WO2008084021A1

WO2008084021A1 - Process for making polymer nanocomposites

Info

Publication number: WO2008084021A1
Application number: PCT/EP2008/050082
Authority: WO
Inventors: Sachin Jain; Hans-Helmut Görtz
Original assignee: Basf Se
Priority date: 2007-01-11
Filing date: 2008-01-07
Publication date: 2008-07-17

Abstract

A process for producing a polymer nanocomposite comprises the steps of: a) preparing a mixture of a thermoplastic polymer and a nanoparticulate metal or half-metal oxide in a solvent, which is in the supercritical state, and b) removing the supercritical solvent.

Description

Process for making polymer nanocomposites

Description

The invention relates to a process for making polymer nanocomposites and to polymer nanocomposites obtainable by such a process. The invention further relates to the use of such nanocomposites for producing shaped articles.

The design of thermoplastic products is always a challenge since high molecular weight is required for superior mechanical properties but affects the processibility. On the other hand, low molecular weight is desired for better processibility, however, it hampers the mechanical performance of the product. Many attempts have been made in the past to overcome this problem by tailoring molecular weight distribution in poly- olefins. However, these approaches are not necessarily feasible for other classes of thermoplastics such as polycondensation polymers. Another approach is to use conventional fillers to improve the strength of the products but this hampers processibility as well as toughness.

A recently developed approach is the use of nanoparticles in thermoplastics to improve various rheological, mechanical and other physical properties, simultaneously (see, e.g., WO-A 2004/74360). However, to synthesize or to incorporate the nanoparticles in the polymer with a uniform dispersion and distribution is a key challenge. Currently, there are no convenient techniques for in-situ synthesizing inorganic nanoparticles in solid-state polymers, especially engineering plastics.

Accordingly, the task of the invention is to provide a simple and convenient process for making polymer nanocomposites with improved processibility and improved - or at least unchanged - mechanical properties, compared to polymers without nano-fillers.

It has been found that this task can be achieved by an in-situ synthesis of inorganic nanoparticles in the presence of solid-state polymers without chemical modification of the polymers, with the aid of supercritical media. The nanocomposites prepared by this method give uniformly dispersed and distributed nanoparticles in polymers.

The method is aimed to improve the flowability, strength and toughness, transparency, creep resistance, thermal stability, heat deflection temperature (HDT) and similar properties. Accordingly, in one aspect of the invention there is provided a process for producing a polymer nanocomposite, comprising the steps of

a) preparing a mixture of a thermoplastic polymer and a nanoparticulate metal or half-metal oxide in a solvent, which is in the supercritical state, and

b) removing the supercritical solvent.

In a further aspect of the invention there is provided a polymer nanocomposite, obtain- able by the above process.

In yet a further aspect of the invention there is provided the use of polymer nanocom- posites, obtainable by the above process, for producing shaped articles.

The nanocomposites prepared by the process of the present invention show a uniform dispersion and distribution of the nanoparticles in the polymer.

The thermoplastic polymer, which is used in the process according to the invention, can be any thermoplastic polymer, i.e., any polymer that becomes plastically formable upon heating.

In principle, thermoplastics of any type can be used in the process according to the invention. By way of example, a list of suitable thermoplastics is found in Kunststoff- Taschenbuch [Plastics Handbook] (Ed. Saechtling), 1989 edition, which also mentions references. Processes for preparing these thermoplastics are known per se to the person skilled in the art, and many products are also commercially available.

Examples of suitable thermoplastics include polyamides, polyesters, like polybutylen terephthalate and polyethylene terephthalate, polyurethanes, polycarbonates, vinylaromatic polymers, such as polystyroles, and mixtures thereof.

Some preferred types of thermoplastic polymers are described in more detail below.

1. Polyamides

Polyamides suitable for the inventive process generally have a viscosity number of from 90 to 350 ml/g, preferably from 110 to 240 ml/g, determined to ISO 307 in 0.5 % strength by weight solution in 96 % strength by weight sulfuric acid at 25°C. Preference is given to semicrystalline or amorphous resins with molecular weights (weight-average) of at least 5000, as described, for example, in US patents 2 071 250, 2 071 251 , 2 130 523, 2 130 948, 2 241 322, 2 312 966, 2 512 606 and 3 393 210. Examples of these are polyamides which derive from lactams having from 7 to 13 ring members, such as polycaprolactam, polycaprylolactam and polylaurolactam, and also polyamides obtained by reacting dicarboxylic acids with diamines.

Dicarboxylic acids which can be used are alkanedicarboxylic acids having from 6 to 12 carbon atoms, in particular from 6 to 10 carbon atoms, and aromatic dicarboxylic acids. Adipic acid, azelaic acid, sebacic acid, dodecanedioic acid and terephthalic and/or isophthalic acid are a few acids which may be mentioned here.

Particularly suitable diamines are alkanediamines having from 6 to 12 carbon atoms, in particular from 6 to 8 carbon atoms, or else m-xylylenediamine, di(4-aminophenyl) methane, di(4-aminocyclohexyl)methane, 2,2-di(4-aminophenyl)propane or 2,2-di(4- aminocyclohexyl)propane.

Preferred polyamides are polyhexamethyleneadipamide, polyhexamethyleneseba- camide and polycaprolactam, and also nylon-6/6,6, in particular with a proportion of from 5 to 95 % by weight of caprolactam units. Polycaprolactam (polyamide-6 or nylon- 6) and polyhexamethylene adipamide (polyamide-6, 6 or nylon-6,6) are particularly preferred. These compounds are available, e.g., under the brand name Ultramid^® B and Ultramid^® A respectively, from BASF, Ludwigshafen, Germany.

In addition, mention may also be made of polyamides obtained, for example, by condensing 1 ,4-diaminobutane with adipic acid at elevated temperature (nylon-4,6). Preparation processes for polyamides of this structure are described, for example, in EP-A 38 094, EP-A 38 582 and EP-A 39 524.

