Patent Publication Number: US-2007123655-A1

Title: Weatherable, high modulus polymer compositions and method

Description:
BACKGROUND  
      The present invention relates to weatherable high modulus polymer compositions with improved ductility derived from rigid thermoplastic resins. Rigid, weatherable thermoplastic resins such as PMMA and MMASAN are known to be brittle with low impact strength. For many applications there is a need to improve the modulus of such base resins and at the same time provide enhanced ductility. Traditionally fillers such as glass fibers are used for modulus enhancement in polymer compositions, but ductility remains low and the surface appearance of molded parts is often poor, thus limiting their applications. Such compositions can also cause damage to compounding and molding equipment due to the presence of abrasive glass fibers.  
      U.S. Pat. No. 5,962,587 discloses the use of polytetrafluoroethylene (PTFE) to improve the modulus of rubber modified thermoplastic resin compositions. These compositions also comprise a rubber component.  
      Commonly owned U.S. patent application Ser. No. 2005/0143508, filed Jun. 30, 2005, discloses the use of PTFE to improve the modulus of thermoplastic resin compositions. These compositions also comprise a filler.  
      There is a need for developing polymer compositions derived from rigid thermoplastic resins, the compositions having high modulus and smooth molded surfaces without surface defects and without the presence of filler components. There is also a need for developing polymer compositions derived from rigid thermoplastic resins, the compositions having enhanced ductility without the presence of a rubber component.  
     BRIEF DESCRIPTION  
      In one embodiment the invention comprises a composition comprising (i) a rigid thermoplastic resin comprising structural units derived from a (C 1 -C 12 )alkyl (meth)acrylate monomer, and optionally a second monomer selected from the group consisting of a vinyl aromatic monomer, a monoethylenically unsaturated nitrile monomer and mixtures thereof, and (ii) 2 parts by weight to 25 parts by weight of a fluoropolymer; wherein the composition is free of both any rubber component and any filler.  
      In another embodiment the invention comprises a method for increasing either the modulus or the impact strength of a composition comprising a rigid thermoplastic resin comprising structural units derived from a (C 1 -C 12 )alkyl (meth)acrylate monomer, and optionally a second monomer selected from the group consisting of a vinyl aromatic monomer, a monoethylenically unsaturated nitrile monomer and mixtures thereof, which comprises the steps of: (i) combining the composition with from 2 parts by weight to 25 parts by weight of a fluoropolymer, and (ii) processing the composition from (i) at a temperature less than the melting point of the fluoropolymer; wherein the composition is free of both any rubber component and any filler.  
      In still another embodiment the invention comprises articles made from compositions of the invention. Various other features, aspects, and advantages of the present invention will become more apparent with reference to the following description and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a micrograph of a composition comprising 5 wt. % PTFE in PMMA wherein the composition was processed at a temperature of less than about 325° C.  
       FIG. 2  shows a micrograph of a composition comprising 5 wt. % PTFE in MMASAN wherein the composition was processed at a temperature of less than about 325° C. 
    
    
     DETAILED DESCRIPTION  
      In the following specification and the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings. The singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. The terminology “(meth)acrylate” refers collectively to acrylate and methacrylate; for example, the term “(meth)acrylate monomers” refers collectively to acrylate monomers and methacrylate monomers.  
      Polymer compositions in embodiments of the invention comprise at least one rigid thermoplastic resin. Illustrative rigid thermoplastic resins comprise those with structural units derived from one or more monomers selected from the group consisting of (C 1 -C 12 )alkyl (meth)acrylate monomers. Optionally, the rigid thermoplastic resin may further comprise structural units derived from a vinyl aromatic monomer, or a monoethylenically unsaturated nitrile monomer, or mixtures thereof. In embodiments of the invention the rigid thermoplastic resins are free of any rubber component.  
