WO2008088619A1

WO2008088619A1 - Nanocomposite and method of making the same

Info

Publication number: WO2008088619A1
Application number: PCT/US2007/086514
Authority: WO
Inventors: Terri A. Shefelbine; John W. Longabach; Ryan E. Marx; James M. Nelson
Original assignee: 3M Innovative Properties Company
Priority date: 2006-12-21
Filing date: 2007-12-05
Publication date: 2008-07-24

Abstract

A method of making a nanocomposite material that results in a preferred exfoliation level of a layered silicate in a host polymer. The method enables one of ordinary skill in the art to efficiently determine a preferred formulation and thereby make a nanocomposite material without lengthy process and material experimentation.

Description

NANOCOMPOSITE AND METHOD OF MAKING THE SAME

BACKGROUND

Many materials have been added to polymeric resins to reinforce them. Such reinforced polymeric resins are generally referred to as composite materials or "composites". Particulate materials have been used to reinforce polymer matrices. In particular, a type of composite has emerged in recent years in which the reinforcing material has one or more dimensions on the order of a nanometer. Such a composite is known in the art as a "nanocomposite". One type of nanocomposite has an exfoliated layered silicate as the reinforcing material wherein the layered structure is broken down and individual silicate platelets are dispersed throughout the polymeric resin.

Layered silicates are typically composed of stacked silicate platelets. The silicate platelets typically have a thickness on the order of about one nanometer and typically have an aspect ratio of at least about 100. The spaces between these platelets are called gallery spaces. Under the proper conditions, the gallery spaces can be filled with monomer, oligomer, or polymer. This increases the distance between silicate platelets, swelling the layered silicate in a method termed intercalation. If the layered silicate swells so much that at least some of the individual silicate platelets are no longer organized into stacks, those individual silicate platelets are said to be "exfoliated".

One difficulty in applying clay nanomaterials in host polymers is the attainment of uniformly dispersed exfoliated materials throughout the host polymer matrix. An even greater problem can be selecting a dispersing agent to meet the varied chemistries and the extrusion operating characteristics involved in the combination of exfoliated materials and host resins.

SUMMARY

The present invention is directed to a method of making a nanocomposite material that results in a preferred exfoliation level of a layered silicate in a host polymer. The resulting nanocomposite materials are preferred for specific end use applications, such as automotive parts and electronic housing, because of the enhanced desired physical characteristics resulting from the inventive process. The method of making a nanocomposite according to the present invention comprises combining a layered silicate, a host polymer and block copolymer. The block copolymer has a block that is compatible with the layered silicate. Additionally the block copolymer has a polydispersity of about 1.8 or greater and a viscosity ratio to the host polymer of about 0.7 to about 1.5. The admixture is exfoliated by heat, shear, processing rate and combined chemistries resulting in a nanocomposite material having at least 20 percent by weight of the layered silicate forming a plurality of exfoliated silicate platelets dispersed in the host polymer.

Methods according to the present invention broaden the range of processes and materials that may be used to prepare nanocomposites.

As used herein, the term "block" refers to a portion of a block copolymer, comprising many monomeric units, that has at least one feature which is not present in the adjacent portions; the term "block copolymer" refers to a copolymer composed of constitutionally different blocks in linear sequence; the term "monomeric unit" refers to the largest constitutional unit contributed by a single monomer molecule to the structure of a polymer; the phrase "compatible with the layered silicate" means capable of intercalating the layered silicate; the term "exfoliated silicate platelet" refers to an individual silicate platelet that is less than about 5 nanometers thick and has an aspect ratio of at least about 10, and is not associated as a face-to-face stack with at least one other such silicate platelet, regardless of whether the silicate platelet was made by exfoliating a layered silicate or by some other method; and the term "immiscible" means spontaneously forming two phases if intimately mixed together, each phase independently being continuous or discontinuous. the term "miscible" means spontaneously forming one phase if intimately mixed together; the term "Polydispersity Index (PDI)"refers to a measure of the distribution of molecular weights in a given polymer sample. The PDI calculated is the weight average molecular weight (M_w) divided by the number average molecular weight (M_n). It indicates the distribution of individual molecular weights in a batch of polymers. the terms "AB, ABA, and ABC Block copolymers" described herein are notably different than the traditional segmented multiblock copolymers, refer to as (AB)_n block copolymers, derived by condensation reactions. Such segmented systems are traditionally derived, for example by reaction of difunctional alcohols with diisocyanates. Thermoplastic polyurethanes are perhaps the most notable example of such polymers formed by reaction of polyglycols with excess diisocyanates and are typically referred to as segmented polyurethanes (see Odian, Principles of polymerization 3^rd edition, 1991, John Wiley and Sons, pg 148-149). the term "di-block copolymer" or "tri-block copolymer" means a polymer in which all the neighboring monomer units (except at the transition point) are of the same identity, for example, AB is a di-block copolymer comprised of an A block and a B block that are compositionally different, ABA is a tri-block copolymer in which the A blocks are compositionally the same, but different from the B block, and ABC is a tri-block copolymer in which the A, B, and C blocks are all compositionally different. the term "living anionic polymerization" means, in general, a chain polymerization that proceeds via an anionic mechanism without chain termination or chain transfer. (For a more complete discussion of this topic, see Anionic Polymerization Principles and Applications. H. L. Hsieh, R. P. Quirk, Marcel Dekker, NY, N.Y. 1996. Pg. 72-127).

DETAILED DESCRIPTION

Compositions of the present invention comprise exfoliated silicate platelets, a thermoplastic polymer, and a block copolymer, typically, in the form of a nanocomposite.

Silicates

Useful layered silicates that may be used as the layered silicate (for example, intercalated and/or exfoliated) according to the present invention include, for example, natural phyllosilicates, synthetic phyllosilicates, organically modified phyllosilicates (for example, organoclays), and combinations thereof. Examples of natural phyllosilicates include smectite and smectite-type clays such as montmorillonite, nontronite, bentonite, beidellite, hectorite, saponite, sauconite, fluorohectorite, stevensite, volkonskoite, magadiite, kenyaite, halloysite, and hydrotalcite.

Suitable synthetic phyllosilicates include, for example, those prepared by hydrothermal processes as disclosed in U.S. Pat. Nos. 3,252,757 (Granquist); 3,666,407 (Orlemann); 3,671,190 (Neumann); 3,844,978 (Hickson); 3,844,979 (Hickson); 3,852,405 (Granquist); and 3,855,147 (Granquist). Commercially available synthetic smectite clays are commercially available, for example, from Southern Clay Products, Gonzales, Texas, under the trade designation "LAPONITE" including, for example, "LAPONITE B" (a synthetic layered fluorosilicate), "LAPONITE D"(a synthetic layered magnesium silicate), and "LAPONITE RD"(a synthetic layered silicate).

