DE102009046416A1 - Preparing impact modified copolymer, used in molded mass, comprises polymerizing monomer to form acrylate rubber in the presence of copolymer containing alpha, beta-unsaturated monocarboxylic acid nitrile and aromatic vinylmonomer - Google Patents

Abstract

Preparing impact modified copolymer comprises in situ polymerizing a monomer that forms an acrylate rubber (B), in presence of a copolymer (A) containing at least one alpha , beta -unsaturated monocarboxylic acid nitrile and at least one an aromatic vinylmonomer as a monomer component. An independent claim is included for impact modified mass comprising the copolymer (20-99.9 wt.%); acrylate (0.1-80 wt.%); and other additives (0-50 wt.%).

Description

The The invention relates to an improved process for the production of impact-modified copolymers.

Farther The invention relates to the inventively available Molding compounds, their use and the available here Shaped body of any kind.

It is generally known in the art that rubbers increase the impact strength, especially with thermoplastics, however, lower their modulus of elasticity. This also applies to thermoplastic Copolymers containing at least one α, β-unsaturated Monocarboxylic acid nitrile and at least one aromatic vinyl monomer as monomer components (in the context of the present invention such copolymers also referred to as "SAN").

Often are used for the impact modification of thermoplastics previously separately prepared rubbers by melt mixing incorporated into the thermoplastic melt, for example a SAN melt, especially about extruders of any kind.

A homogeneous distribution of the rubber in the polymer matrix is after as a challenge, since both polymers are usually not compatible with each other. Even at high shear rates you usually do not have regular distributions uniform particle size, but agglomeration of the rubber in the matrix.

Corresponding the mechanical properties are not optimal, in particular also for parts with thin wall thicknesses.

In the non-prepublished International Application PCT / EP2008 / 063831 (File reference) describes processes for the in situ polymerization of acrylate rubbers in polyoxymethylene molding compositions; SAN are not named.

task The present invention was therefore an improved process for the production of impact-modified SAN to provide a more even distribution of the rubber in the SAN matrix and a reduction in the number individual process steps compared. known methods of Melt admixture in advance separately prepared rubbers permits.

Accordingly, became found an improved method, which characterized is that monomers which form an acrylate rubber B), in Presence of a copolymer A) which contains at least one α, β-unsaturated Monocarboxylic acid nitrile and at least one aromatic vinyl monomer contains as monomer components, polymerized in situ.

preferred Embodiments are the dependent claims remove.

Component (A):

When Component A), all copolymers are suitable which contain at least one α, β-unsaturated Monocarboxylic acid nitrile and at least one aromatic vinyl monomer as monomer components (SAN). Preferred components A) are SAN, which themselves are not impact and / or impact modified are. The components A) and processes for their preparation are the person skilled in principle known and in the literature described.

Suitable α, β-unsaturated Monocarboxylic acid nitriles are selected from the Group consisting of acrylonitrile, methacrylonitrile and mixtures thereof.

eingesetzt werden, wobei
R¹ unabhängig voneinander Wasserstoff, C₁-C₁₀-Alkyl, C₁-C₁₀-Cycloalkyl, C₁-C₁₀-Alkoxy, C₆-C₁₈-Aryl, C₆-C₁₈-Aralkyl, C₆-C₁₈-Aryloxy, Chlor oder Brom und
R² unabhängig voneinander Wasserstoff, C₁-C₁₀-Alkyl, Chlor oder Brom bedeuten.Suitable aromatic vinyl monomers in component A) may be compounds of the general formula (I)

be used, where
R ^{1 is} independently hydrogen, C ₁ -C ₁₀ -alkyl, C ₁ -C ₁₀ -cycloalkyl, C ₁ -C ₁₀ -alkoxy, C ₆ -C ₁₈ -aryl, C ₆ -C ₁₈ -aralkyl, C ₆ -C ₁₈ -Aryloxy, chlorine or bromine and
R ² independently of one another are hydrogen, C ₁ -C ₁₀ -alkyl, chlorine or bromine.

preferred Aromatic vinyl monomers of the general formula (I) are selected from the group consisting of styrene, 3-methylstyrene, 3,5-dimethylstyrene, 4-n-propylstyrene, α-methylstyrene, α-methylvinyltoluene, α-chlorostyrene, α-bromostyrene, Dichlorostyrene, dibromostyrene and mixtures thereof. Especially preferred Aromatic vinyl monomers are styrene and / or α-methylstyrene.