      As used herein, the term “(C 1 -C 12 )alkyl” means a straight or branched alkyl substituent group having from 1 to 12 carbon atoms per group, and includes, for example, methyl, ethyl, n-butyl, sec-butyl, t-butyl, n-propyl, iso-propyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl. Suitable (C 1 -C 12 )alkyl (meth)acrylate monomers include (C 1 -C 12 )alkyl acrylate monomers, for example, ethyl acrylate, butyl acrylate, iso-pentyl acrylate, n-hexyl acrylate, 2-ethyl hexyl acrylate, and their (C 1 -C 12 )alkyl methacrylate analogs, such as, for example, methyl methacrylate (MMA), ethyl methacrylate, propyl methacrylate, iso-propyl methacrylate, butyl methacrylate, hexyl methacrylate, and decyl methacrylate.  
      Suitable vinyl aromatic monomers include, for example, styrene and substituted styrenes having one or more alkyl, alkoxyl, hydroxyl or halo substituent groups attached to the aromatic ring, including, for example, alpha-methyl styrene, p-methyl styrene, vinyl toluene, vinyl xylene, trimethyl styrene, butyl styrene, chlorostyrene, dichlorostyrene, bromostyrene, p-hydroxystyrene, methoxystyrene and vinyl-substituted condensed aromatic ring structures, such as, for example, vinyl naphthalene and vinyl anthracene, as well as mixtures of vinyl aromatic monomers. As used herein, the term “monoethylenically unsaturated nitrile monomer” means an acyclic compound that includes a single nitrile group and a single site of ethylenic unsaturation per molecule, and includes, for example, acrylonitrile, methacrylonitrile, and alpha-chloro acrylonitrile.  
      In a particular embodiment the rigid thermoplastic resin comprises poly(methyl methacrylate) (PMMA). As is well known in the art, PMMA may be produced by the polymerization of methyl methacrylate monomer to form a homopolymer. PMMA homopolymer exists in its pure form only theoretically and is generally available commercially as a mixture of the homopolymer and one or more copolymers of methyl methacrylate with C 1 -C 4  alkyl acrylates, such as ethyl acrylate. Such commercially available PMMA copolymers contain structural units derived from methyl methacrylate and from about 1 percent to about 30 percent by weight of one or more C 1 -C 4  alkyl acrylates. In some embodiments the rigid thermoplastic resin comprises a mixture of PMMA and at least one additional rigid thermoplastic resin comprising structural units derived from at least one vinyl aromatic monomer and at least one monoethylenically unsaturated nitrile monomer, wherein PMMA is present is an amount in a range of between 1 wt. % and 99 wt. % based on the total weight of the rigid thermoplastic resin. In a particular embodiment the rigid thermoplastic resin comprises a mixture of PMMA and styrene-acrylonitrile copolymer (SAN).  
      In another particular embodiment the rigid thermoplastic resin comprises a copolymer comprising structural units derived from methyl methacrylate and at least one of styrene or acrylonitrile. In still another particular embodiment the rigid thermoplastic resin comprises a copolymer comprising structural units derived from methyl methacrylate, and styrene and acrylonitrile (often referred to herein as MMASAN), and the range of ratios of MMA:S:AN in the MMASAN is from about 80/15/5 to about 30/50/20. In one embodiment MMASAN comprises structural units derived from about 80% MMA, 15% styrene, and 5% acrylonitrile; in another embodiment, about 60% MMA, 30% styrene and 10% acrylonitrile; and in still another embodiment, about 45% MMA, 40% styrene and 15% acrylonitrile. In still another particular embodiment MMASAN comprises structural units derived from about 35 wt. % MMA, 40 wt. % styrene, and 25 wt. % acrylonitrile. The molecular weight of the MMASAN resin, either as homopolymer or copolymer, can range from about 50,000 to about 450,000, and particularly from about 100,000 to about 250,000 as a weight average molecular weight. In some embodiments the rigid thermoplastic resin comprises a mixture of MMASAN and at least one additional rigid thermoplastic resin comprising structural units derived from at least one vinyl aromatic monomer and at least one monoethylenically unsaturated nitrile monomer, wherein MMASAN is present is an amount in a range of between 1 wt. % and 99 wt. % based on the total weight of the rigid thermoplastic resin. In a particular embodiment the rigid thermoplastic resin comprises a mixture of MMASAN and SAN.  