Organoclays are typically smectite or smectite-type clays produced by interacting the unfunctionalized clay with one or more suitable intercalants. These intercalants are typically organic compounds, which are neutral or ionic. Useful neutral organic intercalants include polar compounds such as amides, esters, lactams, nitriles, ureas, carbonates, phosphates, phosphonates, sulfates, sulfonates, nitro compounds, and the like. The neutral organic intercalants can be monomeric, oligomeric or polymeric. Neutral organic intercalants may intercalate into the layers of the clay through hydrogen bonding without completely replacing the original charge balancing ions. Useful ionic intercalants are typically cationic surfactants such as, for example, onium compounds such as ammonium (primary, secondary, tertiary, and quaternary), phosphonium, or sulfonium derivatives of aliphatic, aromatic or aliphatic amines, phosphines and sulfides. Useful onium ions include, for example, quaternary ammonium ions having at least one long chain aliphatic group (for example, octadecyl, myristyl, or oleyl) bound to the quaternary nitrogen atom. Further details concerning organoclays and methods for their preparation may be found, for example, in U.S. Pat. Nos. 4,469,639 (Thompson et al); 6,036,765 (Farrow et al.); and 6,521,678Bl (Chaiko).

A variety of organoclays are available from commercial sources. For example, Southern Clay Products offers various organoclays under the trade designations "CLOISITE" (derived from layered magnesium aluminum silicate) and "CLAYTONE" (derived from natural sodium bentonite) including "CLAYTONE HY", "CLAYTONE AF", "CLOISITE 6A" (modifier concentration of 140 meq/100 g), "CLOISITE 15A" (modifier concentration of 125 meq/100 g), and "CLOISITE 2OA" (modifier concentration of 95 meq/100 g). Organoclays are also available commercially from Nanocor, Arlington Heights, Illinois, under the trade designation "NANOMER".

Typically, layered silicates exhibit a d-layer spacing that can be determined by well-known techniques such as X-ray diffraction (XRD) and/or transmission electron microscopy (TEM). During the method of the present invention the d-layer spacing typically increases as intercalation between individual silicate layers by the block copolymer proceeds until the layers become so widely separated that they are considered exfoliated and no d-layer spacing is observable by XRD or TEM.

Host Polymer

Host polymers in accordance with the present invention include both thermoplastic and thermoset polymers. End use applications often dictate the specific type of polymer required. One of ordinary skill in the art is capable of selecting either a thermoplastic or thermoset polymer based upon a desired application.

Useful thermoplastic polymers include, for example, polylactones; polyurethanes; polycarbonates; polysulfones; polyether ether ketones; polyamides; polyesters; poly(arylene oxides); poly(arylene sulfides); acrylic polymers; styrenic polymers; polyolefins; ionomers; poly(epichlorohydrins); polysulfones; furan resins; cellulose ester plastics; protein plastics; polyarylene ethers; polyimides; polyvinylidene halides; polycarbonates; aromatic polyketones; polyacetals; polysulfonates; polyester ionomers; and polyolefin ionomers. Copolymers and/or combinations of these aforementioned polymers can also be used.

Non- limiting Examples of polylactones include poly(pivalolactone) and poly(caprolactone).

Non- limiting examples of polyurethanes include those derived from reaction of diisocyanates such as 1,5 -naphthalene diisocyanate, p-phenylene diisocyanate, m- phenylene diisocyanate, 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'- dimethyl-4,4'-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-biphenyl diisocyanate, 4,4'-diphenylisopropylidene diisocyanate, 3,3'-dimethyl-4,4'-diphenyl diisocyanate, 3,3'- dimethyl-4,4'-diphenylmethane diisocyanate, 3,3'-dimethoxy-4,4'-biphenyl diisocyanate, dianisidine diisocyanate, toluidine diisocyanate, hexamethylene diisocyanate, or 4,4'- diisocyanatodiphenylmethane with linear long-chain diols such as poly(tetramethylene adipate), poly(ethylene adipate), poly(l,4-butylene adipate), poly(ethylene succinate), poly(2,3-butylenesuccinate), polyether diols and the like.

Polycarbonates may include the following non-limiting examples poly(methane bis(4-phenyl) carbonate), poly( 1,1 -ether bis(4-phenyl) carbonate), poly(diphenylmethane bis(4-phenyl)carbonate), poly(l,l-cyclohexane bis(4-phenyl)carbonate), or poly(2,2-(bis4- hydroxyphenyl) propane) carbonate.

Non- limiting examples of polyamides include poly(4-aminobutyric acid), poly(hexamethylene adipamide), poly(6-aminohexanoic acid), poly(m-xylylene adipamide), poly(p-xylylene sebacamide), poly(m-phenylene isophthalamide), and poly(p- phenylene terephthalamide).

Non- limiting examples of polyesters include; poly(ethylene azelate), poly(ethylene- 1 ,5-naphthalate), poly(ethylene-2,6-naphthalate), poly(l ,4-cyclohexane dimethylene terephthalate), poly(ethylene oxybenzoate), poly(para-hydroxy benzoate), poly(l,4-cyclohexylidene dimethylene terephthalate) (cis), poly(l,4-cyclohexylidene dimethylene terephthalate) (trans), polyethylene terephthalate, and polybutylene terephthalate.

Non- limiting examples of poly(arylene oxides) include; poly(2,6-dimethyl-l,4- phenylene oxide) and poly(2,6-diphenyl-l,l-phenylene oxide).

Poly(arylene sulfides) may include polyphenylene sulfide.

Non- limiting examples of vinyl polymers and their copolymers include; polyvinyl acetate, polyvinyl alcohol, polyvinyl chloride, polyvinyl butyral, polyvinylidene chloride, and ethylene-vinyl acetate copolymers.

Acrylic polymers may include the following non-limiting examples; poly(ethyl acrylate), poly(n-butyl acrylate), poly(methyl methacrylate), poly(ethyl methacrylate), poly(n-butyl methacrylate), poly(n-propyl methacrylate), polyacrylamide, polyacrylonitrile, polyacrylic acid, ethylene-ethyl acrylate copolymers, ethylene-acrylic acid copolymers; acrylonitrile copolymers (for example, poly(acrylonitrile-co-butadiene- co-styrene) and poly(styrene-co-acrylonitrile)).

Non- limiting examples of styrenic polymers include; polystyrene, poly(styrene-co- maleic anhydride) polymers, high impact polystyrene (HIPS) and their derivatives, methyl methacrylate-styrene copolymers, and methacrylated butadiene-styrene copolymers. Polyolefins may include the following non-limiting examples polyethylene, polybutylene, polypropylene, chlorinated low density polyethylene, poly(4-methyl-l- pentene); ionomers; and poly(epichlorohydrins).

