MXPA96006540A - PROCESS FOR THE PREPARATION OF POLYMEROSVINILAROMATICOS CRISTALINOS WITH A STRUCTURAPREDOMINANTmente SINDIOTACT - Google Patents

Abstract

The present invention relates to a process for the preparation of crystalline vinylaromatic polymers with a predominantly syndiotactic structure, which is characterized in that it comprises polymerizing vinylaromatic monomers, alone or mixed with at least one other copolymerizable, ethylenically unsaturated monomer, in the presence of a catalyst system which consists essentially of: a) a titanium or zirconium complex selected from those having the general formula: MR1R2R3R4, A1MR1R2R3, A1A2MR1R2 (I) in which the groups R1, R2, R3 and R4, equal or different, represent (iso ) C1-C10 alkyl, (iso) alkoxy, alkylamide radical, a C6-C10 aryl radical or a halogen such as chlorine, while the same or different groups A1 and A2, represent a cyclopentadienyl ligand, optionally substituted with radicals C1-C10 alkyl, or an indenyl ligand, M represents a titanium or zirconium atom, b) a cocatalyst selected from an alkyl ilaluminoxane and a boron compound having the formula (II): BX1X2X3 (II) or one of its salts, in which X1, X2 and X3, are the same or different, represent a fluorinated hydrocarbon radical of C1-C20; and c) a tin derivative having the general formula: SnR5R6R7R8 (III) in which the groups R5, R6, R7 and R8, equal or different, represent an (iso) alkyl or aryl radical of C1-C

Description

PROCESS FOR THE PREPARATION OF VINI AROMATIC CRYSTAL POLYMERS WITH A PREDOMINANTLY STRUCTURE SINDIOTACTICA DESCRIPTION OF THE INVENTION The present invention relates to a process for the preparation of vinylaromatic crystalline polymers with a predominantly syndiotactic structure. More specifically, the present invention relates to a process for the preparation of crystalline polystyrene, in which the polymer chains have an essentially syndiotactic configuration and the catalyst suitable for this purpose. Polystyrene is a thermoplastic polymer obtained by polymerization of styrene radicals and is used in the production of molded articles, films, electrical materials, packaging materials, etc. It is an amorphous, atactic polymer that has excellent insulation properties and reasonable thermal resistance. For many applications, however, it is preferable to use crystalline materials with high thermal resistance and solvent resistance, characteristics which atactic polystyrene does not have.

