DESCRIPTION

The present invention relates to a process for the preparation of 1 ,2 syndiotactic polybutadiene.

More in particular, the present invention relates to a process for the preparation of 1 ,2 syndiotactic polybutadiene comprising polymerizing 1 ,3-butadiene in the presence of a catalytic system comprising: at least one cobalt complex with a phosphine ligand selected from high sterically hindered aromatic phosphines; at least one aluminoxane; said process being carried out at a temperature greater than or equal to 0°C.

it is a further subject matter of the present invention is a cobalt complex with a phosphine ligand selected from high sterically hindered aromatic phosphines having general formula (I) reported below.

It is known that the stereospecific (co)polymerization of conjugated dienes is a very important process in the chemical industry in order to obtain products that are among the most widely used rubbers.

It is also known that among the different polymers that can be obtained from the stereospecific polymerization of 1 ,3-butadiene (i.e. 1 ,4-c/s, ,Λ-trans, 1 ,2 syndiotactic, 1 ,2 isotactic, 1 ,2 atactic, mixed structure 1 ,4-c/ ^' s/1 ,2 having a variable 1 ,2 unit content), only 1 ,4-c/s polybutadiene and 1 ,2 syndiotactic polybutadiene are industrially commercialized products. Further details on said polymers can be found, for example, in: Takeuchi Y. et al., "New Industrial Polymers", "American Chemical Society

Symposium Series" (1974), Vol. 4, pp. 15-25; Halasa A. F. et al., "Kirk-Othmer

Encyclopedia of Chemical Technology" (1989), 4 ^th Ed., Kroschwitz J. I. Ed., John Wiley and Sons, New York, Vol. 8, pp. 1031-1045; Tate D. et al., "Encyclopedia of Polymer Science and Engineering (1989), 2 ^nd Ed., Mark H. F. Ed., John Wiley and Sons, New York, Vol. 2, pp. 537-590; Kerns M. et al., "Butadiene Polymers", in "Encyclopedia of Polymer Science and Technology" (2003), Mark H. F. Ed., Wiley, Vol. 5, pp. 317-356. Generally, 1 ,4-c/s polybutadiene is prepared through polymerization processes that use different catalytic systems comprising catalysts based on titanium (Ti), cobalt (Co), nickel (Ni), neodymium (Nd). Catalytic systems comprising cobalt based catalysts have high catalytic activity and stereospecificity and can be considered the most versatile of those mentioned above since, when their formulation is changed, they are able to provide all the possible stereoisomers of polybutadiene mentioned above, as described, for example, in: Porri L. et al., "Comprehensive Polymer Science" (1989), Eastmond G.C. et al. Eds., Pergamon Press, Oxford, UK, Vol. 4, Part II, pp. 53-108; Thiele S. K. H. et al., "Macromolecular Science. Part C: Polymer Reviews" (2003), C43, pp. 581-628;

Osakada, K. et al., "Advanced Polymer Science" (2004), Vol. 171 , pp. 137-194; Friebe L. et al., "Advanced Polymer Science" (2006), Vol. 204, pp. 1-154.

1 ,2 syndiotactic polybutadiene is a crystalline, not very water soluble, polymer, with a variable melting point, ranging from 200°C to 220°C, according to the degree of syndiotacticity (i.e. the percentage of syndiotactic triads) and, generally, it is used for manufacturing transparent films, tubes, but the main use is that of manufacturing shoe soles.

1 ,2 syndiotactic polybutadiene can be obtained through the polymerization of 1 ,3- butadiene in the presence of different types of catalytic systems as described, for example, in Porri L. et al., "Comprehensive Polymer Science" (1989), Eastmond G.C. et al. Eds., Pergamon Press, Oxford, UK, Vol. 4, Part II, pp. 53-108, reported above.

Among said catalytic systems, the following ones can be mentioned: catalytic systems comprising titanium complexes [e.g., AI(R)3-Ti(OR)4, polymerization carried out in heptane, at 0°C-15°C)] as described, for example, in Natta G. et al., in Italian patent application IT 538453; catalytic systems comprising vanadium complexes [e.g., AIEt3- V(acac)3, polymerization carried out in benzene at 15°C] as described, for example, in Natta G. et al., "La Chimica e I'lndust a" (1959), Year 41 , pp. 526; catalytic systems comprising molybdenum complexes (e.g., AIR3-Mo(acac)3, polymerization in benzene at 15°C) as described, for example, in Porri L. et al., "Comprehensive Polymer Science" (1989), Eastmond G.C. et al. Eds., Pergamon Press, Oxford, UK, Vol. 4, Part II, pp. 53- 108, reported above; catalytic systems comprising chromium complexes [e.g.,

Cr(CNPh)6-AIEt3 with a low Al/Cr ratio, polymerization carried out in benzene, at 15°C] as described, for example, in Natta G. et al., "La Chimica e I'lndustria" (1959), Year 41 , pp. 1163; catalytic systems comprising chromium complexes [e.g., CrCl2(dmpe)2-MAO] as described, for example, in Ricci G. et al., "Macromolecules" (2001), Vol. 34(17), pp. 5766-5769.

Catalytic systems comprising cobalt complexes are however those that have up to now permitted 1 ,2 syndiotactic polybutadiene with higher stereoregularity to be obtained, at the same time also allowing the maximum level of catalytic activity.

For example, 1 ,2 syndiotactic polybutadiene with high crystallinity having a 1 ,2 unit content equal to 99.7%, a degree of syndiotacticity equal to 99.6% and a melting point of 208°C, was obtained using the catalytic system Co(lll) (acetylacetonate)/triethyl aluminum carbon disulfide [Co(acac)3-AIEt3-CS2] as described, for example, in Ashitaka H. et al., "Journal of Polymer Science Part A: Polymer Chemistry" (1983), Vol. 21 , Issue 6, pp. 1853-1860. Other catalytic systems comprising cobalt and carbon disulfide (CS2) able to produce 1 ,2 syndiotactic polybutadiene with high crystallinity having a 1 ,2 unit content > 99%, a degree of syndiotacticity > 99% and a melting point > 200°C, up to 216°C, are also described in: Ashitaka H. et al., "Journal of Polymer Science Part A: Polymer Chemistry" (1983), Vol. 21 , Issue 7, pp. 1951-1972; Ashitaka H. et al., "Journal of Polymer Science Part A: Polymer Chemistry" (1983), Vol. 21 , Issue 7, pp. 1973-1988; Ashitaka H. et al., "Journal of Polymer Science Part A: Polymer Chemistry" (1983), Vol. 21 , Issue 7, pp. 1989-1995.

The aforementioned catalytic systems comprising cobalt and carbon disulfide (CS2), are by far the most active and stereospecific among those reported for the synthesis of 1 ,2 syndiotactic polybutadiene.

Another very active and stereospecific catalytic system for the preparation 1 ,2 syndiotactic polybutadiene can be obtained from the combination of the cobalt allyl complex (η ⁴ -θ4Η6)(η ⁵ -ΟδΗΐ3)Οο described, for example, in Natta G. et al., "Chemical Communications" (1967), Issue 24, pp. 1263-1265, with carbon disulfide (CS ₂ ), as described, for example, in Ricci G. et al., "Polymer Communication" (1988), Vol. 29, pp. 305-307. Said cobalt allyl complex alone is able to dimerize 1 ,3-butadiene at ambient temperature as described, for example, in american patent US 5,879,805, but is also able to provide 1 ,2 syndiotactic polybutadiene operating only at low temperatures (- 30°C) as described, for example, in Ricci G. et al., "Polymer Communication" (1988), Vol. 29, pp. 305-307, reported above.