Component A) can be obtained by all methods known to the person skilled in the art, for example free-radical, anionic or cationic polymerization. Component A) is preferably obtained by continuous or discontinuous polymerization in bulk or in solution. In a preferred embodiment, the Polymerization solution as a solvent 0 to 20 wt .-% of an aromatic solvent, for example toluene, xylenes or ethylbenzene. Component A) can be obtained by methods such as those in A. Echte, Handbuch der Technischen Polymerchemie, VCH Weinheim, 1993, especially p. 482 ff. , to be discribed.

In a preferred embodiment contains component A) as α, β-unsaturated monocarbonitrile Acrylonitrile and as the aromatic vinyl monomer styrene and / or α-methylstyrene.

Consequently is in a particularly preferred embodiment component A) the resin composition of the invention Copolymer composed of acrylonitrile and α-methylstyrene is. In this copolymer is acrylonitrile in a proportion of 20 to 40 wt .-%, preferably 25 to 35 wt .-% and α-methylstyrene in a proportion of 60 to 80% by weight, preferably 65 to 75% by weight before, wherein the sum of the amounts of the two monomers gives 100 wt .-%.

In Another particularly preferred embodiment Component A) of the resin composition of the invention a copolymer composed of acrylonitrile and styrene. In this copolymer is acrylonitrile in a proportion of 20 to 40 wt .-%, preferably 25 to 37 wt .-% and styrene in one portion from 60 to 80 wt .-%, preferably 63 to 75 wt .-% before, wherein the Sum of the amounts of the two monomers 100 wt .-% results.

The weight-average molecular mass M _{w of} the polymer used as component A) is preferably 60 000 to 300 000 g / mol, particularly preferably 100 000 to 200 000 g / mol, in each case measured by GPC with UV detection using polystyrene calibration standards and a 5 × MixedB- Pillar.

The number-average molecular mass M _{n of} the polymer used as component A) is preferably 20000 to 130 000 g / mol, particularly preferably 40 000 to 80 000 g / mol, in each case measured by GPC with UV detection using polystyrene calibration standards and a 5 × mixed binder. Pillar.

The polydispersity M _w / M _n with respect to the molecular masses M _w and M _n is preferably 2.0 to 3.5.

The viscosity number VZ of the polymer used as component A) is in a preferred embodiment, measured according to DIN 53726 at 25 ° C in a 0.5 wt .-% solution in DMF, 40 to 100 ml / g, particularly preferably 50 to 90 ml / g.

For the compositions of this invention component A) suitable are commercially available, for example under the brand name Luran ^® from BASF SE.

When Monomers B1) (for the preparation of the acrylate rubber B)) find esters based on a 3 to 6 carbon atoms, in particular one 3 or 4 carbon atoms having α, β-monoethylenic unsaturated mono- or dicarboxylic acid, in particular Acrylic acid, methacrylic acid, maleic acid, Fumaric acid and itaconic acid and 1 to 12 C atoms having alkanols, preferably a 1 to 8 carbon atoms alkanols, in particular methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-methylpropanol-1, tert-butanol, n-pentanol, 3-methylbutanol-1, n-hexanol, 4-methylpentanol-1, n-heptanol, 5-methylhexanol-1, n-octanol, 6-methylheptanol-1, n-nonanol, 7-methyl-octanol-1, n-decanol, 8-methylnonanol-1, n-dodecanol, 9-methyldecanol-1 or 2-ethylhexanol-1 Use. Preferably, acrylic acid and methacrylic acid methyl, ethyl, n-butyl, iso-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, 2-ethylhexyl, or dodecyl, fumaric and Maleinsäuredimethylester or di-n-butyl ester used. Of course, mixtures of the aforementioned Ester can be used.