European Patent 210,615 describes a polystyrene having a structure characterized by an extremely high degree of stereoregularity, in which phenyl substituents are arranged to provide a syndiotactic polymer. This material does not have the above disadvantages of atactic polystyrene since it is crystalline and therefore, once transformed, it can be subjected to orientation processes, it is almost completely insoluble in organic solvents and has a melting point within the range of 260- 280 ° C and therefore have high thermal resistance, comparable to or greater than that of thermoplastic condensation polymers (polyesters, polyamides, polyimides, etc.). The syndiotactic polystyrene can be prepared as described in the literature, for example in accordance with what was described in European Patent EP 272,584 or US Patent 4,978,730, by polymerization catalyzed by the compounds of Ti, Zr in presence of a cocatalyst represented by methylaluminoxane (a mixture of cyclic and linear oligomers containing the periodic units -AlCH-jO-) or, as described in European Patent Application, published 421,629, of boron-containing fluorinated group derivatives . Examples of catalysts for the synthesis of syndiotactic polystyrene mentioned in the literature are titanium halides (chloride, bromide, etc.), titanium alcoholates (methoxide, ethoxide, propoxide, isopropoxide, butoxide, etc.), titanium carboxylates, metallocenes (cyclopentadienyltitanium trichloride, dichloride, cyclopentadienyltitanium trichloride pentametilciclopenta-dieniltitanio alkoxides cyclopentadienyltitanium cyclopentadienyltitanium alkyls, alkyls pentametilciclopenta-dieniltitanio dichloride diciclopentadieniltitanio alkoxides diciclopentadieniltitanio, etc.), titanium alkyls (tetrabenzyl, tetrametiltitanio, tetraethyl -titanium, etc.) and the corresponding zirconium compounds. It has now been found that it is possible to synthesize crystalline vinylaromatic polymers and in particular crystalline polystyrene, which has a predominantly syndiotactic configuration using a novel catalyst system, which has never been described in the literature. The present invention, therefore, relates to a process for the preparation of crystalline vinylaromatic polymers having a predominantly syndiotactic structure, which comprises polymerizing vinylaromatic monomers, alone or mixed with at least one other copolymerizable, ethylenically unsaturated monomer, in the presence of a catalyst system consisting essentially of: a) a titanium or zirconium complex selected from those having the general formula: MR1R2R3R4, A1MR1R2R3, A1A2MR1R2 (I) wherein the groups R1 (R2, R3 and R4, equal or different, represent (iso) alkyl of C - ^ - C- ^ Q, (iso) alkoxy, alkylamide radical, an aryl radical of g-C10 or a halogen such as chlorine, while the groups A- ^ and A2, the same or different, represent a cyclopentadienyl ligand, optionally substituted with alkyl radicals of C- ^ - C- ^ Q, OR an indenyl ligand; M represents a titanium or zirconium atom; b) a cocatalyst selected from an alkylaluminoxane and a boron compound having the formula (II): or one of its salts, in which X1 # X2 and X3, are the same or different, represent a fluorinated hydrocarbon radical of c? ~ c2o; and c) a tin derivative having the general formula: SnR5R6R7R8 (III) in which the groups R5, Rg, R7 and Rg / same or different, represent an (iso) alkyl or aryl of C1-C1Q radical. With respect to traditional catalyst systems, the compounds based essentially on (a) and (b), the catalyst system of the present invention causes increases in one or more of the following parameters: activity of the catalyst system; molecular weight of the syndiotactic polystyrene obtained; degree of stereoregularity of the polymer. The compounds having the general formula (I) are products known in the literature and are described in European Patent 210,615 or in United States Patent 4,978,730. Typical examples of the titanium or zirconium complexes having the formula (I), particularly suitable for the present invention are Ti (CH2CgH5) 4; Ti (OCH3) 4; Ti (OC2H5) 4; Ti (OC3H7) 4; Ti (Oi-C3H7) 4; Ti (OC4H9) 4; Ti [N < CH3) 2] V Ti [N (C2H5) 2] 4; Ti [N (C3H7) 2JV Ti [N (i-C3H7) 2] 4; Ti [N (C4H9) 2] 4; CpTiCl3; CpTi (OCH3) 3; CpTi (OC2H5) 3; CpTÍ (OCjH7) 3; CpTÍ (OÍ-C3H7) 3? CpTiÍOC ^ H,) ^ CpTi [N (CH3) 2] 3; CpTi [N (C2H5) 2] 3; CpTi [N (C3H7.}. 2] 3; CpTi [N (i-C3H7) 2] 3 cpti [N (c4H9) 2] 3 # - cptici3; cp * ti (0CH3) 3; cp * ti (oc2H5) 3; Cp'Ti (OC3H7) 3; Cp * Ti (Oi-C3H7) 3 Cp * Ti (OC4H9) 3; Cp * TÍ [N (CH3) 2] 3; Cp * TÍ [N (C2H5) 2] 3; Cp * TÍ [N (C3H7) 2] 3; Cp * Ti [N (i-c3H7) 2] 3; Cp * Ti [N (C4H9) 233; InTiCl3; lnTi (OCH3) 3; InTi (0C2H5) 3; inTi (OC3H7) 3; InTi (Oi-C3H7) 3; InTi (0C4H9) 3 InTi [N (CH3) 2] 3; InTi [N (C2H5) 2] 3; InTi [N (C3H7) 233; InTi [N (i-C3H7) 2] 3; InTi [N (C4H9) 2] 3; etc., and the corresponding derivatives of Zirconium. (Cp = cyclopentadienyl; In = indenyl; Cp * = pentamethyl-cyclopentadienyl). The titanium or zirconium compounds having the general formula (I) are added to the polymerization mixture in such an amount that the molar ratio of vinylaromatic monomer / M (M = titanium or zirconium) is between 1,000 and 200,000, preferably between 10,000 and 150,000. The alkylaluminoxane cocatalyst consists essentially of mixtures of products having a linear or cyclic or box structure. In the first case The structure is represented by the general formula (IV): while in the second case by the general formula (V) wherein m represents an integer between 1 and 40 and R 'an alkyl radical of C - ^ - C ^, preferably of C-j-Cg, - an aryl radical of Cg-C20, preferably of Cg-C12; a C7-C20 aralkyl or alkylaryl radical, preferably C7-C12; or a C3-C2Q cycloalkyl radical, preferably C? -Cg; or an O-R 'radical, in which R' represents an alkyl radical of preferably C? -C4 * an aryl radical of Cg-C20, preferably Cg-C12; or a halogen atom, such as chlorine, fluorine or bromine, with the proviso that not all radicals R ^ are contemporaneously O-R 'or halogens. The box structure was described in Molecular Symposium, Vol. 97, 1995. The above cocatalysts, having the general formula (IV) and (V) are known in the literature and were described, for example, in Patent Applications.

