Functionalized diene elastomer, and rubber composition containing same

Abstract

The present invention relates to a specific functionalized diene elastomer. This functionalized elastomer exhibits a reduced cold flow without, however, damaging the properties of a reinforced rubber composition in which it is present, in particular the processing properties and the hysteresis properties. This functionalized diene elastomer carries, at the chain end, a silanol functional group or a polysiloxane block having a silanol end and is partially coupled by or star-branched by tin.

Claims

1. A diene elastomer, wherein: from 75% to 95% by weight of the diene elastomer is monofunctional and carries, at just one chain end, a silanol functional group or a polysiloxane block having a silanol end, the other end being devoid of any functionalization, and from 5% to 25% by weight of the diene elastomer is coupled by or star-branched by tin.

2. The elastomer according to claim 1, wherein the polysiloxane block having a silanol end corresponds to the formula:
[(SiR.sub.1R.sub.2O).sub.xH] wherein: R.sub.1 and R.sub.2, which are identical or different, represent an alkyl, cycloalkyl, aryl, alkaryl, aralkyl or vinyl group having from 1 to 10 carbon atoms, and x is an integer ranging from 1 to 1500.

3. The elastomer according to claim 2, wherein R.sub.1 and R.sub.2, which are identical or different, represent an alkyl group having from 1 to 5 carbon atoms.

4. The elastomer according to claim 1, wherein 10% to 25% by weight of the diene elastomer is the diene elastomer coupled by or star-branched by tin.

5. The elastomer according to claim 1, wherein the diene elastomer coupled by or star-branched by tin is an elastomer star-branched by tin.

6. The elastomer according to claim 5, wherein the diene elastomer star-branched by tin is an elastomer comprising four branches.

7. The elastomer according to claim 1, wherein the diene elastomer is a butadiene/styrene copolymer.

8. An elastomer rubber composition based on at least one reinforcing filler comprising an inorganic filler and on an elastomer matrix, wherein the elastomer matrix comprises at least one diene elastomer according to claim 1.

9. The composition according to claim 8, wherein the elastomer matrix further comprises at least one conventional diene elastomer.

10. The composition according to claim 8, wherein the proportion of inorganic filler in the reinforcing filler is greater than 50% by weight, with respect to the total weight of the reinforcing filler.

11. The composition according to claim 8, wherein the reinforcing inorganic filler is composed of silica.

12. A semifinished article made of rubber for tires, comprising: a crosslinkable or crosslinked rubber composition according to claim 8.

13. A semifinished article according to claim 12, wherein said article is a tread.

14. A tire comprising: a semifinished article according to claim 12.

15. A process for reducing the cold flow of a monofunctional diene elastomer carrying, at just one chain end, a silanol functional group or a polysiloxane block having a silanol end, the other end being devoid of any functionalization, comprising, prior to its conditioning, modifying the monofunctional diene elastomer by adding a diene elastomer coupled by or star-branched by tin in a proportion of from 5 to 35% by weight, with respect to the weight of the monofunctional diene elastomer.

16. A process for reducing the cold flow of a monofunctional diene elastomer carrying, at just one chain end, a silanol functional group or a polysiloxane block having a silanol end, the other end being devoid of any functionalization, comprising: on conclusion of polymerization of a diene elastomer, coupling or star-branching from 5 to 25% by weight of the living elastomer by a tin-based compound, and then functionalizing the 75 to 95% by weight of a remaining living elastomer with a functionalization agent capable of introducing the silanol functional group or the polysiloxane block having a silanol end.

Description

EXAMPLES

(1) I Preparation of an elastomer matrix according to the invention

(2) 1) Measurements and Tests UsedExperimental Techniques Used for the Precuring Characterization of the Polymers Obtained:

(3) (a) Determination of the distribution in molar masses by the steric exclusion chromatography technique (conventional SEC)

(4) The SEC (size exclusion chromatography) technique was used to determine the distributions in molecular weights relative to samples of these polymers. This technique has made it possible, starting from standard products having the characteristics described in Example 1 of the document of European Patent EP-A-692 493, to evaluate, for a sample, a number-average molecular weight (Mn) which has a relative value, unlike that determined by osmometry, and also a weight-average molecular weight (Mw). The polydispersity index (PI=Mw/Mn) of this sample, calculated via a Moore calibration, was subsequently deduced.

(5) According to this technique, the macromolecules are separated physically, according to their respective sizes in the swollen state, in columns filled with a porous stationary phase. Before carrying out this separation, the sample of polymer is dissolved in tetrahydrofuran at a concentration of approximately 1 g/l. The solution is then filtered through a filter with a porosity of 0.45 m before injection.

(6) A chromatograph sold under the name Waters Alliance 2690, equipped with an in-line degasser, is used for the abovementioned separation. The elution solvent is tetrahydrofuran, the flow rate is 1 ml/min, the temperature of the system is 35 C. and the analysis time is 30 min. Use is made of a set of two Waters columns, Styragel HT6E type, arranged in series.