When Monomers B2) are optionally 3 to 6 carbon atoms having α, β-monoethylenic unsaturated mono- or dicarboxylic acids and / or their amides, in particular acrylic acid, methacrylic acid, Maleic acid, fumaric acid or itaconic acid or acrylamide or methacrylamide used. Of course It is also possible to use mixtures of the abovementioned monomers B2) become.

As monomers B3), which differ from the monomers B1) and B2), find, for example α, β-ethylenically unsaturated compounds such as vinyl aromatic monomers such as styrene, α-methyl styrene, o-chlorostyrene or vinyl toluenes, vinyl halides such as vinyl chloride or Vinylidene chloride, esters of vinyl alcohol and 1 to 18 carbon atoms monocarboxylic acids, such as vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl laurate and vinyl stearate, nitriles α, β-mono- or diethylenisch unsaturated carboxylic acids, such as acrylonitrile, methacrylonitrile, fumaronitrile, maleic acid and also conjugated dienes containing 4 to 8 C atoms, such as 1,3-butadiene and isoprene, moreover vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid and its water-soluble salts, and N-vinylpyrrolidone, 2-vinylpyridine, 4- Vinylpyridine, 2-vinylimidazole, 2- (N, N-dimethylamino) ethyl acrylate, 2- (N, N-dimethylamino) ethyl methacrylate, 2- (N, N-diethylamino) ethyl acrylate , 2- (N, N-Diethylamino) ethyl methacrylate, 2- (N-tert-butylamino) ethyl methacrylate, N- (3-N ', N'-dimethylaminopropyl) methacrylamide or 2- (1-imidazolin-2-onyl) ethyl methacrylate.

Other monomers B3) have at least one epoxy, hydroxyl, N-methylol or carbonyl group, or at least two non-conjugated ethylenically unsaturated double bonds. Examples include two vinyl radicals containing monomers, two vinylidene radicals having monomers and two alkenyl radicals having monomers. Particularly advantageous are the diesters of dihydric alcohols with α, β-monoethylenically unsaturated monocarboxylic acids, among which acrylic and methacrylic acid are preferred. Examples of such two non-conjugated ethylenically unsaturated double bonds monomers are alkylene glycol diacrylates and dimethacrylates such as ethylene glycol diacrylate, 1,2-propylene glycol diacrylate, 1,3-propylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-butylene glycol diacrylate and ethylene glycol dimethacrylate, 1, 2-propylene glycol dimethacrylate, 1,3-propylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate and divinylbenzene, vinyl methacrylate, vinyl acrylate, allyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate, methylenebisacrylamide, cyclopentadienyl acrylate, triallyl cyanurate or triallyl isocyanurate. In this context, of particular importance are the methacrylic acid and acrylic acid C ₁ -C ₈ hydroxyalkyl esters such as n-hydroxyethyl, n-hydroxypropyl or n-hydroxybutyl acrylate and methacrylate and compounds such as glycidyl acrylate or methacrylate, diacetoneacrylamide and acetylacetoxyethyl acrylate or . -methacrylate. Of course, mixtures of monomers B3) can be used.

Preferably the release of the free-radically initiated aqueous solution takes place Emulsion polymerization by means of a radical polymerization initiator (radical initiator B4)). In principle, it can be both peroxides and to act azo compounds. Of course, too Redox initiator systems into consideration. As peroxides can in principle inorganic peroxides, such as hydrogen peroxide or peroxodisulfates, such as the mono- or di-alkali metal or ammonium salts of peroxydisulphuric acid, such as their mono- and di-sodium, potassium or ammonium salts or organic peroxides, such as alkyl hydroperoxides, for example tert-butyl, p-menthyl or cumyl hydroperoxide, as well as dialkyl or diaryl peroxides, such as di-tert-butyl or di-cumyl peroxide used become.

Farther may be dibenzoyl peroxide, diacetyl peroxide, succinyl peroxide, tert-butyl perpivalate, tert-butyl 2-ethylhexanoate, tert-butyl permaleate, bis (tert-butylperoxy) cyclohexane, tert-butyl peroxyisopropyl carbonate, tert-butyl peracetate, 2,2-bis (tert-butylperoxy) butane, Dicumyl peroxide, di-tert-amyl peroxide, di-tert-butyl peroxide, p-menthane hydroperoxide, Pinane hydroperoxide, cumene hydroperoxide, tert-butyl hydroperoxide and Hydrogen peroxide can be used.

