Process for the preparation of vinylaromatic polymers with a high degree of syndiotaxy

Process for the preparation of crystalline vinylaromatic polymers with a high degree of syndiotaxy which comprises polymerizing vinylaromatic monomers in the presence of a catalytic system essentially consisting of: PA1 a) a complex of titanium having the general formula: EQU CpTiX.sub.1 X.sub.2 X.sub.3 (I) PA2 wherein Cp represents a cyclopentadienyl ligand whereas X.sub.1, X.sub.2, X.sub.3, the same or different, are selected from a halogen such as chlorine, or from alkyl groups, alkoxides, carboxylates, di(alkyl)amides; PA1 b) a polyalkylaluminoxane wherein the alkyl group contains from 1 to 8 carbon atoms; PA1 c) aluminum trifluoride.

The present invention relates to a process for the preparation of
 vinylaromatic polymers with a high degree of syndiotaxy.
 More specifically, the present invention relates to a process for the
 preparation of crystalline poly-styrene in which the polymeric chains have
 an essentially syndiotactic configuration and the catalyst suitable for
 the purpose.
 Polystyrene is a thermoplastic polymer obtained by the radicalic
 polymerization of styrene having an atactic stereo structure. It is an
 amorphous polymer, with excellent insulating properties and reasonable
 thermal resistance and is used in the production of moulded articles,
 films, materials for household appliances, packaging, etc. For numerous
 applications however, it is preferable to use crystalline materials with a
 high thermal resistance and resistance to solvents, characteristics which
 atactic polystyrene does not have.
 European patent 210.615 describes a polystyrene having a structure
 characterized by a high degree of stereoregularity, in which the phenyl
 substituents are arranged, in the polymeric chain, in such a way as to
 give a syndiotactic polymer. This material does not have the above
 disadvantages of atactic polystyrene as it is crystalline and
 consequently, once transformed, can be subjected to orientation processes;
 it is insoluble in almost all organic solvents and has a melting point
 within the range of 260-280.degree. C., giving it a high thermal
 resistance, comparable to or higher than that of condensation
 thermoplastic polymers (polyesters, polyamides, polyimides, etc.).
 Syndiotactic polystyrene can be prepared according to what is described in
 literature, for example according to what is disclosed in European patent
 EP 272.584 or in U.S. Pat. No. 4,978,730, by polymerization catalyzed by
 compounds of Ti, Zr, in the presence of a cocatalyst represented by MAO,
 methylaluminoxane (a mixture of cyclic and linear oligomers containing the
 repetitive unit --AlCH.sub.3 O--), or, as described in published European
 patent application 421.659, by derivatives of boron containing fluorinated
 groups.
 Both the cocatalyst MAO and fluorinated boranes are costly high-quality
 products and it would therefore be preferable to reduce the amount in the
 catalytic formulation.
 Scientific literature cites studies for finding alternatives to MAO or
 fluorinated boranes. For example, it is known that the addition of certain
 aluminum alkyls, such as aluminum triisobutyl, to titanium/MAO systems can
 increase, under particular experimental conditions, the catalytic activity
 even if this result is not verified under all conditions such as, for
 example, with low molar ratios aluminum/titanium. Apart from this, a
 non-correct concentration of aluminum alkyl may cause a considerable
 reduction in the molecular weight of the polymer or, in the case of
 aluminum trimethyl, act in the completely opposite way causing a lowering
 in the polymerization yields ("Polymer", 39, 959, 1998).
 It has also been observed that zinc diphenyl increases the catalytic
 activity of titanium metallocenes activated with MAO ("Polymer Bulletin",
 Berlin, 39, 693, 1997). However, zinc diphenyl is also an expensive
 high-quality product and also causes the formation of fractions of atactic
 polymer to a greater degree than MAO.
 By treating hydrated salts such as Ti(SO.sub.4).sub.2.4H.sub.2 O or K.sub.2
 TiO(C.sub.2 O.sub.4).sub.2.2H.sub.2 O with aluminum trimethyl, catalysts
 are obtained with a reasonable activity ("Makromoleculare Chemie, Rapid
 Communications", 9, 351, 1988). These however are systems based on MAO
 which is formed in situ by the reaction of aluminum alkyl with the
 hydration water of the salt.
