High performance tire

Abstract

The present invention relates to a process for the preparation of a copolymer having a high content of styrene and / or substituted styrene, in particular a stereoregular copolymer of butadiene with styrene and / or substituted styrene, which copolymer is used in an elastomeric composition which is used for the production of tyres or parts thereof, such as treads.

Description

TECHNICAL FIELD

[0001] The present invention relates to a process for the preparation of a copolymer with a high content of styrene and / or substituted styrene, in particular a stereoregular copolymer of butadiene with styrene and / or substituted styrene, which is used in an elastomeric compound for the production of tyres or components thereof, such as treads. PRIOR ART

[0002] Some catalysts and processes for the production of polymers and copolymers are described in documents US 3,903,019, US 4,112,210, US 4,129,705, US 4,933,401, US 5,100,965, US 5,753,579, US 6,103,842 and US 6,627,715.

[0003] The use of polymers and copolymers for the production of at least one tyre component is described in documents US 4,669,518, US 5,317,062, US 6,429,245, US 6,581,659, US 6,872,772, US 6,889,737, US 7,048,023, US 2004 / 0039104, US 2004 / 0177907, EP 1 593 528, WO 2010 / 006655, EP 2 643 367 B1 and EP 3 328 664 B1.

[0004] The use of copolymers with a high content of styrene in the tyre industry, in particular in elastomeric compounds for the manufacture of tyre treads, is well known.

[0005] In fact, it is believed that the grip characteristics of tyre treads are positively affected by the presence of a high percentage of styrene in the elastomeric polymers and / or copolymers used to prepare the elastomeric compositions, in particular under extreme driving conditions, at high speeds and in turns. In fact, the use of polymers and / or copolymers with a high content of styrene allows to increase the hysteresis value of the finished tyre treads.

[0006] Conventional polymerization and catalysis techniques generally do not allow to obtain styrene-butadiene copolymers with a percentage of styrene monomer greater than 30-40%, since the presence of a high percentage of styrene during the polymerization promotes the formation of block copolymers, i.e. copolymers in which there are 10 or more consecutive styrene units, which can have the typical Tg of polystyrene (+100°C), are thermoplastic and, therefore, unsuitable for the production of tyre treads, since their mechanical properties and wear resistance would be severely compromised.

[0007] The Applicant has already provided a solution to the above problem in patent EP2643367B1, in which a styrene-butadiene copolymer (in particular with butadiene in trans conformation and styrene in isotactic configuration) having a molecular weight lower than 500,000, in particular ranging from about 10,000 to about 100,000, a random distribution and a styrene content greater than 40% by weight has been described.

[0008] In fact, EP2643367B1 describes a process for the preparation of a styrene-butadiene copolymer by using a catalyst having general formula (A)

[0009]

[0010] where Tr is a transition metal, X and X', equal to or different from each other, are halogen atoms, R1-R2 are H atoms or linear or branched alkyl groups having from 1 to 10 carbon atoms, R3-R6 are H atoms or linear or branched alkyl groups having from 1 to 10 carbon atoms, Y and Y' are oxygen, sulfur, selenium, tellurium atoms or are NR7 or PR7 groups, D and D' are oxygen, sulfur, selenium, tellurium atoms or are NR7 or PR7 groups, R7 is a H atom or a linear or branched alkyl group having from 1 to 10 carbon atoms and n is an integer from 1 to 10.

[0011] As described in EP3328664B1, the Applicant has also found that it is possible to obtain a styrene-butadiene copolymer having a molecular weight greater than 500,000 using a homogeneous catalyst of formula (B):

[0012]

[0013] The preparation process described in EP3328664B1 is carried out in toluene, in the presence of the above homogeneous catalyst and of the activator compound methylaluminoxane (MAO), at a temperature ranging from 0°C to 25°C, for a period of time ranging from 24 to 48 hours. SUMMARY

[0014] Although the processes described in EP2643367B1 and EP3328664B1 have a high conversion yield, from an industrial point of view the long reaction times and the use of toluene are not advantageous. In fact, industrial production plants preferably use aliphatic hydrocarbons, such as hexane, and the reaction time is equal to or less than 12 hours.

[0015] The Applicant is therefore faced with the problem of finding a production process which will allow to obtain a styrene-butadiene copolymer with reduced solvents and reaction times and with a good reaction yield.

[0016] In attempts to employ industrially usable solvents, such as aliphatic hydrocarbons, instead of toluene, and to reduce the reaction time by increasing the reaction temperature and using the catalyst described in EP 3 328 664 B1, the Applicant observed the formation of a heterogeneous system in which the copolymer precipitated and formed a dispersion that was not easily handled in industrial plants.

[0017] The Applicant also tried to use catalysts other than those described in EP 2 643 367 B1 and EP 3 328 664 B1, observing a sharp decrease in the reaction yield and a likewise sharp decrease in the molecular weight of the resulting copolymer, even below 10,000 Dalton (Da).