Non- limiting examples of polysulfones include the reaction product of the sodium salt of 2,2-bis(4-hydroxyphenyl) propane and 4,4'-dichlorodiphenyl sulfone.

Cellulose ester plastics may include the following non-limiting examples cellulose acetate, cellulose acetate butyrate, and cellulose propionate.

Elastomeric polymeric resins (that is, elastomers) suitable for use in the present invention include thermoplastic and thermoset elastomeric polymeric resins, for example, polybutadiene, polyisobutylene, ethylene-propylene copolymers, ethylene -propylene-diene terpolymers, sulfonated ethylene-propylene-diene terpolymers, polychloroprene, poly(2,3- dimethylbutadiene), poly(butadiene-co-pentadiene), chlorosulfonated polyethylenes, polysulfide elastomers, silicone elastomers, poly(butadiene-co-nitrile), hydrogenated nitrile-butadiene copolymers, acrylic elastomers, ethylene-acrylate copolymers.

Useful thermoplastic elastomeric polymer resins include block copolymers, made up of blocks of glassy or crystalline blocks such as, for example, polystyrene, poly(vinyltoluene), poly(t-butylstyrene), and polyester, and the elastomeric blocks such as polybutadiene, polyisoprene, ethylene-propylene copolymers, ethylene-butylene copolymers, polyether ester and the like as, for example, poly(styrene-butadiene-styrene) block copolymers marketed by Shell Chemical Company, Houston, Texas, under the trade designation "KRATON". Copolymers and/or mixtures of these aforementioned elastomeric polymeric resins can also be used

Polymeric resins also include fluoropolymers, that is, at least partially fluorinated polymers. Useful fluoropolymers include, for example, those that are preparable (for example, by free-radical polymerization) from monomers comprising chlorotrifluoroethylene, 2-chloropentafluoropropene, 3 -chloropentafluoropropene, vinylidene fluoride, trifluoroethylene, tetrafluoroethylene, 1-hydropentafluoropropene, 2- hydropentafluoropropene, 1 , 1 -dichlorofluoroethylene, dichlorodifluoroethylene, hexafluoropropylene, vinyl fluoride, a perfluorinated vinyl ether (for example, a perfluoro(alkoxy vinyl ether) such as CF3θCF2CF2CF2θCF=CF2, or a perfluoro(alkyl vinyl ether) such as perfluoro(methyl vinyl ether) or perfluoro(propyl vinyl ether)), cure site monomers such as for example, nitrile containing monomers (for example, CF₂=CFO(CF₂)LCN, CF₂=CFO[CF2CF(CF3)O]_q(CF₂O)_yCF(CF3)CN, CF₂=CF[OCF₂CF(CF₃)]_rO(CF₂)_tCN, or CF₂=CFO(CF₂)_UOCF(CF₃)CN where L = 2- 12; q = 0-4; r = 1-2; y = 0-6; t = 1-4; and u = 2-6), bromine containing monomers (for example, Z-Rf-O_x-CF=CF₂, wherein Z is Br or I, Rf is a substituted or unsubstituted C₁-

C₁₂ fluoroalkylene, which may be perfluorinated and may contain one or more ether oxygen atoms, and x is 0 or 1); or a combination thereof, optionally in combination with additional non-fluorinated monomers such as, for example, ethylene or propylene. Specific examples of such fluoropolymers include polyvinylidene fluoride; copolymers of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride; copolymers of tetrafluoroethylene, hexafluoropropylene, perfluoropropyl vinyl ether, and vinylidene fluoride; tetrafluoroethylene-hexafluoropropylene copolymers; tetrafluoroethylene- perfluoro(alkyl vinyl ether) copolymers (for example, tetrafluoroethylene -perfluoro(propyl vinyl ether)); and combinations thereof.

Useful commercially available thermoplastic fluoropolymers include, for example, those marketed by Dyneon, LLC, Oakdale, Minnesota, under the trade designations "THV" (for example, "THV 220", "THV 400G", "THV 500G", "THV 815", and "THV 610X"), "PVDF", "PFA'V'HTE", "ETFE", and "FEP"; those marketed by Atofma Chemicals, Philadelphia, Pennsylvania, under the trade designation "KYNAR" (for example, "KYNAR 740"); those marketed by Solvay Solexis, Thorofare, New Jersey, under the trade designations "HYLAR" (for example, "HYLAR 700") and "HALAR ECTFE".

In an additional embodiment, useful thermoset polymers can generally include aminos, furans, polyesters, phenolics, epoxies, polyurethanes, silicones, allyls, and cross- linked thermoplastics. Phenolic thermoset polymers include phenol-formaldehyde, such as novolac phenol-formaldehyde resins and resole phenolic resins. Thermoset epoxy polymers include the diglycidyl ether of bisphenol A, glycidyl amines, novolacs, peracid resins, and hydantoin resins. Other examples of useful thermoset polymers include those described in "Handbook of Thermoset Plastics" by Goodman (2nd ed., 1998).

In a most preferred embodiment, host polymers are selected from a polyolefm, a (meth)acrylate, a fluoropolymer, a polyester, a polyvinyl chloride, or a polystyrene. Block Copolymers

Block copolymers suitable for use in the present invention may have any number of blocks greater than or equal to two (for example, di-, tri-, tetra-block copolymers), and may have any form such as, for example, linear, star, comb, or ladder. Generally, at least one block should have an affinity for the chosen layered silicate (including organoclay). This block may be hydrophilic or hydrophobic (for example, when using organoclays) in nature. Additionally, specific segments of the block copolymer may be either miscible or immiscible with the host polymer. Additionally, a block copolymer may have discrete segments some of which are miscible with the host polymer and some of which are immiscible with the host polymer.

Hydrophilic blocks typically have one or more polar moieties such as, for example, acids (for example, -CO2H, -SO3H, -PO3H); -OH; -SH; primary, secondary, or tertiary amines; ammonium N-substituted or unsubstituted amides and lactams; N-substituted or unsubstituted thioamides and thiolactams; anhydrides; linear or cyclic ethers and polyethers; isocyanates; cyanates; nitriles; carbamates; ureas; thioureas; heterocyclic amines (for example, pyridine or imidazole)). Useful monomers that may be used to introduce such groups include, for example, acids (for example, acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and including methacrylic acid functionality formed via the acid catalyzed deprotection of t-butyl methacrylate monomeric units as described in U.S. Pat. Publ. No. "2004/0024130" (Nelson et al.)); acrylates and methacrylates (for example, 2-hydroxyethyl acrylate), acrylamide and methacrylamide, N-substituted and N,N-disubstituted acrylamides (for example, N-t-butylacrylamide, N₅N- (dimethylamino)ethylacrylamide, N,N-dimethylacrylamide, N₅N- dimethylmethacrylamide), N-ethylacrylamide, N-hydroxyethylacrylamide, N- octylacrylamide, N-t-butylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, and N-ethyl-N-dihydroxyethylacrylamide), aliphatic amines (for example, 3- dimethylaminopropyl amine, N,N-dimethylethylenediamine); and heterocyclic monomers (for example, 2-vinylpyridine, 4-vinylpyridine, 2-(2-aminoethyl)pyridine, l-(2- aminoethyl)pyrrolidine, 3-aminoquinuclidine, N-vinylpyrrolidone, and N- vinylcaprolactam). Block copolymers with all hydrophilic block segments, such as poly(propylene oxide-δ-ethylene oxide) known as Pluronic^Tm surfactants are not suitable for use with the invention. Hydrophobic blocks typically have one or more hydrophobic moieties such as, for example, aliphatic and aromatic hydrocarbon moieties such as those having at least about 4, 8, 12, or even 18 carbon atoms; fluorinated aliphatic and/or fluorinated aromatic hydrocarbon moieties, such as for example, those having at least about 4, 8, 12, or even 18 carbon atoms; and silicone moieties.