      Suitable fluoropolymers and methods for making such fluoropolymers are known, as described for example, in U.S. Pat. Nos. 3,671,487 and 3,723,373. Suitable fluoropolymers include homopolymers and copolymers that comprise repeating units derived from one or more fluorinated olefin monomers. The term “fluorinated-olefin monomer” means an olefin monomer that includes at least one fluorine atom substituent. Suitable fluorinated olefin monomers comprise fluoroethylenes including, but are not limited to, CF 2 ═CF 2 , CHF═CF 2 , CH 2 ═CF 2 , CH 2 ═CHF, CClF═CF 2 , CCl 2 ═CF 2 , CClF═CClF, CHF═CCl 2 , CH 2 ═CClF, and CCl 2 ═CClF and fluoropropylenes including, but are not limited to, CF 3 CF═CF 2 , CF 3 CF═CHF, CF 3 CH═CF 2 , CF 3 CH═CH 2 , CHF 2 CF═CHF, CHF 2 CH═CHF and CHF 2 CH═CH 2 . In a particular embodiment, the fluorinated olefin monomer comprises one or more of tetrafluoroethylene, chlorotrifloroethylene, vinylidene fluoride or hexafluoropropylene. Suitable fluorinated olefin homopolymers include for example, poly(tetrafluoroethylene) and poly(hexafluoroethylene).  
      Suitable fluorinated olefin copolymers include copolymers comprising repeating units derived from two or more fluorinated olefin monomers such as, for example, poly(tetrafluoroethylene-hexafluoroethylene), and copolymers comprising structural units derived from one or more fluorinated monomers and one or more non-fluorinated monoethylenically unsaturated monomers that are copolymerizable with the fluorinated monomers, including, but are not limited to, poly(tetrafluoroethylene-ethylene-propylene) copolymers. Suitable non-fluorinated monoethylenically unsaturated monomers comprise olefin monomers including, but are not limited to, ethylene, propylene, butene, acrylate monomers such as, for example, methyl methacrylate and butyl acrylate, vinyl ethers, such as, for example, cyclohexyl vinyl ether, ethyl vinyl ether, and n-butyl vinyl ether, and vinyl esters such as, for example, vinyl acetate and vinyl versatate. In particular embodiments suitable fluoropolymers comprise polytetrafluoroethylene (PTFE), perfluoropolyethers, and fluoroelastomers. In other particular embodiments suitable fluoropolymers are in particulate form or in fibrous form. In another particular embodiment suitable fluoropolymers are in particulate form with particles ranging in size in one embodiment from about 50 nanometers (nm) to about 500 nm, and in another embodiment from about 150 nm to about 400 nm, as measured by electron microscopy.  
      In some embodiments a fluoropolymer is combined with the rigid thermoplastic resin in the form of a fluoropolymer additive that comprises both fluoropolymer and a second rigid thermoplastic polymer, sometimes referred to herein after as a “carrier polymer”. Illustrative examples of carrier polymer comprise those with structural units derived from a vinyl aromatic monomer, or a monoethylenically unsaturated nitrile monomer, or a (C 1 -C 12 )alkyl (meth)acrylate monomer, or mixtures thereof. Particular examples of the carrier polymer include, but are not limited to, polystyrene, poly-alpha-alkylstyrene, poly-alpha-methylstyrene, maleic anhydride-modified styrenic polymers, styrene/maleic anhydride copolymers, maleimide-modified styrenic polymers, styrene/N-aryl maleimide copolymers, styrene/N-phenyl maleimide copolymers, styrene/acrylonitrile copolymers, alpha-alkylstyrene/acrylonitrile copolymers, alpha-methylstyrene/acrylonitrile copolymers, styrene/alpha-alkylstyrene/acrylonitrile copolymers, styrene/alpha-methylstyrene/acrylonitrile copolymers, styrene/acrylonitrile/methyl methacrylate copolymers, styrene/alpha-alkylstyrene/acrylonitrile/methyl methacrylate copolymers, styrene/alpha-methylstyrene/acrylonitrile/methyl methacrylate copolymers, alpha-alkylstyrene/acrylonitrile/methyl methacrylate copolymers, and alpha-methylstyrene/acrylonitrile/methyl methacrylate copolymers. In another particular embodiment the fluoropolymer additive comprises from 30 wt. % to 70 wt. %, more particularly from 40 wt. % to 60 wt. %, fluoropolymer, and from 30 wt. % to 70 wt. %, more particularly from 40 wt. % to 60 wt. %, carrier polymer based on the total weight of the fluoropolymer additive.  