 Catalytic systems containing hemimetallocene derivatives of titanium,
 activated with aluminum trimethyl and hexaalkyldistannoxanes or dialkyltin
 oxides, are described in U.S. Pat. No. 5,326,837. Also in this case
 however the activities are lower than those of the systems based on MAO
 and additionally contain toxic derivatives of tin.
 The Applicant has now found that it is possible to obtain crystalline
 vinylaromatic polymers, in particular crystalline polystyrene, having a
 configuration with a high degree of syndiotaxy and with high yields, by
 adding to the traditional catalytic systems based on titanium and MAO,
 aluminum trifluoride also in partial substitution of the MAO itself.
 The present invention therefore relates to a process for the preparation of
 crystalline vinylaromatic polymers with a high degree of syndiotaxy which
 comprises polymerizing vinylaromatic monomers, alone or mixed with at
 least another copolymerizable ethylenically unsaturated monomer, in the
 presence of a catalytic system essentially consisting of:
 a) a complex of titanium having the general formula:
EQU CpTiX.sub.1 X.sub.2 X.sub.3 (I)
 wherein Cp represents a cyclopentadienyl ligand optionally substituted with
 C.sub.1 -C.sub.10 alkyl radicals, whereas X.sub.1, X.sub.2, X.sub.3, the
 same or different, are selected from a halogen such as chlorine, or from
 alkyl groups, alkoxides, carboxylates, di(alkyl)amides having from 1 to 10
 carbon atoms;
 b) a polyalkylaluminoxane in which the alkyl group contains from 1 to 8
 carbon atoms, preferably MAO;
 c) aluminum trifluoride.
 The use of component (c) in the catalytic mixture of the present invention
 allows, as shown hereafter, higher conversions to be obtained (even higher
 than 100%) under the same reactions conditions, with respect to the
 mixture without this component, or a reduction in the absolute quantity of
 component (b) to reach a specific conversion.
 The compounds having general formula (I) are products known in literature
 and described in "Progress in Polymer Science" vol. 21, page 47, 1996.
 Typical examples of titanium complexes having formula (I), particularly
 suitable for the present invention are: CpTiCl.sub.3 ;
 CpTi(OCH.sub.3).sub.3 ; CpTi(OC.sub.2 H.sub.5).sub.3 ; CpTi(OC.sub.3
 H.sub.7).sub.3 ; CpTi(Oi--C.sub.3 H.sub.7).sub.3 ; CpTi(OC.sub.4
 H.sub.9).sub.3 ; [Cp(CH.sub.3).sub.5 ]TiCl.sub.3 ; [Cp(CH.sub.3).sub.5
 ]TiBr.sub.3 ; [Cp(CH.sub.3).sub.5 ]TiF.sub.3 ; CpTi(OC.sub.5
 H.sub.6).sub.3 ; [Cp(CH.sub.3).sub.5 ]Ti(OCH.sub.3).sub.3 ;
 [Cp(CH.sub.3).sub.5 ]Ti(OC.sub.2 H.sub.5).sub.3 ; [Cp(CH.sub.3).sub.5
 ]Ti(OC.sub.3 H.sub.7).sub.3 ; [Cp(CH.sub.3).sub.5 ]Ti(OC.sub.4
 H.sub.9).sub.3 ; [Cp(CH.sub.3).sub.5 ]Ti(OC.sub.5 H.sub.6).sub.3 ;
 CpTiH.sub.3 ; CpTi(CH.sub.3).sub.3 ; CpTi(C.sub.2 H.sub.5); CpTi(CH.sub.2
 C.sub.5 H.sub.6).sub.3 ; [Cp(CH.sub.3).sub.5 ]TiH.sub.3 ;
 [Cp(CH.sub.3).sub.5 ]Ti(CH.sub.3).sub.3 ; [Cp(CH.sub.3).sub.5 ]Ti(C.sub.2
 H.sub.5).sub.3 ; [Cp(CH.sub.3).sub.5 ]Ti(CH.sub.2 C.sub.5 H.sub.6).sub.3 ;
 CpTi(OPh).sub.3 ; [Cp(CH.sub.3).sub.5 ]Ti(OPh).sub.3. Particularly
 preferred are the complexes in which the cyclopentadienyl group is
 pentamethyl substituted.