[0018] After extensive experimentation, the Applicant has finally surprisingly found that the use of certain catalysts with an activator mixture comprising modified methylaluminoxane (m-MAO) and triisobutylaluminium (TIBA) allows to solve the problems encountered, while providing good reaction yields, acceptable molecular weights and forming a homogeneous system without precipitating the copolymer.

[0019] The Applicant has also observed that the percentage of conversion and the molecular weight depend on the ratio between catalyst and activator. In particular, the Applicant has observed that in order to obtain higher yields and higher molecular weights, the molar ratio between m-MAO and catalyst is preferably equal to or greater than 50:1, more preferably greater than 100:1. Advantageously, the molar ratio between m-MAO and catalyst ranges from 200:1 to 500:1. Preferably, the molar ratio between TIBA and catalyst is greater than 10:1, more preferably not greater than 300:1, even more preferably it ranges from 20:1 to 200:1, and advantageously from 20:1 to 120:1.

[0020] Furthermore, the Applicant has observed that the use of para-methylstyrene in the partial or total substitution of styrene increases the percentage of conversion and the molecular weight of the resulting copolymer, as well as its solubility in reaction solvents based on aliphatic hydrocarbons.

[0021] The Applicant has also surprisingly observed that the Tg of the resulting polymer is affected by the type of catalyst used and by the relative amount of styrene and substituted styrene present in the copolymer, for the same molecular weight of the copolymer, thus providing an instrument to adjust the Tg according to the desired purpose.

[0022] Based on the applicant's experience, the styrene component in the styrene-butadiene copolymer determines the increase in hysteresis of the copolymer relative to the butadiene homopolymer, and thus has a favorable effect on grip and driving performance under extreme conditions. Specifically, the styrene component determines the increase in the glass transition temperature (Tg) of the copolymer relative to the homopolymer, and this increase in Tg leads to increased dissipation in the rubber compound based on this copolymer, and therefore results in the desired effect on grip. However, the increase in Tg also leads to disadvantages: at temperatures close to Tg, the rubber compound becomes very hard, and therefore grip is compromised despite the high hysteresis.

[0023] Depending on the tire's operating range (summer, winter, all-weather, sport) and the pattern of the rubber compound's hysteresis curve, experiments allow for the determination of the optimal Tg value for the copolymer that maximizes the hysteresis effect, thereby keeping the compound's hardening at a tolerable level. For example, in the extreme cases of competing tires, the Tg of the tread compound can be above 0°C. For road-use tires, even in summer, it will be on the order of -25°C.

[0024] Therefore, the applicant unexpectedly observed that the method of the present invention provides the possibility of obtaining polymers with controlled Tg by utilizing process parameters and, most obviously, compositional parameters (i.e., the amount of styrene incorporated into the polymer). This possibility is particularly interesting, especially for obtaining a higher Tg with the same amount of styrene, because a high amount of styrene can lead to problems such as lower solubility of the copolymer in other polymer phases present in the rubber compound, and lower reactivity to the vulcanization system because styrene units, once incorporated into the copolymer, do not have reactive groups with the vulcanization system.

[0025] Therefore, a first aspect of the present invention relates to a method for copolymerizing butadiene and styrene and / or substituted styrene, the method comprising (i) preparing a solution of butadiene and styrene and / or substituted styrene in a solvent, (ii) adding a homogeneous catalytic system to the solution, (iii) conducting a copolymerization reaction at a temperature in the range of 30°C to 100°C for 12 hours or less, and (iv) recovering the resulting copolymer.

[0026] Its features

[0027] The solvent is selected from aliphatic and alicyclic hydrocarbons, and

[0028] The homogeneous catalytic system includes

[0029] (a) Catalysts of general formula (I)

[0030]

[0031] Where R 1 and R3 , equal to or different from each other, are linear or branched alkyl groups having 1 to 10 carbon atoms, and R 2 and R 4 , equal to or different from each other, are linear or branched arylalkyl groups having 7 to 14 carbon atoms, and

[0032] (b) a cocatalyst mixture comprising modified methylaluminoxane (m-MAO) and triisobutylaluminium (TIBA).

[0033] A second aspect of the present application is the use of the copolymer obtained with the process of the first aspect of the present application in an elastomeric compound for the production of a tyre component for vehicle wheels.

[0034] A third aspect of the present application is a tyre for vehicle wheels comprising a crosslinked elastomeric material obtained by crosslinking an elastomeric compound which is crosslinkable, wherein said elastomeric compound comprises the copolymer obtained with the process of the first aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 A cross-sectional view of a portion of a tyre is shown. DETAILED DESCRIPTION

[0037] The process of the first aspect of the present application uses a cocatalyst mixture comprising modified methylaluminoxane (m-MAO) and triisobutylaluminium (TIBA).