      The fluoropolymer additive may be made by combining a fluoropolymer, for example, in the form of an aqueous dispersion of fluoropolymer particles, with a carrier polymer, precipitating the combined fluoropolymer particles and carrier polymer, and then drying the precipitate to form the fluoropolymer additive. In a particular embodiment the fluoropolymer additive particles range in size from 50 nm to 500 nm, as measured by electron microscopy. In another particular embodiment the aqueous fluoropolymer dispersion comprises water and from 1 part by weight (pbw) to 80 pbw, based on 100 pbw of the dispersion, of fluoropolymer and from 0.1 pbw to 10 pbw, based on 100 pbw of the fluoropolymer, of a fatty acid salt of the structural formula R 1 COOH where R 1  is H, alkyl, cycloalkyl, aryl or HOOC—CH x ) n —; wherein x=0, 1, or 2; and n=0-70. In a particular embodiment, R 1  is (C 1 -C 30 )alkyl or (C 4 -C 12 )cycloalkyl. As used herein, the term “(C 1 -C 30 )alkyl” means a straight or branched alkyl substituent group having from 1 to 30 carbon atoms per group and comprising, for example, methyl, ethyl, n-butyl, sec-butyl, t-butyl, n-propyl, iso-propyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, stearyl, or eicosyl; and the term “(C 4 -C 12 )cycloalkyl” means a cyclic alkyl substituent group having from 4 to 12 carbon atoms per group, comprising, for example, cyclohexyl or cylcooctyl. The term “aryl” means an organic radical derived from an aromatic hydrocarbon by removal of one hydrogen atom, which may optionally be substituted on the aromatic ring with one or more substituent groups. Illustrative examples of aryl groups are phenyl, tolyl, xylyl, and naphthyl.  
      In a particular embodiment, the fluoropolymer additive is made by emulsion polymerization of one or more monoethylenically unsaturated monomers in the presence of the aqueous fluoropolymer dispersion to form a carrier polymer in the presence of the fluoropolymer. The emulsion is then precipitated, for example, by addition of sulfuric acid. The precipitate is dewatered, for example, by centrifugation, and then dried to form a fluoropolymer additive that comprises fluoropolymer and an associated carrier polymer. The dry emulsion polymerized fluoropolymer additive is typically in the form of a free-flowing powder.  
      In a particular embodiment, the monoethylenically unsaturated monomers that are emulsion polymerized to form the carrier polymer comprise one or more monomers selected from vinyl aromatic monomers and monoethylenically unsaturated nitrile monomer. In another particular embodiment, the carrier polymer comprises repeating units derived from styrene and acrylonitrile. More particularly, the carrier polymer comprises from 60 wt. % to 90 wt. % repeating units derived from styrene and from 10 wt. % to 40 wt. % repeating units derived from acrylonitrile. The emulsion polymerization reaction is typically initiated using a conventional free radical initiator such as, for example, an organic peroxide compound, such as for example, benzoyl peroxide, a persulfate compound, such as, for example, potassium persulfate, an azonitrile compound such as for example, 2,2′-azobis-2,3,3-trimethylbutyronitrile, or a redox initiator system, such as, for example, a combination of cumene hydroperoxide, ferrous sulfate, tetrasodium pyrophosphate and a reducing sugar or sodium formaldehyde sulfoxylate. A chain transfer agent such as, for example, a (C 9 -C 13 )alkyl mercaptan compound such as, for example, nonyl mercaptan or t-dodecyl mercaptan, may optionally be added to the reaction vessel during the polymerization reaction to reduce the molecular weight of the carrier polymer. In a particular embodiment, no chain transfer agent is used. In another particular embodiment the stabilized fluoropolymer dispersion is charged to a reaction vessel and heated with stirring. The initiator system and the one or more monoethylenically unsaturated monomers are then charged to the reaction vessel and heated to polymerize the monomers in the presence of the fluoropolymer particles of the dispersion to thereby form the carrier polymer. Suitable fluoropolymer additives and emulsion polymerization methods are disclosed, for example, in European Patent Application 0739914.  