Polybutadienes with a 1 ,2 syndiotactic or mixed c/s-1 ,4/1 ,2 structure having the 1 ,4-c/s and 1 ,2 units with a random distribution along the polymer chain, can also be produced using the catalytic systems obtained through the combination of cobalt dichloride (C0CI2) or cobalt dibromide (CoBr2) with organic aluminum compounds (e.g., alkylaluminum compounds or aluminoxanes), in the presence of phosphines (e.g., triphenylphosphine) as described, for example, in the following american patents: US 5,879,805, US

4,324,939, US 3,966,697, US 4,285,833, US 3,498,963, US 3,522,332, US 4, 182,813, US 5,548,045, US 7,009,013.

Further details related to the polymerization of 1 ,3-butadiene with catalytic systems comprising preformed cobalt complexes with different phosphines, are reported, for example, in Italian patents IT 1 ,349, 141 , IT 1 ,349, 142, IT 1 ,349, 143, and in international patent application WO 2003/018649. The use of different phosphines comes from the fact that it is well known how the steric and electronic properties of phosphines depend strongly on the type of substituents on the phosphorus atom as described, for example, in: Dierkes P. et al., "Journal of Chemical Society, Dalton Transactions" (1999), pp.

1519-1530; van Leeuwen P. et al., "Chemical Reviews" (2000), Vol. 100, pp. 2741-2769; Freixa Z. et al., "Dalton Transactions" (2003), pp. 1890-1901 ; Tolman C, "Chemical Reviews" (1977), Vol. 77, pp. 313-348.

The documents related to the use phosphines reported above, show how the use of preformed cobalt phosphine complexes in combination with methylaluminoxane (MAO) is able to allow the microstructure of polybutadiene to be managed so as to obtain polybutadienes with a different structure according to the type of phosphine coordinated to the cobalt atom.

The stereospecific polymerization of 1 ,3-butadiene with catalytic systems comprising cobalt complexes with hindered monodentate aliphatic phosphines (e.g., P¾U3, P'Pr3, P¾u ₂ 'Pr, P'BuaMe, P'Bu ₂ Cy, P'BuCy ₂ , PCy ₃ , PCyp ₃ wherein P = phosphorus, ¾u = tert- butyl, 'Pr = / ^' so-propyl, Cy = cyclohexyl and Cyp = cyclopentyl), provides polybutadienes with a prevalently 1 ,4-c/s structure, whereas polybutadienes having a mixed 1 ,4-c/ ^' s/1 ,2 structure were obtained using catalytic systems comprising cobalt complexes with less sterically-hindered phosphines (e.g., PCy2H; P¾U2H ; PEt3; P"Pr3 wherein P =

phosphorus, Cy = cyclohexyl, ¾u = te/f-butyl, Et = ethyl and "Pr = n-propyl), as described, for example, in international patent application WO 2003/1018649. Polybutadienes with a high 1 ,4-c/s unit content (≥ 96%) were obtained with catalytic systems comprising cobalt complexes with bidentate phosphines [e.g.,

CoCI ₂ [R2P(CH ₂ )nPR2]/MAO, wherein Co = cobalt, CI = chlorine, R = methyl, ethyl, phenyl, n = 1 or 2, P = phosphorus and MAO = methylaluminoxane), regardless of the type of bidentate phosphine coordinated with the cobalt atom as described, for example, in Ricci G. et al., "Coordination Chemistry Reviews" (2010), Vol. 254, pp. 661-676; Ricci G. et al., "Cobalt: Characteristics, Compounds, and Applications" (201 1), Lucas J. Vidmar Ed., Nova Science Publisher, Inc., USA, pp. 39-81.

Catalytic systems comprising cobalt complexes with ligands selected from aromatic phosphines [e.g., CoCI ₂ (PRPh ₂ )2/MAO (wherein Co = cobalt, CI = chloride, P = phosphorus, R = methyl, n-propyl, ethyl, / ^' so-propyl, cyclohexyl, Ph = phenyl, MAO = methylaluminoxane] have instead been shown to be extremely active for the 1 ,2 polymerization of 1 ,3-butadiene as described, for example, in Italian patents IT

1 ,349, 142, IT 1 ,349, 143. In fact, using said catalytic systems, polybutadienes were obtained with an essentially 1 ,2 structure (in a range ranging from 70% to 90%), having a variable 1 ,2 unit content as a function of the type of complex and of the polymerization conditions. It has also been seen that the tacticity of the polybutadienes obtained depends strongly on the type of complex, i.e. the type of phosphine bonded to the cobalt atom, and that the syndiotacticity index, expressed as the content (i.e.

percentage) of syndiotactic triads [(rr) %], determined by the ¹³ C-NMR spectra, increases as the steric demand of the alkyl group bonded to the phosphorus atom increases.

The 1 ,2 polybutadienes obtained with the cobalt systems with less sterically hindered phosphines (e.g., PMePh ₂ ; PEtPh ₂ ; P"PrPh ₂ wherein P = phosphorus, Me = methyl, Et = ethyl, Ph = phenyl, "Pr = n-propyl) had a lower crystallinity and a syndiotactic triad content [(rr) %] ranging from 20% to 50%, whereas the polybutadienes obtained with catalytic systems that use more sterically hindered phosphines (e.g., P'PrP fc, PCyPh2 wherein P = phosphorus, 'Pr = / ^' so-propyl, Ph = phenyl, Cy = cyclohexyl) were crystalline, with a melting point (T _m ) ranging from 100°C to 164°C and a syndiotactic triad content [(/T) %] ranging from 60% to 88%, according to the polymerization conditions: in particular, polybutadienes with a melting point (T _m ) > 150°C and syndiotactic triad content [(n) %] > 85% were obtained only operating at a temperature of -30°C, a temperature that cannot be used in industrial processing plants.

The polymerization of 1 ,3-butadiene with catalytic systems comprising cobalt complexes with aromatic phosphines having formula CoCl2(P 2Ph)2/MAO (wherein Co = cobalt, CI = chlorine, R = methyl, ethyl, cyclohexyl, Ph = phenyl, MAO = methylaluminoxane) has also been studied as described, for example, in Italian patents IT 1 ,349, 141 , IT

1 ,349, 142. Using said catalytic systems, essentially 1 ,2 polybutadienes were obtained, but the syndiotactic index of the polymers, under the same polymerization conditions, was slightly lower than that of the 1 ,2 polybutadienes obtained with catalytic systems comprising cobalt complexes with aromatic phosphines having formula

CoCl2(P Ph2)2 MAO described above: in fact, the syndiotactic triad content [(n) %] is ranging from 15% to 45%.

As 1 ,2 syndiotactic polybutadiene can be advantageously used in different sectors such as, for example, in the footwear industry, in particular for the production of shoe soles, the study of new processes able to provide said polybutadiene is still of great interest. The Applicant therefore set out to solve the problem of finding a new process able to provide 1 ,2 syndiotactic polybutadiene having a 1 ,2 unit content greater than or equal to 80%, a syndiotactic triad content [(n) %] greater than or equal to 76%, and a melting point greater than or equal to 139°C. In particular, the Applicant set out to find a new process able to provide 1 ,2 syndiotactic polybutadiene having the aforementioned characteristics that can be advantageously carried out in industrial processes.