Other suitable polyamides are obtained by copolymerizing two or more of the monomers mentioned above. Mixtures of more than one polyamide are also suitable, and the mixing ratio may be as desired.

Other copolyamides which have proven particularly advantageous are partially aro- matic copolyamides, such as nylon-6/6,T and nylon-6,6/6,T which have a triamine content of less than 0.5 % by weight, preferably less than 0.3 % by weight (see EP-A 299 444). Partially aromatic copolyamides with low triamine content may be prepared by the processes described in EP-A 129 195 and 129 196. Other suitable polyamides include uncoloured polyamides based on polyamide-6,6 and containing suitable stabilizers, like amines. Such compounds are available as Ultramid^® A E products from BASF, Ludwigshafen, Germany.

Further suitable polyamides are glass fibre reinforced compounds based on polyamide 6. Such products are available as the Ultramid^® B G brands from BASF, Ludwigshafen, Germany.

2. Polycarbonates and polyesters

Use is generally made of polyesters based on aromatic dicarboxylic acids and on an aliphatic or aromatic dihydroxy compound.

A first group of preferred polyesters is that of polyalkylene terephthalates whose alco- hoi moiety has from 2 to 10 carbon atoms.

Polyalkylene terephthalates of this type are known per se and are described in the literature. Their main chain contains an aromatic ring which derives from the aromatic dicarboxylic acid. There may also be substitution of the aromatic ring, e.g. by halogen, such as chlorine or bromine, or by CrC₄-alkyl groups, such as methyl, ethyl, iso- or n- propyl, or n-, iso- or tert-butyl groups.

These polyalkylene terephthalates may be prepared by reacting aromatic dicarboxylic acids, or their esters or other ester-forming derivatives, with aliphatic dihydroxy com- pounds in a manner known per se.

Preferred dicarboxylic acids are 2,6-naphthalenedicarboxylic acid, terephthalic acid and isophthalic acid, or a mixture of these. Up to 30 mol-%, preferably not more than 10 mol-%, of the aromatic dicarboxylic acids may be replaced by aliphatic or cycloaliphatic dicarboxylic acids, such as adipic acid, azelaic acid, sebacic acid, do- decanedioic acids and cyclohexanedicarboxylic acids.

Preferred aliphatic dihydroxy compounds are diols having from 2 to 8 carbon atoms, in particular 1 ,2-ethanediol, 1 ,3-propanediol, 1 ,4-butanediol, 1 ,6-hexanediol, 1 ,4- hexanediol, 1 ,4-cyclohexanediol, 1 ,4-cyclohexanedimethanol and neopentyl glycol, or a mixture of these.

Particularly preferred polyesters are polyalkylene terephthalates derived from al- kanediols having from 2 to 6 carbon atoms. Among these, particular preference is given to polyethylene terephthalate, polypropylene terephthalate and polybutylene terephthalate, or a mixture of these. Preference is also given to PET and/or PBT which comprise, as other monomer units, up to 1-% by weight, preferably up to 0.75 % by weight, of 1 ,6-hexanediol and/or 2-methyl-1 ,5-pentanediol.

The viscosity number of the polyesters is generally in the range from 50 to 220, pref- erably from 80 to 160, measured in a 0.5 % strength by weight solution in a phenol/o- dichlorobenzene mixture in a weight ratio of 1 :1 at 25⁰C, in accordance with ISO 1628.

Particular preference is given to polyesters whose carboxy end group content is up to 100 mval/kg of polyester, preferably up to 50 mval/kg of polyester and in particular up to 40 mval/kg of polyester. Polyesters of this type may be prepared, for example, by the process of DE-A 44 01 055. The carboxy end group content is usually determined by titration methods (e.g. potentiometry).

Possible compositions also include a mixture of polyesters which are different from PBT, for example polyethylene terephthalate (PET), and/or polycarbonate. The proportion e.g. of the polyethylene terephthalate and/or of the polycarbonate in the mixture is preferably up to 50 % by weight, in particular from 10 to 30 % by weight, based on 100 % by weight of A).

Suitable polyesters to be used according to the invention also include biodegradable polyesters, such as random aliphatic aromatic copolyesters based on, e.g., adipic acid, succinic acid, sebacic acid, 1 ,4-butandiol and 1 ,3-butandiol. These products are not only biodegradable but the monomers are also available from renewable resources.

Biodegradable polyesters are available under the brand name Ecoflex^® from BASF, Ludwigshafen, Germany.

It is also advantageous to use recycled PET materials (also termed scrap PET), if appropriate in a mixture with polyalkylene terephthalates, such as PBT.

Recycled materials are generally:

1 ) Those known as post-industrial recycled materials: these are production wastes during polycondensation or during processing, e.g. sprues from injection molding, start- up material from injection molding or extrusion, or edge trims from extruded sheets or films.

2) post-consumer recycled materials: these are plastic items which are collected and treated after utilization by the end consumer. Blow-molded PET bottles for mineral water, soft drinks and juices are easily the predominant items in terms of quantity. Both types of recycled material may be used either as ground material or in the form of pellets. In the latter case, the crude recycled materials are isolated and purified and then melted and pelletized using an extruder. This usually facilitates handling and free flow, and metering for further steps in processing.

The recycled materials used may either be pelletized or in the form of ground material, the edge length being not more than 6 mm, preferably less than 5 mm.

Because polyesters undergo hydrolytic cleavage during processing (due to traces of moisture), it is advisable to predry the recycled material. The residual moisture content after drying is preferably from 0.01 to 0.7 %, in particular from 0.2 to 0.6 %.

Another group to be mentioned is that of fully aromatic polyesters deriving from aromatic dicarboxylic acids and aromatic dihydroxy compounds.