      In another illustrative example of fluoropolymer additive preparation an aqueous dispersion of PTFE fluoropolymer and an aqueous styrene-acrylonitrile resin emulsion may be precipitated to form a fluoropolymer concentrate and then dried to provide a PTFE-comprising fluoropolymer additive as a powder as disclosed in, for example, U.S. Pat. No. 4,579,906. Other suitable methods of forming a fluoropolymer additive are disclosed in, for example, U.S. Pat. Nos. 4,647,602; 5,539,036; 5,679,741; and 5,681,875.  
      In another particular embodiment the compositions of the present invention comprise an intimate mixture of at least one rigid thermoplastic resin and a fluoropolymer additive wherein the fluoropolymer additive is present in an amount effective to provide an increase in modulus or impact strength or both compared to those properties of the same composition prepared without fluoropolymer. In other embodiments the compositions comprise, based on 100 pbw of the composition, from 75 pbw to 98 pbw, particularly 75 pbw to 97 pbw, more particularly 80 pbw to 96 pbw, and still more particularly from 80 pbw to 95 pbw of the combined thermoplastic resin and carrier polymer and from 2 pbw to 25 pbw, particularly from 3 pbw to 25 pbw, more particularly from 4 pbw to 20 pbw and still more particularly from 5 pbw to 20 pbw of the fluoropolymer.  
      Thermoplastic resin compositions in embodiments of the present invention may optionally comprise various conventional additives, such as, but not limited to: (1) antioxidants, such as, for example, organophosphites, for example, tris(nonyl-phenyl)phosphite, (2,4,6-tri-tert-butylphenyl)(2-butyl-2-ethyl-1,3-propanediol)phosphite, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite or distearyl pentaerythritol diphosphite, as well as alkylated monophenols, polyphenols, alkylated reaction products of polyphenols with dienes, such as, for example, butylated reaction products of para-cresol and dicyclopentadiene, alkylated hydroquinones, hydroxylated thiodiphenyl ethers, alkylidene-bisphenols, benzyl compounds, acylaminophenols, esters of beta-(3,5-di-tert-butyl-4-hydroxyphenol)-propionic acid with monohydric or polyhydric alcohols, esters of beta-(5-tert-butyl-4-hydroxy-3-methylphenyl)-propionic acid with monohydric or polyhydric alcohols, esters of beta-(5-tert-butyl-4-hydroxy-3-methylphenyl) propionic acid with mono- or polyhydric alcohols, esters of thioalkyl or thioaryl compounds, such as, for example, distearylthiopropionate, dilaurylthiopropionate, ditridecylthiodipropionate, or amides of beta-(3,5-di-tert-butyl-4-hydroxyphenol)-propionic acid; (2) UV absorbers and light stabilizers such as, for example, HALS, 2-(2′-hydroxyphenyl)-benzotriazoles, 2-hydroxy-benzophenones, esters of substituted or unsubstituted benzoic acids, acrylates, or nickel compounds; (3) metal deactivators, such as, for example, N,N′-diphenyloxalic acid diamide, or 3-salicyloylamino-1,2,4-triazole; (4) peroxide scavengers, such as, for example, (C 10 -C 20 )alkyl esters of beta-thiodipropionic acid, or mercapto benzimidazole; (5) basic co-stabilizers, such as, for example, melamine, polyvinylpyrrolidone, triallyl cyanurate, urea derivatives, hydrazine derivatives, amines, polyamides, or polyurethanes; (6) sterically hindered amines such as, for example, triisopropanol amine or the reaction product of 2,4-dichloro-6-(4-morpholinyl)-1,3,5-triazine with a polymer of 1,6-diamine, or N,N′-bis(2,2,4,6-tetramethyl-4-piperidenyl) hexane; (7) neutralizers such as magnesium stearate, magnesium oxide, zinc oxide, zinc stearate, or hydrotalcite; (8) other additives such as, for example, lubricants such as, for example, pentaerythritol tetrastearate, EBS wax, or silicone fluids, plasticizers, optical brighteners, pigments, dyes, pigments, colorants, flameproofing agents, anti-static agents, or blowing agents; or (9) flame retardant additives such as, for example, halogen-containing organic flame retardant compounds, organophosphate flame retardant compounds, or borate flame retardant compounds. In embodiments of the invention the rigid thermoplastic resins are free of any filler component. In particular embodiments compositions of the invention may further comprise an additive selected from the group consisting of lubricants, neutralizers, stabilizers, heat stabilizers, light stabilizers, antioxidants, UV screeners, UV absorbers, dyes, pigments, colorants, and mixtures thereof.  