European, published 272,584 and 421,659 or in U.S. Patent 4,978,730. Cocatalysts having the general formula (II), or its salt, are known in the literature and described in European Patent Applications, published 421,659 and 482,934. Preferred cocatalysts between those having the general formulas (II), (IV) or (V) is methylaluminoxane (MAO), a mixture of linear oligomers with an average m of between 10 and 20 and cyclic oligomers with average m of between 10 and 20. and 20. The cocatalyst is generally used in amounts such that the molar ratio of aluminum / M is between 50 and 2,000 or such that the boron / M ratio is between 0.5 and 10. The preferred tin derivatives of the present invention are Sn (CH 3) 4; Sn (C2H5) 4; Sn (C3H7) 4; Sn (i-C3H7) 4; Sn (C4Hg) 4; Sn (CgH5) 4; Sn (CH2CgH5) 4; etc. These compounds are added to the polymerization mixture in such an amount that the molar ratio of Sn / M is between 0.01 and 100, preferably between 0.1 and 50. According to the process of the present invention, the catalyst system described in above may also optionally consist of an alkylaluo in which the alkyl group contains from 1 to 6 carbon atoms, for example trimethylaluminum, triethylaluminum, triisobutylaluminum, etc., in amounts such that the molar ratio of alkylaluminum / M is between 0 and 800. The term "vinylaromatic polymers" as used in the present description and in the claims, refers essentially to styrene polymers and styrene derivatives and relative copolymers containing up to 20 mole% of another monomer copolymerizable selected from those having the general formula (V): CH2 = CH - R "(V) wherein R "represents a hydrogen atom or an alkyl radical of C ^ -Cg or a C4-C12 cycloalkyl radical.The styrene derivatives comprise alkylstyrenes, in which the alkyl group contains from 1 to 4 carbon atoms, show halogenated, C-, C4-alkoxystyrenes, carboxystyrenes, vinylnaphthalenes, such as alpha- or beta-vinylnaphthalene, vinyltetrahydronaphthalene such as 1, 2, 3, 4-tetrahydro-6-vinylnaphthalene, etc. Typical examples of substituted styrenes are p-methylstyrene, m-methylstyrene, alone or mixed together, ethylstyrene, butylstyrene, p-tert-butylstyrene, dimethylstyrene, chlorostyrene, bromostyrene, fluorostyrene, chloromethyl-styrene, methoxystyrene, acetoxymethylstyrene, etc. The polymerization reaction can be carried out mass or solvent In the second case, the solvent may consist of aliphatic or aromatic hydrocarbons or their mixtures and is used in quantities such that the volume ratio of solvent / monomer The numbers are between 0 and 10. The preferred solvent is toluene. More specifically, according to the general procedure adopted for this type of reaction, vinylaromatic monomers are subjected to treatment, before polymerization, to eliminate catalytic poisonings, such as phenol, water, phenylacetylene stabilizers and consisting of distillation, steps on columns containing activated molecular sieves or activated alumina, etc. The monomers and optionally, the solvent are charged to the reaction equipment together with the possible aluminum alkyl and cocatalyst. After a time ranging from 5 seconds to 30 minutes, the catalyst system comprising the titanium complex having the general formula (I) and the tin derivative having the general formula (III) is added, preferably in the form of a solution. The reaction proceeds for times ranging from 15 minutes to 10 hours at temperatures between 20 and 100 ° C. In the end, the obtained polymer is recovered using traditional methods. Some illustrative but non-limiting examples are provided for a better understanding of the present invention and its modality. Analysis procedures: The percentage of the syndiotactic polymer is determined by extracting the polymer with acetone or methyl ethyl ketone (MEK) at the boiling point for 10-20 hours. The degree of stereoregularity is determined by L3 carbon nuclear magnetic resonance spectroscopy as described in U.S. Patent 4,680,353. The molecular weights of the polymers obtained were determined by Gel Percent Chromatography in trichlorobenzene at 135 ° C. The percentages indicated in the examples are relative percentages.