Suitable aromatic dicarboxylic acids are the compounds previously mentioned for the polyalkylene terephthalates. The mixtures preferably used are made of from 5 to 100 mol-% of isophthalic acid and from 0 to 95 mol-% of terephthalic acid, in particular from about 50 to about 80 % of terephthalic acid and from 20 to about 50 % of isophthalic acid.

The aromatic dihydroxy compounds preferably have the general formula

where Z is an alkylene or cycloalkylene group having up to 8 carbon atoms, an arylene group having up to 12 carbon atoms, a carbonyl or a sulfonyl group, an oxygen or sulfur atom, or a chemical bond, and m is from 0 to 2. The phenylene groups of these compounds may also have substitution by Ci-C₆-alkyl or alkoxy groups and fluorine, chlorine or bromine.

Examples of parent substances for these compounds are

dihydroxydiphenyl, di(hydroxyphenyl)alkane, di(hydroxyphenyl)cycloalkane, di(hydroxyphenyl) sulfide, di(hydroxyphenyl) ether, di(hydroxyphenyl) ketone, di(hydroxyphenyl) sulfoxide, α,α'-di(hydroxyphenyl)dialkylbenzene, di(hydroxyphenyl) sulfone, di(hydroxybenzoyl)benzene resorcinol and hydroquinone and also the ring-alkylated and ring-halogenated derivatives of these.

Among these, preference is given to

4,4'-dihydroxydiphenyl,

2,4-di(4'-hydroxyphenyl)-2-methylbutane, α,α'-di(4-hydroxyphenyl)-p-diisopropylbenzene,

2,2-di(3'-methyl-4'-hydroxyphenyl)propane and

2,2-di(3'-chloro-4'-hydroxyphenyl)propane,

and in particular to

2,2-di(4'-hydroxyphenyl)propane, 2,2-di(3',5-dichlorodihydroxyphenyl)propane, 1 ,1-di(4'-hydroxyphenyl)cyclohexane, 3,4'-dihydroxybenzophenone, 4,4'-dihydroxydiphenylsulfone and 2,2-di(3',5'-dimethyl-4'-hydroxyphenyl)propane

or a mixture of these.

It is, of course, also possible to use mixtures of polyalkylene terephthalates and fully aromatic polyesters and/or polycarbonates. These generally comprise from 20 to 98 % by weight, preferably from 50 to 96 % by weight, of the polyalkylene terephthalate and from 2 to 80 % by weight, preferably from 4 to 50 % by weight of the fully aromatic polyester and/or of the polycarbonate.

It is, of course, also possible to use polyester block copolymers, such as copolyether- esters. Products of this type are known per se and are described in the literature, e.g. in US-A 3 651 014. Corresponding products are also available commercially, e.g. Hy- trel^® (DuPont).

Halogen-free polycarbonates are also used with preference as component A). Examples of suitable halogen-free polycarbonates are those based on diphenols of the gen- eral formula

where Q is a single bond, a Ci-C₈-alkylene group, a C₂-C₃-alkylidene group, a C₃-C₆- cycloalkylidene group, a C₆-Ci₂-arylene group, or -O-, -S- or -SO₂-, and m is a whole number from 0 to 2.

The phenylene radicals of the diphenols may also have substituents, such as d-C₆- alkyl or d-C₆-alkoxy.

Examples of preferred diphenols of the formula are hydroquinone, resorcinol, 4,4'- dihydroxybiphenyl, 2,2-bis(4-hydroxyphenyl)propane, 2,4-bis(4-hydroxyphenyl)-2- methylbutane and 1 ,1-bis(4-hydroxyphenyl)cyclohexane. Particular preference is given to 2,2-bis(4-hydroxyphenyl)propane and 1 ,1-bis(4-hydroxyphenyl)cyclohexane, and also to 1 ,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.

Either homopolycarbonates or copolycarbonates are suitable as component A, and preference is given to the copolycarbonates of bisphenol A, as well as to bisphenol A homopolymer.

Suitable polycarbonates may be branched in a known manner, specifically and preferably by incorporating 0.05 to 2.0 mol-%, based on the total of the biphenols used, of at least trifunctional compounds, for example those having three or more phenolic OH groups.

Polycarbonates which have proven particularly suitable have relative viscosities n_reι of from 1.10 to 1.50, in particular from 1.25 to 1.40. This corresponds to an average molecular weight M_w (weight-average) of from 10 000 to 200 000, preferably from 20 000 to 80 000.

The diphenols of the general formula are known per se or can be prepared by known processes.

The polycarbonates may, for example, be prepared by reacting the diphenols with phosgene in the interfacial process, or with phosgene in the homogeneous-phase process (known as the pyridine process), and in each case the desired molecular weight may be achieved in a known manner by using an appropriate amount of known chain terminators (in relation to polydiorganosiloxane-containing polycarbonates see, for example, DE-A 33 34 782). Examples of suitable chain terminators are phenol, p-tert-butylphenol, or else long- chain alkylphenols, such as 4-(1 ,3-tetramethylbutyl)phenol as in DE-A 28 42 005, or monoalkylphenols, or dialkylphenols with a total of from 8 to 20 carbon atoms in the alkyl substituents as in DE-A-35 06 472, such as p-nonylphenyl, 3,5-di-tert-butylphenol, p-tert-octylphenol, p-dodecylphenol, 2-(3,5-dimethylheptyl)phenol and 4-(3,5-dimethyl- heptyl)phenol.

For the purposes of the present invention, halogen-free polycarbonates are polycar- bonates made from halogen-free biphenols, from halogen-free chain terminators and, if used, halogen-free branching agents, where the content of subordinate amounts at the ppm level of hydrolyzable chlorine, resulting, for example, from the preparation of the polycarbonates with phosgene in the interfacial process, is not regarded as meriting the term halogen-containing for the purposes of the invention. Polycarbonates of this type with contents of hydrolyzable chlorine at the ppm level are halogen-free polycarbonates for the purposes of the present invention.