Useful monomers for introducing such hydrophobic blocks include, for example, hydrocarbon olefins such as, for example, ethylene, propylene, isoprene, styrene, and butadiene; cyclic siloxanes such as for example, decamethylcyclopentasiloxane and decamethyltetrasiloxane; fluorinated olefins such as for example, tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, difluoroethylene, and chlorofluoroethylene; nonfluorinated alkyl acrylates and methacrylates such as for example, butyl acrylate, isooctyl methacrylate lauryl acrylate, stearyl acrylate; fluorinated acrylates such as, for example, perfluoroalkylsulfonamidoalkyl acrylates and methacrylates having the formula H2C=C(R2)C(O)O-X-N(R)SO2Rf wherein: Rf is -CgF 13, -C4F9, or -C3F7; R is hydrogen, C^ to C ^Q alkyl, or Cg-C 10 ^aryl; ^and X is a divalent connecting group. Examples include

C4F9Sθ2N(CH3)C2H₄OC(O)NH(C6H4)CH2C6H4NHC(O)OC2H₄OC(O)CH=CH2 and C4F9SO2N(CH3)C2H4OC(O)NH(C6H4)CH2C6H4NH-

^■C(O)OC2H4θC(O)C(CH3)=CH2 .

Such monomers may be readily obtained from commercial sources or prepared, for example, according to the procedures in U.S. Pat. No. 6,903,173 (Cernohous et al).

Examples of particularly useful AB diblock and ABA triblock copolymers derived from combinations of A and B blocks wherein the A block consists of styrene, alkyl/aryl methacrylates,isoprene, butadiene, cyclohexadiene or hydrogenated versions of such dienes and the B block consists of 4-vinyl pyridine, 2-vinyl pyridine, diethylaminostyrene, N,N-(dimethylamino)ethyl methacrylate, methacrylic anhydride, methacrylic acid, acrylic acid, glycidyl methacrylate, 2-hydroxyethyl methacrylate and 2-(N- methylperfluorobutanesulfonamido)ethyl methacrylate (MeFBSEMA).

Examples of particularly useful ABC block copolymers derived from combinations of A, B, and C blocks wherein the A or B block consists of styrene, alkyl/aryl methacrylates,isoprene, butadiene or hydrogenated versions of such dienes and the C block consists of 4-vinyl pyridine, 2-vinyl pyridine, diethylaminostyrene, N ,N- (dimethylamino)ethyl methacrylate, methacrylic anhydride, methacrylic acid, acrylic acid, glycidyl methacrylate, 2-hydroxyethyl methacrylate and 2-(N-methylperfluorobutane- sulfonamido)ethyl methacrylate (MeFBSEMA).

In a preferred embodiment, the block copolymer contains at least one additional segment of the block copolymer that is not compatible with the layered silicate and wherein no additional block contains a segment of 5 consecutive monomeric units that is identical to a segment contained in the host polymer. Further, each additional block is immiscible with the host polymer and no additional block forms hydrogen bonds or chemical bonds with the host polymer.

Most preferred block copolymers include poly(styrene-block-4-vinylpyridine), poly(styrene-block-isoprene-block-4-vinylpyridine), poly(styrene-block-butadiene-block- 4-vinylpyridine), poly(isoprene-block-4-vinylpyridine), poly(butadiene-block-4- vinylpyridine), poly(methyl methacrylate-block-4-vinylpyridine), hydrogenated versions of poly(butadiene-block-4-vinylpyridine), poly(styrene-block-isoprene-block-4- vinylpyridine), poly(styrene-block-butadiene-block-4-vinylpyridine), and poly(isoprene- block-4-vinylpyridine) .

The compositions of the present invention may be made by any process suitable for carrying out a "living" polymerization technique. Various apparatus are suitable for carrying out this type of reaction. The process may be carried out using a batch, semi- batch or continuous reactor. Other suitable reactors include continuous stirred tank reactors (CSTR), tubular reactors, stirred tubular reactors (STR) or combinations of STRs and extruders, such as those described in U.S. Pat. No. 6,969,491, U.S. Pat. No. 20060047092, U.S. Pat. No. 6,716,935, U.S. Pat. No. 6,969,490, U.S. Pat. No. 7,022,780, U.S. Pat. App. No. 20040023398, U.S. Pat. App. No. 20040024130, U.S. Pat. App. No. 20030114553, U.S. Pat. App. No. 20030035756, U.S. Pat. No. 6,448,353, static mixers, continuous loop reactor, extruders, and shrouded extruders as described in WO 9740929, and pouched reactors as described in WO 9607522 and WO 9607674.

In accordance with the present invention, blends of block copolymers may be created by blending different block copolymer powders in suitable ratios to create mixtures with specific polydispersity and viscosities. Generally, the block copolymer should be chosen such that at least one block is capable of intercalating the layered silicate. For natural and synthetic clays, this typically means that at least one block should be hydrophilic; while in the case of organoclays the block may be hydrophilic or hydrophobic. The choice of remaining blocks of the block copolymer will typically be directed by the nature of any polymeric resin with which the layered silicate and block copolymer will be subsequently combined. While the additional blocks must be immiscible with the thermoplastic polymer, at least one (for example, all) of the additional blocks is typically selected to be more compatible with the thermoplastic polymer than the clay itself. For example, oleophilic blocks such as polyolefms, poly(alkyl acrylates), styrenics, polysiloxanes, and fluoropolymers are typically useful with oleophilic thermoplastic polymers such as polyolefms, styrenics, and fluoropolymers.

Any amount of block copolymer may be used, however, typically the block copolymer is included in an amount in a range of 0.01 to 10 parts or more by weight for every part of the layered silicate included in the first mixture. More typically, the block copolymer is included in an amount in a range of 0.05 to 2 parts or more by weight for every part of the layered silicate included in the first mixture.