COMPARATIVE EXAMPLE 1 16 ml of styrene (0.140 moles) purified by the passage in a column of basic alumina, 2 ml of a solution 0. 01 M in tetramethyltin toluene (2 x 10"5 moles) and then 0.5 ml of a 0.01 M solution in toluene of (pentamethylcyclopentadienyl) titanium trichloride (5 x 10 ~ 6 moles), are introduced into a subsequent test tube in an inert atmosphere The reaction is carried out for 2 hours at 60 ° C At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl. No solid product is obtained.

COMPARATIVE EXAMPLE 2 16 ml of styrene (0.140 moles) purified by the passage in a basic alumina column, 0.75 ml of a 2 M solution in triethylaluminum toluene (1.5 x 10 ~ 3 moles), 2 ml of a 0.01 M solution in tetramethyltin toluene (2 x 10"^ moles) and then 0.5 ml of a 0.01 M solution in toluene of (pentamethylcyclopentadienyl) titanium trichloride (5 x 10" 6 moles), are introduced into a subsequent test tube in an inert atmosphere. The reaction is carried out for 2 hours at 60 ° C. At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered. The solid is again suspended in methanol, filtered and dried under vacuum. 126 mg (0.9% yield) of atactic polystyrene are obtained.

COMPARATIVE EXAMPLE 3 16 ml of styrene (0.140 moles) purified by the passage in a basic alumina column and 0.96 ml of a 1.57 M solution in toluene of methylaluminoxane (1.5 x 10 ~ 3 moles) are introduced into a subsequent test tube in an inert atmosphere . After 5 minutes, 0.5 ml of a 0.01 M solution in toluene of tetra ethyl ethyl (5 x 10 ~ 6 moles) is added. The reaction is carried out for 5 hours at 60 ° C.

At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered. The solid is again suspended in methanol, filtered and dried under vacuum. 711 mg (4.9% yield) of atactic polystyrene are obtained. Average molecular weight weight (Mw): 78,000; Average number of molecular weight (Mn): 14,000.

COMPARATIVE EXAMPLE 4 ml of styrene (0.175 moles) purified by the passage in a basic alumina column and 1.2 ml of a 1.57 M solution in toluene of methylaluminoxane (1.88 x 10 ~ 3 moles) are introduced into a subsequent test tube in an inert atmosphere . After 5 minutes, 0.5 ml of a 0.0125 M solution in toluene of (pentamethylcyclopentadienyl) titanium trichloride (6.25 x 10 ~ 6 moles) is added. The reaction is carried out for 2 hours at 60 ° C. At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered. The solid is again suspended in methanol, filtered and dried under vacuum. 1.13 g (6.2% yield) of the polymer are obtained. The fraction insoluble in methyl ethyl ketone (MEK): 77%. 13-C NMR analysis showed that the insoluble fraction had a percentage of syndiotactic dyads of 99.99%. Average molecular weight weight (Mw): 300,000; Average number of molecular weight (Mn): 167,000.

COMPARATIVE EXAMPLE 5 ml of styrene (0.175 moles) purified by the passage in a basic alumina column and 1.2 ml of a 1.57 M solution in toluene of methylaluminoxane (1.88 x 10"3 moles) are introduced into a subsequent test tube in an inert atmosphere After 5 minutes, 0.5 ml of a 0.0125 M solution in toluene of titanium tetraethoxide (6.25 x 10 ~ 6 moles) is added in. The reaction is carried out for 5 hours at 60 ° C.

At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered. The solid is again suspended in methanol, filtered and dried under vacuum. 1.38 g (7.6% yield) of the polymer are obtained.

The fraction insoluble in methyl ethyl ketone (MEK): 86%. The analysis by 13-C NMR showed that the insoluble fraction had a percentage of syndiotactic dyads of 99.5%. Average molecular weight weight (Mw): 368,000; Average number of molecular weight (Mn): 164,000.

COMPARATIVE EXAMPLE 6 ml of styrene (0.175 moles) purified by the passage in a basic alumina column and 1.2 ml of a 1.57 M solution in toluene of ethylaluminoxane (1.88 x 10"3 moles) are introduced into a subsequent test tube in an inert atmosphere After 5 minutes, 2.2 ml of a 0.0285 M solution in toluene of (indenyl) titanium trichloride (6.25 x 10 ~ 6 moles) are added in. The reaction is carried out for 2 hours at 60 ° C. The mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered, the solid is again suspended in methanol, filtered and dried under vacuum to obtain 2.11 g (11.6% yield) of the polymer. Insoluble fraction in methyl ethyl ketone (MEK): 86% The analysis by NMR-C showed that the insoluble fraction had a percentage of syndiotactic dyads of 99.5% Average weight of molecular weight (Mw): 250,000 Average number of molecular weight ( Mn): 127,000.