When Azo compounds find essentially 2,2'-azobis (2-methylbutyronitrile), 2,2'-azobis (isobutyronitrile), 2,2'-azobis (2,4-dimethylvaleronitrile) and 2,2'-azobis (amidinopropyl) dihydrochloride (AIBA, corresponds to V-50 from Wako Chemicals) use. As oxidizing agent for Redox initiator systems come essentially the above Peroxides into consideration. Suitable reducing agents may be sulfur compounds with low oxidation state, such as alkali metal sulfites, for example Potassium and / or sodium sulfite, alkali hydrogen sulfites, for example Potassium and / or sodium bisulfite, alkali metal bisulfites, for example Potassium and / or sodium metabisulfite, formaldehyde sulfoxylates, for example potassium and / or sodium formaldehyde sulfoxylate, alkali salts, especially potassium and / or sodium salts, aliphatic sulfinic acids and alkali metal hydrogensulfides, such as potassium and / or sodium hydrosulfide, salts polyvalent metals, such as iron (II) sulfate, iron (II) ammonium sulfate, Iron (II) phosphate, endiols such as dihydroxymaleic acid, Benzoin and / or ascorbic acid and reducing saccharides, such as sorbose, glucose, fructose and / or dihydroxyacetone used become. As a rule, the amount of used Free radical initiator, based on the total amount of monomers 0 to 10 Wt .-%, preferably 0.01 to 3 wt .-% and more preferably 0.2 to 1.5% by weight.

According to the invention, an acrylate rubber B) is used which is obtainable in situ from the monomers B1) to B4) in the following amounts:
B1) 60 to 100, preferably 70 to 99.89 wt .-%
B2) 0 to 30, preferably 0.1 to 25 wt .-%
B3) 0 to 30, preferably 0.1 to 25 wt .-%
B4) 0 to 10, preferably 0.01 to 5% by weight,
where the sum of the weight percent B1) to B4) is 100%. Preferably, the monomers B2) and B3) in combination in amounts of 0 to 30, preferably from 0.01 to 25 wt .-%, based on 100 wt .-% B1) to B4) in the acrylate rubber B) are present.

For the implementation of the invention Procedure, the addition of the monomers B1) to B4) for the in situ polymerization either in the melt of the component A) or in the solution.

When Solvents which dissolve component A), Tetrachloroethane, hexafluoroacetone, cyclohexanone, N-methylpyrrolidone, DMSO, benzyl alcohol and DMF are used.

The Temperature is 130 according to the invention to 300 ° C, preferably 150 to 280 ° C.

The Residence time in the solution is usually 1 to 120 minutes, preferably 2 to 60 minutes

In the melt is the residence time of preferably 0.5 to 10 minutes, especially from 1 to 5 minutes

suitable Devices for the polymerization in the melt are for example kneaders, extruders or static mixers.

For the solution in solution are as apparatuses, for example Pistons or shaking reactors called.

To In situ polymerization in solution usually becomes the solution cooled and the resulting rubber-modified SAN product dried in the oven. The addition of other additives is preferably carried out by mixing in the extruder or premixing of the components and subsequent extrusion.

Becomes the inventive in situ polymerization in carried out the melt, can advantageously the Addition of further additives C) carried out without further intermediate step become, by the components C) ("hot feed") can be added at a later date.

Contain the molding compositions obtainable by the process according to the invention
A) 20 to 99.9, preferably 50 to 99.5 wt .-%
B) 0.1 to 80, preferably 0.5 to 50 wt .-%
C) 0 to 50, preferably 0 to 40 wt .-%,
wherein the sum of the weight percentages of components A) to C) is 100%.

When Component C), the inventive Molding compositions preferably 0 to 50 wt .-% and in particular 0 to 40 Wt .-% of other additives. These other additives as well their preparation are known in the art and in the literature described.

When Such additives may be mentioned as examples: reinforcing agents such as fibers, in particular glass fibers, dyes, pigments, colorants, antistatic agents, Antioxidants, stabilizers to improve the thermal stability, to increase light stability and UV stability, for increasing hydrolysis resistance and chemical resistance, Anti-thermal agents and lubricants; For example, waxes used for the production of moldings or moldings are appropriate.