[0038] According to a preferred aspect of the first aspect of the present application, the molar ratio between said m-MAO and said catalyst is equal to or greater than 50:1, preferably greater than 100:1, more preferably ranging from 150:1 to 1000:1, and advantageously ranging from 200:1 to 500:1.

[0039] Methylaluminoxane (MAO) and its modified form (m-MAO) are known and commercially available cocatalysts. Useful examples of m-MAO are sold by the companies Azko Nobel (Holland) and Albemarle (USA). The generally accepted structural formula of methylaluminoxane is

[0040] (R)2AIO (RAIO) m Al(R)2

[0041] wherein R is mainly methyl and m is an integer from 0 to 50. For the purposes of the present specification and the appended claims, the term "m-MAO" or "modified methylaluminoxane" means methylaluminoxane in which a certain proportion of the methyl groups is replaced by longer alkyl groups having 2 to 6 carbon atoms, such as ethyl, propyl and butyl, in order to increase the solubility of the MAO thus modified in aliphatic solvents.

[0042] According to a preferred aspect of the first aspect of the present application, the molar ratio between the TIBA and the catalyst is greater than 10:1 and preferably not greater than 300:1, more preferably in the range of 20:1 to 200:1, even more preferably 20:1 to 120:1.

[0043] Triisobutylaluminium is a known catalyst, for example commercially available from Witco GmbH (Germany). The generally accepted structural formula of triisobutylaluminium is

[0044] (iBu)3Al

[0045] where iBu is an isobutyl group.

[0046] The process of the first aspect of the present application uses a solvent selected from aliphatic and cycloaliphatic hydrocarbons, preferably aliphatic and cycloaliphatic hydrocarbons having a number of carbon atoms in the range of 5 to 10.

[0047] According to a preferred aspect of the first aspect of the present application, the solvent is selected from pentane, hexane, cyclohexane, heptane and mixtures thereof.

[0048] The process of the first aspect of the present application uses a catalyst having the general formula (I):

[0049]

[0050] According to a preferred aspect of the first aspect of the present application, R 1 and R 3 , equal to or different from each other, are linear or branched alkyl groups having 1 to 6 carbon atoms.

[0051] According to a preferred aspect of the first aspect of the present application, R 1 and R 3 , equal to or different from each other, are linear or branched alkyl groups selected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, isopentyl, 2-methyl-but-2-yl, 1-hexyl, 2-methyl-pent-2-yl, 3-methyl-pent-3-yl and isohexyl.

[0052] According to a preferred aspect of the first aspect of the present application, R 2 and R 4 , equal to or different from each other, are linear or branched arylalkyl groups having 7 to 10 carbon atoms.

[0053] According to a preferred aspect of the first aspect of the present application, R 2 and R 4 , equal to or different from each other, are linear or branched arylalkyl groups selected from compounds of general formula (2):

[0054]

[0055] wherein R 5 and R 6 , equal to or different from each other, are hydrogen or a linear or branched alkyl group having from 1 to 3 carbon atoms, and n is an integer from 0 to 3, with the proviso that the total number of carbon atoms of the compound of general formula (II) is from 7 to 10.

[0056] According to a preferred aspect of the first aspect of the application, the catalyst is present in an amount ranging from 0.0001 to 0.01 mol%, preferably from 0.0005 to 0.005 mol%, with respect to the total molar weight of the butadiene and styrene and / or substituted styrene.

[0057] The process of the first aspect of the application provides that the copolymerization reaction is carried out at a temperature ranging from 30°C to 100°C for a time equal to or less than 12 hours.

[0058] According to a preferred aspect of the first aspect of the application, the copolymerization reaction is carried out at a temperature ranging from 40°C to 90°C, advantageously from 50°C to 80°C.

[0059] According to a preferred aspect of the first aspect of the application, the copolymerization reaction is carried out for a time equal to or less than 10 hours, more preferably equal to or less than 6 hours, advantageously equal to or less than 3 hours.

[0060] According to a preferred aspect of the first aspect of the application, the copolymerization reaction is carried out at atmospheric pressure.

[0061] According to a preferred aspect of the first aspect of the application, the solution of butadiene and styrene and / or substituted styrene comprises butadiene in an amount ranging from 10% to 70% by weight, styrene in an amount ranging from 0% to 90% by weight and substituted styrene in an amount ranging from 90% to 0% by weight, with respect to the total weight of butadiene, styrene and / or substituted styrene contained in the solution.

[0062] According to a preferred aspect of the first aspect of the application, the solution comprises a total concentration of butadiene and styrene and / or substituted styrene equal to or greater than 2% by weight, preferably equal to or greater than 5% by weight, and advantageously ranging from 7% to 30% by weight, with respect to the total weight of the solution.

