The present invention relates to a composition based on impact resistant vinyl aromatic polymers.

More specifically, the present invention relates to compositions comprising an impact resistant vinyl aromatic polymer, a vinyl aromatic polymer having a predominantly syndiotactic structure and, possibly, a polyphenyl ether.

Compositions based on impact resistant vinyl aromatic polymers and vinyl aromatic polymers having a predominantly syndiotactic structure are known in literature. US patent 6,169, 146, for example, describes polymeric compositions having an improved resistance to solvents, containing an atactic polystyrene, possibly impact resistant, in a quan- tity ranging from 30 to 95% by weight and a syndiotactic polystyrene having a melting point not higher than 255°C, in a quantity ranging from 5 to 70% by weight. The composi- tions of the known technique can contain, in addition to these two components, one or more of the following addi-

tives selected from a polyphenylene ether, an inorganic filler and a polymer compatible with atactic or syndiotac- tic polystyrene, having a polar group in the chain.

These compositions, according to the known art, are prepared by kneading the components at a temperature rang- ing from the melting point of the syndiotactic polystyrene to 270°C.

As the prejudices of the state of the art are re- versed, the Applicant has surprisingly found that it is possible to obtain compositions based on atactic or syndio- tactic polystyrene with a high resistance to solvents, starting from traditional products, i. e. from a product having a melting point of about 270°C, in the case of syn- diotactic polymers. Even more surprisingly, these blends can also be advantageously prepared at temperatures lower than the melting points of the syndiotactic product.

The object of the present invention therefore relates to polymeric compositions comprising: a) 70-97% by weight, preferably 75-95%, of a vinyl aro- matic polymer modified with rubber; b) 3-30% by weight, preferably 5-25%, of a vinyl aromatic polymer having a predominantly syndiotactic structure with a melting point higher than 255°C ; c) 0-10% by weight with respect to (a) + (b), preferably 0. 5-5%, of a polyphenylene ether having an intrinsic

viscosity higher than or equal to 0.1 dl/g measured in chloroform at 25°C ; d) 0-10% by weight with respect to (a) + (b) of an elas- tomer selected from block copolymers consisting of at least one polymeric non-elastomeric block of a vinyl aromatic monomer and at least one elastomeric block based on a 1,3-conjugated diene, possibly hydrogenated, having the same or different molecular weight, wherein the diene content is higher than or equal to 50% by weight, preferably between 50 and 90%.

The term"vinyl aromatic polymer", as used in the pres- ent description and claims for identifying both components (a) and (b), essentially refers to a product obtained by the polymerization of at least one monomer having the fol- lowing general formula: wherein n is zero or an integer ranging from 1 to 5, R is a hydrogen atom or a methyl and Y is a halogen, such as chlo- rine or bromine, or an alkyl or alkoxyl radical having from 1 to 4 carbon atoms.

Examples of vinyl aromatic monomers having the above general formula are: styrene, a-methyl styrene, methyl sty- rene, ethyl styrene, butyl styrene, dimethyl styrene,

mono-, di-, tri-, tetra-and penta-chloro styrene, bromo styrene, methoxy-styrene, acetoxy-styrene, etc. Styrene and a-methyl styrene are the preferred vinyl aromatic monomers.

The vinyl aromatic monomers having general formula (I) can be used alone or mixed, up to 50% by weight, with other copolymerizable monomers. Examples of these monomers are (meth) acrylic acid, Cl-C4 alkyl esters of (meth) acrylic acid, such as methacrylate, methyl methacrylate, ethyl ac- rylate, ethyl methacrylate, isopropyl acrylate, butyl ac- rylate, amides and nitriles of (meth) acrylic acid, such as acrylamide, methacrylamide, acrylonitrile, methacryloni- trile, butadiene, ethylene, divinyl benzene, maleic anhy- dride, etc.. Preferred copolymerizable monomers are acrylo- nitrile and methyl methacrylate.

The vinyl aromatic polymer, or copolymer, (a) which is obtained has an average molecular weight Mw ranging from 50,000 to 1,000, 000, preferably from 70,000 to 300,000.