A solvent may, optionally, be combined with the block copolymer and layered silicate, for example, to aid in intercalation and/or exfoliation of the layered silicate. Useful solvents include, for example, organic solvents, water, supercritical CO2, and combinations thereof. Examples of organic solvents include esters (for example, ethyl acetate, butyl acetate, beta-ethoxyethyl acetate, beta-butoxy-beta-ethoxyethyl acetate, methylcellosolve acetate, cellosolve acetate, diethylene glycol monoacetate, methoxytriglycolacetate, and sorbitol acetate), ketones (for example, methyl isobutyl ketone, 2-butanone, acetonylacetone, and acetone), aromatic hydrocarbons (for example, benzene, toluene, and xylene), aliphatic hydrocarbons (for example, cyclohexane, heptane, octane, decane, and dodecane), nitriles (for example, acetonitrile), ethers (for example, tetrahydrofuran, dioxane, and diglyme), alcohols (for example, methanol, ethanol, isopropanol, butanol, octanol, decanol, butylcarbitol, methylcarbitol, diethylene glycol, dipropylene glycol, ethylene glycol, propylene glycol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, and diacetone alcohol), halocarbons (for example, carbon tetrachloride, trifluorotoluene, methylene chloride, trifluorotoluene, and chloroform), and combinations thereof. However, if a solvent is used its content in the mixture comprising block copolymer and intercalated layered silicate and/or exfoliated silicate platelets is typically reduced to a low level, although this is not a requirement. For example, mixtures and/or nanocomposites according to the present invention may be essentially free of (that is, contain less than about one percent of) solvent. Methods for removing solvent include, for example, oven drying and evaporation under reduced pressure.

Optionally, the composition may further contain one or more additives such as, for example, surfactants, flame proofing agents, fillers, ultraviolet absorbers, antioxidants, tackifier resins, colorants, fragrances, or antimicrobial agents.

While compositions according to the present invention are typically prepared and processed in a fluid state (for example, as a melt or in optional solvent), they may also be utilized as solids; for example after cooling and/or after removing any optional solvent.

Compositions according to present invention may be made according to any suitable method.

In one exemplary method, the layered silicate, thermoplastic polymer, block copolymer, and a solvent capable of swelling the layered silicate and dissolving the thermoplastic polymer and the block copolymer are mixed, and then the solvent is evaporated (for example, in an oven or on a rotary evaporator).

In another exemplary method, the components of the present composition are masticated in a kneader or extruder. Such equipment is well known and/or readily commercially available; typically equipped with devolatilizing capabilities (for example, vacuum ports) and/or temperature-controlled zones. The equipment may have a single port (other than any vacuum ports) for introducing and extracting material, or it may have separate inlet and outlet ports as in the case of an extruder or high viscosity processor.

If the components of the composition comprise a solvent, then the solvent is typically removed under partial vacuum during mastication. For example, as described in concurrently filed U.S. Publ. No. US2006/0074167A1, entitled "METHOD OF MAKING A COMPOSITION AND NANOCOMPOSITES THEREFROM" (Nelson et al).

One example of a suitable high viscosity processor (that is, a kneader), typically supplied with vacuum equipment, is a high viscosity processor marketed under the trade designation "DISCOTHERM B" by List USA, Inc., Acton, Massachusetts. Another example of a suitable kneader, fitted with a vacuum system, is that marketed by IKA Works, Inc., Wilmington, North Carolina, under the trade designation "MKD 0,6 - H 60 HIGH-PERFORMANCE MEASURING KNEADER".

Yet another example of a suitable high performance kneader is commercially available under the trade designation "SRUGO SIGMA KNEADER" from Srugo Machines Engineering, Netivot, Israel. This kneader can be connected to vacuum equipment by vacuum ports on the kneader.

Useful extruders include, for example, single- and multiple-screw extruders and reciprocating extruders. Examples of suitable extruders include those marketed by Coperion Buss AG, Pratteln, Switzerland, under the trade designation "MKS", for example, "MKS 30".

The extent of intercalation and /or exfoliation of the layered silicate can be controlled in large part through variables including, for example, concentration or composition of components, pressure (that is, vacuum) in the mixing apparatus, the temperature profile of the process (for example, isothermal or ramped), screw design, order of addition of materials, the level of applied shear force and/or rate, and the duration of the mixing process. For example, intercalation and/or exfoliation may typically be enhanced by increasing the temperature or reducing the rate of solvent removal (for example, by lessening the degree of an applied vacuum). In selecting the temperature the physical properties and chemical properties of the solvent, layered silicate, and block copolymer should be considered, for example, such that decomposition of the layered silicate and/or block copolymer may be kept at a relatively low level. Such variables may be modified in a continuous or stepwise manner, or they may be maintained at a constant level. To aid in processing, the temperature of kneader or extruder is typically kept above the glass transition temperature and/or melting temperature of the block copolymer, although this is not a requirement. Controlling the process variables above yields exfoliated nanocomposites in certain cases. In the present embodiment the creation of exfoliated nanocomposites is controlled by careful selection of the components in the formulation.

Whatever the method utilized, the method should be of sufficient duration to ensure that at least 20, 30, 40, 50, 60, 70, 80 or even at least 90 percent by weight of the layered silicate is exfoliated to form a plurality of exfoliated silicate platelets dispersed in the thermoplastic polymer.

Methods according to the present invention may be carried out in a batch process or in a continuous manner. The present inventive method enables one of ordinary skill in the art to efficiently determine a preferred formulation. Thus one can make a nanocomposite material without lengthy process and material experimentation.

Compositions prepared according to the present invention are dispersions; typically, isotropic dispersions of exfoliated silicate platelets in the thermoplastic polymer. The block copolymer typically associates with the exfoliated silicate platelets and serves as a dispersing aid so that the exfoliated silicate platelets can be dispersed in the thermoplastic resin. The amount of exfoliated silicate platelets in the composition may be in any amount, but are typically in a range of from 0.1 to 10 percent by weight, more typically in a range of from 0.5 to 7 percent by weight, and even more typically in a range of from 1 to 5 percent by weight, based on the total weight of the composition.

Similarly, in some embodiments, the weight ratio of the exfoliated silicate platelets to the layered silicate in the composition may be at least 0.2, 0.5, 1, 2, 3, 4, 5, 10, 50 or more, although lesser weight ratios may also be used. For example, in methods according to the present invention, the layered silicate may be at least 40, 50, 60, 70, or even at least 95 percent exfoliated, based in the initial weight of layered silicate utilized. In some cases, substantially all of the layered silicate may become exfoliated.

Nanocomposites prepared according to the present invention are useful, for example, in the manufacture of barrier films or bottles, automotive components, wire and cable jacketing formulations, electronic housings, and flame retardant materials.