      In one embodiment the compositions of the present invention may be prepared by mixing the rigid thermoplastic resin and the fluoropolymer as described herein to form a first mixture. The mixing can be typically carried out in any conventional mixer like drum mixers, ribbon mixers, vertical spiral mixers, Muller mixers, Henschel mixers, sigma mixers, chaotic mixers, static mixers or the like. The first mixture is then compounded under melt-mixing conditions using any conventional method, such as extrusion kneading or roll kneading, a two-roll mill, in a Banbury mixer or in a single screw or twin-screw extruder, or in any high shear mixing device to mix the components to produce an intimate mixture, and optionally, to reduce the composition so formed to particulate form, for example, by pelletizing or grinding the composition. The twin screw extruder, when employed, can be co-rotating, counter rotating, intermeshing, non-intermeshing, a planetary gear extruder, a co-continuous mixer, or the like. The compounding process can be a continuous, semi-continuous, or a batch process. In other embodiments all or a portion of fluoropolymer either neat or in the form of fluoropolymer additive, itself either neat or combined with a portion of rigid thermoplastic resin, may be added to the composition at some stage of a blending process, such as in an extrusion process. Those of ordinary skill in the art will be able to adjust blending times, as well as component addition location and sequence, without undue additional experimentation. Also optionally, a portion of the rigid thermoplastic resin may be mixed with fluoropolymer or fluoropolymer additive to prepare a master batch, and then the remaining rigid thermoplastic resin may be added and mixed therewith later for multistage mixture.  
      Compositions in embodiments of the present invention can be formed into useful articles by a variety of means such as injection molding, extrusion molding, profile extrusion, calendering, rotary molding, blow molding, foam molding, or thermoforming. illustrative articles comprise automotive interior and exterior components, computer and business machine housings, electrical components, home appliances and media storage devices, such as, for example, audiovisual cassettes and disk drive components. Compositions in embodiments of the invention are also useful in sheet and film applications and in articles derived from sheet and film, such as, but not limited to, coextruded, multilayer sheet articles.  
      Processing temperatures for both compounding the compositions and for forming the compounded compositions into useful articles are typically less than the melting point of the fluoropolymer. In particular embodiments processing temperatures for both compounding the compositions and for forming the compounded compositions into useful articles are typically less than about 325° C. At temperatures above the melting point of the fluoropolymer, the increase in modulus or impact strength or both properties is not as high as is obtained when the compositions are processed at temperatures below the melting point of the fluoropolymer. When the compositions are processed at temperatures below the melting point of the fluoropolymer, the fluoropolymer typically disperses as fibrils into the matrix of rigid thermoplastic resin. Although the invention is not meant to be limited by any theory of operation, it is believed that the presence of fibrils comprising fluoropolymer aids in increasing modulus or impact strength or both properties of the compositions. For example, when test parts comprising compositions in embodiments of the invention comprising PTFE are heated, they typically shrink, and physical properties such as modulus typically decrease, often to the value of that property observed before addition of fluoropolymer. In the test parts so heated, fibrils comprising fluoropolymer may lose their fibril shape as they aggregate into large particles and/or segregate into isolated islands of fluoropolymer.  