The vinyl aromatic polymer of step (a) comprises a polymeric matrix wherein a rubber-like phase is dispersed, or grafted, in the form of substantially spherical parti- cles, having an average diameter of between 0.1 and 2 pm, preferably between 0.2 and 1.2 Fm, in a quantity ranging from 4 and 15% by weight with respect to the total of com- ponent (a). The rubber-like phase can be selected from di- ene rubbers (i) and/or from block copolymers (ii) consist-

ing of at least one non-elastomeric polymeric block of a vinyl aromatic monomer and at least one elastomeric block based on a 1,3-conjugated diene, having the same or differ- ent molecular weight, wherein the diene content is equal to or higher than 50% by weight, preferably between 50 and 90%. Further rubbers which can be used as rubber-like phase dispersed in the polymeric matrix are low unsaturated rub- bers (iii), such as ethylene/propylene (EPR) or ethylene- propylene-diene (EPDM) rubbers.

The diene rubbers are usually of the synthetic type consisting, in particular, of a polymer of a 1,3-conjugated diene containing from 4 to 6 carbon atoms. Examples of these rubbers are polybutadiene and polyisoprene. Polybuta- diene is particularly preferred, having: - a Mooney viscosity ranging from 20 to 70 ML 1+4 at 100°C, measured according to the ASTM D 1646-80 stan- dard method; - a viscosity in solution ranging from 40 to 200 cps measured in a solution at 5% by weight in styrene at 25°C ; - a 1,2 vinyl content ranging from 5 to 35% wt; and a content of 1, 4-cis ranging from 20 to 85% by weight.

The block copolymers (ii) are, for example, of the type: S-B; S,-B-S2 ; B,-S,-B2-S2 ;

wherein S, Sl and S2 represent non-elastomeric polymeric blocks having an average molecular weight Mw ranging from 5,000 to 250,000, whereas B, B1 e B2 are elastomeric blocks based on a conjugated diene having an average molecular weight Mw ranging from 2.000 to 250, 000.

Particularly preferred block copolymers are those hav- ing: a Mooney viscosity ranging from 25 to 50 ML 1+4 at 100°C, measured according to the ASTM D 1646-80 standard method ; a viscosity in solution ranging from 25 to 60 cps, measured in solution at 5% by weight in styrene at 25°C ; and wherein the polymeric, non-elastomeric block is polystyrene; and the 1,3-conjugated diene used for the preparation of the elastomeric polymeric block is selected from those hav- ing from 4 to 8 carbon atoms. Examples of these dienes are: 1,3-butadiene, isoprene, 2, 3-dimethyl-1, 3-butadiene, piperylene and mixtures thereof.

Details on vinyl aromatic polymers modified with a rubber are available in Italian patent 1,264, 623 and in European patents 429,986, 716,664 and 286,071.

The vinyl aromatic polymer having a predominantly syn- diotactic structure has a melting temperature of about 265-

270°C, an average molecular weight Mw higher than 20,000, generally between 50,000 and 500,000, and a stereo regular- ity of the syndiotactic type higher than 90%, generally be- tween 95 and 100%. These polymers can be obtained by means of well-known processes described in literature. Syndiotac- tic vinyl aromatic polymers having the above characteris- tics can be prepared, for example, by means of a catalytic system based on organometallic complexes of titanium acti- vated by alkyl alumoxanes or fluorinated derivatives of bo- ron, possibly in the presence of alkyl metals as described in US patent 4,680, 353 and in the European patent 421,659 or in the US patents 5,629, 391,5, 728,784, 5,830, 959 and 6,174, 973- The polyphenylene ether used to prepare the polymeric compositions object of the present invention is a well known polymer or co-polymer widely used in industry, espe- cially as engineering polymer, in applications in which impact strength and thermal resistance are required.

Polyphenylene ethers are polymers and co-polymers which comprise several structural units having general formula (II): -Ar-0- wherein-Ar-represents an arylenic radical possibly substituted with one or more halogen atoms, one or more (iso) alkyl or (iso) alkoxyl radicals containing from 1 to 4

carbon atoms, one or more phenyls.