[0063] The copolymerization process is preferably carried out under controlled reaction conditions, i.e. under conditions excluding oxygen and humidity. If necessary, an inert gas such as argon or nitrogen can be used. The polymerization reaction starts with the addition of the catalyst to the solution of the comonomers and the co-catalyst mixture, and the temperature is brought to the desired value. The catalyst can be added as such or in solution.

[0064] The copolymerisation process is interrupted by the addition of a protic compound, for example an optionally acidified low molecular weight alcohol, such as methanol, ethanol and isopropanol, or by removal of solvent.

[0065] The copolymer formed is generally solid and can be recovered by conventional techniques, for example decanting, filtering, centrifuging and the like. The copolymer can then be purified by conventional techniques, for example washing or steam extraction, to remove impurities, typically impurities represented by volatile organic compounds.

[0066] The copolymer obtained from the process of the first aspect of the application has a stereoregular conformation, in particular the butadiene is in the trans conformation, the styrene and / or substituted styrene is in the isotactic conformation, and a random distribution.

[0067] For the purposes of the present specification and the following claims, the term "copolymer" is intended to include styrene / butadiene copolymers, substituted styrene / butadiene copolymers, and / or styrene / substituted styrene / butadiene copolymers obtained from the process of the first aspect of the application.

[0068] The trans conformation of butadiene refers to the geometric arrangement of butadiene monomers in which the two single chain growth bonds are arranged on opposite sides relative to the central double bond, as shown in the following structural formula:

[0069]

[0070] The isotactic conformation of styrene or substituted styrene refers to the isotactic arrangement of styrene or substituted styrene monomers, i.e. an arrangement in which the carbon atom carrying the styrene or substituted styrene group has the same relative configuration and the styrene or substituted styrene group has the same spatial arrangement relative to the plane (i.e. the styrene groups are all arranged above the plane or all arranged below the plane), as shown in the following structural formula (where R is hydrogen or a substituent group):

[0071]

[0072] The random arrangement of the copolymer refers to the random arrangement of butadiene, styrene and / or substituted styrene monomers in the polymer chain.

[0073] Preferably, the term substituted styrene refers to a compound of the formula S-R, wherein S is a styrene residue and R can be a substituent group, preferably attached in the para or ortho position relative to the vinyl group, selected from linear or branched alkyl groups containing 1 to 20, preferably 1 to 10, more preferably 1 to 5 carbon atoms, linear or branched alkenyl groups containing 2 to 20, preferably 2 to 10, more preferably 2 to 5 carbon atoms, halogens or groups containing one or more silicon atoms.

[0074] Advantageously, the substituted styrene monomer is selected from p-methylstyrene, o-methylstyrene, p-isopropylstyrene, p-tert-butylstyrene, p-fluorostyrene, p-chlorostyrene and p-trimethylsilylstyrene.

[0075] Preferably, the copolymer obtained by the method of the first aspect of the invention has a molecular weight dispersion index (D) in the range of 1 to 5, more preferably 1.5 to 3.5. The dispersion index is calculated by the relationship D = Mw / Mn, where Mw represents the weight-average molecular weight and Mn represents the number-average molecular weight.

[0076] From different perspectives, the second and third aspects of the present invention both relate to tires for vehicle wheels and elastomeric compounds for producing the tires.

[0077] According to preferred aspects of the second and third aspects of the invention, the tire comprises:

[0078] - A carcass structure having opposite side edges connected to a corresponding bead structure;

[0079] - Optionally, a belt structure applied at a radially outer position relative to the carcass structure;

[0080] - A crown applied at a radially external position relative to the carcass and / or belt structure.

[0081] According to preferred aspects of the second and third aspects of the invention, the elastomeric compound is used to produce the tire crown.

[0082] According to preferred aspects of the second and third aspects of the invention, the elastomeric compound comprises the copolymer in an amount ranging from 1 phr to 30 phr, preferably from 5 phr to 20 phr, and more preferably from 7 phr to 15 phr.

[0083] According to preferred aspects of the second and third aspects of the invention, the copolymer has a molecular weight of less than 500,000, preferably less than 300,000, more preferably less than 200,000, and even more preferably in the range of 50,000 to 200,000.

[0084] According to preferred aspects of the second and third aspects of the invention, the copolymer has a butadiene content ranging from 30% to 90% by weight, preferably from 40% to 80% by weight, relative to the total weight of the copolymer, and a styrene and / or substituted styrene content ranging from 10% to 70% by weight, preferably from 20% to 60% by weight, relative to the total weight of the copolymer.

[0085] Advantageously, the copolymer is co-crosslinked with the crosslinkable elastomer during vulcanization.

[0086] In the present description, the term "elastomeric compound" means the product obtained by mixing at least one elastomeric polymer with at least one of the additives commonly used for preparing tire compounds and with the copolymer described herein and optionally heating.