 The compounds of titanium having general formula (I) are added to the
 polymerization mixture in such a quantity that the molar ratio
 vinylaromatic monomer/Ti is between 10,000 and 1,000,000, preferably
 between 100,000 and 500,000.
 The polyalkylaluminoxane (cocatalyst) essentially consists of mixtures of
 products having a linear, cyclic or caged structure. In the first case the
 structure is represented by general formula (II):
 ##STR1##
 whereas in the second case by general formula (III):
 ##STR2##
 wherein m represents an integer between 1 and 40 and R' is a C.sub.1
 -C.sub.8 alkyl radical, for example it is preferably a methyl. The caged
 structure is described in Molecular Symposium, Vol 97, 1995.
 Polyalkylaluminoxanes are known in literature and described, for example,
 in published European patent applications 272.584 and 421.659 or in U.S.
 Pat. No. 4,978,730.
 The cocatalyst can be treated at a temperature ranging from 20 to
 80.degree. C. under vacuum for at least an hour, and can then be added to
 the polymerization mixture as such or in the form of a solution in a
 suitable solvent, for example toluene.
 The cocatalyst is generally used in such quantities that the molar ratio
 aluminum/Ti is between 50 and 5,000.
 According to the process of the present invention, the catalytic system
 described above may optionally also comprise an aluminum alkyl in which
 the alkyl group contains from 1 to 6 carbon atoms, for example aluminum
 trimethyl, aluminum triethyl, aluminum triisobutyl, etc. so as to
 substitute a part of cocatalyst corresponding to a percentage varying from
 0 to 75% in moles.
 The catalytic composition of the present invention also comprises aluminum
 trifluoride in such a quantity that the ratio between the moles of
 polyalkylaluminoxane (b), or the sum of polyalkylaluminoxane moles and the
 possible aluminum alkyl, and moles of aluminum fluoride is between 15 and
 1.
 The aluminum fluoride can be used as such or complexed with water
 (trifluoride hydrate) or with linear or cyclic ethers such as, for
 example, diethylether, tetrahydrofuran, dioxane or dimethoxyethane, with
 ketones such as acetone or methylethylketone, esters such as ethylacetate
 or ethylbenzoate, etc. Aluminum trifluoride hydrate is preferred.
 The term "vinylaromatic polymers" as used in the present description and
 claims essentially refers to polymers of styrene and derivatives of
 styrene and the relative copolymers containing up to 20% in moles of
 another copolymerizable monomer selected from those having general formula
 (IV):
EQU CH.sub.2.dbd.CH--R" (IV)
 wherein R" represents a hydrogen atom or a C.sub.1 -C.sub.6 alkyl radical
 or a C.sub.4 -C.sub.12 cycloalkyl radical.
 Derivatives of styrene comprise styrene alkyls, in which the alkyl group
 contains from 1 to 4 carbon atoms, halogenated styrenes, C.sub.1 -C.sub.4
 alkoxy styrenes, carboxy styrenes, vinylnaphthalenes, such as alpha- or
 beta-vinyl naphthalene, vinyl tetrahydro naphthalene such as
 1,2,3,4-tetrahydro-6-vinyl naphthalene, etc. Typical examples of
 substituted styrenes are p-methyl-styrene, m-methylstyrene, alone or mixed
 with each other, ethylstyrene, butylstyrene, p-ter-butylstyrene,
 dimethylstyrene, chlorostyrene, bromostyrene, fluorostyrene,
 chloromethylstyrene, methoxystyrene, acetoxy methylstyrene, etc.
 The polymerization reaction can be carried out in mass or in a solvent. In
 the latter case the solvent may consist of aliphatic or aromatic
 hydrocarbons or their mixtures and is used in such quantities that the
 volume ratio solvent/monomers is between 0 and 10. The preferred solvent
 is toluene.
 More specifically, according to the general procedure adopted for this type
 of reaction, the vinylaromatic monomers are subjected, before
 polymerization, to treatment for eliminating catalytic poisons such as
 phenolic stabilizers, water, phenylacetylene, consisting in distillation,
 passage on columns containing activated molecular sieves or activated
 alumina, etc. The monomers and, optionally, the solvent are charged into
 the reaction apparatus together with the possible aluminum alkyl and
 cocatalyst. After a time varying from 5 seconds to 30 minutes, the
 catalytic system is then added, preferably in the form of a solution. The
 reaction proceeds for times ranging from 15 minutes to 10 hours at
 temperatures varying from 20 to 100.degree. C. At the end, the polymer
 obtained is recovered with the traditional methods.
