Polydiene polymers are widely known in the art. In particular, butadiene based elastomers, having a high content of cis-1, 4 units are extensively used for the production of tires and other elastomeric products.

Generally these products are obtained by solution polymerization of conjugated dienes using Z/N catalysts based on Titanium, Cobalt or rare earth elements. In particular, Nd-based catalysts have been found of great interest because of yielding linear high cis polymer from butadiene, the polymers from isoprene, pentadiene, 2,3-dimethylbutadiene, (E)-2-methyl-1, 3- pentadiene being also predominantly cis.

These catalyst systems are usually obtained by reacting (a) a halogen donating compound (like AlEt2Cl, AlEtC12), (b) a hydrocarbon soluble Nd-compound (for example a Nd carboxylate) and (c) an Al-alkyl, such as Al (i-Bu) 3 or AlH (i-Bu) 2. The catalyst is generally "pre-formed"and then introduced into the monomer-solvent mixture. The preparation of the catalyst normally includes two steps. First, the halogenating compound is added to a solution of the Nd-compound in hydrocarbon solvent, leading to the formation of a precipitate containing Nd halide or a product of partial halogenation. Second, the aluminium-alkyl compound is added to this suspension in a molar ratio of about 10-40 with respect to Nd.

After optional ageing, the resulting catalytic suspension is ready for use. It is usually introduced into the polymerization reactor containing monomer and solvent in such a way that Nd concentration in the range of 10-4 mol/L is obtained in the polymerization medium.

As mentioned above these catalyst systems are able to give polydienes with good properties.

However, the yields provided are not satisfactory.

According to the Italian Patent Application 19504A89 catalyst components based on Nd compounds with improved activities are obtainable from the product of the reaction between a Mg (allyl) halide with a Nd trihalide in an ether solvent. These catalyst components, once converted into catalysts by reaction with Al-alkyl compounds, are able to give activities higher than those obtainable from the Nd carboxylates disclosed above. However, the catalyst components disclosed in said Italian application show a poor solubility in the organic solvents normally used for the preparation of the catalyst systems. This constitutes an objective disadvantage when said catalyst components have to be supported on organic or inorganic substrates in order to prepare catalysts of improved morphological properties to be used in the gas-phase polymerization process. It would be therefore important to have available a catalyst precursor exhibiting, at the same time, enhanced catalytic activity and solubility in hydrocarbon media. We have now found that the above requirements are met by the catalyst components obtained by reacting a Nd trihalide with Mg diallyl compounds of formula MgA2 where the radicals A same or different to each other, are allyl radicals which can be optionally substituted. Preferred allyl radicals are those of formula: R1 R3 R in which Rl to R5, same or different to each other, are hydrogen or Cl-C10 alkyl radicals. The use of allyl radicals in which the Rl to R4 groups are hydrogen is preferred. Most preferably the reaction between the MgA2 compounds and the Nd trihalide is carried out in an ether diluent. Particularly preferred ethers to be used as the reaction medium are tetrahydrofurane (THF), 1,4-dioxane, 1,2-dimethoxyethane (DME), and diethyl ether. The temperature of the reaction is not particularly critical, however overexposure to elevated temperatures should be avoided in order to prevent thermal decomposition of the product. Generally, temperatures from-50°C up to the boiling point of the ether medium can be used, but usually temperatures between 0 and 30°C are preferred. The stoichiometry of the reaction can vary from 0.5 to 1.5 mol of MgA2 to a mol of Nd, corresponding to 1-3 allyl groups per Nd atom. The preferred Nd trihalide to be reacted with MgA2 is NdCl3, preferably in complex with THF for improved solubility. When the reaction is carried out between NdC13 and Mg (allyl) 2 in molar ratio 1: 1 in THF as reaction medium the semisolid product recovered has been found particularly suitable for the preparation of the final catalyst system to be used in the diene polymerization. As mentioned above, the catalyst components of the invention form, upon reaction with suitable cocatalyst compounds, the catalyst systems advantageously usable for the polymerization of dienes.

Suitable co-catalysts include organo-Al compounds. In particular, preferred organo-Al compounds are those of formula AlHpRqXr where R is a hydrocarbon group, preferably an alkyl group, having from 1 to 20 carbon atoms, X is halogen, preferably chlorine, p is from 0 to 2, r is from 1 to 3 and q is from 0 to 2. Specific examples are triethylaluminum (TEAL), triisobutylaluminium (TIBA), diethyl aluminium chloride (DEAC), diisobutyaluminium hydride, and partially hydrolyzed diethyl aluminium chloride (DEACO).

Alumoxanes can also be used as cocatalysts. In particular, the alumoxane used in the catalyst according to the invention is considered to be a linear, branched or cyclic compound containing at least one group of the type: wherein the R7 substituents, the same or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated C-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing Si or Ge atoms, or R7 is a groupai (R7) 2.

In particular, linear alumoxanes have formula: wherein m is an integer ranging from 0 to 40 and R7 has the meaning reported above; and cyclic alumoxanes have formula : wherein m is an integer ranging from 2 to 40 and R7 has the meaning reported above.

In the above-mentioned linear and cyclic alumoxanes, R7 is preferably methyl, ethyl, isobutyl or 2,4,4-trimethyl-pentyl.

Examples of alumoxanes suitable as activating cocatalysts in the catalyst systems according to the present invention are methylalumoxane (MAO), tetraisobutylalumoxane (TIBAO) and 2,4,4-trimethyl-pentylalumoxane (TIOAO) and 2-methyl-pentylalumoxane. Mixtures of different alumoxanes can also be used.