[0087] The expression "elastomeric polymer" or "rubber" means a natural or synthetic polymer which, after vulcanization, can be repeatedly stretched at room temperature to at least twice its original length and substantially immediately after removal of the stretching load, forcibly recovers to approximately its original length (according to the definition of the standard terminology relating to rubber, ASTM D1566-11).

[0088] The elastomeric polymer can be selected from those commonly used in sulfur-crosslinkable elastomeric materials particularly suitable for the production of tires, i.e. from elastomeric polymers or copolymers having unsaturated chains with a glass transition temperature (Tg) generally lower than 20°C, preferably ranging from 0°C to -110°C. These polymers or copolymers can be of natural origin or can be obtained by solution, emulsion or gas-phase polymerization of one or more conjugated dienes, optionally mixed with an amount not higher than 60% by weight of at least one comonomer selected from monovinylarenes and / or polar comonomers.

[0089] Preferably, the diene elastomeric polymer can be selected, for example, from: cis-1,4-polyisoprene (natural or synthetic, preferably natural rubber), 3,4-polyisoprene, polybutadiene (in particular polybutadiene with a high 1,4-cis content), optionally halogenated isoprene / isobutylene copolymers, 1,3-butadiene / acrylonitrile copolymers, styrene / 1,3-butadiene copolymers, styrene / isoprene / 1,3-butadiene copolymers, styrene / 1,3-butadiene / acrylonitrile copolymers and mixtures thereof.

[0090] Examples of additives commonly used for preparing tire compounds are represented by: (a) reinforcing fillers, such as carbon black and / or silica, (b) coupling agents, which usually comprise silane groups, (c) vulcanizing agents, such as sulfur or sulfur derivatives, (d) accelerators, such as dithiocarbamates, guanidines, thioureas, thiazoles, sulfenamides, thiurams, amines, xanthates and mixtures thereof, (e) activators, usually zinc and / or zinc compounds, (f) flame retardants, (g) antioxidants, (h) anti-aging agents, (i) tackifiers, (1) anti-ozonants, (m) modifying resins, or mixtures thereof.

[0091] Figure 1 A cross-sectional half of a tire for motor vehicle wheels is shown, which illustrates an embodiment according to the second and third aspects of the application.

[0092] In Figure 1In the drawings, "a" indicates the axial direction, "X" indicates the radial direction, in particular X-X indicates the profile of the equatorial plane. For simplicity, Figure 1 Only a portion of the tyre is shown, the remaining portion not being shown is identical and arranged symmetrically with respect to the equatorial plane "X-X".

[0093] The tyre 100 for vehicle wheels comprises at least one carcass structure comprising at least one carcass layer 101 made of elastomeric compound having respectively opposite end flaps 101a joined with respective annular anchoring structures 102, called bead cores, possibly associated with bead fillers 104. The tyre region comprising the bead cores 102 and the filler strips 104 forms a bead structure 103 intended to anchor the tyre to the respective mounting rim (not shown). Reinforcing layers 120 can be added between the at least one carcass layer 101 and the bead structure 103, consisting of a plurality of textile cords incorporated within elastomeric compound layers, commonly called "turnups". Protective layers 121 can be added between the at least one carcass layer 101 and the wear strip 105, consisting of a plurality of cords incorporated within elastomeric compound rubber layers, commonly called "bead turnups". The carcass structure is associated with a belt structure 106 comprising one or more belt layers 106a, 106b placed radially superimposed with respect to each other and with respect to the carcass layer, usually having textile and / or metal reinforcing cords incorporated within elastomeric compound layers. In radially outermost position of the belt layers 106a, 106b, at least one zero-degree reinforcing layer 106c can be applied, commonly called "0° belt", which usually comprises textile and / or metal reinforcing cords incorporated within elastomeric compound layers. In radially external position with respect to the belt structure 106, the crown 109 is applied made of elastomeric compound comprising at least one of butadiene and styrene and / or substituted styrene copolymers obtained by the above described method.

[0094] In radially external position, the crown 109 has a rolling portion 109a intended for ground contact. A circumferential groove is usually formed in this portion 109a, for simplicity indicated as smooth in the drawings, by transversal notches (not shown in the drawings) connected so as to define a plurality of blocks of various shapes and sizes distributed in the rolling portion 109a. Figure 1 Figure 1

[0095] In order to optimize the performance of the tread, the crown can be made in two-layer structure.

[0096] ​​This two-layer structure comprises a rolling layer or portion 109a, referred to as a cap, and a substrate 111, referred to as a base, forming a so-called cap-base structure. Thus, it is possible to use an elastomeric material capable of providing a low rolling resistance for the cap, while providing high wear resistance and crack formation resistance, while the elastomeric material of the base can be specifically targeted for low hysteresis, to cooperate in reducing the rolling resistance, one or both layers can be made of an elastomeric material comprising at least one of butadiene and styrene and / or a substituted styrene copolymer obtained by the above-mentioned process.