Other suitable components A) which may be mentioned are amorphous polyester carbonates, where during the preparation process phosgene has been replaced by aro- matic dicarboxylic acid units, such as isophthalic acid and/or terephthalic acid units. Reference may be made at this point to EP-A 71 1 810 for further details.

EP-A 365 916 describes other suitable copolycarbonates having cycloalkyl radicals as monomer units.

It is also possible for bisphenol A to be replaced by bisphenol TMC (trimethyl- cyclohexyl-bisphenol). Polycarbonates of this type are obtainable from Bayer Material Science under the trademark APEC HT^®.

3. Vinylaromatic polymers

The molecular weight of these polymers, which are known per se and are available commercially, is generally in the range from 1500 to 2 000 000, preferably in the range from 70 000 to 1 000 000.

Merely as examples, mention may be made here of vinylaromatic polymers made from styrene, chlorostyrene, α-methylstyrene and p-methylstyrene; comonomers, such as (meth)acrylonitrile or (meth)acrylates, may also be subordinate participants in the structure with preferably not more than 20 % by weight, in particular not more than 8 % by weight. Particularly preferred vinylaromatic polymers are polystyrene and impact- modified polystyrene. Mixtures of these polymers may, of course, also be used. Preparation is preferably by the process described in EP-A-302 485.

Preferred ASA (acrylonitrile-styrol-acrylate) polymers are composed of a soft or rubber phase made from a graft polymer composed of:

A₁ from 50 to 90 % by weight of a graft base based on

A₁₁ from 95 to 99.9 % by weight of a C₂-C₁₀-alkyl acrylate, and

A₁₂ from 0.1 to 5 % by weight of a bifunctional monomer having two non- conjugated olefinic double bonds, and

A₂ from 10 to 50 % by weight of a graft composed of

A₂₁ from 20 to 50 % by weight of styrene or of substituted styrenes or a mixture of these, and

A₂₂ from 10 to 80 % by weight of acrylonitrile, methacrylonitrile, acrylates or methacrylates, or a mixture of these,

mixed with a hard matrix based on an SAN (strylol-acrylonitrile) copolymer A₃) composed of:

A₃₁ from 50 to 90 % by weight, preferably from 55 to 90 % by weight and in particular from 65 to 85 % by weight, of styrene and/or of substituted styrenes and

A₃₂ from 10 to 50 % by weight, preferably from 10 to 45 % by weight and in particular from 15 to 35 % by weight, of acrylonitrile and/or methacrylonitrile.

Component A₁) is an elastomer which has a glass transition temperature below -20⁰C, in particular below -30⁰C.

The main monomers A₁₁) used to prepare the elastomer are acrylates having from 2 to 10 carbon atoms, in particular from 4 to 8 carbon atoms. Particularly preferred monomers are tert-butyl, isobutyl and n-butyl acrylate, and also 2-ethylhexyl acrylate, and the two last-named monomers are particularly preferred.

Besides these acrylates, use is made of from 0.1 to 5 % by weight, in particular from 1 to 4 % by weight, based on the total weight Of A₁₁ + A₁₂, of a polyfunctional monomer having at least two nonconjugated olefinic double bonds. Among these, preference is given to the use of bifunctional compounds, i.e. those having two nonconjugated double bonds. Examples of these are divinylbenzene, diallyl fumarate, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, tricyclodecenyl acrylate and dihydrodicyclopen- tadienyl acrylate, and particular preference is given to the two compounds last named.

Processes for preparing the graft base A₁ are known per se and described, for example, in DE-B 1 260 135. Corresponding products are also commercially available.

Preparation by emulsion polymerization has proven particularly advantageous in some cases.

The precise polymerization conditions, in particular the type, feed rate and amount of emulsifier, are preferably selected in such a way as to give an acrylate latex with at least some degree of crosslinking and an average particle size (weight average d₅o) of from about 200 to 700 nm, in particular from 250 to 600 nm. The latex preferably has a narrow particle size distribution, i.e. the quotient

_{Q =} ^d90 ^{" d}10 d50

is preferably less than 0.5, in particular less than 0.35.

The proportion of the graft base A₁ in the graft polymer A₁ + A₂ is from 50 to 90 % by weight, preferably from 55 to 85 % by weight and in particular from 60 to 80 % by weight, based on the total weight Of A₁ + A₂.

Grafted onto the graft base A₁ is a graft envelope A₂ obtainable by copolymerizing

A₂₁ from 20 to 90 % by weight, preferably from 30 to 90 % by weight and in particu- lar from 30 to 80 % by weight, of styrene or of substituted styrenes of the general formula

R-C=CH₂

where R are alkyl radicals having from 1 to 8 carbon atoms, or are hydrogen or halogen atoms, and R¹ are alkyl radicals having from 1 to 8 carbon atoms, or are halogen atoms, and n is 0, 1 , 2 or 3, and

A₂₂ from 10 to 80 % by weight, preferably from 10 to 70 % by weight and in particular from 20 to 70 % by weight, of acrylonitrile, methacrylonitrile, acrylates or meth- acrylates, or a mixture of these.

Examples of substituted styrenes are α-methylstyrene, p-methylstyrene, p-chloro- styrene and p-chloro-α-methylstyrene, among which preference is given to styrene and α-methylstyrene.

Preferred acrylates and methacrylates are those whose homopolymers or copolymers with the other monomers of component A₂₂) have glass transition temperatures above 2O⁰C; however, in principle use may also be made of other acrylates, preferably in amounts which result in a glass transition temperature T₉ of above 20⁰C for component A₂ overall.

Particular preference is given to (meth)acrylates with CrCs alcohols and to esters con- taining epoxy groups, such as glycidyl acrylate or glycidyl methacrylate. Very particularly preferred examples are methyl methacrylate, tert-butyl methacrylate, glycidyl methacrylate and n-butyl acrylate. It is preferable to avoid using too high a proportion of the last-named compound since it forms polymers with very low T₉.