The Applicant has now found a process for the preparation of 1 ,2 syndiotactic polybutadiene comprising polymerizing 1 ,3-butadiene in the presence of a catalytic system comprising: at least one cobalt complex with a phosphine ligand selected from high sterically hindered aromatic phosphines having the specific general formula (I) reported below; at least one aluminoxane; said process being carried out at a

temperature greater than or equal to 0°C. Operating at a temperature greater than or equal to 0°C, therefore at a temperature that can be used in industrial processing plants, the use of said catalytic system makes it possible to obtain a 1 ,2 syndiotactic

polybutadiene having the following characteristics: a 1 ,2 unit content greater than or equal to 80%, a syndiotactic triad content [(rr) %] greater than or equal to 76%, and a melting point greater than or equal to 139°C. Thanks to these characteristics, the 1 ,2 syndiotactic polybutadiene obtained can be advantageously used in different sectors such as, for example, in the footwear industry, in particular for the production of shoe soles.

Therefore, the present invention relates to a process for the preparation of 1 ,2 syndiotactic polybutadiene which comprises polymerizing 1 ,3-butadiene in the presence of a catalytic system comprising:

at least one cobalt complex with a phosphine ligand having general formula (I):

wherein:

Ri , R2 and R3, mutually identical or different, are selected from branched C4-C20 alkyi groups, preferably C4-C15, C6-C30 cycloalkyl groups, preferably Ce-Cis, said cycloalkyl groups being substituted, C6-C30 aryl groups, preferably Ce-Cis, optionally substituted;

provided that at least two of Ri , R2 and R3, are selected from C6-C30 aryl groups, preferably Ce-Cis, optionally substituted

Xi and X2, mutually identical or different, represent a halogen atom such as, for example, chlorine, bromine, iodine;

at least one aluminoxane having general formula (I I) :

(R4)2-AI-0-[-AI(R ₅ )-0-] _m -AI-(R ₆ )2 (I I)

wherein R ₄ , R5 and R6, mutually identical or different, represent a hydrogen atom or a halogen atom such as, for example, chlorine, bromine, iodine, fluorine; or are selected from linear or branched C1-C20 alkyi groups, cycloalkyl groups, aryl groups, said groups being optionally substituted with one or more silicon or germanium atoms; and m is an integer ranging from 0 to 1000;

said process being carried out at a temperature ranging from 0°C to +60°C, preferably ranging from 0°C to +30°C.

For the purpose of the present description and of the following claims, the definitions of the numeric ranges always include the extremes unless specified otherwise.

For the purpose of the present description and of the following claims, the term

"comprising" also includes the terms "which essentially consists of" or "which consists of".

For the purpose of the present description and of the following claims, the term "C ₄ -C2o alkyi groups" means branched alkyi groups having from 4 to 20 carbon atoms. Specific examples of branched C4-C20 alkyl groups are: te/f-butyl, te/f-pentyl, / ^' so-pentyl, 3- ethylpent-3-yl, 3-methyl-pent-3-yl.

For the purpose of the present description and of the following claims, the term "C6-C30 cycloalkyl groups" and "said cycloalkyl groups being substituted" means cycloalkyl groups having from 6 to 30 carbon atoms, substituted with one or more groups, mutually identical or different, selected from: C1-C12 alkyl groups; C1-C12 alkoxyl groups. Specific examples of cycloalkyl groups are: hexamethylcyclohexyl, 2-/ ^' so-propyl-5-methyl- cyclohexyl (neomenthyl), pentamethylcyclopentyl, 2-cyclooctylethyl, methylcyclohexyl, m eth oxy cy cl o h exy I , phenyl cy cl oh exy I .

For the purpose of the present description and of the following claims, the term "C6-C30 aryl groups" means carbocyclic aromatic groups having from 6 to 30 carbon atoms. Said aryl groups can also be optionally substituted with one or more groups, mutually identical or different, selected from: C1-C12 alkyl groups; C1-C12 alkoxy groups. Specific examples of aryl groups are: phenyl, 2-methylphenyl, 4-methylphenyl, 2- tert- butylphenyl, 2,4,6-trimethylphenyl, 2-/ ^' so-propyl phenyl, methoxyphenyl, 1 , 1- diphenylethyl, phenyloxyphenyl, naphthyl, phenylnaphthyl, phenanthrene, anthracene. In accordance with a preferred embodiment of the present invention, in said cobalt complex with a phosphine ligand having general formula (I):

Ri is selected from branched C4-C20 alkyl groups, preferably C4-C15, or from C6-C30 cycloalkyl groups, preferably Ce-Cis, said cycloalkyl groups being substituted; preferably is a terf-butyl group or a 2-/ ^' so-propyl-5-methyl-cyclohexyl (neomenthyl); R2 and R3, mutually identical, are selected from C6-C30 aryl groups, preferably C6- Ci5, optionally substituted; preferably they represent a phenyl group;

Xi and X2, mutually identical, represent a halogen atom such as, for example, chlorine, bromine, iodine; preferably they represent a chlorine atom; Further details on said cobalt complex with a phosphine ligand having general formula (I), as well as to its preparation, can be found in the following documents, whose contents are incorporated herein for reference purposes: international patent application WO 2003/018649; Italian patents IT 1 ,349, 143, IT 1 ,349, 142; Ricci G. et al., "Journal of Molecular Catalysis A: Chemical" (2005), Vol. 226, pp. 235-241 ; Ricci G. et al.,

"Macromolecules" (2005), Vol. 38, pp. 1064-1070; Ricci G. et al., "Journal of

Organometallic Chemistry" (2005), Vol. 690, pp. 1845-1854; Ricci G. et al., "Advanced in Organometallic Chemistry Research" (2007), K. Yamamoto Ed., Nova Science

Publisher, Inc. USA, pp. 1-36; Ricci G. et al., "Coordination Chemistry Reviews" (2010), Vol. 254, pp. 661-676; Ricci G. et al., "Cobalt: Characteristics, Compounds, and

Applications" (201 1), Lucas J. Vidmar Ed., Nova Science Publisher, Inc., USA, pp. 39- 81 ; Ricci G. et al., "Phosphorus: Properties, Health effects and the Environment' (2012), Ming Yue Chen and Da-Xia Yang Eds., Nova Science Publisher, Inc., USA, pp. 53-94. The cobalt complex with a phosphine ligand having general formula (I) can be considered, in accordance with the present invention, under any physical form such as, for example, the isolated and purified solid form, the form solvated with a suitable solvent, or the one supported on suitable organic or inorganic solids, preferably having a granular or powdered physical form.

The cobalt complex with a phosphine ligand having general formula (I) can be prepared according to processes known in the prior art. For example, said cobalt complex with a phosphine ligand having general formula (I) can be prepared by reaction between cobalt compounds having general formula Co(X)2 wherein X is a halogen atom such as, for example, chlorine, bromine, iodine, preferably chlorine, as such or complexed with ethers [for example, diethylether, tetrahydrofuran (THF), dimethoxyethane], with phosphines such as, for example, te/f-butyldiphenylphosphine (P'BuP ), (S)- (+)neomenthyl diphenylphosphine [(S)-NMDPP], said phosphines being used in stoichiometric quantities, preferably operating in the presence of at least one solvent that can be selected, for example, from: alcohols (for example, ethanol), hydrocarbon solvents (for example, toluene), chlorinated solvents (for example, methylene chloride), ether solvents [for example, tetrahydrofuran (THF)], or mixtures thereof, at a

temperature ranging from ambient temperature to 1 10°C, preferably at ambient temperature. The cobalt complex with a phosphine ligand thus obtained can be subsequently recovered through methods known in the prior art such as, for example, precipitation through a nonsolvent (for example, pentane), followed by separation through filtration or decantation and any subsequent solubilization in a suitable solvent followed by crystallization at a low temperature.