[0097] In fact, the Applicant believes that the above-mentioned copolymers can find advantageous application in other components of the tyre, in addition to the tread.

[0098] Furthermore, respective side walls 108 of the elastomeric compound are applied in axially external positions on the lateral surfaces of the carcass structure, each side wall 108 extending from one of the lateral edges of the crown 109 at the respective bead structure 103.

[0099] Optionally, a wear strip 105 made of an elastomeric material comprising at least one of butadiene and styrene and / or a substituted styrene copolymer obtained by the above-mentioned process is arranged in an external position of each bead structure 103, so as to enclose the bead structure 103 along the axially internal and external and radially internal regions of the bead structure 103, so as to be interposed between the bead structure 103 and the rim when the tyre 100 is mounted on the rim.

[0100] A strip 110, commonly referred to as "mini side wall", composed of an elastomeric compound can be present in the connection region between the side walls 108 and the crown 109. In the case of a tubeless tyre, a rubber layer 112, commonly referred to as "liner", which provides the necessary impermeability to the inflation air of the tyre, can also be provided in a radially internal position with respect to the carcass layer 101.

[0101] The present application will be further illustrated below by a number of preparative examples, which are for illustrative purposes only and not any limitation of the present application.

[0102] For the purposes of the present description and of the following claims, unless otherwise indicated, all numbers expressing quantities, values, percentages, etc. must be interpreted as being modified in all instances by the term "about". Furthermore, all ranges include any combination of the maximum and minimum points described, including any intermediate ranges that can or can not be specifically enumerated herein. Examples

[0103] Example 1

[0104] The hexane solvent, styrene monomer and m-MAO activator (m-MAO 3A-Akzo Nobel, The Netherlands) were added to a flask equipped with a magnetic stirrer at room temperature. After cooling the mixture to 0°C, the butadiene solution was added. After stirring for about 20 minutes, the catalyst was added to the solution and the reaction was carried out at the temperatures and times indicated in Table 1 below. The reaction was ended by adding ethanol and then the solution was poured into an acidified solution of ethanol and butylated hydroxytoluene (BHT). The precipitated copolymer was recovered by filtration and dried in an oven at 40°C under vacuum. The amounts of the components of the reaction solution and the reaction conditions are summarized in Table 1 below.

[0105] Table 1

[0106] butadiene 14g styrene 9.3g Catalyst 1 (CAT1) 10 μmol m-MAO:CAT1 ratio 500:1 hexane 130ml reaction temperature 70℃ reaction time 3 hours

[0107] The catalyst 1 present in an amount equal to about 0.003 mole % (with respect to the total moles of styrene and butadiene) has the following formula, wherein Ph represents a phenyl group:

[0108]

[0109] The reaction yield was 59% obtaining a styrene-butadiene copolymer having a weight average molecular weight (Mw) equal to about 191,000 Dalton (Da) and a polydispersity index equal to 2.2.

[0110] During the reaction, it was observed that an inhomogeneous dispersion was formed by the precipitation of the copolymer. The precipitation of the copolymer during the reaction leads to the formation of an inhomogeneous system, which is not advantageous in an industrial process.

[0111] Example 2

[0112] The steps of Example 1 were repeated, the amounts of the components of the reaction solution and the reaction conditions being as indicated in Table 2.

[0113] Table 2

[0114] butadiene 4.50g styrene 2.73g Catalyst 2 (CAT2) 25 μmol m-MAO:CAT2 ratio 500:1 hexane 40ml reaction temperature 50℃ reaction time 4 hours

[0115] The catalyst 2 present in an amount equal to about 0.02 mole % (with respect to the total moles of styrene and butadiene) has the following formula:

[0116]

[0117] The reaction yield was 27% obtaining a styrene-butadiene copolymer having a weight average molecular weight (Mw) equal to about 25,000 Dalton (Da) and a polydispersity index equal to 1.6.

[0118] During the reaction, the solution remained clear or slightly turbid, forming a light precipitate that did not affect the homogeneity of the mixture. The reaction yield and the molecular weight were considered too low, thus both from an industrial and an applicative point of view.

[0119] Example 3

[0120] The procedure of Example 1 was repeated with the amounts of the components of the reaction solution and the reaction conditions shown in Table 3.

[0121] Table 3

[0122] butadiene 14g styrene 6g Catalyst 3 (CAT3) 10 μmol m-MAO:CAT3 ratio 500:1 hexane 130ml reaction temperature 70℃ reaction time 16 hours

[0123] The catalyst 3, present in an amount equal to about 0.003% by moles (with respect to the total moles of styrene and butadiene), has the following formula, wherein Ad indicates an adamantyl group:

[0124]

[0125] The reaction yield was 10% and a styrene-butadiene copolymer was obtained having a weight average molecular weight (Mw) equal to about 20,000 Dalton (Da) and a polydispersity index equal to 1.7.