The graft envelope A₂) may be prepared in one or more, e.g. two or three, steps, its overall makeup remaining unaffected thereby.

The graft envelope is preferably prepared in emulsion, as described, for example, in DE-C 12 60 135, DE-A 32 27 555, DE-A 31 49 357 and DE-A 34 14 118.

Depending on the conditions selected, the graft copolymerization gives a certain proportion of free copolymers of styrene and/or substituted styrene derivatives and (meth)acrylonitrile and/or (meth)acrylates.

The graft copolymer A₁ + A₂ generally has an average particle size of from 100 to 1000 nm, in particular from 200 to 700 nm (d₅₀ weight average). The conditions for preparation of the elastomer D₁) and for the grafting are therefore preferably selected in such a way as to give particle sizes in this range. Measures for this purpose are known and are described, for example, in DE-C 1 260 135 and DE-A 28 26 925, and also in Jour- nal of Applied Polymer Science, Vol. 9 (1965), pp. 2929 - 2938. The particle size of the elastomer latex may be enlarged, for example, by agglomeration. For the purposes of this invention the free, ungrafted homo- and copolymers produced in the graft copolymerization to prepare the component A₂) count as part of the graft polymer (A₁M₂).

Some preferred graft polymers are given below:

1 : 60 % by weight of graft base A₁ composed of

A₁₁ 98 % by weight of n-butyl acrylate and A₁₂ 2 % by weight of dihydrodicyclopentadienyl acrylate, and

40 % by weight of graft envelope A₂ composed of A₂₁ 75 % by weight of styrene and A₂₂ 25 % by weight of acrylonitrile

2: graft base as in 1 with 5 % by weight of a first graft envelope composed of styrene and

35 % by weight of a second graft composed of A₂₁ 75 % by weight of styrene, and A₂₂ 25 % by weight of acrylonitrile

3: graft base as in 1 with 13 % by weight of a first graft composed of styrene and 27 % by weight of a second graft composed of styrene and acrylonitrile in a weight ratio of 3:1.

The products present as component A₃) may, for example, be prepared by the process described in DE-B 10 01 001 and DE-B 10 03 436. Copolymers of this type are also available commercially. The weight-average molecular weight determined by light scattering is preferably from 50 000 to 500 000, in particular from 100 000 to 250 000.

The weight ratio of (A₁ + A₂):A₃ is from 1 :2.5 to 2.5:1 , preferably from 1 :2 to 2:1 and in particular from 1 :1.5 to 1.5:1.

SAN polymers suitable as component A) have been described above (see A₃₁ and A₃₂).

The viscosity number of the SAN polymers, measured to DIN 53 727 as a 0.5 % strength by weight solution in dimethylformamide at 23°C is generally in the range from 40 to 100 ml/g, preferably from 50 to 80 ml/g.

ABS (acrylonitrile-butadiene-styrol) polymers used as polymer A) in the novel polymer mixtures having two or more phases have the same structure as described above for ASA polymers. Instead of the acrylate rubber A₁) of the graft base in the ASA polymer use is usually made of conjugated dienes, preferably giving the following makeup for the graft base A₄:

A₄₁ from 70 to 100 % by weight of a conjugated diene, and

A₄₂ from 0 to 30 % by weight of a bifunctional monomer having two non-conjugated olefinic double bonds.

Graft A₂ and the hard matrix of the SAN copolymer A₃) remain unchanged in the makeup. Products of this type are commercially available. Preparation processes are known to the skilled worker, and no further details need therefore be given here.

The weight ratio of (A₄ + A₂):A₃ is from 3:1 to 1 :3, preferably from 2:1 to 1 :2.

Particularly preferred makeups of the novel molding compositions comprise, as component A), a mixture of:

A₁) from 10 to 90 % by weight of a polybutylene terephthalate, A₂) from 0 to 40 % by weight of a polyethylene terephthalate, and A₃) from 1 to 40 % by weight of an ASA or ABS polymer or a mixture of these.

Products of this type are available under the trademark Ultradur^® S (previously Ultra- blend^® S) from BASF Aktiengesellschaft.

Other preferred makeups for component A) comprise

A₁) from 10 to 90 % by weight of a polycarbonate,

A₂) from 0 to 40 % by weight of a polyester, preferably polybutylene terephthalate, and A₃) from 1 to 40 % by weight of an ASA or ABS polymer or a mixture of these.

Products of this type are available under the trademark Terblend^® from BASF Aktiengesellschaft.

4. Thermoplastic polyurethanes

Other suitable thermoplastics which may be mentioned are thermoplastic polyurethanes (TPUs), as described by way of example in EP-A 115 846, EP-A 115 847, and EP-A 117 664.

5. Other thermoplastics Other suitable polymers which may be mentioned are polyphenyl ethers, polyolefins, such as polyethylene homo- or copolymers and/or polypropylene homo- or copolymers, and also polyketones, polyarylene ethers (known as HT thermoplastics), in particular polyether sulfones, polyvinyl chlorides, poly(meth)acrylates, and also mixtures (blends) composed of any of the thermoplastics listed above.

Preferred as thermoplastic polymers are polycondensates. More preferred are polyam- ides, in particular polyamide-6,6 and polyamide-6. Such polyamides are available un- der the brand name Ultramid^® from BASF, Ludwigshafen, Germany.

Also preferred are polyesters, in particular polybutylen terephthalates (PBTs), such as PBTs available under the brand name Ultradur^®from BASF Aktiengesellschaft, Ludwigshafen, Germany. Further preferred are polycarbonates.

Also preferred are vinyl aromatic polymers, such as styrol acrylonitrile copolymers (SAN).

