart impact values were lower for polycarbonate blends containing LDPE than for blends containing the copolymer of ethylene and carbon monoxide, as illustrated in Table III.

Claims: A thermoplastic molding composition, comprising, based upon the total weight of the composition: A. from 50 to 95 % of an aromatic polycarbonate; and B. from 50 to 5 % of an olefin/carbon monoxide copolymer, this copolymer not being one derived from ethylene, carbon monoxide and one or more termonomers, and comprising from 0.1 to 50 percent by weight carbon monoxide. A thermoplastic molding composition as claimed in Claim 1, wherein the aromatic polycarbonate is characterized by repeated units corresponding to the general formula: wherein X is a divalent C₁-C₁₅ hydrocarbon radical, a single bond, -O-, -S-, -S₂-, -SO-, -SO₂-, or -CO-, and further wherein each aromatic ring may optionally contain 1 or 2 C₁-C₄ alkyl hydrocarbon radical or halo radical substituents. A thermoplastic molding composition as claimed in Claim 1 wherein said aromatic polycarbonate is a homopolymer or copolymer and is blended with one or more aromatic homopolycarbonates or copolycarbonates. A thermoplastic molding composition as claimed in Claim 1, wherein the aromatic polycarbonate is a copolymer prepared from two or more of the dihydroxy compounds selected from Bisphenol A, Bisphenol-A-P, Tetrabromo Bisphenol-A and Tetramethyl Bisphenol-A. A thermoplastic molding composition as claimed in Claim 1 wherein the aromatic polycarbonate comprises from 75 percent to 95 percent of the composition, based upon the total weight of the composition. A thermoplastic molding composition as claimed in Claim 5 wherein the olefin/carbon monoxide copolymer comprises from 5 percent to 25 percent of the composition, based upon the total weight of the composition. A thermoplastic molding composition as claimed in anyone of the preceding claims wherein the olefin/carbon monoxide copolymer comprises from 2 percent to 15 percent by weight carbon monoxide. A thermoplastic molding composition as claimed in anyone of the preceding claims wherein the olefin/carbon monoxide copolymer comprises an ethylene/carbon monoxide copolymer. A thermoplastic molding composition as claimed in anyone of the preceding claims further comprising an elastomeric impact modifier selected from acrylonitrile-butadiene-styrene copolymers, methylmethacrylate-butadiene-styrene copolymers, hydrogenated styrene-butadiene copolymers, functionalized EPDM copolymers, acrylic latexes, polybutadiene, polyisoprene and polybutene. A process for preparing a thermoplastic molding composition which comprises dry blending (A) from 50 to 95 % of an aromatic polycarbonate; and (B) from 50 to 5 % of an olefin/carbon monoxide copolymer, this copolymer not being one derived from ethylene, carbon monoxide and one or more termonomers, and comprising from 0.1 to 50 percent by weight carbon monoxide, and subsequently melt-mixing the dry blend of (A) and (B).

Inventors: CHOU CHAI JING, FARAH HANI, HOENIG STEPHEN M, CHOU, CHAI JING, FARAH, HANI, HOENIG, STEPHEN M.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1989
Main classification: C08L69
IPC codes: C08L73, C08L69