COMPARATIVE EXAMPLE 7 ml of styrene (0.175 moles) purified by the passage in a column of basic alumina and 1.2 ml of a 1.57 M solution in toluene of methylaluminoxane (1.88 x "3 moles) are introduced into a subsequent test tube in an inert atmosphere.After 5 minutes, 0.5 rnl of a 0.0125 M solution in toluene of sodium trichloride is added. (cyclopentadienyl) titanium (6.25 x 10"6 moles) The reaction is carried out for 2 hours at 60 ° C.

At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered. The solid is again suspended in methanol, filtered and dried under vacuum. 4.18 g (31.6% yield) of the polymer are obtained. The fraction insoluble in methyl ethyl ketone (MEK): 89.3%. The analysis by 13-C NMR showed that the insoluble fraction had a percentage of syndiotactic dyads of 97.8%. Average molecular weight weight (Mw): 93,000; Average number of molecular weight (Mn): 50,000.

COMPARATIVE EXAMPLE 8 22. 9 ml of styrene (0.2 moles) purified by the passage in a basic alumina column and 0.4 ml of a 1.57 M solution in toluene of methylaluminoxane (6 x 10 ~ 4 moles) are introduced into a subsequent test tube in an inert atmosphere . After S minutes, 0.2 ml of a 0.01 M solution in toluene of (cyclopentadienyl) titanium trichloride (2 x 10"6 moles) is added.The reaction is carried out for 2 hours at 60 ° C. The mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered, the solid is again suspended in methanol, filtered and dried under vacuum to obtain 4.55 g (21.9% yield) of the polymer. insoluble in methyl ethyl ketone (MEK): 85% The analysis by 13 C-NMR showed that the insoluble fraction had a percentage of syndiotactic dyads of 98.5% Average molecular weight (Mw): 132,000 Average number of molecular weight (Mn) ): 47,000.

EXAMPLE 1 16 mi of styrene (0.14 moles) purified by the passage in a basic alumina column, 0.96 ml of a 1.57 M solution in MAO toluene (1.51 x 10 ~ 3 moles I, 0.5 ml of a 0.01 M solution in toluene of tetra ethyltin (5 x 10-moles) and then 0.5 ml of a 0.01 M solution in toluene of (pentamethylcyclopentadienyl) titanium trichloride (5 x 10 ~ 6 moles), are introduced into a subsequent test tube in an inert atmosphere. The reaction is carried out for 2 hours at 60 ° C. At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered, the solid is again suspended in methanol, filtered and dried under vacuum, 1.84 g (yield of 12.7%) of the polymer are obtained, the fraction insoluble in methyl ethyl ketone (MEK): 65% The analysis by 13-C NMR showed that the insoluble fraction had a percentage of syndiotactic dyads greater than 99.99%. Average molecular weight weight (Mw): 505,000; Average number of molecular weight (Mn): 221,000.

EXAMPLE 2 16 ml of styrene (0.14 moles) purified by the passage in a basic alumina column, 0.96 ml of a 1.57 M solution in MAO toluene (1.5 x 10"3 moles), 2 ml of a 0.01 M solution in tetramethyltin toluene (2 x 10 ~ 5 moles) and then 0.5 ml of a 0.01 M solution in toluene of (pentamethylcyclopentadienyl) titanium trichloride (5 x 10 ~ 6 moles), are introduced into a subsequent test tube in an inert atmosphere. It is carried out for 2 hours at 60 ° C. At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered.The solid is suspended again in methanol, filtered and dried under vacuum 2.5 g (yield of 17.7%) of the polymer are obtained The fraction insoluble in methyl ethyl ketone (MEK): 76% The analysis by 13 C-NMR showed that the insoluble fraction had a percentage of syndiotactic dyads greater than 99.99%. average molecular weight (Mw): 1,350,000; Average number of molecular weight (M) n): 300,000.