It is also to be noted that, in accordance with the present invention, said cobalt complex with a phosphine ligand having general formula (I), can be prepared in situ, i.e. directly in the polymerization environment. On this point, said cobalt complex with a phosphine ligand having general formula (I), can be prepared by separately introducing the ligand (obtained, for example, in accordance with the description in the documents mentioned above, or commercially available), the cobalt-containing compound [for example, cobalt dichloride (CoC )] and the 1 ,3-butadiene to be polymerized, preselected, operating at the conditions wherein the polymerization is carried out.

For the purpose of the present description and of the following claims the expression "ambient temperature" means a temperature ranging from 20°C to 25°C.

As is known, aluminoxanes are compounds containing AI-O-AI bonds, with a variable O/AI ratio, obtainable according to processes known in the prior art such as, for example, by reaction, in controlled conditions, of an aluminum alkyi or an aluminum alkyi halogenide, with water, or with other compounds containing predetermined quantities of available water such as, for example, in the case of the reaction of aluminum trimethyl with aluminum sulfate hexahydrate, copper sulfate pentahydrate, or iron sulfate pentahydrate.

Said aluminoxanes and, in particular, methylaluminoxane (MAO), are compounds that can be obtained through known organometallic chemical processes such as, for example, by adding trimethyl aluminum to an hexane suspension of aluminum sulfate hexahydrate.

In accordance with a preferred embodiment of the present invention, said aluminoxane having general formula (II) can be selected, for example, from: methylaluminoxane (MAO), ethylaluminoxane, n-butylaluminoxane, tetra-/ ^' so-butylaluminoxane (TIBAO), tert- butylaluminoxane, tetra-(2,4,4-trimethylpentyl)aluminoxane (TIOAO), tetra-(2,3- dimethylbutyl)aluminoxane (TDMBAO), tetra-(2,3,3-trimethylbutyl)aluminoxane

(TTMBAO), or mixtures thereof. Methylaluminoxane (MAO) is particularly preferred. Further details on the aluminoxane having general formula (II) can be found, for example, in international patent application WO 2011/061 151.

In general, the formation of the aforementioned catalytic system is preferably carried out in an inert liquid means, more preferably in a hydrocarbon solvent. The choice of the cobalt complex with a phosphine ligand having general formula (I) and of the

aluminoxane having general formula (II), as well as the particular methodology used, may vary according to the molecular structures and the desired result, according to what is similarly reported in the relevant literature accessible to an expert skilled in the art for other transition metal complexes with ligands of various kinds, such as, for example, in: Ricci G. et al., "/ dvances in Organometallic Chemistry Research" (2007), Yamamoto K. Ed., Nova Science Publisher, Inc., USA, pp. 1-36; Ricci G. et al., "Coordination

Chemistry Reviews" (2010), Vol. 254, pp. 661-676; Ricci G. et al., "Cobalt: Characteristics, Compounds, and Applications" (2011), Lucas J. Vidmar Ed., Nova Science Publisher, Inc., USA, pp. 39-81 ; Ricci G. et al., "Phosphorus: Properties, Health effects and Environment' (2012), Ming Yue Chen and Da-Xia Yang Eds., Nova Science Publisher, Inc., USA, pp. 53-94.

For the purpose of the present invention, the aluminoxane having general formula (II) can be placed in contact with a cobalt complex with a phosphine ligand having general formula (I), in proportions such that the molar ratio between the aluminum present in the aluminoxane having general formula (II) and the cobalt present in the cobalt complex with a phosphine ligand having general formula (I) is ranging from 10 to 1000, preferably ranging from 10 to 100. The sequence with which the cobalt complex with a phosphine ligand having general formula (I) and the aluminoxane having general formula (II) are placed in contact with each other is not particularly critical.

For the purpose of the present description and of the following claims, the terms "mole" and "molar ratio" are used both with reference to compounds consisting of molecules and with reference to atoms and ions, omitting for the latter ones the terms gram atom or atomic ratio, even if they are scientifically more accurate.

For the purpose of the present invention, other additives or components may optionally be added to the aforementioned catalytic system so as to adapt it to satisfy specific practical requirements. The catalytic systems thus obtained can therefore be considered included within the scope of the present invention. Additives and/or components that can be added in the preparation and/or formulation of the aforementioned catalytic system are, for example: inert solvents, such as, for example, aliphatic and/or aromatic hydrocarbons; aliphatic and/or aromatic ethers; weakly coordinating additives (e.g., Lewis bases) selected, for example, from non-polymerizable olefins; sterically hindered or electronically poor ethers; halogenating agents such as, for example, silicon halides, halogenated hydrocarbons, preferably chlorinated; or mixtures thereof.

Said catalytic system can be prepared, as already reported above, according to methods known in the prior art.

For example, said catalytic system can be prepared separately (preformed) and subsequently introduced into the polymerization environment. On this point, said catalytic system can be prepared by reacting at least one cobalt complex with a phosphine ligand having general formula (I) with at least one aluminoxane having general formula (II), optionally in the presence of other additives or components selected from those cited above, in the presence of a solvent such as, for example, toluene, heptane, at a temperature ranging from 20°C to 60°C, for a time ranging from 10 seconds to 10 hours, preferably ranging from 30 seconds to 5 hours.

Alternatively, said catalytic system can be prepared in situ, i.e. directly in the

polymerization environment. On that point, said catalytic system can be prepared by separately introducing the cobalt complex with a phosphine ligand having general formula (I), the aluminoxane having general formula (II) and the 1 ,3-butadiene, operating under the conditions wherein the polymerization is carried out.

Further details on the preparation of said catalytic system can be found in the examples reported below.

For the purpose of the present invention, the aforementioned catalytic system can also be supported on inert solids, preferably consisting of silicon and/or aluminum oxides, such as, for example, silica, alumina or silico-aluminates. For supporting said catalytic system the known supporting techniques can be used, generally comprising contact, in a suitable inert liquid medium, between the support, optionally activated by heating to temperatures over 200°C, and one or both components of said catalytic system. It is not necessary, for the purposes of the present invention, for both components to be supported, since only the cobalt complex with a phosphine ligand having general formula (I), or the aluminoxane having general formula (II) can be present on the support surface. In the latter case, the missing component on the surface is subsequently placed in contact with the supported component when the active catalytic system is to be formed for the polymerization.

The scope of the present invention also includes the cobalt complex with a phosphine ligand having general formula (I), and the catalytic systems based thereon, which are supported on a solid through the functionalization of the latter and the formation of a covalent bond between the solid and the cobalt complex with a phosphine ligand having general formula (I).

The quantity of the cobalt complex with a phosphine ligand having general formula (I) and the aluminoxane having general formula (II) which can be used in the process according to the present invention varies according to the polymerization process to be carried out. As mentioned above, said quantity is however such as to obtain a molar ratio between the aluminum present in the aluminoxane having general formula (II) and the cobalt present in the cobalt complex with a phosphine ligand having general formula (I) ranging from the values stated above.