Preferred polyphenylene ethers according to the present invention are those having the following general formula (III): wherein the Ri radicals independently represent a C1-C4 (iso) alkyl or (iso) alkoxyl radical and m is an integer higher than 50, preferably between 60 and 600.

Illustrative examples of polyphenylene ethers par- ticularly suitable for the present invention are: - poly (2, 6-dimethyl-1, 4-phenylene) ether ; - poly (2, 6-diethyl-1, 4-phenylene) ether; - poly (2-methyl-6-ethyl-1, 4-phenylene) ether ; - poly (2, 6-diprophyl-1, 4-phenylene) ether Poly (2, 6-dimethyl-1, 4-phenylene) ether is the preferred polyphenylene ether.

These polyphenylene ethers generally have an average molecular weight Mw, determined by means of Gel Permeation Chromatography, ranging from 5,000 to 120,000 and their in- trinsic viscosity is higher than 0.1 dl/g, preferably be- tween 0.3 and 0.9 dl/g.

The polyphenylene ethers used in the composition ob-

ject of the present invention can be prepared by the oxida- tion of a phenolic compound with oxygen, or a gas contain- ing oxygen, preferably in the presence of a catalyst for oxidative coupling, as described in US patents 3,226, 361, 3,234, 183,3, 306,874, 3,257, 357,3, 337,501, 3,956, 242, 3,965, 069,4, 075,174, 4,102, 865,4, 184,034, 4,385, 168.

The elastomers (ii), optionally partially hydrogen- ated, used in combination with the vinyl aromatic polymer modified with rubber, described under item (a), can be used as elastomers (d).

The compositions object of the present invention can also contain, in addition to components (a), (b), (c) and (d), reinforcing additives, such as, for example, glass fi- bers, carbon fibers, high modulus organic or inorganic fi- bers, inorganic fillers, flame retardant agents, nucleating agents, dyes, pigments, stabilizers, lubricants, etc. which are well known to technical experts in the field.

The reinforcing additives can generally be used in amounts not higher than 50% by weight, preferably not higher than 30%, with respect to the total composition.

Stabilizers suitable for being used in the composi- tions of the present invention include a large number of the known thermal stabilizers and oxidation stabilizers used for polyphenylene ether resins or vinyl aromatic poly- mers. Liquid phosphates, for example, and sterically hin-

dered phenols can be added to the compositions of the pres- ent invention in a quantity varying from 0.05 to 5% by weight.

The compositions object of the present invention can be prepared with any conventional kneading method. The preparation temperature of the mixture can be maintained, for example, at between 180°C and 300°C or, more prefera- bly, between 180°C and 5°C below the melting point of the vinyl aromatic polymer having a predominantly syndiotactic structure (b). Any kneading unit can be used, operating in continuous or batchwise, such as, for example, twin-or single-screw mixers or extruders. The kneading, moreover, can be carried out in a number of steps as desired, for ex- ample by pre-mixing components (a) and (c) and then adding (b); or pre-mixing (b), (c) and (d) and then adding (a), and so on.

The present compositions can be easily processed by injection or extrusion and have a combination of properties which make them suitable for being used for the production of molded articles having a high impact resistance together with a good thermal resistance and resistance to solvents.

Thanks to these characteristics, the compositions, object of the present invention, are used in the fields of motor vehicles, household appliances (for example television sets, refrigerators, air conditioners), for the production

of manufactured products which must be oven-painted, parts in contact with engines, household appliances, electronic and technical articles, in the form of cups, boxes, con- tainers, panels, sheets, bars, etc..

Some illustrative but non-limiting examples are pro- vided for a better understanding of the present invention and its embodiment. Examples of the materials used and de- tails on the characterization of the samples are provided below.