The Mixing of the additives C) in the inventive thermoplastic molding compounds by mixing the components in a known manner, which is why detailed information here unnecessary. Advantageously, the mixture of components takes place on an extruder. The incorporation of these other additives can be done at any stage of the manufacturing process, preferably however, at an early date to early the stabilization effects (or other special effects) of the Take advantage of additive.

Out The molding compositions can be shaped bodies (also semi-finished, Produce foils, films and foams) of all kinds. The molding compounds are characterized by good mechanics, in particular impact resistance out. The distribution of the rubber in the matrix is essential even.

The particle size of the rubber B) in the matrix is preferably 0.01 to 10 .mu.m, in particular 0.05 to 5 .mu.m, determined by TEM transmission electron microscopy (sample sections at -120 to -100 ° C with an Ultracut S from Reichert-Jung Thin sections are introduced into the TEM with a Cu lattice at 120 dV, and contrasting with RuO ₄ darkens the SAN and the acrylate particles (or the holes formed in the SAN matrix, resulting from the tearing out of the rubber particles when making the thin sections are) appear bright in the dark SAN matrix).

Especially is the processing of the individual components (without clumping or caking) easily and in short cycle times, so that in particular thin-walled components as an application come into question.

These are suitable for the production of fibers and monofilaments, films and Moldings of any kind, in particular for applications, which require good weather stability.

Examples

It the following components were used:

Component A-i:

A commercially available styrene-acrylonitrile copolymer consisting of 65 wt .-% of styrene and 35 wt .-% acrylonitrile and having a viscosity number VZ of 80 ml / g (determined after DIN 53726 on a 0.5% strength by weight solution of the polymer in dimethylformamide)

Component A-ii:

A commercially available α-methylstyrene-acrylonitrile copolymer consisting of 70 wt .-% α-methyl styrene and 30 wt .-% acrylonitrile and with a visco unit VZ of 57 ml / g (determined after DIN 53726 on a 0.5% strength by weight solution of the polymer in dimethylformamide)

Component B1-i: 2-ethylhexyl acrylate

Component B4-i: t-butyl perpivalate

example 1

90 parts by weight of component Ai DSM were 15 microseconds Compounder from in a twin-screw Midi extruder Xplore ^® 5. Melted at 220 ° C and 80 U / min. Subsequently, a mixture of 10 parts by weight of 2-ethylhexyl acrylate (component B1-i) and 0.3 part by weight of t-butyl perpivalate (component B4-i) was added as an initiator. After three minutes of melt mixing of the components, the thermoplastic melt was extruded. The obtained impact-modified thermoplastic extrudates were opaque; the size and distribution of the rubber particles in the thermoplastic matrix have been determined (by transmission electron microscopy (TEM) to C were produced with an Ultracut ^® S of Reichert-Jung thin sections of Thermoplastextrudate at -120 to -100 °, and the thin sections were obtained with a Cu grid introduced into the TEM at 120 dV) and are placed in 1 played.

Example 2

As described in Example 1, but with component A-ii (instead of component Ai) and a melt temperature of 250 ° C (instead of 220 ° C), impact-modified thermoplastic extrudates were prepared; the size and distribution of the rubber particles in the thermoplastic matrix were determined by transmission electron microscopy (TEM) and are reported in 2 played.

Example 3-V (for comparison)

90 parts by weight of component Ai were mixed with 10 parts by weight of a butyl acrylate rubber prepared by emulsion polymerization (prepared from 98% by weight of butyl acrylate and 2% by weight of dihydrodicyclopentadienyl acrylate "DCPA") having an average particle diameter of 80 nm at 200 ° C melt-blended and extruded in an ordinary manner over a period of 4 minutes on an extruder. The size and distribution of the rubber particles in the thermoplastic matrix were determined by transmission electron microscopy (TEM) and are reported in 3 played.