In accordance with a preferred embodiment of the present invention, said process can be carried out in the presence of at least one inert organic solvent selected, for example, from: saturated aliphatic hydrocarbons such as, for example, butane, pentane, hexane, heptane, or mixtures thereof; saturated cyclo-aliphatic hydrocarbons such as, for example, cyclopentane, cyclohexane, or mixtures thereof; mono-olefins such as, for example, 1-butene, 2-butene, or mixtures thereof; aromatic hydrocarbons such as, for example, benzene, toluene, xylene, or mixtures thereof; halogenated hydrocarbons such as, for example, methylene chloride, chloroform, carbon tetrachloride, trichloroethylene, perchloroethylene, 1 ,2-dichloroethane, chlorobenzene,

bromobenzene, chlorotoluene, or mixtures thereof. Hexane, heptane, toluene are preferred.

In accordance with a preferred embodiment of the present invention, in said process, the concentration of 1 ,3-butadiene in said inert organic solvent can be ranging from 5% by weight to 50% by weight, preferably ranging from 10% by weight to 20% by weight, with respect with the total weight of the mixture of 1 ,3-butadiene and inert organic solvent. With regard to pressure, it is preferable to operate at the pressure of the components of the mixture to be polymerized.

Said process can be carried out both continuously and in batches, preferably

continuously.

The process according to the present invention allows 1 ,2 syndiotactic polybutadiene with the following characteristics to be obtained:

1 ,2 unit content greater than or equal to 80%, preferably ranging from 85% to

95%;

syndiotactic triad content [(/r) %], greater than or equal to 76%, preferably ranging from 79% to 86%;

melting point greater than or equal to 139°C, preferably ranging from 140°C to 165°C;

weight average molecular weight (M _w ) ranging from 100000 gxmol ^"1 to 300000 gxmol ^"1 , preferably ranging from 120000 gxmol ^"1 to 250000 gxmol ^"1 .

As mentioned above, the 1 ,2 syndiotactic polybutadiene obtained according to the process of the present invention can be advantageously used in different sectors, such as in the footwear industry, in particularly for the production of shoe soles.

It is therefore a further object of the present invention to use the 1 ,2 syndiotactic polybutadiene obtained according to the process described above in the footwear industry, in particular for the production of shoe soles.

As mentioned above, further subject matter of the present invention is a cobalt complex with a phosphine ligand selected from high sterically hindered aromatic phosphines having general formula (I):

wherein:

Ri , R2 and R3, mutually identical or different, are selected from branched C4-C20 alkyl groups, preferably C4-C15, branched, C6-C30 cycloalkyl groups, preferably C6- Ci5, said cycloalkyl groups being substituted, C6-C30 aryl groups, preferably Ce-Cis, optionally substituted;

provided that at least two of Ri , R2 and R3, are selected from C6-C30 aryl groups, preferably Ce-Cis, optionally substituted;

Xi and X2, mutually identical or different, represent a halogen atom such as for example, chlorine, bromine, iodine.

In accordance with a preferred embodiment of the present invention, in said cobalt complex with a phosphine ligand having general formula (I):

Ri is selected from branched C4-C20 alkyl groups, preferably C4-C15, or from C6-C30 cycloalkyl groups, preferably Ce-Cis, said cycloalkyl groups being substituted; preferably is a terf-butyl group or a 2-/ ^' so-propyl-5-methyl-cyclohexly (neomenthyl); R2 and R3, mutually identical, are selected from C6-C30 aryl groups, preferably C6- Ci5, optionally substituted; preferably they represent a phenyl group;

Xi and X2, mutually identical, represent a halogen atom such as, for example, chlorine, bromine, iodine; preferably they represent a chlorine atom.

For the purpose of understanding the present invention better and to put it into practice, below are some illustrative and non-limiting examples thereof.

EXAMPLES

Reagents and materials

The list below reports the reagents and materials used in the following examples of the invention, any pre-treatments thereof and their manufacturer:

cobalt dichloride anhydrous (C0CI2) (Strem Chemicals): used as such;

ethanol (Sigma-Aldrich): pure,≥ 99,8%, used as such;

terf-butyl(diphenyl)phosphine (P¾uPh2) (Sigma-Aldrich): purity 97%, used as such; (S)-(+)neomenthyl diphenylphosphine [(S)-NMDPP] (Strem Chemicals): purity 98%, used as such;

pentane (Aldrich): pure,≥ 99.5%, distilled over sodium (Na) in an inert

atmosphere;

methylaluminoxane (MAO) (toluene solution 10% in weight) (Aldrich): used as such;

1 ,3-butadiene (Air Liquide): pure,≥ 99.5%, evaporated from the container before each production, dried by passing it through a molecular sieve packed column and condensed inside the reactor that was pre-cooled to -20°C;

hydrochloric acid in 37% aqueous solution (Aldrich): used as such;

methanol (Carlo Erba, RPE): used as such; toluene (Aldrich): pure,≥ 99.5%, distilled over sodium (Na) in an inert atmosphere; hydrofluoric acid (HF) (40% aqueous solution) (Aldrich): used as such;

sulfuric acid (H2SO4) (96% aqueous solution) (Aldrich): used as such, or diluted with distilled water (1/5);

nitric acid (HNO3) (70% aqueous solution) (Aldrich): used as such;

sodium carbonate (Na2CC>3) (Aldrich): used as such;

silver nitrate (AgNC ) (Aldrich): used as such;

deuterated tetrachloroethylene (C2D2CI4) (Acros): used as such;

hexamethyldisilazane (HMDS) (Acros): used as such;

deuterated chloroform (CDC ) (Acros): used as it is;

tetramethyldisilane (TMS) (Acros): used as such.

The analysis and classification methodologies reported below were used.

Elementary analysis

a) Determination of Co

For the determination of the quantity by weight of cobalt (Co), in the cobalt complexes with a phosphine ligand used for the purpose of the present invention, an exactly weighed aliquot, operating in dry-box under nitrogen flow, of about 30 mg - 50 mg of sample, was placed in a 30 ml platinum crucible, together with a 1 ml mixture of 40% hydrofluoric acid (HF), 0.25 ml of 96% sulfuric acid (H ₂ S0 ₄ ) and 1 ml of 70% nitric acid (HNO3). The crucible was then heated on a hot plate increasing the temperature until white sulfur fumes appeared (about 200°C). The mixture thus obtained was cooled to ambient temperature and 1 ml of 70% nitric acid (HNO3) was added, then it was left again until fumes appeared. After repeating the sequence another two times, a clear, almost colorless, solution was obtained. 1 ml of nitric acid (HNO3) and about 15 ml of water were then added cold, then heated to 80°C for about 30 minutes. The sample thus prepared was diluted with MilliQ pure water until it weighed about 50 g, precisely weighed, to obtain a solution on which the instrumental analytical determination was carried out using a Thermo Optek IRIS Advantage Duo ICP-OES (plasma optical emission) spectrometer, for comparison with solutions of known concentration. For this purpose, for every analyte, a calibration curve was prepared in the range 0 ppm - 10 ppm, measuring calibration solutions by dilution by weight of certified solutions.