The content of the polymer in the nanocomposite is in general from 1 to 99.9 % by weight preferably from 5 to 99,9 % by weight and in particular from 8 to 99,9 % by weight.

The inorganic nanoparticles used in the process according to the invention are in general oxides of metals and half-metals.

Preferred are SiO₂, TiO₂, ZnO, AI₂O₃, ZrO₂, SnO₂ and Fe₂O₃, more preferred are SiO₂, AI₂O₃ and TiO₂, in particular SiO₂.

The inorganic nanoparticles generally have an average particle size (d₅₀ value) from 1 to 250 nm, preferably from 1 to 100 nm, more preferred from 1 to 50 nm, and in particular from 2 to 20 nm.

The nanoparticles are preferably in a particulate state, and have an aspect ratio (L/D, i. e. length: diameter) of preferably from 1 to 3.

The method usually employed for particle size determination and distribution is dynamic light scattering, an ultracentrifuge, or field flow fractionation, and that usually used for the aspect ration is a combination of the above methods with transmission or scanning electron microscopy. The content of the nanoparticles in the nanocomposite is generally from 0.1 to 99 % by weight, preferably from 0.1 to 20 % by weight, and in particular from 0.1 to 10 % by weight.

In principle any oxide of a metal or half-metal in nanoform can be used in the process according to the invention, e.g. oxidic compounds prepared by flame pyrolysis or precipitation, such as SiO₂ prepared by flame pyrolysis.

In a preferred embodiment the nanoparticles are prepared in situ in the course of the inventive process by hydrolysis of an alkoxide of the respective metal or half-metal. In particular, the nanoparticles are prepared by a sol-gel-method.

The sol-gel method is known per se, see e.g. S. Jain et al. Polymer 2005, 46, 6666. According to this method a precursor compound is brought into contact with a porous polymer. A sol is produced by hydrolyzing the precursor compound with an aqueous solution having a pH > 1. The sol is further gelled by keeping the polyolefin/sol at elevated temperature, e.g. 60-100 ⁰C, for a couple of hours, e.g. for 2-24 hours to effect condensation. The thus obtained nanocomposite is dried.

Suitable precursors include (CrC₄)-alkoxides of the respective metals and half-metals, preferred are tetraethyl orthosilicate (TEOS) and titanium isopropoxide (TPOT).

In principle any solvent may be used with a critical temperature of from 20 to 200 ⁰C and a critical pressure of from 25 to 150 bar may be used.

Preferred is a solvent or solvent mixture selected from perfluoropropane, propane, chloropentafluoroethane, perfluoroacetone, carbon dioxide, pentafluoroethane, 1 ,1 ,1- trifluoroethane, 1 ,1-difluoroethene, chlorodifluoromethane, trifluoromethane, methyl fluoride, and difluoromethane.

According to this method the nanocomposite is preferably prepared by preparing a mixture of one or more thermoplastic polymers with a compound of the formula (R-O-)_nM, where R is a linear or branched alkyl with 1-6 carbon atoms, n is an integer from 1-4 and M is a metal or half-metal, preferably selected from the group consisting of Si, Ti, Zr, Sn, Zn, Fe and Al, at a temperature of from 30-80 ⁰C, adding an aqueous solution having a pH-value of > 1 , where the molar ration between (R-O-)_nM and H₂O is from 1 :1 to 1 :20, keeping the temperature of the mixture at 30-80 ⁰C for 1-10 hours and raising the temperature to 50-100 ⁰C and keeping the temperature for 3-10 hours. Preferably, an aqueous solution having a pH-value of > 7 is a solution of H₂O and NH₄OH. It is particularly preferred, that the amount of NH₄OH is from 1-10 mol-% based on the amount of (R-0-)_nM.

Preferably, an aqueous solution having a pH-value of < 7 is a solution of H₂O and HCI. It is particularly preferred that the amount of HCI is from 1-10 mol-% based on the amount of (R-0-)_nM.

These alkoxides are commercially available or can be made by methods well known to those skilled in the art.

Accordingly, in a preferred embodiment of the invention there is provided a process for producing a polymer nanocomposite, comprising the steps of

a1 ) preparing a mixture of a thermoplastic polymer and a metal or half-metal alkoxide in a solvent which is in the supercritical state,

a2) hydrolyzing the alkoxide followed by condensation and

b) removing the solvent.

The process according to the invention is carried out in a solvent which is in the supercritical state. In principle, any solvent is suitable which has a critical temperature in the range of 35 to 180 ⁰C, and a critical pressure in the range of 10 to 150 bar, and which further has solubility for both metal or half metal oxide and thermoplastic polymers.

Preferred solvents are perfluoropropane, propane, chloropentafluoropentane, per- fluoroacetone, carbon dioxide, pentafluoroethane, 1 ,1 ,1-trifluoroethane, 1 ,1-difluoro- ethene, chlorodifluoromethane, trifluoromethane, methylfluoride, and difluoromethane.

Preferably, the supercritical solvent is combined with one or more other polar solvents, preferably a polar protic solvent or a polar aprotic solvent, more preferred one or more alcohols, preferably having from 1 to 6 carbon atoms, in particular methanol, ethanol, n- or i-propanol. The ratio of supercritical solvent to polar solvent, such as alcohols, is generally 100:10, preferably 100:5, in particular 100:3.

Carbon dioxide and trifluoromethane are particularly preferred, specifically in combination with one or more protic solvents, in particular with methanol.

The weight-ratio of solvent to polymer is generally 1 : 1-7, preferably 1 : 2-5, in particular 1 : 3. Preferably, the solvent is used in an amount to swell the polymer but not to dissolve it.

The temperature for the process needs to be at least sufficient for the solvent to remain in the supercritical state.

In general the temperature is in the range of from 40 to 180 ⁰C, preferably from 60 to 150 ⁰C, and in particular from 80 to 100 ⁰C.