 Some illustrative but non-limiting examples are provided for a better
 understanding of the present invention and for its embodiment.
 Analysis procedures:
 The percentage of syndiotactic polymer is determined by extracting the
 polymer with acetone or methylethylketone (MEK) at boiling point for 10-20
 hours.
 The degree of stereoregularity is determined by means of nuclear magnetic
 resonance spectroscopy of carbon 13 as described in U.S. Pat. No.
 4,680,353.

EXAMPLE 1
 20 ml of styrene (0.175 moles) purified by passage on a basic alumina
 column, 0.84 ml of a 1.57 M solution of MAO in toluene
 (1.31.times.10.sup.-3 moles), 20 mg of aluminum trifluoride trihydrate
 (1.45.times.10.sup.-4 moles) and 0.15 ml of an 0.01M solution of
 Cp.TiCl.sub.3 in toluene (1.5.times.10.sup.-6 moles) were charged into a
 tailed test-tube under an inert atmosphere.
 The reaction was carried out for 2 hours at 90.degree. C. At the end, the
 mixture was suspended in 200 ml of methanol acidified with 0.5 ml of
 concentrated HCl. The solid obtained was filtered, washed with ethanol and
 dried in an oven at 70.degree. C. 9.402 g of polymeric product were
 obtained (yield 51.7%).
 2.859 g of polymer were extracted with methylethylketone at boiling point
 for 8 hours, producing 2.578 g of syndiotactic polystyrene (insoluble
 fraction of 90.2%, syndiotactic polystyrene yield: 46.6%) with
 stereoregularity of 99.9% and with a weight average molecular weight Mw of
 468,000.
 COMATIVE EXAMPLE 1
 13.7 ml of styrene (0.12 moles) purified by passage on a basic alumina
 column, 0.57 ml of a 1.57M solution of MAO in toluene (8.8.times.10.sup.-4
 moles) and 0.1 ml of an 0.01M solution of Cp.TiCl.sub.3 in toluene
 (1.0.times.10.sup.-6 moles) were charged into a tailed test-tube under an
 inert atmosphere.
 The reaction was carried out for 2 hours at 90.degree. C. At the end, the
 mixture was suspended in 200 ml of methanol acidified with 0.5 ml of
 concentrated HCl. The solid obtained was filtered, washed with ethanol and
 dried in an oven at 70.degree. C. 5.020 g of polymeric product were
 obtained (yield 40.3%).
 2.581 g of polymer were extracted with methylethylketone at boiling point
 for 8 hours, producing 2.374 g of syndiotactic polystyrene (insoluble
 fraction of 92%, syndiotactic polystyrene yield: 37.1%) with
 stereoregularity of 99.9% and with a weight average molecular weight Mw of
 619,000.
 COMATIVE EXAMPLE 2
 20 ml of styrene (0.175 moles) purified by passage on a basic alumina
 column, 0.84 ml of a 1.57M solution of MAO in toluene
 (1.32.times.10.sup.-3 moles), 18 mg of sodium fluoride
 (4.3.times.10.sup.-4 moles) and 0.15 ml of an 0.01M solution of
 Cp.TiCl.sub.3 in toluene (1.5.times.10.sup.-6 moles) were charged into a
 tailed test-tube under an inert atmosphere.
 The reaction was carried out for 2 hours at 90.degree. C. At the end, the
 mixture was suspended in 200 ml of methanol acidified with 0.5 ml of
 concentrated HCl. The solid obtained was filtered, washed with ethanol and
 dried in an oven at 70.degree. C. 467 mg of polymeric product were
 obtained (yield 2.6%) which was not analyzed further.
 Comparative example 2 shows that it is not sufficient to have any fluoride
 to obtain an improvement in the catalytic activity.
 COMATIVE EXAMPLE 3
 13.7 ml of styrene (0.12 moles) purified by passage on a basic alumina
 column, 0.57 ml of a 1.57M solution of MAO in toluene (8.8.times.10.sup.-3
 moles), 25 mg of calcium sulfate dihydrate (1.45.times.10.sup.-4 moles)
 and 0.1 ml of an 0.01M solution of Cp.TiCl.sub.3 in toluene
 (1.0.times.10.sup.-6 moles) were charged into a tailed test-tube under an
 inert atmosphere.