EXAMPLE 3 16 ml of styrene (0.14 moles) purified by the passage in a basic alumina column, 0.96 ml of a 1.57 M solution in MAO toluene (1.5 x 10"3 moles), 2 ml of a 0.01 M solution in tetraphenyl tin toluene (2 x 10"5 moles) and then 0.5 ml of a 0.01 M solution in toluene of (pentamethylcyclopentadienyl) titanium trichloride (5 x 10 ~ 6 moles), are introduced into a subsequent test tube in an inert atmosphere. The reaction is carried out for 2 hours at 60 ° C.

At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered. The solid is again suspended in methanol, filtered and dried under vacuum. 2.13 g (14.6% yield) of the polymer are obtained. The fraction insoluble in methyl ethyl ketone (MEK): 79%. The analysis by 13-C NMR showed that the insoluble fraction had a percentage of syndiotactic dyads greater than 99.99%. Average molecular weight weight (Mw): 590,000; Average number of molecular weight (Mn): 257,000.

EXAMPLE 4 16 ml of styrene (0.14 moles) purified by the passage in a basic alumina column, 0.48 ml of a 1.57 M solution in MAO toluene (7.5 x 10 ~ 4 moles), 2 ml of a 0.01 M solution in tetraphenyl tin toluene (2 x 10 ~ 5 moles) and then 0.5 ml of a 0.01 M solution in toluene of (pentamethylcyclopentadienyl) titanium trichloride (5 x 10"^ moles), are introduced into a subsequent test tube in an inert atmosphere. It is carried out for 2 hours at 60 ° C. At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered.The solid is suspended again in methanol, filtered and dried under vacuum 1.39 g (9.6% yield) of the polymer are obtained, the fraction insoluble in methyl ethyl ketone (MEK): 84%, The analysis by 13 C-NMR showed that the insoluble fraction had a percentage of syndiotactic dyads greater than 99.99%. average molecular weight (Mw): 624,000; Average number of molecular weight (Mn) : 300,000.

EXAMPLE 5 16 ml of styrene (0.14 moles) purified by the passage in a basic alumina column, 0.96 ml of a 1.57 M solution in MAO toluene (1.5 x 10"3 moles), 0.5 ml of a 0.01 M solution in tetramethyltin toluene (5 x 10"6 moles) and then 0.5 ml of a 0.01 M solution in toluene of titanium tetraethoxide (5 x 10" 6 moles) are introduced into a subsequent test tube in an inert atmosphere.

The reaction is carried out for 5 hours at 60 ° C. At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered. The solid is again suspended in methanol, filtered and dried under vacuum. 3.13 g (21.5% yield) of the polymer are obtained. The fraction insoluble in methyl ethyl ketone (MEK): 79%. The analysis by 13-C NMR showed that the insoluble fraction had a percentage of syndiotactic dyads of 99.4%. Average molecular weight weight (Mw): 352,000; Average number of molecular weight (Mn): 166,000.

EXAMPLE 6 16 ml of styrene (0.14 moles) purified by the passage in a basic alumina column, 0.96 ml of a 1.57 M solution in MAO toluene (1.5 x 10 ~ 3 moles), 2 ml of a 0.01 M solution in tetramethyltin toluene (2 x 10"5 moles) and then 0.5 ml of a 0.01 M solution in toluene of titanium tetraethoxide (5 x 10" 6 moles) are introduced into a subsequent test tube in an inert atmosphere. The reaction is carried out for 5 hours at 60 ° C. At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered. The solid is again suspended in methanol, filtered and dried under vacuum. 2.04 g (14% yield) of the polymer are obtained. The insoluble fraction in methyl ethyl ketone (MEK): 84%. The 13-C NMR analysis showed that the insoluble fraction had a percentage of syndiotactic dyads of 99.6%. Average molecular weight weight (Mw): 390,000; Average number of molecular weight (Mn): 190,000.

EXAMPLE 7 16 ml of styrene (0.14 moles) purified by the passage in a basic alumina column, 0.96 ml of a 1.57 M solution in MAO toluene (1.5 x 10"3 moles), 2 ml of a 0.01 M solution in tetraphenyl tin toluene (2 x 10"5 moles) and then 0.5 ml of a 0.01 M solution in toluene of titanium tetraethoxide (5 x 10" ^ moles), are introduced into a subsequent test tube in an inert atmosphere. Hold for 5 hours at 60 ° C.

At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered. The solid is again suspended in methanol, filtered and dried under vacuum. 1.8 g (12.4% yield) of the polymer are obtained.