The pressure for the process needs to be at least sufficient for the solvent to remain in the supercritical state.

In general the pressure is in the range of from 10 to 150 bar, preferably from 40 to 120 bar, and in particular from 50 to 80 bar.

The reaction time is generally from 2 to 8 hours, preferably from 3 to 4.

The process is carried out under conditions well known to those skilled in the art. In a typical embodiment the reaction is carried out in a closed high temperature and high pressure steel reactor (with a glass window) equipped with temperature controller and pressure transducer. A magnetic stirrer is used to stir the solvent-polymer mixture during the synthesis of nanoparticles. Polymer is first fed to the reactor, and then the reactor is closed and the temperature is raised to a desired value. At this stage, supercritical solvent is injected in the reactor using steel tubes at a controlled rate with stirring. Later, after the swelling of the polymer by solvent is completed, metal- or half metal alkoxide is fed by separate pipe followed by water/catalyst solution. The reaction is then carried out as specified above. The solvent can be removed by releasing the pressure and applying vacuum to the reactor. The product is removed after solvent removal.

Work up of the reaction mixture can be effected by conventional methods well known to those skilled in the art. For example, the solvent can be removed, and the crude product can then be washed and dried at elevated temperatures.

As a further component, the nanocomposites obtainable by the process of the invention may comprise the usual processing aids, such as stabilizers, oxidation retarders, agents to counteract decomposition due to heat and decomposition due to ultraviolet light, nucleating agents, plasticizers etc.

Examples which may be mentioned of oxidation retarders and heat stabilizers are sterically hindered phenols and/or phosphites, hydroquinones, aromatic secondary amines, such as diphenylamines, various substituted members of these groups, and mixtures of these in concentrations of up to 1 % by weight, based on the weight of the nanocomposite.

UV stabilizers which may be mentioned, and are generally used in amounts of up to 2 % by weight, based on the molding composition, are various substituted resorcinols, salicylates, benzotriazoles, and benzophenones.

The nanocomposites of the invention show advantageous properties with respect to viscosity, mechanical performance, to improve sliding, abrasion resistance, flowability, deformation, and creep resistance specifically for gear wheels.

In a preferred embodiment nanocomposites of the invention containing a high content of nanoparticles are prepared as master batches, which are diluted with a thermoplas- tic polymer for further use.

The nanocomposites of the invention can be used (if desired diluted) for producing shaped articles, like fibers, foils, and moldings of any type, in particular for applications in injection molding for components, for example in the electrical sector, e.g. cable har- nesses, cable harness elements, hinges, plugs, plug parts, plug connectors, circuit melts, electrical connector elements, mechatronic components, optoelectronic modules, in particular uses in the automotive sector and under the engine hood.

The invention is further illustrated by the following examples.

Examples

The following materials were used in the examples:

- Ultramid^® B3 (polyamide-6), BASF Aktiengesellschaft;

- Ultramid^® B50 01 (polyamide), BASF Aktiengesellschaft;

- Ultradur^® B4520 (polybutylenterephthalate), BASF Aktiengesellschaft; RT 51 (polyethylenterephthalate);

Lexan 161 (polycarbonate); - Luran^® VLN (styrol-acrylonitrile copolymer), BASF Aktiengesellschaft;

- Tetraethoxysilane (TEOS), purity > 99.9 %, Alfa Aesan;

- Ti (IV)-ethylate, technical grade, Aldrich;

- Carbondioxide, purity > 99.9 %, BASF Aktiengesellschaft; Trifluoromethane; - Ammonia solution, NH₃ content 9 %;

- Methanol, purity > 99.5 %, Merck. Example 1

Preparation of a polyamide/silica nanocomposite in supercritical CO₂

25 g of polyamide-6 (Ultramid^® B3) and 0.4 g of methanol were mixed with 12 g of supercritical CO₂ at 25 ⁰C and then temperature was increased to 95 ⁰C and kept for 2 hours with continuous stirring at a pressure of 56 bars. The temperature was reduced to 60 ⁰C and after 10 min 7.2 g of TEOS (tetraethyl orthosilicate) was added dropwise under continuous stirring. After 10 min, 8.8 g of mixture of water and ammonium hydroxide was added at 48 bars and the reaction was continued for 3 hours in the reactor. Later, samples were taken out and dried at 80 ⁰C for 24 hours. FTIR spectrum shows the formation of silica particles in the thermoplastics matrix. TEM (transmissions electron spectroscopy) showed the uniform dispersion of particles with monodisperse size.

Example 2

Preparation of a polyamide/silica nanocomposite in supercritical trifluoromethane

25 g of polyamide-6 (Ultramid^® B3) and 0.4 g of methanol were mixed with 25 g of supercritical trifluromethane at 25 ⁰C and then temperature was increased to 95 ⁰C and kept for 2 hours with continuous stirring at a pressure of 79 bars. The temperature was reduced to 60 ⁰C and after 10 min 7.2 g of TEOS (tetraethyl orthosilicate) was added dropwise under continuous stirring at 55 bars. After 20 min, 8.8 g of mixture of water and ammonium hydroxide was added at 55 bars and the reaction was continued for 3 hours in the reactor. Later, samples were taken out and dried at 80 ⁰C for 24 hours. FTIR spectrum showed the formation of silica particles in the thermoplastics matrix. TEM showed the uniform dispersion of particles with monodisperse size.

Example 3

Preparation of polybutylenterephthalate (PBT)/silica nanocomposites in supercritical carbondioxide (PBT: Ultradur B4520)

40 g of polybutylenterephthalate (Ultradur B4520) and 0.5 g of methanol were mixed with 17 g of supercritical CO₂ at 25 ⁰C and then temperature was increased to 95 ⁰C and kept for 2 hours with continuous stirring at a pressure of 90 bars. The temperature is reduced to 80 ⁰C and after 10 min 11.5 ml of TEOS (tetraethyl orthosilicate) was added dropwise under continuous stirring within 2 min at 77 bars. After 20 min, 14 ml of mixture of water and ammonium hydroxide was added at 85 bars and the reaction was continued for 4 hours in the reactor. Later, samples were taken out and dried at 80 ⁰C for 24 hours. FTIR spectrum showed the formation of silica particles in the thermoplastics matrix. TEM showed the uniform dispersion of particles with monodisperse size.