 The reaction was carried out for 2 hours at 90.degree. C. At the end, the
 mixture was suspended in 200 ml of methanol acidified with 0.5 ml of
 concentrated HCl. The solid obtained was filtered, washed with ethanol and
 dried in an oven at 70.degree. C. 1.622 g of polymeric product were
 obtained (yield 13%) which was not analyzed further.
 COMATIVE EXAMPLE 4
 20 ml of styrene (0.175 moles) purified by passage on a basic alumina
 column, 0.84 ml of a 1.57M solution of MAO in toluene
 (1.31.times.10.sup.-3 moles), 61 mg of ytterbium acetate tetrahydrate
 (1.45.times.10.sup.-4 moles) and 0.15 ml of an 0.01M solution of
 Cp.TiCl.sub.3 in toluene (1.5.times.10.sup.-6 moles) were charged into a
 tailed test-tube under an inert atmosphere.
 The reaction was carried out for 2 hours at 90.degree. C. At the end, the
 mixture was suspended in 200 ml of methanol acidified with 0.5 ml of
 concentrated HCl. The solid obtained was filtered, washed with ethanol and
 dried in an oven at 70.degree. C. 2.176 g of polymeric product were
 obtained (yield 12%) which was not analyzed further.
 Comparative examples 3 and 4 show that the activator component is not
 represented by complexation water of aluminum fluoride and that any salt
 hydrate is therefore not sufficient to obtain improvements (on the
 contrary, there are deteriorations).
 EXAMPLE 2
 20 ml of styrene (0.175 moles) purified by passage on a basic alumina
 column, 0.42 ml of a 1.57M solution of MAO in toluene
 (6.59.times.10.sup.-4 moles), 10 mg of aluminum trifluoride trihydrate
 (7.24.times.10.sup.-5 moles) and 0.15 ml of an 0.01M solution of
 Cp.TiCl.sub.3 in toluene (1.5.times.10.sup.-6 moles) were charged into a
 tailed test-tube under an inert atmosphere.
 20 The reaction was carried out for 2 hours at 90.degree. C. At the end,
 the mixture was suspended in 200 ml of methanol acidified with 0.5 ml of
 concentrated HCl. The solid obtained was filtered, washed with ethanol and
 dried in an oven at 70.degree. C. 7.546 g of polymeric product were
 obtained (yield 41.5%).
 2.092 g of polymer were extracted with methylethylketone at boiling point
 for 8 hours, producing 1.942 g of syndiotactic polystyrene (insoluble
 fraction of 92.8%, syndiotactic polystyrene yield: 38.5%) with
 stereoregularity of 99.9% and with Mw of 546,000.
 EXAMPLE 3
 22.9 ml of styrene (0.2 moles) purified by passage on a basic alumina
 column, 0.57 ml of a 1.57M solution of MAO in toluene
 (8.95.times.10.sup.-4 moles), 14 mg of aluminum trifluoride trihydrate
 (1.01.times.10.sup.-4 moles) and 0.1 ml of an 0.01M solution of
 Cp.TiCl.sub.3 in toluene (1.0.times.10.sup.-6 moles) were charged into a
 tailed test-tube under an inert atmosphere.
 The reaction was carried out for 2 hours at 90.degree. C. At the end, the
 mixture was suspended in 200 ml of methanol acidified with 0.5 ml of
 concentrated HCl. The solid obtained was filtered, washed with ethanol and
 dried in an oven at 70.degree. C. 5.320 g of polymeric product were
 obtained (yield 25.6%).
 20 3.070 g of polymer were extracted with methylethylketone at boiling
 point for 8 hours, producing 2.800 g of syndiotactic polystyrene
 (insoluble fraction of 91.2%, syndiotactic polystyrene yield: 23.3%) with
 stereoregularity of 99.9% and with Mw of 493,000.