Example 4-V (for comparison)

90 parts by weight of component Ai were mixed with 10 parts by weight of a prepared in emulsion polymerization Butylacryatkautschuks (prepared from 98 wt .-% butyl acrylate and 2 wt .-% Dihydrodicyclopentadienylacrylat "DCPA") having an average particle diameter of 500 nm at 200 ° C melt-blended and extruded in an ordinary manner over a period of 4 minutes on an extruder. The size and distribution of the rubber particles in the thermoplastic matrix were determined by transmission electron microscopy (TEM) and are reported in 4 played.

Example 5-V (for comparison)

Ninety parts by weight of Component A-ii was added with 10 parts by weight of a butyl acrylate rubber prepared by emulsion polymerization (prepared from 98% by weight of butyl acrylate and 2% by weight of dihydrodicyclopentadienyl acrylate "DCPA") having an average particle diameter of 80 nm 200 ° C over a period of 4 min melt-extruded in an ordinary manner on an extruder and extruded. The size and distribution of the rubber particles in the thermoplastic matrix were determined by transmission electron microscopy (TEM) and are reported in 5 played.

Example 6-V (for comparison)

Ninety parts by weight of component A-ii was added with 10 parts by weight of a butyl acrylate rubber prepared by emulsion polymerization (prepared from 98% by weight of butyl acrylate and 2% by weight of dihydrodicyclopentadienyl acrylate "DCPA") having an average particle diameter of 500 nm 200 ° C over a period of 4 min melt-extruded in an ordinary manner on an extruder and extruded. The size and distribution of the rubber particles in the thermoplastic matrix were determined by transmission electron microscopy (TEM) and are reported in 6 played.

The Examples prove that by the invention Process for producing impact-modified SAN a more even distribution of the rubber in the SAN matrix and a reduction in the number of individual process steps yoy. known methods of melt mixing in advance separately produced rubbers is achieved.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 2008/063831 [0007]

Cited non-patent literature

• - A. Echte, Handbuch der Technischen Polymerchemie, VCH Weinheim, 1993, especially p. 482 et seq. [0015]
• - DIN 53726 [0022]
• - DIN 53726 [0050]
• - DIN 53726 [0051]

Claims (9)

Process for the production of impact-modified copolymers, characterized in that monomers which form an acrylate rubber B) are polymerized in situ in the presence of a copolymer A) which contains at least one α, β-unsaturated monocarboxylic acid nitrile and at least one aromatic vinyl monomer as monomer components. Method according to claim 1, characterized in that then one uses an acrylate rubber B), which is constructed from the following monomers B1) 60 to 100 wt .-% of an ester an α, β-monoethylenically unsaturated Mono- or dicarboxylic acid having 3 to 6 carbon atoms and one Alkanols having 1 to 12 C atoms, B2) 0 to 30 wt .-% of an α, β-monoethylenic unsaturated mono- or dicarboxylic acid with 3 bis 6 C atoms or their amides or mixtures thereof B3) 0 to 30 wt .-% of an α, β-monoethylenically unsaturated Compound, different from B1) and B2), B4) 0 to 10% by weight a radical initiator, where the sum of the weight percent B1) to B4) gives 100%. Process according to claims 1 or 2, characterized in that the in situ polymerization in a Solvent is carried out. Process according to claims 1 to 2, characterized characterized in that the in situ polymerization in the melt the component A) is carried out. Process according to claims 1 to 4, characterized characterized in that the in situ polymerization at temperatures from 130 to 300 ° C is performed. Process according to claims 1 to 5, characterized in that the ester monomers B1) are esters of acrylic acid, Methacrylic acid, maleic acid, fumaric acid, Itaconic acid or mixtures thereof with an alkanol with 1 to 12 carbon atoms. Impact-modified molding compositions obtainable in accordance with Process claims 1 to 6, containing A) 20 to 99.9 wt .-% of a copolymer containing at least one α, β-unsaturated Monocarboxylic acid nitrile and at least one aromatic vinyl monomer as Contains monomer components, - ("SAN"), B) 0.1 to 80 wt .-% of an acrylate rubber and C) 0 to 50 % By weight of other additives, where the sum of the weight percent of components A) to C) gives 100%. Use of the impact-modified molding compositions according to claim 7 for the production of fibers, films and moldings. Fibers, films and moldings available from the impact-modified molding compositions according to claim 7th