Example 4

Preparation of polyethylenterephthalate (PET)/silica nanocomposites in supercritical carbondioxide (PET: RT51 )

40 g of polyethyleneterephthalate (RT 51 ) and 0.5 g of methanol were mixed with 17 g of supercritical CO₂ at 25 ⁰C and then temperature was increased to 95 ⁰C and kept for 2 hours with continuous stirring at a pressure of 86 bars. The temperature was reduced to 80 ⁰C and after 10 min 11.2 ml of TEOS (tetraethyl orthosilicate) was added drop- wise under continuous stirring within 2 min at 76 bars. After 20 min, 14 ml of mixture of water and ammonium hydroxide was added at 80 bars and the reaction was continued for 4 hours in the reactor. Later, samples were taken out and dried at 80 ⁰C for 24 hours. FTIR spectrum showed the formation of silica particles in the thermoplastics matrix. TEM showed the uniform dispersion of particles with monodisperse size.

Example 5

Preparation of styrol-acrylonitrile copolymer (SAN)/silica nanocomposites in supercritical carbondioxide (SAN: Luran VLN)

40 g of SAN (Luran VLN) and 0.5 g of methanol were mixed with 17 g of supercritical CO₂ at 25 ⁰C and then temperature was increased to 95 ⁰C and kept for 2 hours with continuous stirring at a pressure of 90 bars. The temperature was reduced to 80 ⁰C and after 10 min 1 1.5 ml of TEOS (tetraethyl orthosilicate) was added dropwise under continuous stirring within 2 min at 76 bars. After 20 min, 14 ml of mixture of water and ammonium hydroxide was added at 81 bars and the reaction was continued for 4 hours in the reactor. Later, samples were taken out and dried at 80 ⁰C for 24 hours. FTIR spectrum showed the formation of silica particles in the thermoplastics matrix. TEM showed the uniform dispersion of particles with monodisperse size.

Example 6

Preparation of polycarbonate (PC)/silica nanocomposites in supercritical carbondioxide (PC: Lexan 161 )

40 g of polycarbonate (Lexan 161 ) and 0.5 g of methanol were mixed with 17 g of supercritical CO₂ at 25 ⁰C and then temperature was increased to 95 ⁰C and kept for 2 hours with continuous stirring at a pressure of 96 bars. The temperature was reduced to 80 ⁰C and after 10 min 1 1.5 ml of TEOS (tetraethyl orthosilicate) was added drop- wise under continuous stirring within 2 min at 79 bars. After 20 min, 14 ml of mixture of water and ammonium hydroxide was added at 82 bars and the reaction was continued for 4 hours in the reactor. Later, samples were taken out and dried at 80 ⁰C for 24 hours. FTIR spectrum showed the formation of silica particles in the thermoplastics matrix. TEM showed the uniform dispersion of particles with monodisperse size.

Example 7

Preparation of polyamide (PA)/TiC>₂ nanocomposites in supercritical carbondioxide

40 g of polyamide (B50 01 ) and 0.5 g of methanol were mixed with 17 g of supercritical CO₂ at 25 ⁰C and then temperature was increased to 95 ⁰C and kept for 2 hours with continuous stirring at a pressure of 90 bars. The temperature was reduced to 80 ⁰C and after 10 min 1 1.5 ml of Ti (IV)-ethylate was added dropwise under continuous stirring within 2 min at 80 bars. After 20 min, 14 ml of mixture of water and ammonium hydroxide was added at 95 bars and the reaction was continued for 3 hours in the reactor. Later, samples were taken out and dried at 80 ⁰C for 24 hours. FTIR spectrum showed the formation of titan oxide in the thermoplastics matrix. TEM showed the uniform dispersion of particles with monodisperse size.

Claims

1. A process for producing a polymer nanocomposite, comprising the steps of

b) removing the supercritical solvent.

2. The process as claimed in claim 1 , further comprising the steps of

a1 ) preparing a mixture of a thermoplastic polymer and a metal or half-metal alkoxide in a solvent which is in the supercritical state, and

a2) hydrolyzing the alkoxide followed by condensation.

3. The process as claimed in claim 1 or 2, where the thermoplastic polymer is a polyamide, a polyester, a polyurethane, a polycarbonate or vinyl aromatic polymer.

4. The process as claimed in claim 3, where the thermoplastic polymer is a polyamide, a polyester, a polycarbonate or a styrol-acrylonitrile copolymer.

5. The process as claimed in any one of claims 1 to 4, where the supercritical sol- vent is from the group perfluoropropane, propane, chloropentafluoropentane, per- fluoroacetone, carbon dioxide, pentafluoroethane, 1 ,1 ,1-trifluoroethane, 1 ,1- difluoroethene, chlorodifluoromethane, trifluoromethane, methylfluoride, and di- fluoromethane.

6. The process as claimed in any one of claims 1 to 5, where the supercritical solvent is mixed with one or more polar solvents.

7. The process as claimed in any one of claims 1 to 6, where the solvent is used in an amount to swell the thermoplastic polymer.

8. The process as claimed in any one of claims 1 to 7, where the nanoparticles are from the group SiO₂, TiO₂, AI₂O₃, ZnO, ZrO₂, SnO₂ and Fe₂O₃.

9. A polymer nanocomposite obtainable by a process as claimed in any one of claims 1 to 8.

10. The use of a polymer nanocomposite as claimed in claim 9 for producing shaped articles.