Objects and advantages of this invention are further illustrated by the following non- limiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and, details, should not be construed to unduly limit this invention.

EXAMPLES

Unless otherwise noted, all parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, and all reagents used in the examples were obtained, or are available, from general chemical suppliers such as, for example, Sigma- Aldrich Company, Saint Louis, Missouri, or may be synthesized by conventional methods.

The following abbreviations are used throughout the Examples: Table 1. Block copolymers

Table 2. Clays

Table 3. Resins

The following procedures were used in the Examples:

Film Preparation for XRD and TEM Analysis

Analysis via XRD and TEM was done on 1 mm thick films. To form the films, each material to be analyzed was placed between 0.051 mm thick untreated polyester liners, which in turn were placed between 2 aluminum plates (3.2 mm thick each) to form a stack. Two shims (1 mm thick each) were placed to either side of the stack such that upon pressing the assembled stack the mixture would not come into contact with either shim. Each stack was placed in a heated hydraulic press available under the trade designation "WABASH MPI MODEL G30H-15-LP" from Wabash MPI, Wabash, Indiana. Both the top and bottom press plates were heated at 193⁰C. The stack was pressed for 1 minute at 1500 psi (10 MPa). The hot stack was then moved to a low- pressure water-cooled press for 30 seconds to cool the stack. The stack was disassembled and the liners were removed from both sides of the film disc that resulted from pressing the mixture.

X-Ray Diffraction (XRD)

Reflection geometry X-ray scattering data were collected using a four-circle diffractometer (available under the trade designation "HUBER (424/511.1)" from Huber Diffraktionstechnik GmbH, D83253 Rimsting, Germany), copper K-alpha radiation, and scintillation detector registry of the scattered radiation. The incident beam was collimated to a circular aperture of 0.70 mm. Scans were conducted in a reflection geometry from 0.5 to 10 degrees (2 theta) using a 0.05 degree step size and 10 second dwell time. A sealed tube X-ray source and X-ray generator settings of 40 kV and 20 mA were used. Data analysis and peak position definition were determined using X-ray diffraction analysis software available under the trade designation "JADE" from MDI, Inc., Livermore, California.

Molecular Weight and Polydispersity

Average molecular weight and polydispersity were determined by Gel Permeation Chromatography (GPC) analysis. Approximately 25 mg of a sample were dissolved in 10 milliliters (mL) of THF to form a mixture. The mixture was filtered using a 0.2-micron pore size polytetrafluoroethylene syringe filter. Then, about 150 microliters of the filtered solution were injected into a gel-packed column 25 cm long by 1 cm diameter available under the trade designation "PLGEL-MIXED B" from PolymerLabs, Amherst, Massachusetts, that was part of a GPC system equipped with an autosampler and a pump. The GPC was system operated at room temperature using THF eluent that moved at a flow rate of approximately 0.95 mL/minute. A refractive index detector was used to detect changes in concentration. Number average molecular weight (M_n) and polydispersity index (PDI) calculations were calibrated using narrow polydispersity polystyrene controls ranging in molecular weight from 600 to 6 x 10" g/mole. The actual calculations were made with software (available under the trade designation "CALIBER" from Polymer Labs).

IH NMR Spectroscopy

The relative concentration of each block was determined by ^H Nuclear Magnetic

Resonance (^H NMR) spectroscopy analysis. Specimens were dissolved in deuterated chloroform at a concentration of about 10 percent by weight and placed in a 500 MHz NMR Spectrometer available under the trade designation "UNITY 500 MHZ NMR SPECTROMETER" from Varian, Inc., Palo Alto, California. Block concentrations were calculated from relative areas of characteristic block component spectra.

The following general procedures are used in the examples:

General Procedure for Melt Rheology

Frequency sweeps were conducted on virgin thermoplastic polymers and block copolymer additives. The compounds were formed into sheets slightly greater than 2 mm thick with pressure at room temperature. 25 mm disks were cut to load into the parallel plate rheometer fixture on an ARES rheometer from TA instruments. The samples were loaded and pressed to 2 mm thick at the testing temperature. For each resin and additive we measured the viscosity as a function of shear rate at 180 ⁰C (356⁰F). Frequency sweeps were then run from 0.1-500 rad/s on thermally equilibrated samples that had been loaded into the parallel plate fixture and the edges trimmed. The strain used was 10 %. The calculated viscosity ratio of the block copolymer to the matrix resin was determined at a frequency of 500 rad/s and is defined as Π_BL_OCK copθLYMER/πMatπx@ 500 rad/sec as used in Table 5.

General Procedure for Continuous Twin-Screw Extrusion

Extrusion was carried out using a co-rotating, 25mm twin-screw extruder with 41 :1 L/D available under the trade designation "COPERION ZSK-25 WORLD LAB EXTRUDER" from Coperion, Ramsey, New Jersey. Barrel zones for the extruder model utilized in these examples are 4D (100 mm) in length. Two screw designs may be utilized. Screw Design A:

In order to create a uniform melt stream prior to the addition of the block copolymer and clay materials in barrel zones 2 and 3 the screw design incorporates a distributive mixing section of 1.76D (that is, 1.76 times the bore diameter) total length, consisting mainly of gear-type mixing elements, under the trade designation "ZME" available from Coperion. A low- to medium-shear-intensity kneading section is utilized in barrel zone 4 for incorporating and melting the hand-blended block copolymer and clay powder additives into the molten resin after their addition to the extruder in barrel zone 3 through a 2D port open to the atmosphere. Total length for this kneading section is 2.5D. The temperature of the melt stream is monitored and recorded over this kneading section by an immersion-depth thermocouple. A small atmospheric vent, ID in length, at the beginning of barrel zone 5 allowed the venting of any entrapped air from the powder addition. Spanning barrel zone 5, 6, and 7, a 5.28D kneading section with shear-intensive forward kneading blocks is designed for dispersion and exfoliation of the clay into the host resin. This mixing section is sealed on the downstream end by three, narrow-paddled, reverse kneading blocks to ensure that the mixing section is filled with melt as well as to distribute the exfoliated clay material throughout the composite. The melt temperature of the material in this kneading section is monitored and recorded using an immersion-depth thermocouple. Another 4.8D mixing section with shear-intensive, forward kneading blocks was used in zones 8 and 9 to provide additional shear for further exfoliation of the clay particles. This section is not sealed with reverse kneading blocks in order to allow a nitrogen sweep gas, which may be injected in barrel zone 7, to flow freely across the mostly- filled mixing zone to the vacuum vent, 2D in length, in barrel zone 9 to remove any volatiles. A vacuum of 52 torr (6.9 kPa) is pulled on this vent. The continuous extrusion of molten resin into the feed zone of the twin screw extruder is accomplished by using a 1.25-inch (3.18 cm) single-screw extruder equipped with a 3.0:1 compression general-purpose screw with 24 flights, available under the trade designation "KILLION KTS-125" from Davis-Standard, Pawcatuck, Connecticut. Powder additives were hand-blended and fed into barrel zone 3 of the twin-screw extruder using a gravimetric feeder equipped with twin auger screws available under the trade designation "K-TRON GRAVIMETRIC FEEDER, MODEL KCLKT20" from K-Tron International, Pitman, New Jersey. The molten composite was metered through a 10.3 mL/revolution gear pump available under the trade designation "NORMAG" from Dynisco Extrusion, Hickory, North Carolina, and extruded through a 1/2 inch (1.3 cm) diameter pipe to form strands. This extruded strand was cooled in an 8 foot (2.4 m) water bath available from Berlyn Corporation, Worcester, Massachusetts, and pelletized using a strand pelletizer available under the trade designation "CONAIR MODEL 304" from Reduction Engineering, Kent, Ohio. Screw Design B:

Continuous twin-screw extrusion is carried out using a co-rotating 25 -mm twin- screw extruder (TSE) with 41 :1 L/D, available under the trade designation "COPERION ZSK-25 WORLD LAB EXTRUDER" from Coperion, Ramsey, New Jersey. Barrel zones for this extruder are 4D in length (100mm).

In order to create a uniform melt stream prior to the addition of the block copolymer and clay materials, the screw design incorporates a kneading section of 2.88D (that is, 2.88 times the bore diameter) total length to ensure complete melting of the resin in barrel zones 2 and 3. This mixing section utilized a combination of wide-paddled, forward-pumping, kneading blocks, lower shear-intensity, forward-pumping, kneading blocks, and narrow-paddled, reverse-pumping, kneading blocks to ensure material fill of the kneading zone. A low- to medium-shear-intensity kneading section is utilized in barrel zone 4 for melting and incorporating the hand-blended block copolymer and clay powder additives into the molten resin after their addition to the extruder in barrel zone 3 through a 2D port open to the atmosphere. Total length for this kneading section is 2.4D. The temperature of the melt stream is monitored and recorded over this kneading section by an immersion-depth thermocouple. A small atmospheric vent, ID in length, at the beginning of barrel zone 5 allowed the venting of any entrapped air from the powder addition that occurs via a side stuffer slightly downstream in barrel zone 5. Spanning barrel zones 5, 6, and 7, a 5.28D kneading section with wide-paddled, shear-intensive, forward-pumping kneading blocks was designed for dispersing any agglomerated talc into the host resin. Smaller-paddled, forward-pumping kneading blocks were also included in this mixing section to provide additional dispersive and distributive mixing. This mixing section was sealed on the downstream end by three narrow-paddled, reverse-pumping kneading blocks to ensure that the mixing section is filled with melt as well as to distributively mix the clay particles throughout the composite. The melt temperature of the material in this kneading section was monitored and recorded using an immersion-depth thermocouple. Another 4.8D mixing section with high- to intermediate-shear, forward-pumping and neutral- pumping kneading blocks was employed in zones 8 and 9 to provide additional dispersive and distributive mixing in order to promote additional exfoliation and ensure homogeneity of the composite. The melt temperature of the material in this kneading section was monitored and recorded using an immersion-depth thermocouple. The composite material was then conveyed past a vacuum vent, 2D in length, in barrel zone 9 to remove any volatiles. A vacuum of 52 torr (6.9 kPa) was pulled on this vent.

Polyolefin resin pellets are fed into the barrel zone 1 feed port utilizing a gravimetric feeder equipped with double spiral screws, available under the trade designation "K-TRON GRAVIMETRIC FEEDER, MODEL KCLKT20" from K-Tron International, Pitman, New Jersey. Powder additives are hand-blended and fed into the 2D feed port in barrel zone 3 using a gravimetric feeder equipped with twin auger screws, available under the trade designation "K-TRON GRAVIMETRIC FEEDER, MODEL KCLKT20" from K-Tron International, Pitman, New Jersey. The molten composite is metered through a 10.3 mL/revolution gear pump available under the trade designation "NORMAG" from Dynisco Extrusion, Hickory, North Carolina, and extruded through a 1 /2-inch (1.3 -cm) diameter pipe to form a strand. The strand is cooled at 8⁰C in a water bath and pelletized using a strand pelletizer available under the trade designation "CONAIR MODEL 304" from Reduction Engineering; Kent, Ohio. Procedures

A wide range of resins were compounded with clays and controlled architecture materials (block copolymer's) in a Coperion ZSK-25 twin screw extruder. The materials used are shown in Tables 1-3. The formulations were held constant at 90/5/5 wt. % resin/block copolymer/clay . For each combination a range of extruder screw speeds and barrel temperatures were employed to test the breadth of the processing window. The process conditions are defined in Table 4.

The techniques for compounding and analyzing nanocomposites are those described under " General Procedure for Continuous Twin-Screw Extrusion " and "X-Ray Diffraction". In addition to the neat block copolymer materials, two blends of block copolymers were made by dry blending powdered forms of each component.

The XRD patterns for each formulation at each processing condition were analyzed to determine whether the clay is exfoliated and/or intercalated. An exfoliated system has a featureless XRD pattern. An intercalated system has XRD peaks corresponding to domain spacings larger than the neat clay and/or broad, diffuse peaks indicating a range of domain spacings. In Table 5 the percentage of processing conditions that show exfoliated or intercalated clay is shown for five different formulations.

Comparative Examples 1, 2, and 3 (CE1-CE3)

A blend of block copolymers, layered silicate clay, and thermoplastic polymer as outlined in Table 5 is mixed in a 5:5:90 wt ratio respectively and extruded according to the "General Procedure for Continuous Twin-Screw Extrusion" and processing conditions listed in Table 4. The viscosity ratio is determined by analyzing samples of block copolymer formulations and appropriate thermoplastic resins, as listed in Table 5, according to the "General Procedure for Melt Rheology".

Various process conditions as outlined in Tables 4 and 5 were attempted in a failed effort to produce exfoliated composites at more than 40% of processing conditions. None of the comparative examples possess both a viscosity ratio of Block Copolymer to matrix resin between 0.7 and 1.5, while possessing a polydispersity of greater than 1.8.

Table 5: Experimental Details

Examples 1-4 (EX1-EX4)

Various process conditions as outlined in Tables 4 and 5 were attempted in an effort to produce exfoliated composites. All of examples EX1-EX4 possess both a viscosity ratio of Block Copolymer to matrix resin between 0.7 and 1.5, while possessing a polydispersity of greater than 1.8 and thus produced an exfoliated composite in greater than 40 % of the process conditions explored. Example 5

A blend of PSVP block copolymer, CLOISITE Na⁺ layered silicate, and Noryl EM7100 thermoplastic polymer is mixed in a 5:5:90 wt ratio respectively and extruded according to the "General Procedure for Continuous Twin-Screw Extrusion". Care is taken to match the viscosity of the PSVP block copolymer with the Noryl resin prior to extrusion. The Viscosity ratio is confirmed by analyzing samples of PSVP block copolymer and Noryl EM7100 according to the "General Procedure for Melt Rheology". An exfoliated composite is expected.