      The following examples are included to provide additional guidance to those skilled in the art in practicing the claimed invention. The examples provided are merely representative of the work that contributes to the teaching of the present application. Accordingly, these examples are not intended to limit the invention, as defined in the appended claims, in any manner.  
      In the following examples MMASAN comprised structural units derived from 40 wt. % styrene, 35 wt. % MMA, and 25 wt. % acrylonitrile, and had a weight average molecular weight of about 150,000 and a melt volume rate of about 40, determined at 220° C. using a 10 kilogram weight. PMMA was ACRYLITE® H-12 poly(methyl methacrylate) obtained from CYRO Industries, Rockaway, N.J., and having an average melt flow of 7.0 grams per 10 minutes determined by ASTM D-1238 at 230° C. using a 3.8 kilogram weight. PTFE-comprising fluoropolymer additive comprised 50 wt. % PTFE and 50 wt. % SAN as carrier polymer. Amounts of PTFE reported in the following examples refer to PTFE by itself unless otherwise noted. All compositions were compounded and then molded into test parts at processing temperatures of less than 325° C. Tensile properties of molded test parts were determined according to ASTM D-638. Izod impact strength values of molded test parts were determined according to ASTM D-256. Multiaxial impact strength values of molded test parts were determined at room temperature according to ISO 6603-2. The abbreviation “C.Ex.” means comparative example.  
     COMPARATIVE EXAMPLES 1-4  
      SAN was obtained from General Electric Plastics, Pittsfield, Mass., and comprised structural units derived from 72 wt. % styrene and 28 wt. % acrylonitrile. SAN pellets were compounded with PTFE-comprising fluoropolymer additive powder using standard compounding conditions. The fluoropolymer additive amount was varied to adjust PTFE levels in the final formulations to the amounts as shown in Table 1. Compositions were compounded by extrusion to produce pellets. Pellets were injection molded into standard test parts for physical property measurements. Physical properties are shown in Table 1.  
                           TABLE 1                               Tensile   Notched Izod       Comparative       modulus,   impact,       Example   Components   megapascals   Joules per meter                                                C. Ex. 1   SAN/   5426   58.6           5 wt. % PTFE       C. Ex. 2   SAN/   6371   90.6           10 wt. % PTFE       C. Ex. 3   SAN/   6233   106           15 wt. % PTFE       C. Ex. 4   SAN/   6826   197           20 wt. % PTFE                  
 
     EXAMPLES 1-4 AND COMPARATIVE EXAMPLE 5  
      PMMA pellets were compounded with PTFE-comprising fluoropolymer additive using standard compounding conditions. The fluoropolymer additive amount was varied to adjust PTFE levels in the final formulations to the amounts as shown in Table 2. Compositions were compounded by extrusion to produce pellets. Pellets were injection molded into standard test parts for physical property measurements. Physical properties are shown in Table 2.  
                               TABLE 2                                   Notched                   Tensile   Izod   Multiaxial       Example or       modulus,   impact,   impact       Comparative       mega-   Joules per   strength,       Example   Components   pascals   meter   Joules                                                    C. Ex. 5   PMMA   3241   26.7   —                   (brittle)       Ex. 1   PMMA/   5102   58.6   3.22           5 wt. % PTFE       Ex. 2   PMMA/   5378   85.2   4.48           10 wt. % PTFE       Ex. 3   PMMA/   7722   90.6   4.78           15 wt. % PTFE       Ex. 4   PMMA/   6205   208   6.92           20 wt. % PTFE       Ex. 5   25 wt. % PMMA +   5864   90   —           65 wt. % SAN* +           10 wt. % PTFE       Ex. 6   25 wt. % PMMA +   6037   112   —           60 wt. % SAN* +           15 wt. % PTFE                 *includes SAN from fluoropolymer additive             
 
      In comparison to comparative example 5 without PTFE, compositions comprising PTFE with the rigid thermoplastic resin PMMA show an improvement in tensile modulus and, in addition, an improvement in impact strength despite the fact that no rubber component is present in the compositions. Molded test parts comprising PMMA and PTFE also showed smooth surfaces after injection molding. The molded test parts also show good weatherability upon exposure to typical weatherability test conditions.  