The solution of sample prepared as above was then diluted again by weight in order to obtain concentrations close to the reference ones, before carrying out

spectrophotometric measurement. All the samples were prepared in double quantities. The results were considered acceptable if the individual repeated test data did not have a relative deviation of more than 2% relative to their mean value.

b) Determination of chlorine

For said purpose, samples of the cobalt complexes with a phosphine ligand used for the purpose of the present invention, about 30 mg - 50 mg, were precisely weighed in 100 ml glass beakers in dry-box under nitrogen flow. 2 g of sodium carbonate (Na2COs) were added and, outside the dry-box, 50 ml of MilliQ water. It was brought to the boil on the hot plate, under magnetic stirring, for about 30 minutes. It was left to cool, then 1/5 diluted sulfuric acid (H2SO4) was added, until acid reaction and was then titrated with 0.1 N silver nitrate (AgNOs) with a potentiometric titrator.

c) Determination of carbon, hydrogen, nitrogen and phosphorus

The determination of carbon, hydrogen and nitrogen, in the cobalt complexes with a phosphine ligand used for the purpose of the present invention, was carried out through a Carlo Erba automatic analyzer Mod. 1 106.

X-ray diffraction (XRD)

For this purpose, samples of the cobalt complexes with a phosphine ligand used for the purpose of the present invention, of about 1 g, were loaded onto the porous baffle of a hot extractor for solids and continuously extracted with boiling pentane for about 2 days obtaining crystalline products (individual crystals) that were analyzed through X-ray diffraction (XRD) using a Bruker AXS Smart Apex II diffractometer equipped with CCD detector and an Oxford Cryostram unit for nitrogen flow assembled at the base of the goniometer to allow data to be collected at different temperatures, i.e. in a temperature range ranging from 100 K (-173.15°C) to 300 K (26.85°C): the operating conditions are reported in Table 1 and in Table 2.

Table 1 and Table 2 also report the crystallographic data of the samples analyzed. ¹³ C-HMR and ¹ H-HMR spectra

The ¹³ C-HMR and ¹ H-HMR spectra were recorded using a nuclear magnetic resonance spectrometer mod. Bruker Avance 400, using deuterated tetrachloroethylene (C2D2CI4) at 103°C, and hexamethyldisiloxane (HDMS) as internal standard, or using deuterated chloroform (CDC ), at 25°C, and tetramethylsilane (TMS) as internal standard. For this purpose, polymeric solutions were used with concentrations equal to 10% by weight with respect to the total weight of the polymeric solution.

The microstructure of the polymers [i.e. 1 ,4-c/s (%) and 1 ,2 (%) unit content and syndiotactic triad content [(rr) %], was determined through the analysis of the aforementioned spectra based on the contents of literature by Mochel V. D., in "Journal of Polymer Science Part A-1: Polymer Chemistry" (1972), Vol. 10, Issue 4, pp. 1009- 1018.

I.R. Spectra

The I.R. spectra were recorded through Thermo Nicolet Nexus 670 and Bruker IFS 48 spectrophotometers.

The I.R. spectra of the polymers were obtained from polymeric films on potassium bromide (KBr) tablets, said films being obtained through the deposition of a solution in hot 1 ,2-dichlorobenzene of the polymer to be analyzed. The concentration of the polymeric solutions analyzed was equal to 10% by weight with respect to the total weight of the polymeric solution.

Thermal analysis (DSC)

The DSC - Differential Scanning Calorimetry - thermal analysis, for the purpose of determining the melting point (T _m ) of the polymers obtained, was carried out using a Perkin Elmer Pyris differential scanning calorimeter. For this purpose, 5 mg of polymer were analyzed, with a scanning speed ranging from 1 °C/min to 20°C/min, in an inert nitrogen atmosphere.

Determination of the molecular weight

The determination of the molecular weight (Mw) of the polymers obtained was carried out through GPC ("Gel Permeation Chromatography"), using the Waters ^® Alliance ^® GPC/V 2000 System by Waters Corporation which uses two detection lines: "Refractive Index" - Rl and "Viscometer" operating under the following conditions:

two PLgel Mixed-B columns;

solvent/eluent: o-dichlorobenzene (Aldrich);

flow rate: 0.8 ml/min;

temperature: 145°C;

molecular mass calculation: Universal Calibration method.

The weight-average molecular weight (M _w ) and the Polydispersion Index (PDI) are reported, corresponding to the ratio M _w /M _n (M _n = number-average molecular weight). EXAMPLE 1

Synthesis of CoCI ₂ (P ^t BuPh ₂ ) fsample G13781

Cobalt dichloride (C0CI2) anhydrous (1.24 g, 9.6 mmoles) and 40 ml of ethanol were placed in a 250 ml flask: the blue solution obtained was kept under stirring (500 rpm), at 22°C, for about 2 hours. Subsequently, te/f-butyldiphenylphosphine (P¾uPh ₂ ) (5.1 g, 21 mmoles) dissolved in ethanol (30 ml) was added: everything was kept under stirring (500 rpm), at ambient temperature, for 24 hours and subsequently placed, under vacuum, at ambient temperature, for the purpose of almost completely removing the ethanol. Then pentane (40 ml) was added and everything was kept under stirring (500 rpm), at ambient temperature, for 2 hours: at the end, the light blue/blue suspension obtained was filtered and the residue obtained was washed further with pentane (2 x 10 ml) and vacuum dried, at ambient temperature, obtaining 4.71 g of a solid product corresponding to the complex CoCbiP'BuPha) equal to an 80% conversion with respect to the cobalt dichloride (C0CI2) anhydrous loaded.

Individual crystals of the aforementioned solid product corresponding to the complex CoCbiP'BuP ) were obtained by continuous extraction, hot, with pentane: Table 1 and Table 2 show the crystallographic data obtained.

Elementary analysis [found (calculated) for C32H38CI2C0P2]: C: 62.50% (62.55%); H: 6.20% (6.23%); CI: 1 1.50% (1 1.54%); P: 10.00% (10.08%); Co: 9.50% (9.59%).

Molecular weight: 614.43.

Figure 1 shows the XRD structure of the complex CoCbiP'BuPha) obtained. Figure 2 shows the FT-IR spectrum of the complex CoCbCP'BuP ) obtained.

EXAMPLE 2

Synthesis of CoCI ₂ rPPh ₂ (NMDPP)l [sample G15191

Cobalt dichloride (CoC ) anhydrous (0.182 g, 1.4 mmoles) and 20 ml of ethanol were placed in a 100 ml flask: the blue solution obtained was kept under stirring (500 rpm), at ambient temperature, for 1 hour. Subsequently, (S)-(+)neomenthyl-diphenylphosphine [(S)-NMDPP] (1 g, 3.08 mmoles) dissolved in ethanol (30 ml) were added: everything was brought to 60°C and kept, under stirring (500 rpm), at said temperature, for 24 hours. Subsequently, the mixture obtained was vacuum dried, at ambient temperature and then pentane (30 ml) was added and everything was kept under stirring (500 rpm), at ambient temperature, for 2 hours. At the end, the light blue/blue suspension obtained was filtered and the residue obtained was washed further with pentane (2 x 10 ml) and vacuum dried, at ambient temperature, obtaining 0.950 g of a solid product

corresponding to the complex CoCl2[PPh2(NMDPP)] equal to an 87% conversion with respect to the cobalt dichloride (C0CI2) anhydrous loaded.

Elementary analysis [found (calculated) for C44H58CI2C0P2]: C: 67.60% (67.86%); H: 7.40% (7.51 %); CI: 8.90% (9.1 1 %); P: 7.90% (7.96%); Co: 7.50% (7.57%).