 EXAMPLE 4
 20 ml of styrene (0.175 moles) purified by passage on a basic alumina
 column, 0.22 ml of a 1.57M solution of MAO in toluene
 (3.45.times.10.sup.-4 moles), 20 mg of aluminum trifluoride trihydrate
 (1.45.times.10.sup.-4 moles), 0.35 ml of a 1M solution of aluminum
 triisobutyl in toluene (3.5.times.10.sup.-4 moles) and 0.12 ml of an 0.01M
 solution of Cp.TiCl.sub.3 in toluene (1.2.times.10.sup.-6 moles) were
 charged into a tailed test-tube under an inert atmosphere.
 The reaction was carried out for 2 hours at 90.degree. C. At the end, the
 mixture was suspended in 200 ml of methanol acidified with 0.5 ml of
 concentrated HCl. The solid obtained was filtered, washed with ethanol and
 dried in an oven at 70.degree. C. 9.261 g of polymeric product were
 obtained (yield 50.1%).
 3.800 g of polymer were extracted with methylethylketone at boiling point
 for 8 hours, producing 3.523 g of syndiotactic polystyrene (insoluble
 fraction of 92.7%, syndiotactic polystyrene yield: 46.4%) with
 stereoregularity of 99.9% and with Mw of 368,000.
 COMATIVE EXAMPLE 5
 17.2 ml of styrene (0.15 moles) purified by passage on a basic alumina
 column, 0.19 ml of a 1.57M solution of MAO in toluene (3.times.10.sup.-4
 moles), 0.3 ml of a 1M solution of aluminum triisobutyl in toluene
 (3.times.10.sup.-4 moles) and 0.1 ml of an 0.01M solution of Cp.TiCl.sub.3
 in toluene (1.0.times.10.sup.-6 moles) were charged into a tailed
 test-tube under an inert atmosphere.
 The reaction was carried out for 2 hours at 90.degree. C. At the end, the
 mixture was suspended in 200 ml of methanol acidified with 0.5 ml of
 concentrated HCl. The solid obtained was filtered, washed with ethanol and
 dried in an oven at 70.degree. C. 3.759 g of polymeric product were
 obtained (yield 24%).
 2.812 g of polymer were extracted with methylethylketone at boiling point
 for 8 hours, producing 2.609 g of syndiotactic polystyrene (insoluble
 fraction of 92.9%, syndiotactic polystyrene yield: 22.3%).
 EXAMPLE 5
 17.2 ml of styrene (0.15 moles) purified by passage on a basic alumina
 column, 0.19 ml of a 1.57M solution of MAO in toluene (3.times.10-4
 moles), 14 mg of aluminum trifluoride trihydrate (1.0.times.10.sup.-4
 moles), 0.1 ml of a 1M solution of aluminum triisobutyl in toluene
 (1.0.times.10.sup.-4 moles) and 0.1 ml of an 0.01M solution of
 Cp.TiCl.sub.3 in toluene (1.0.times.10.sup.-6 moles) were charged into a
 tailed test-tube under an inert atmosphere.
 The reaction was carried out for 2 hours at 90.degree. C. At the end, the
 mixture was suspended in 200 ml of methanol acidified with 0.5 ml of
 concentrated HCl. The solid obtained was filtered, washed with ethanol and
 dried in an oven at 70.degree. C. 6.327 g of polymeric product were
 obtained (yield 40.5%).
 2.329 g of polymer were extracted with methylethylketone at boiling point
 for 8 hours, producing 2.227 g of syndiotactic polystyrene (insoluble
 fraction of 95.6%, syndiotactic polystyrene yield: 38.7%) with
 stereoregularity of 99.9% and with Mw of 378,000.
 COMATIVE EXAMPLE 6
 17.2 ml of styrene (0.15 moles) purified by passage on a basic alumina
 column, 0.19 ml of a 1.57M solution of MAO in toluene (3.times.10.sup.-4
 moles), 0.1 ml of a 1M solution of aluminum triisobutyl in toluene
 (1.0.times.10.sup.-4 moles) and 0.1 ml of an 0.01M solution of
 Cp.TiCl.sub.3 in toluene (1.0.times.10.sup.-6 moles) were charged into a
 tailed test-tube under an inert atmosphere.
 The reaction was carried out for 2 hours at 90.degree. C.
 At the end, the mixture was suspended in 200 ml of methanol acidified with
 0.5 ml of concentrated HCl. The solid obtained was filtered, washed with
 ethanol and dried in an oven at 70.degree. C. 2.972 g of polymeric product
 were obtained (yield 18.7%).