     EXAMPLES 7-10 AND COMPARATIVE EXAMPLE 6  
      MMASAN pellets were compounded with PTFE-comprising fluoropolymer additive powder using standard compounding conditions. The fluoropolymer additive amount was varied to adjust PTFE levels in the final formulations to the amounts as shown in Table 3. Compositions were compounded by extrusion to produce pellets. Pellets were injection molded into standard test parts for physical property measurements. Physical properties are shown in Table 3.  
                               TABLE 3                                   Notched                   Tensile   Izod   Multiaxial       Example or       modulus,   impact,   impact       Comparative       mega-   Joules   strength,       Example   Components   pascals   per meter   Joules                                                    C. Ex. 6   MMASAN   3516   26.7   —                   (brittle)       Ex. 7   MMASAN/   5378   58.6   5.02           5 wt. % PTFE       Ex. 8   MMASAN/   7446   149   4.98           10 wt. % PTFE       Ex. 9   MMASAN/   8136   293   6.24           15 wt. % PTFE       Ex. 10   MMASAN/   7722   293   8.40           20 wt. % PTFE                  
 
      In comparison to the comparative example without PTFE, compositions comprising PTFE with the rigid thermoplastic resin MMASAN show a significant improvement in both tensile modulus and impact strength despite the fact that no rubber component is present in the compositions. Surprisingly, the MMASAN compositions with PTFE show a larger increase in tensile modulus and impact strength at comparable loading of PTFE than do blends of PTFE with either polymeric component of MMASAN by itself (i.e. PTFE blends with PMMA and with SAN). Note particularly the properties of examples 8 and 9 compared to those of examples 2 and 3 and comparative examples 2 and 3. Molded test parts comprising MMASAN and PTFE also showed smooth surfaces after injection molding. The molded test parts also show good weatherability upon exposure to typical weatherability test conditions.  
     EXAMPLE 11 AND COMPARATIVE EXAMPLE 7  
      A composition comprising PMMA and 5 wt. % PTFE (derived from the fluoropolymer additive) was formed into test parts at processing temperatures of less than about 325° C.  FIG. 1  shows a micrograph of the composition which shows the presence of fibrils comprising PTFE. The modulus of the test part was higher than that observed in a similar composition without PTFE. For comparison a test part comprising a similar composition was heated. The test part showed shrinkage compared to the original test part.  
     EXAMPLE 12 AND COMPARATIVE EXAMPLE 8  
      A composition comprising MMASAN and 5 wt. % PTFE (derived from the fluoropolymer additive) was formed into test parts at processing temperatures of less than about 325° C.  FIG. 2  shows a micrograph of the composition which shows the presence of fibrils comprising PTFE. The modulus of the test part was higher than that observed in a similar composition without PTFE. For comparison a test sample of a related composition comprising MMASAN and PTFE was heated and the modulus value measured both before and after heating. The modulus value for the test sample so heated had decreased by about 40% compared to the value observed before heating.  
      While the invention has been illustrated and described in typical embodiments, it is not intended to be limited to the details shown, since various modifications and substitutions can be made without departing in any way from the spirit of the present invention. As such, further modifications and equivalents of the invention herein disclosed may occur to persons skilled in the art using no more than routine experimentation, and all such modifications and equivalents are believed to be within the spirit and scope of the invention as defined by the following claims. All Patents and published articles cited herein are incorporated herein by reference.