Molecular weight: 778.72.

Figure 3 shows the FT-I R spectrum of the complex CoCl2[PPh ₂ (NMDPP)] obtained. EXAM PLE 3

2 ml of 1 ,3-butadiene equal to about 1 .4 g were condensed, cold (-20°C), in a 25 ml test tube. Subsequently, 12.3 ml of toluene were added and the temperature of the solution thus obtained was brought to +20°C. Then, methylaluminoxane (MAO) in toluene solution (0.63 ml; 1 x10 ^"3 moles, equal to about 0.058 g) was added, and, subsequently, CoCbiP'BuP ) complex [sample G1378] (3.07 ml of toluene solution at concentration of 2 mg/ml; 1 x10 ^"5 moles, equal to about 6.14 mg) obtained as described in Example 1. Everything was kept under magnetic stirring, at +20°C, for 10 minutes. The

polymerization was then stopped by adding 2 ml of methanol containing some drops of hydrochloric acid. The polymer obtained was then coagulated by adding 40 ml of a methanol solution containing 4% of Irganox ^® 1076 antioxidant (Ciba) obtaining 1 .4 g of 1 ,2 syndiotactic polybutadiene: further characteristics of the process and of the 1 ,2 syndiotactic polybutadiene obtained are reported in Table 3.

Figure 4 shows the FT-I R spectrum of the 1 ,2 syndiotactic polybutadiene obtained. Figure 5 shows the ¹ H-NMR (top) and ¹³ C-NMR (bottom) spectra of the 1 ,2 syndiotactic polybutadiene obtained.

Figure 6 shows the RX spectrum of the 1 ,2 syndiotactic polybutadiene obtained.

EXAM PLE 4

2 ml of 1 ,3-butadiene equal to about 1 .4 g were condensed, cold (-20°C), in a 25 ml test tube. Subsequently, 6.61 ml of toluene were added and the temperature of the solution thus obtained was brought to +20°C. Then, methylaluminoxane (MAO) in toluene solution (0.19 ml; 3x10 ^"4 moles, equal to about 0.017 g) was added, and, subsequently, CoCbiP'BuP ) complex [sample G1378] (9.2 ml of toluene solution at concentration of 2 mg/ml; 3x10 ^"5 moles, equal to about 18.4 mg) obtained as described in Example 1. Everything was kept under magnetic stirring, at +20°C, for 30 minutes. The

polymerization was then stopped by adding 2 ml of methanol containing some drops of hydrochloric acid. The polymer obtained was then coagulated by adding 40 ml of a methanol solution containing 4% of Irganox ^® 1076 antioxidant (Ciba) obtaining 1.4 g of 1 ,2 syndiotactic polybutadiene: further characteristics of the process and of the 1 ,2 syndiotactic polybutadiene obtained are reported in Table 3.

Figure 7 shows the FT-IR spectrum of the 1 ,2 syndiotactic polybutadiene obtained. Figure 8 shows the ¹ H-NMR (top) and ¹³ C-NMR (bottom) spectra of the 1 ,2 syndiotactic polybutadiene obtained.

Figure 9 shows the RX spectrum of the 1 ,2 syndiotactic polybutadiene obtained.

EXAMPLE 5

2 ml of 1 ,3-butadiene equal to about 1.4 g were condensed, cold (-20°C), in a 25 ml test tube. Subsequently, 9.7 ml of heptane were added and the temperature of the solution thus obtained was brought to +20°C. Then, methylaluminoxane (MAO) in toluene solution (0.19 ml; 3x10 ^"4 moles, equal to about 0.017 g) was added, and, subsequently, CoCl2(P'BuPh2) complex [sample G1378] (9.2 ml of heptane solution at concentration of 2 mg/ml; 3x10 ^"5 moles, equal to about 18.4 mg) obtained as described in Example 1. Everything was kept under magnetic stirring, at +20°C, for 60 minutes. The

polymerization was then stopped by adding 2 ml of methanol containing some drops of hydrochloric acid. The polymer obtained was then coagulated by adding 40 ml of a methanol solution containing 4% of Irganox ^® 1076 antioxidant (Ciba) obtaining 1.4 g of 1 ,2 syndiotactic polybutadiene: further characteristics of the process and of the 1 ,2 syndiotactic polybutadiene obtained are reported in Table 3.

Figure 10 shows the FT-IR spectrum of the 1 ,2 syndiotactic polybutadiene obtained. Figure 1 1 shows the ¹ H-NMR (top) and ¹³ C-NMR (bottom) spectra of the 1 ,2 syndiotactic polybutadiene obtained.

Figure 12 shows the RX spectrum of the 1 ,2 syndiotactic polybutadiene obtained.

EXAMPLE 6

2 ml of 1 ,3-butadiene equal to about 1.4 g were condensed, cold (-20°C), in a 25 ml test tube. Subsequently, 6.6 ml of toluene were added and the temperature of the solution thus obtained was brought to +20°C. Then, methylaluminoxane (MAO) in toluene solution (0.48 ml; 7.5x10 ^"4 moles, equal to about 0.043 g) was added, and,

subsequently, CoCbiP'BuPha) complex [sample G1378] (9.2 ml of heptane solution at concentration of 2 mg/ml; 3x10 ^"5 moles, equal to about 18.4 mg) obtained as described in Example 1. Everything was kept under magnetic stirring, at 0°C, for 60 minutes. The polymerization was then stopped by adding 2 ml of methanol containing some drops of hydrochloric acid. The polymer obtained was then coagulated by adding 40 ml of a methanol solution containing 4% of Irganox ^® 1076 antioxidant (Ciba) obtaining 1.4 g of 1 ,2 syndiotactic polybutadiene: further characteristics of the process and of the 1 ,2 syndiotactic polybutadiene obtained are reported in Table 3.

Figure 13 shows the FT-IR spectrum of the 1 ,2 syndiotactic polybutadiene obtained. Figure 14 shows the ¹ H-NMR (top) and ¹³ C-NMR (bottom) spectra of the 1 ,2 syndiotactic polybutadiene obtained.

Figure 15 shows the RX spectrum of the 1 ,2 syndiotactic polybutadiene obtained.

EXAMPLE 7

2 ml of 1 ,3-butadiene equal to about 1.4 g were condensed, cold (-20°C), in a 25 ml test tube. Subsequently, 11.5 ml of toluene were added and the temperature of the solution thus obtained was brought to +20°C. Then, methylaluminoxane (MAO) in toluene solution (0.63 ml; 1 x10 ^"3 moles, equal to about 0.058 g) was added, and, subsequently, the CoCI ₂ [PPh ₂ (NMDPP)] complex [sample G1519] (3.9 ml of toluene solution at concentration of 2 mg/ml; 1 x10 ^"5 moles, equal to about 7.79 mg) obtained as described in Example 2. Everything was kept under magnetic stirring, at +20°C, for 15 minutes. The polymerization was then stopped by adding 2 ml of methanol containing some drops of hydrochloric acid. The polymer obtained was then coagulated by adding 40 ml of a methanol solution containing 4% of Irganox ^® 1076 antioxidant (Ciba) obtaining 1.4 g of 1 ,2 syndiotactic polybutadiene: further characteristics of the process and of the 1 ,2 syndiotactic polybutadiene obtained are reported in Table 3.