The insoluble fraction in methyl ethyl ketone (MEK): 53%. The analysis by 13-C NMR showed that the insoluble fraction had a percentage of syndiotactic dyads of 99.5%. Average molecular weight weight (Mw): 364,000; Average number of molecular weight (Mn): 186,000.

EXAMPLE 8 ml of styrene (0.175 moles) purified by the passage in a basic alumina column, 1.2 ml of a 1.57 M solution in MAO toluene (1.88 x 10 ~ 3 moles), 2.35 ml of a 0.0013 M solution in tetramethyltin toluene (3.12 x 10 ~ 6 moles) and a 0.0027 M solution of (indenyl) titanium trichloride (6.25 x 10 ~ 6 moles) are introduced into a subsequent test tube in an inert atmosphere. The reaction is carried out for 2 hours at 60 ° C. At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered. The solid is again suspended in methanol, filtered and dried under vacuum. 3.65 g (20% yield) of the polymer are obtained. The fraction insoluble in methyl ethyl ketone (MEK): 94% The 13-C NMR analysis showed that the insoluble fraction had a percentage of syndiotactic dyads of 99.6%. Average molecular weight weight (Mw): 233,000; Average number of molecular weight (Mn): 99,000.

EXAMPLE 9 16 ml of styrene (0.14 moles) purified by the passage in a basic alumina column, 0.96 ml of a 1.57 M solution in MAO toluene (1.5 x 10 ~ 3 moles), 2 ml of a 0.01 M solution in tetraphenyl tin toluene (2 x 10"5 moles) and then 0.5 ml of a 0.01 M solution in toluene of (cyclopentadienyl) titanium trichloride (5 x 10-6 moles), are introduced into a subsequent test tube in an inert atmosphere. It is carried out for 2 hours at 60 ° C. At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered.The solid is suspended again in methanol, filtered and dried under vacuum Obtained 6.13 g (42.1% yield) of the polymer The fraction insoluble in methyl ethyl ketone (MEK): 84% The 1 C-NMR analysis showed that the insoluble fraction had a percentage of syndiotactic dyads of 98.1%.

Average molecular weight weight (Mw): 140,000; Average number of molecular weight (Mn): 52,000.

EXAMPLE 10 16 ml of styrene (0.14 moles) purified by the passage in a basic alumina column, 0.96 ml of a 1.57 M solution in MAO toluene (1.5 x 10 ~ 3 moles), 0.5 ml of a 0.01 M solution in tetramethyltin toluene (5 x 10 ~ 6 moles) and then 0.5 ml of a 0.01 M solution in toluene of (cyclopentadienyl) titanium trichloride (5 x 10 ~ 6 moles), are introduced into a subsequent test tube in an inert atmosphere. The reaction is carried out for 2 hours at 60 ° C. At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered. The solid is again suspended in methanol, filtered and dried under vacuum. 3.16 g (21.7% yield) of the polymer are obtained. The fraction insoluble in methyl ethyl ketone (MEK): 75% The analysis by 13-C NMR showed that the insoluble fraction had a percentage of syndiotactic dyads of 98.2%. Average molecular weight weight (Mw): 124,000; Average number of molecular weight (Mn): 63,000.

EXAMPLE 11 22. 9 ml of styrene (0.2 moles) purified by the passage in a basic alumina column, 0.2 ml of a 1.57 M solution in MAO toluene (3 x 10 ~ 4 moles), 2 ml of a 0.01 M solution in tetraphenyl tin toluene (5 x 10"5 moles), they are introduced into a subsequent test tube in an inert atmosphere.After 5 minutes, 0.2 ml of a 0.01 M solution in toluene of (cyclopentadienyl) titanium trichloride (2 x 10") is added. 6 moles). The reaction is carried out for 2 hours at 60 ° C. At the end, the mixture is suspended in 200 ml of methanol containing 2 ml of concentrated HCl and filtered. The solid is again suspended in methanol, filtered and dried under vacuum. 4.33 g (20.8% yield) of the polymer are obtained. The fraction insoluble in methyl ethyl ketone (MEK): 90%. The analysis by 13-C NMR showed that the insoluble fraction had a percentage of syndiotactic dyads of 98.3%. Average molecular weight weight (Mw): 146,000; Average number of molecular weight (Mn): 86,000.