Claims

What is claimed is:

1. A method of making a nanocomposite, the method comprising: combining components comprising: a layered silicate; a host polymer; a block copolymer comprising a block that is compatible with the layered silicate, wherein the block copolymer has a polydispersity of about 1.8 or greater and a viscosity ratio to the host polymer of about 0.7 to about 1.5; and exfoliating at least 20 percent by weight of the layered silicate to form a plurality of exfoliated silicate platelets dispersed in the host polymer.

2. A method according to claim 1, wherein the block copolymer has at least one additional block that is not compatible with the layered silicate and wherein no additional block contains a segment of 5 consecutive monomeric units that is identical to a segment contained in the host polymer, wherein each additional block is immiscible with the host polymer, and wherein no additional block forms hydrogen bonds or chemical bonds with the host polymer.

3. A method according to claim 1, wherein the host polymer comprises a polyolefm, a (meth)acrylate, a fluoropolymer, a polyester, a polyvinyl chloride, or a polystyrene.

4. A method according to claim 1, wherein the layered silicate is at least 40 percent by weight exfoliated, at least 70 percent by weight exfoliated, or at least 95 percent by weight exfoliated.

5. A method according to claim 1, wherein the components further comprise a solvent.

6. A method according to claim 1, wherein the block copolymer comprises a diblock polymer.

7. A method according to claim 1, wherein the block copolymer is selected from the group consisting of poly(styrene-block-4-vinylpyridine), poly(styrene-block-isoprene- block-4-vinylpyridine), poly(styrene -block-butadiene -block-4-vinylpyridine), poly(isoprene-block-4-vinylpyridine), poly(butadiene-block-4-vinylpyridine), poly(methyl methacrylate-block-4-vinylpyridine), hydrogenated versions of poly(butadiene-block-4- vinylpyridine), poly(styrene-block-isoprene-block-4-vinylpyridine), poly(styrene-block- butadiene-block-4-vinylpyridine), and poly(isoprene-block-4-vinylpyridine).

8. A method according to claim 1, wherein the block copolymer is a blend of two block copolymers having different molecular weights and the same monomeric constituents.

9. A method according to claim 1, wherein the layered silicate comprises montmorillonite, nontronite, bentonite, beidellite, hectorite, saponite, sauconite, fluorohectorite, stevensite, volkonskoite, magadiite, kenyaite, halloysite, hydrotalcite, a synthetic layered silicate, or a combination thereof.

10. A method according to claim 1, wherein the layered silicate comprises an organoclay.

11. A method according to claim 1 , wherein the weight ratio of the block copolymer to the layered silicate is in a range of 0.01 to 10.

12. A nanocomposite comprising: exfoliated silicate platelets; a host polymer; and a block copolymer comprising a block that is compatible with the layered silicate, wherein the block copolymer has a polydispersity of 1.8 or greater and a viscosity ratio to the host polymer of about 0.7 to about 1.5, and wherein the nanocomposite is free of any layered silicate, or the weight ratio of exfoliated silicate platelets to the layered silicate is at least 0.2.

13. A nanocomposite according to claim 12, wherein the block copolymer has at least one additional block that is not compatible with the layered silicate and wherein no additional block contains a segment of 5 consecutive monomeric units that is identical to a segment contained in the host polymer, wherein each additional block is immiscible with the host polymer, and wherein no additional block forms hydrogen bonds or chemical bonds with the host polymer.

14. A nanocomposite according to claim 12, wherein the host polymer is a polyolefm, a (meth)acrylate, a fluoropolymer, a polyester, a polyvinyl chloride, or a polystyrene.

15. A nanocomposite according to claim 12, wherein the block copolymer comprises a diblock polymer.

16. A nanocomposite according to claim 12, wherein the block copolymer is selected from the group consisting of poly(styrene-block-4-vinylpyridine), poly(styrene-block- isoprene-block-4-vinylpyridine), poly(styrene-block-butadiene-block-4-vinylpyridine), poly(isoprene-block-4-vinylpyridine), poly(butadiene-block-4-vinylpyridine), poly(methyl methacrylate-block-4-vinylpyridine), hydrogenated versions of poly(butadiene-block-4- vinylpyridine), poly(styrene-block-isoprene-block-4-vinylpyridine), poly(styrene-block- butadiene-block-4-vinylpyridine), and poly(isoprene-block-4-vinylpyridine).

17. A nanocomposite according to claim 12, wherein at least a portion of the silicate platelets comprise a layer of a layered silicate selected from the group consisting of montmorillonite, nontronite, bentonite, beidellite, hectorite, saponite, sauconite, fluorohectorite, stevensite, volkonskoite, magadiite, kenyaite, halloysite, hydrotalcite, and synthetic layered silicates.

18. A nanocomposite according to claim 12, wherein the weight ratio of the block copolymer to the silicate platelets is in a range of 0.01 to 10.

19. A nanocomposite according to claim 12, wherein the exfoliated silicate platelets comprise from 0.1 to 5 percent by weight, inclusive, of the nanocomposite.

20. A nanocomposite according to claim 12, wherein the nanocomposite comprises at least a portion of a film or bottle.

21. A nanocomposite according to claim 12, wherein the block copolymer is a blend of two block copolymers having different molecular weights and the same monomeric constituents.

22. A composition comprising: exfoliated silicate platelets; and a block copolymer comprising a block that is compatible with the layered silicate, wherein the block copolymer has a polydispersity of 1.8 or greater.

23. A composition according to claim 22, wherein the block copolymer is selected from the group consisting of poly(styrene-block-4-vinylpyridine), poly(styrene-block-isoprene- block-4-vinylpyridine), poly(styrene -block-butadiene -block-4-vinylpyridine), poly(isoprene-block-4-vinylpyridine), poly(butadiene-block-4-vinylpyridine), poly(methyl methacrylate-block-4-vinylpyridine), hydrogenated versions of poly(butadiene-block-4- vinylpyridine), poly(styrene-block-isoprene-block-4-vinylpyridine), poly(styrene-block- butadiene-block-4-vinylpyridine), and poly(isoprene-block-4-vinylpyridine).

24. A composition according to claim 22, wherein at least a portion of the silicate platelets comprise a layer of a layered silicate selected from the group consisting of montmorillonite, nontronite, bentonite, beidellite, hectorite, saponite, sauconite, fluorohectorite, stevensite, volkonskoite, magadiite, kenyaite, halloysite, hydrotalcite, and synthetic layered silicates.