Figure 16 shows the FT-IR spectrum of the 1 ,2 syndiotactic polybutadiene obtained. Figure 17 shows the ¹ H-NMR (top) and ¹³ C-NMR (bottom) spectra of the 1 ,2 syndiotactic polybutadiene obtained.

EXAMPLE 8

2 ml of 1 ,3-butadiene equal to about 1.4 g were condensed, cold (-20°C), in a 25 ml test tube. Subsequently, 7.9 ml of heptane were added and the temperature of the solution thus obtained was brought to +20°C. Then, methylaluminoxane (MAO) in toluene solution (0.315 ml; 5 x10 ^"4 moles, equal to about 0.029 g) was added, and,

subsequently, the CoCI ₂ [PPh ₂ (NMDPP)] complex [sample G1519] (7.79 ml of heptane solution at concentration of 2 mg/ml; 2 x10 ^"5 moles, equal to about 15.58 mg) obtained as described in Example 2. Everything was kept under magnetic stirring, at +20°C, for 60 minutes. The polymerization was then stopped by adding 2 ml of methanol containing some drops of hydrochloric acid. The polymer obtained was then coagulated by adding 40 ml of a methanol solution containing 4% of Irganox ^® 1076 antioxidant (Ciba) obtaining 1.4 g of 1 ,2 syndiotactic polybutadiene: further characteristics of the process and of the 1 ,2 syndiotactic polybutadiene obtained are reported in Table 3.

Figure 18 shows the FT-IR spectrum of the 1 ,2 syndiotactic polybutadiene obtained. Figure 19 shows the ¹ H-NMR (top) and ¹³ C-NMR (bottom) spectra of the 1 ,2 syndiotactic polybutadiene obtained.

Figure 20 shows the RX spectrum of the 1 ,2 syndiotactic polybutadiene obtained.

EXAMPLE 9

2 ml of 1 ,3-butadiene equal to about 1.4 g were condensed, cold (-20°C), in a 25 ml test tube. Subsequently, 3.85 ml of heptane were added and the temperature of the solution thus obtained was brought to 0°C. Then, methylaluminoxane (MAO) in toluene solution (0.47 ml; 7.5 x10 ^"4 moles, equal to about 0.044 g) was added, and, subsequently, the CoCI ₂ [PPh ₂ (NMDPP)] complex [sample G1519] (1 1.68 ml of heptane solution at concentration of 2 mg/ml; 3 x10 ^"5 moles, equal to about 23.36 mg) obtained as described in Example 2. Everything was kept under magnetic stirring, at 0°C, for 10 minutes. The polymerization was then stopped by adding 2 ml of methanol containing some drops of hydrochloric acid. The polymer obtained was then coagulated by adding 40 ml of a methanol solution containing 4% of Irganox ^® 1076 antioxidant (Ciba) obtaining 1.01 g of 1 ,2 syndiotactic polybutadiene: further characteristics of the process and of the 1 ,2 syndiotactic polybutadiene obtained are reported in Table 3.

Figure 21 shows the FT-IR spectrum of the 1 ,2 syndiotactic polybutadiene obtained. Figure 22 shows the ¹ H-NMR (top) and ¹³ C-NMR (bottom) spectra of the 1 ,2 syndiotactic polybutadiene obtained.

EXAMPLE 10 (comparative)

Synthesis of CoCl2(PPh ₂ Cv) [sample A711

Cobalt dichloride (C0CI2) anhydrous (1.0652 g, 8.2 mmoles) and 60 ml of ethanol were placed in a 100 ml flask: the blue solution obtained was kept under stirring (500 rpm), at ambient temperature, for 1 hour. Subsequently, cyclohexyldiphenylphosphine (4.854 g, 18.1 mmoles) dissolved in ethanol (60 ml) were added: everything was kept, under stirring (500 rpm), at ambient temperature, for 24 hours. Subsequently, the blue suspension obtained was filtered and the residue obtained was washed with ethanol (2 x 10 ml) and with pentane (2 x 10 ml) and vacuum dried, at ambient temperature, obtaining 4.738 g of a solid product corresponding to the complex CoCl2(PPh2Cy) equal to an 86.7% conversion with respect to the cobalt dichloride (C0CI2) anhydrous loaded. Elementary analysis [found (calculated for C44H58CI2C0P2]: C: 65.0% (64.87%); H: 6.40% (6.35%); CI: 10.5% (10.64%); P: 9.20% (9.29%); Co: 9.0% (8.84%).

Molecular weight: 666.51.

EXAMPLE 1 1 (comparative)

2 ml of 1 ,3-butadiene equal to about 1.4 g were condensed, cold (-20°C), in a 25 ml test tube. Subsequently, 14 ml of toluene were added and the temperature of the solution thus obtained was brought to +20°C. Then, methylaluminoxane (MAO) in toluene solution (0.315 ml; 5x10 ^"4 moles, equal to about 0.029 g) was added, and, subsequently, the CoCl2(PPh2Cy) complex [sample A71] (1.67 ml of toluene solution at concentration of 2 mg/ml; 5x10 ^"6 moles, equal to about 3.34 mg) obtained as described in Example 10 (comparative). Everything was kept under magnetic stirring, at +20°C, for 16 minutes. The polymerization was then stopped by adding 2 ml of methanol containing some drops of hydrochloric acid. The polymer obtained was then coagulated by adding 40 ml of a methanol solution containing 4% of Irganox ^® 1076 antioxidant (Ciba) obtaining 1.4 g of polybutadiene: further characteristics of the process and of the polybutadiene obtained are reported in Table 3.

TABLE 1

Crystallographic data, Data collection details and results of refinement for the complex CoCI ₂ (P'BuPh2) (Example 1) (I)

(I)

formula, M _r C32H38CI2C0P2, 614.39

crystal system Monoclinic

space group, Z P2i/n, 4

Dcaic, g crrr ³ 1 ,347

a, A 1 1 .9782(5)

b, A 15.4120(6)

c, A 16.7851 (7)

a, ° 90

β, ° 102,098(1 )

r, ^° 90

v, A ³ 3029.8(2)

crystal size, mm 0.35x0.20x0.08

color, habit light blue, plate μ, mm ¹ 0,868 radiation ΜθΚα

T, K 153(2)

2 $max, 63.69

-17→17; -22^22;

h, k, 1 ranges

-24→24 intensity decay, % 00:00 adsorption correction multi-scan

7 ^" min, 7 ^" max 0.682, 0.746 measured reflections 60180 independent reflections 9958 reflections with 1>2σ(1) 8422 no. of parameters 340

R, wR [F ² >2o{ F ² )] 0.0353, 0.0900 goodness of fit 1.048

AyO max, AyO min (eA ^-3 ) 1.069, -0.231

TABLE 2

Bond lengths (A) and Angles (°) selected for the complex CoCbiP'BuPha) (Example 1)

(l) ^(a) (I)

Co-CI 2.2356(4)

Co-P 2.4334(4)

P-Car 1 .8260(14)

P-Caiif 1 .8878(14) CI-Co-CI 1 12.41 (2)

P-Co-P 1 13.69(1)

Ca^P-Car 107.92(6)

each value reported was obtained as the mean of all the corresponding parameters present in the structure.

polymerization solvent heptane; ^(2} ; syndiotactic triad content in the polybutadiene obtained;

weight average molecular weight (M _w ); Po!ydispersion Index (PDI);

T _m = melting point;

comparative example.