 2.607 g of polymer were extracted with methylethylketone at boiling point
 for 8 hours, producing 2.434 g of syndiotactic polystyrene (insoluble
 fraction of 93.4%, syndiotactic polystyrene yield: 17.5%).
 EXAMPLE 6
 17.2 ml of styrene (0.15 moles) purified by passage on a basic alumina
 column, 0.13 ml of a 1.57M solution of MAO in toluene (2.times.10.sup.-4
 moles), 14 mg of aluminum trifluoride trihydrate (1.0.times.10.sup.-4
 moles), 0.1 ml of a 1M solution of aluminum triisobutyl in toluene
 (1.0.times.10.sup.-4 moles) and 0.1 ml of an 0.01M solution of
 Cp.TiCl.sub.3 in toluene (1.0.times.10.sup.-6 moles) were charged into a
 tailed test-tube under an inert atmosphere.
 The reaction was carried out for 2 hours at 90.degree. C. At the end, the
 mixture was suspended in 200 ml of methanol acidified with 0.5 ml of
 concentrated HCl. The solid obtained was filtered, washed with ethanol and
 dried in an oven at 70.degree. C. 6.001 g of polymeric product were
 obtained (yield 38.4%).
 2.474 g of polymer were extracted with methylethylketone at boiling point
 for 8 hours, producing 2.259 g of syndiotactic polystyrene (insoluble
 fraction of 91.3%, syndiotactic polystyrene yield: 35.1%) with
 stereoregularity of 99.9% and with Mw of 416,000.
 EXAMPLE 7
 17.2 ml of styrene (0.15 moles) purified by passage on a basic alumina
 column, 0.1 ml of a 1.57M solution of MAO in toluene (1.57.times.10.sup.-4
 moles), 14 mg of aluminum trifluoride trihydrate (1.0.times.10.sup.-4
 moles), 0.1 ml of a 1M solution of aluminum triisobutyl in toluene
 (1.0.times.10.sup.-4 moles) and 0.1 ml of an 0.01M solution of
 Cp.TiCl.sub.3 in toluene (1.0.times.10.sup.-6 moles) were charged into a
 tailed test-tube under an inert atmosphere.
 EXAMPLE 8
 13.3 ml of styrene (0.116 moles) purified by passage on a basic alumina
 column, 0.56 ml of a 1.57M solution of MAO in toluene
 (8.73.times.10.sup.-4 moles), 13 mg of aluminum trifluoride trihydrate
 (9.6.times.10.sup.-5 moles) and 0.1 ml of an 0.01M solution of
 Cp.TiCl.sub.3 in toluene (1.0.times.10.sup.-6 moles) were charged into a
 tailed test-tube under an inert atmosphere.
 The reaction was carried out for 30 minutes at 90.degree. C. At the end,
 the mixture was suspended in 200 ml of methanol acidified with 0.5 ml of
 concentrated HCl. The solid obtained was filtered, washed with ethanol and
 dried in an oven at 70.degree. C. 1.603 g of polymeric product were
 obtained (yield 13.2%).
 1.007 g of polymer were extracted with methylethylketone at boiling point
 for 8 hours, producing 946 mg of syndiotactic polystyrene (insoluble
 fraction of 94%, syndiotactic polystyrene yield: 12.4%).
 COMATIVE EXAMPLE 7
 13.7 ml of styrene (0.116 moles) purified by passage on a basic alumina
 column, 0.56 ml of a 1.57M solution of MAO in toluene (8.8.times.10.sup.-4
 moles) and 0.1 ml of an 0.01M solution of Cp.TiCl.sub.3 in toluene
 (1.0.times.10.sup.-6 moles) were charged into a tailed test-tube under an
 inert atmosphere.
 The reaction was carried out for 30 minutes at 90.degree. C. At the end,
 the mixture was suspended in 200 ml of methanol acidified with 0.5 ml of
 concentrated HCl. The solid obtained was filtered, washed with ethanol and
 dried in an oven at 70.degree. C. 1.132 g of polymeric product were
 obtained (yield 9.3%).
 660 mg of polymer were extracted with methylethylketone at boiling point
 for 8 hours, producing 610 mg of syndiotactic polystyrene (insoluble
 fraction of 92.5%, syndiotactic polystyrene yield: 8.6%).