[0126] During the reaction, the solution remained clear or slightly turbid, forming a light precipitate that did not affect the homogeneity of the mixture. Despite the very long reaction time, the reaction yield and the molecular weight were considered too low, thus both from an industrial and an applicative point of view.

[0127] Example 4

[0128] The procedure of Example 1 was repeated with the amounts of the components of the reaction solution and the reaction conditions shown in Table 4.

[0129] Table 4

[0130]

[0131]

[0132] The catalyst 4, present in an amount equal to about 0.003% by moles (with respect to the total moles of styrene and butadiene), has the following formula, wherein Ph indicates a phenyl group:

[0133]

[0134] The reaction yield was 90% and a styrene-butadiene copolymer was obtained having a weight average molecular weight (Mw) equal to about 125,000 Dalton (Da) and a polydispersity index equal to 2.2.

[0135] During the reaction, the solution remained clear or slightly turbid, forming a light-colored precipitate that did not affect the homogeneity of the mixture. The reaction time required to reach an acceptable yield and molecular weight was equal to 16 hours, which is disadvantageous from an industrial point of view.

[0136] Example 5

[0137] The procedure of Example 1 was repeated with the addition of triisobutylaluminum (TIBA - Witco GmbH, Germany) together with the m-MAO, using the amounts of the components of the reaction solution and the reaction conditions as shown in Table 5.

[0138] Table 5

[0139]

[0140]

[0141] The results in terms of conversion yield (% conversion), weight average molecular weight (Mw) and polydispersity index (D) are summarized in Table 5A below.

[0142] Table 5A

[0143] conversion % Mw (Da) D appearance 1 59.0 191,000 2.2 hazy 2 49.0 100,000 2.2 clear

[0144] Surprisingly, no precipitate was observed in Test 2 and the reaction solution remained clear until the completion of the reaction.

[0145] The reaction yield and the molecular weight of the obtained copolymer, although lower than those of the previous tests, remained at a good level, with a reaction time fully compatible with an industrial process.

[0146] Example 6

[0147] The procedure of Test 2 of Example 5 was repeated with the same amounts of the components of the reaction solution and the reaction conditions shown in Table 5, but using a catalyst 5 (CAT 5) having the following formula:

[0148]

[0149] A conversion yield of 75% was found, obtaining a copolymer having a weight average molecular weight of about 184,000 Da and a polydispersity index of about 2.2. Also in this test, no precipitate was observed and the reaction solution remained clear until the completion of the reaction.

[0150] By comparing the data of the copolymer obtained with Example 5 (obtained with catalyst 1) with the data of the copolymer obtained in that example (with catalyst 5), it was surprisingly observed that the glass transition temperature (Tg) of the latter copolymer (-35.0°C) is higher than the Tg of the first copolymer (-43.4°C), despite having similar composition and molecular weight.

[0151] This feature can be used to employ this copolymer in the production of elastomeric compounds for tires, since by suitably varying the process conditions, it is possible to advantageously determine the optimal values of the Tg of different types of tires (summer, winter, all-season, sport) with the same styrene content and molecular weight of the copolymer.

[0152] Example 7

[0153] The procedure of test 2 of Example 5 was repeated for different reaction times, using different relative amounts of styrene and butadiene, catalysts 1 and 5 being present in an amount equal to about 0.003% by moles (with respect to the total moles of styrene and butadiene), maintaining the m-MAO:CATn ratio equal to 500 and the TIBA / CATn ratio equal to 80.

[0154] The following Tables 7A, 7B and 7C summarize the results obtained with a reaction time of 3, 6 and 10 hours, respectively, with a styrene:butadiene weight ratio equal to 30:70, 35:65 and 40:60, respectively. The following Table 7D summarizes the results obtained with a reaction time of 3 hours, with a styrene:butadiene weight ratio equal to 50:50. The reaction temperature was always 70°C.

[0155] Table 7A

[0156] Styrene 30% - Butadiene 70%

[0157]

[0158] Table 7B

[0159] Styrene 35% - Butadiene 65%

[0160]

[0161]

[0162] Table 7C

[0163] Styrene 40% - Butadiene 60%

[0164] test CATn time (h) conversion % Tg Mw D 1 1 3 44 -36.9 130 1.7 2 5 3 46 -27.5 136 1.8 3 1 6 74 -43.4 167 2.0 4 5 6 75 -35.0 184 2.2 5 1 10 81 -33.6 182 2.6 6 5 10 77 -26.4 176 2.2

[0165] Table 7D

[0166] 50% Styrene - 50% Butadiene

[0167] test CATn time (h) conversion % Tg Mw D 1 1 3 46 -24.6 140 1.9 2 5 3 53 -4.2 99 1.6

[0168] The experiments carried out confirmed that the procedure allows to obtain a clear solution with good yields and molecular weight values, and the reaction time ranges from 6 to 10 hours at different styrene / butadiene percentages, even if the percentage of styrene is equal to 50% w / w.