Materials: Impact resistant atactic polystyrene: commercial product Edistir RR 745 (Polimeri Europa); Atactic polystyrene: commercial product Edistir N 1782 (Polimeri Europa) ; Syndiotactic polystyrene: polymer obtained from the polym- erization of styrene in the presence of Cp*TiCl3/MAO (Tm=273°C, Mn=230,000) ; SEBS (block styrene-hydrogenated butadiene elastomer): com- mercial product Kraton G 1652 (Kraton Polymers) ; Poly (2, 6-dimethyl-1, 4-phenylene ether): commercial product PPO H 51 (Mitsubishi).

Characterization The mechanical properties were determined according to ISO 180 (Izod Impact Strength) and ISO 527 (Tensile Test) on ISO 3167 injection molded test samples.

The resistance to solvents (ESCR, Environmental Stress-Cracking Resistance) was determined on the same test samples according to two different procedures.

1) Blistering tests The procedure used contemplates the deposition, by means of a pipette, of 1 to 6 drops of cyclopentane in several numbered positions (from 1 to 6), at a frequency of 1 drop per minute. The samples are placed in an oven at 60°C for 15 minutes in order to release the cyclopentane penetrated.

After extraction from the oven, the materials are com- pared, and the sample which starts forming blisters at the highest number of drops, is considered as being the best, using a parameter obtained by the sum of the number corre- sponding to the position in which corrosion of the test sample surface is observed and of that corresponding to complete blisters: the value of 7 corresponds to"no effect observed". Consequently, the values which represent solvent resistance range from 2 (very poor resistance) to 14 (per- fect resistance).

Repeated tests confirmed the good reproducibility of the method.

2) ESCR tests 5 test samples of each specimen are clamped in a vice which bends them under flexion so that the external surface reaches a deformation level equal to 0. 7%. A drop of cyclo-

pentane is dripped every 5 minutes onto this surface in a central position with respect to the length of the test sample. After 15 minutes (and consequently after 3 drops of cyclopentane), the test samples are extracted from the vice and subjected to tensile stress according to ISO 527. As a result of the test, the following values are obtained: a) elongation to break, after exposure to solvent under deformation: b) the ratio between this value and that of the elonga- tion to break according to ISO 527 on test samples not exposed (residual elongation).

Example 1 A blend based on 4,500 g of Edistir RR745 impact re- sistant polystyrene and 500 g of syndiotactic polystyrene was prepared in a Berstorff ZE 25 twin-screw extruder. The temperature profile in the nine zones of the extruder was the following: 200-220-240-250-260-260-260-260-250°C.

Comparative example Example 1 was repeated, but using Edistir 1782 atactic polystyrene instead of 500 g of syndiotactic polystyrene.

Example 2 Example 1 was repeated, but using the following tem- perature profile of the extruder: 210-245-265-275-285-285-285-285-275°C.

Example 3

Example 2 was repeated, but using 3,600 g of Edistir RR745 impact resistant polystyrene and 900 g of syndiotac- tic polystyrene.

Example 4 Example 1 was repeated, but using 4,350 g of Edistir RR745 impact resistant polystyrene, 250 g of Kraton G1652 (block styrene-hydrogenated butadiene elastomer), 400 g of syndiotactic polystyrene.

Example 5 Example 1 was repeated, but using 4,350 g of Edistir RR745 impact resistant polystyrene, 200 g of PPO H 51,400 g of syndiotactic polystyrene and 50 g of aluminum tert- butyl benzoate.

Example 6 Example 2 was repeated, but using 4,350 g of Edistir RR745 impact resistant polystyrene, 250 g of Kraton G1652, 400 g of syndiotactic polystyrene.

The results of the tests described in the above exam- ples are indicated in the following table.

Table

Ex. 1 Comp. Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 IZOD (kJ/m2) 6. 3 5 5 5. 7 5. 4 8.0 6.7 7.3 Tensile modulus (MPa) 1550 1490 1550 1680 1480 1580 1510 ESCR (Blistering test) 14 5 14 14 14 14 14 Yield stress (MPa) 19.2 18. 9 20.3 22.5 18. 3 19 5 20 5 Elongation to break (%) 29 46 37 34 45 32 44 Elongation to break after ex-30 29 35 31 43 32 43 posure to cyclopentane (%) Residual elongation (%) 106 64 94 91 96 100 98