The Al/Nd ratio of the catalyst is somewhat critical for the polymerization activity. Preferably the Al/Nd molar ratio is higher than 10 and more preferably is between 15 and 70.

It has generally been observed that the polymerization activity of the catalyst system is improved as a consequence of the ageing of the catalyst. In particular, ageing times higher than 3-4 hours are suitable to obtain improved yields over the fresh catalyst. Also, it has been found particularly advantageous, for the increase of the activity, contacting the catalyst components with small amounts of the dienic monomer before adding the alkylating agent.

As mentioned above this catalyst components, or the catalyst obtained from it, can be easily supported on suitable carriers like porous polymers or porous inorganic substances like silica.

The supportation method can be carried out with the conventional techniques.

One method provides for the contact of the support and the above-disclosed catalyst component dissolved in a liquid medium that is subsequently removed. The supported catalyst component is then reacted with the suitable cocatalyst in order to form the final active catalyst.

According to one preferred embodiment instead, the catalyst component is first converted into a final active catalyst by suitable reaction with the co-catalyst and then the whole system is supported on the porous support. Therefore, this process of supportation specifically comprises : (a) suspending the porous support in a hydrocarbon medium; (b) contacting the so obtained mixture with a hydrocarbon mixture containing the catalyst component, the cocatalyst and, optionally, a dienic monomer; (c) stirring the resulting mixture and finally, (d) removing the liquid hydrocarbon medium.

Step (b) is generally carried out working at a temperature between 0 and 100°C, preferably between 10 and 60°C, while step (c) is carried out for time periods ranging from 1 minute to 10 hours. The use of a low boiling point hydrocarbon medium is preferred since it is then possible to remove it simply by flashing. Preferably, before carrying out the step (a) the porous support is contacted with an Al-alkyl compound. The use of diisobutylaluminum hydride (DIBAH) is preferred.

The catalyst according to this invention can be used in any type of polymerization process.

The supported catalysts are particularly used in the gas-phase polymerization process.

Normally the gas-phase process can be carried out in a fluidized bed reactor or under conditions in which the polymer is mechanically stirred, and operating in one or more reactors. The polymerization temperature is generally in range from-10 to 250°C, preferably between 10 and 160°C. The pressure is generally in range from 0.1 and 50 bar and preferably between 1 and 20 bar.

The molecular weight of the resulting polymers can be regulated by using molecular weight regulator agents, or by using the polymerization conditions.

The polymerization conditions disclosed above can be used for homo-and co-polymerization of conjugated dienes such as 1,3-butadiene, isoprene, pentadiene or dimethyl butadiene.

As it is known in the art the 1,3-dienes can also be used in mixtures with other monomers, such as styrene or non-conjugated dienes, in order to produce copolymers having specific properties.

The polymers obtained with the catalyst of the invention have a cis-1, 4-double bond content of around 60 to 99%. The molecular weight can be adjusted through the composition of the catalyst and by varying the polymerization conditions. Typical molecular weights are in the range from 103 to 106, as measured by GPC (gel permeation chromatography).

The Mooney viscosity, ML (1+4', 100°C), is typically in the range from 30 to 180 MU. It is also possible by the gas-phase polymerization to produce polymers of very high molecular weight that would be extremely difficult to obtain by solution polymerization because of the high viscosity and the possibility of transfer reactions through the solvent used.

The polymer obtained may be compounded and vulcanized in the usual way.

The following examples are given in order to better illustrate the invention without limiting it.

Example 1 Preparation of the catalyst precursor in toluene solution NdCl3-2THF + (allyl) 2Mg- Nd (allyl) 2Cl MgCl2-nTHF Bis (allyl) magnesium was prepared by reacting allylmagnesium chloride with stoichiometric quantity of 1,4-dioxane in diethyl ether solution: 2 (allyl) MgCl + diox- (allyl) ZMg + MgCl2 dioxt The filtrate contained 0.131 mol/L Mg and 7.5-10-3 mol/L Cl, thus the concentration of allyl groups was estimated to be 0.255 mol/L.

To 1.76 g of NdCl3 2THF suspended in 50 mL of anhydrous THF under stirring at 0°C, 38 mL of bis (allyl) magnesium solution described above were added. Stirring the mixture at 0°C under reduced pressure, its volume was brought to ca. 30 mL, thus freeing it of diethyl ether. The dark green solution obtained was stirred for additional 2 h at 0°C and the solvent was completely removed yielding a semisolid product. On treating with 330 mL of dry toluene at-30°C about 80% of Nd was extracted, yielding bright-green solution, unstable at ambient temperature, Cud=1. 1-10-2 mol/L.

Example 2 Preparation of the catalyst for solution polymerization To 30 mL of the toluene solution prepared as in example 1 stirred at-20°C, 9 ml of MAO solution in toluene (CA) =1. 4 mol/1) were added. The fine suspension was stirred for 10 min at- 20°C and then stored at 0°C. cNd=8. 5 10-3 mol/L.

Example 3 Solution polymerization of 1, 3-butadiene To 50 mL of 10% (v/v) solution of butadiene in n-hexane stirred at 25°C 0.1 mL of MAO solution in toluene (cAl=1. 4 mol/1) were added as scavenger followed by 0.4 mL of catalytic suspension prepared according to example 2. The polymerization was stopped after 5 min by addition of methanol, the polymer precipitated with excess of methanol and dried in vacuo.

Several runs were done with freshly prepared catalyst and with catalyst aged at 0°C, giving different yields as follows: Ageing time, h Polymer yield, g Conversion, % 0 1.31 42 1 2. 28 74 21 2.48 80 The obtained polybutadiene polymers were found to be 96-98% cis by IR.