[0169] It was also confirmed that the styrene:butadiene copolymers obtained using catalyst 5 allow to obtain Tg values higher than those obtained from the use of catalyst 1, it was also observed that, under the same conditions, Tg increases with the increase of the percentage of styrene.

[0170] Example 8

[0171] The procedure of Example 1 was repeated as follows: the reaction was carried out at 70°C for 3 hours, substituting partially the styrene (S) with para-methylstyrene (PMS) and keeping constant the amount of butadiene (BD), as shown in Table 8, using catalyst 1 in an amount equal to about 0.003% mol (with respect to the total moles of monomers used) and m-MAO:CAT1 and TIBA / CAT1 ratios equal to 500:1 and 80:1, respectively.

[0172] In tests 4 and 5, the TIBA / CAT1 ratio was increased to 180:1 and in test 5 the reaction time was prolonged to 4 hours.

[0173] Table 8

[0174] test S(％) PMS (%) BD (%) conversion % appearance Mw (Da) D 1 40 0 60 49 clear 100 1.63 2 25 15 60 84 clear 160 2.05 3 10 30 60 90 clear 159 2.09 4 0 40 60 89 clear 164 1.80 5 0 40 60 95 clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear clear 194 1.90

[0175] In the systems used, the increase of the percentage of conversion and of the molecular weight is directly proportional to the increase of the para-methylstyrene content. The increase of the reaction time of test 5 leads to almost quantitative yields (95%) and to the formation of polymers with high molecular weight.

Claims

1. A process for the copolymerization of butadiene and styrene and / or substituted styrene, which process comprises (i) preparing a solution of butadiene and styrene and / or substituted styrene in a solvent, (ii) adding to said solution a homogeneous catalytic system, (iii) carrying out the copolymerization reaction at a temperature ranging from 30°C to 100°C for a time of 12 hours or less, and (iv) recovering the copolymer obtained, characterized in that said solvent is selected from aliphatic and cycloaliphatic hydrocarbons, and said homogeneous catalytic system comprises: (a) a catalyst of general formula (I) Where R 1 and R 3 They may be the same as or different from each other, and are straight-chain or branched alkyl groups having 1 to 10 carbon atoms, and R 2 and R 4 They may be the same as or different from each other, and are straight-chain or branched arylalkyl groups having 7 to 14 carbon atoms. (b) a cocatalyst mixture comprising modified methylaluminoxane (m-MAO) and triisobutylaluminium (TIBA).

2. The copolymerization process according to claim 1, characterized in that The molar ratio between said m-MAO and said catalyst is equal to or greater than 50:

1.

3. The copolymerization process according to claim 1, characterized in that The molar ratio between said TIBA and said catalyst is greater than 10:

1.

4. The copolymerization process according to claim 1, characterized in that said solvent is selected from aliphatic and cycloaliphatic hydrocarbons having from 5 to 10 carbon atoms.

5. The copolymerization process according to claim 1, characterized in that R 1 and R 3 , equal to or different from each other, are linear or branched alkyl groups having from 1 to 6 carbon atoms.

6. The copolymerization process according to claim 1, characterized in that R 1 and R 3 , equal to or different from each other, are linear or branched alkyl selected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, isopentyl, 2-methyl-but-2-yl, 1-hexyl, 2-methyl-pent-2-yl, 3-methyl-pent-3-yl and isohexyl.

7. The copolymerization process according to claim 1, characterized in that R 2 and R 4 , equal to or different from each other, are linear or branched arylalkyl groups having from 7 to 10 carbon atoms.

8. The copolymerization process according to claim 1, characterized in that R 2 and R 4 , equal to or different from each other, are selected from linear or branched arylalkyl groups of general formula (II): characterized in that R 5 and R 6 , equal to or different from each other, are hydrogen or a linear or branched alkyl group having from 1 to 3 carbon atoms, and n is an integer from 0 to 3, provided that the total number of carbon atoms of the compound of general formula (II) is from 7 to 10.

9. The copolymerization process according to claim 1, characterized in that said catalyst is present in an amount ranging from 0.0001% to 0.01% by moles with respect to the total molar weight of said butadiene and styrene and / or substituted styrene.

10. The copolymerization process according to claim 1, characterized in that said copolymerization reaction is carried out at a temperature ranging from 40°C to 90°C.

11. The copolymerization process according to claim 1, characterized in that said copolymerization reaction is carried out for a time equal to or lower than 10 hours.

12. The copolymerization process according to claim 1, characterized in that said solution comprises a total concentration of butadiene and styrene and / or substituted styrene equal to or greater than 2% by weight with respect to the total weight of said solution.

Images