Claims (11)

1. A process for the preparation of crystalline vinyl aromatic polymers with a predominantly syndiotactic structure, which is characterized in that it comprises polymerizing vinylaromatic monomers, alone or mixed with at least one other copolymerizable ethylenically unsaturated monomer, in the presence of a catalyst system consisting essentially of: a) a titanium or zirconium complex selected from those having the general formula: MR1R2R3R, A1MR1R2R3, A1A2MR1R2 (I) wherein the groups R- ^, R2"R3 and R4, equal or different, represent (iso) alkyl of C 1 -cyo (iso) alkoxy, alkylamide radical, an aryl radical of Cg-C- ^ Q or a halogen such as chlorine, while the groups A- ^ and A2, the same or different, represent a cyclopentadienyl ligand, optionally substituted with alkyl radicals of C-^ - C- ^ Q, OR an indenyl ligand; M represents a titanium or zirconium atom; b) a cocatalyst selected from an alkylaluminoxane and a boron compound having the formula (II): BX-j ^^ (II) Or one of its salts, in which X- ^, X2 and X3, are the same or different, represent a fluorinated hydrocarbon radical of C1-C20; and c) a tin derivative having the general formula: SnR5R6R7R8 (III) wherein the groups R5, Rg, R7 and Rg, equal or different, represent an (iso) alkyl or aryl radical of C ^ -C-jo.

2. The process according to claim 1, characterized in that the molar ratio of the vinylaromatic monomer / M is between 1,000 and 200,000.

3. The process in accordance with the claim 1 or 2, characterized in that the cocatalyst is used in amounts such that the molar ratio of aluminum / M is between 50 and 2,000 or the boron / M ratio is between 0.5 and 10.

4. The process according to any of the previous claims, characterized in that the tin derivative is added to the polymerization mixture in such an amount that the molar ratio of Sn / M is between 0.01 and 100.

5. The process according to any of the preceding claims, characterized in that the above catalyst system comprises an alkyl aluminum wherein the alkyl group contains from 1 to 6 carbon atoms.

6. The process according to claim 5, characterized in that the molar ratio of alkylaluminium / M is between 0 and 800.

7. The process according to any of the previous claims, characterized in that the polymerization reaction is carried out in bulk or in a solvent.

8. The process according to claim 7, characterized in that the solvent is used in amounts such that the volume ratio of solvent / monomers is between 0 and 10.

9. The process according to any of the previous claims, characterized in that the polymerization is carried out at temperatures between 20 and 100 ° C.

10. A catalytic composition characterized in that it comprises: a) a titanium complex selected from those having the general formula: MR-LR2R3R4, A1MR1R2R3, A1A2MR1R2 (I) wherein the groups R- ^ R2, R3 and R4, equal or different, represent (iso) alkyl of c? "ci0 '(iso) alkoxy, alkylamido radical, an aryl radical of g-C1Q or a halogen such as chloro , while the groups A- ^ and A, the same or different, represent a cyclopentadienyl ligand, optionally substituted with alkyl radicals of C-, - C- ^ Q, OR an indenyl ligand, M represents a titanium or zirconium atom; ) a cocatalyst selected from an alkylaluminoxane and a boron compound having the formula (II): -D? -i? «^? (II) or one of its salts, in which X- ^, X2 and X3, are the same or different, represent a fluorinated hydrocarbon radical of c? _ c2o; c) a tin derivative having the general formula: SnR5R6R7R8 (III) in which the same or different groups R5, Rg, R7 and RQ I represent an (iso) alkyl or aryl radical of C- ^ - C- ^ Q.

11. The use of a catalytic composition comprises: a) a titanium or zirconium complex selected from those having the general formula: MR1R2R3R4, A1MR1R2R3, A1A2MR1R2 (I) wherein the groups R- ^ R2, R3 and R4, the same or different, represent (iso) alkyl of c? ci0 '(iso) alkoxy, alkylamide radical, an aryl radical of gC- ^ Q or a halogen such as chlorine, while the same or different groups A- ^ and A2 represent-a cyclopentadienyl ligand, optionally substituted with alkyl radicals of C-, -C-, Q, O an indenyl ligand; M represents a titanium or zirconium atom; b) a cocatalyst selected from an alkylaluminoxane and a boron compound having the formula (II): BX ^ X ^ (II) or one of its salts, in which X- ^, X2 and X3, are the same or different, represent a fluorinated hydrocarbon radical of? _ c2o; and c) a tin derivative having the general formula: SnR5R6R7R8 (III) wherein the groups R5, Rg, R7 and Rg, equal or different, represent an (iso) alkyl or aryl radical in the preparation of crystalline vinylaromatic polymers having a predominantly syndiotactic structure.