(7) TABLE-US-00001 Range of Size of molar Internal the References masses Length diameter particles Trade (by way of Number Brand (g/mol) (mm) (mm) (m) name indication) Column 1 Waters 2000-10.sup.7 300 7.8 10 Styragel WAT044219 HT6E Column 2 Waters 2000-10.sup.7 300 7.8 10 Styragel WAT044219 HT6E

(8) The injected volume of the polymer sample solution is 100 l. The detector is a Waters model 2410 differential refractometer. Use is made of systems software for the chromatographic data having the trade name Waters Empower.

(9) The calculated average molar masses are relative to a calibration curve produced for SBRs with the following microstructure: 25% by weight of units of styrene type, 23% by weight of units of 1,2-type and 50% by weight of units of trans-1,4-type. (b) For the polymers and rubber compositions, the Mooney viscosities ML (1+4) at 100 C. are measured according to Standard ASTM D-1646.

(10) Use is made of an oscillating consistometer as described in Standard ASTM D-1646. The Mooney plasticity measurement is carried out according to the following principle: the composition in the raw state (i.e., before curing) is moulded in a cylindrical chamber heated to 100 C. After preheating for one minute, the rotor rotates within the test specimen at 2 revolutions/minute and the working torque for maintaining this movement is measured after rotating for 4 minutes. The Mooney plasticity (ML 1+4) is expressed in Mooney unit (MU, with 1 MU=0.83 N.m). (c) The glass transition temperatures Tg of the polymers are measured using a differential scanning calorimeter. (d) The CH.sub.3Si(SBR).sub.2OH functionalization in the middle of the chain or the SBR(CH.sub.3).sub.2SiOH functionalization at the chain end is characterized by 2D .sup.1H.sup.29Si NMR and quantified by .sup.1H NMR.

(11) The 2D .sup.1H-.sup.29Si NMR spectrum makes it possible to confirm the nature of the functional group by virtue of the chemical shift values of the silicon nuclei and of the protons in the .sup.2J vicinity (via two bonds). It uses a .sup.2J.sub.1H-29Si coupling constant value of 8 Hz. The chemical shift of the silicon of the entity SBR(CH.sub.3).sub.2SiOH at the chain end is approximately 11-12 ppm.

(12) The .sup.1H NMR spectrum makes it possible to quantify the functional group by integration of the signal characteristic of the protons of the methyl group carried by the silicon CH.sub.3Si, situated in the vicinity of =0 ppm. The samples are dissolved in carbon disulphide (CS.sub.2). 100 L of deuterated cyclohexane (C.sub.6D.sub.12) are added for the lock signal. The NMR analyses are carried out on a 500 MHz Bruker spectrometer equipped with a 5 mm broad band BBI probe. For the quantitative .sup.1H NMR experiment, the sequence uses a 30 pulse and a repetition time of 2 seconds. (e) The .sup.13C NMR technique (Beebe, D. H., Polymer, 1978, 19, 231-33, or Bradbury, J. H., Elix, J. A. and Perera, M. C. S., Journal of Polymer Science, 1988, 26, 615-26) is used to determine the microstructure of the elastomers obtained. The .sup.13C NMR analyses are carried out on a 250 MHz Bruker spectrometer equipped with a 10 mm .sup.13C-.sup.1H dual probe. The elastomer is dissolved in CDCl.sub.3 at a concentration of approximately 75 g/l. The quantitative .sup.13C NMR experiment uses a sequence with .sup.1H decoupling and suppression of the Overhauser effect (inverse gated .sup.1H-decoupling), a 90 pulse and a repetition time=6 s. The spectral width is 200 ppm and the number of scans is 8192. The spectra are calibrated on the central peak of the triplet of the CDCl.sub.3 at 77 ppm. (f) For the polymers, the intrinsic viscosity at 25 C. of a 0.1 g/dl solution of polymer in toluene is measured starting from a solution of dry polymer:

(13) Principle:

(14) The intrinsic viscosity is determined by the measurement of the flow time t of the polymer solution and of the flow time t.sub.o of the toluene in a capillary tube.

(15) The flow time of the toluene and the flow time of the 0.1 g/dl polymer solution are measured in a Ubbelohde tube (diameter of the capillary 0.46 mm, capacity from 18 to 22 ml) placed in a bath thermostatically controlled at 250.1 C.

(16) The intrinsic viscosity is obtained by the following relationship:

(17) ${}_{\mathrm{int}}=\frac{1}{C}\ln \left[\frac{\left(t\right)}{\left(t_o\right)}\right]$ with: C: concentration of the toluene solution of polymer in g/dl; t: flow time of the toluene solution of polymer in seconds; t.sub.o: flow time of the toluene in seconds; .sub.int: intrinsic viscosity, expressed in dl/g. (g) For the polymers, the cold flow: CF100(1+6), results from the following measurement method:

(18) It is a matter of measuring the weight of rubber extruded through a calibrated die over a given time (6 hours), under fixed conditions (at 100 C.). The die has a diameter of 6.35 mm for a thickness of 0.5 mm.

(19) The cold flow apparatus is a cylindrical cup pierced at the base. Approximately 40 g4 g of rubber, preprepared in the form of a pellet (thickness of 2 cm and diameter of 52 mm), are placed in this device. A calibrated piston weighing 1 kg (5 g) is positioned on the rubber pellet. The assembly is subsequently placed in an oven thermally stabilized at 100 C.0.5 C.

(20) During the first hour in the oven, the measurement conditions are not stabilized. After one hour, the product which has extruded is thus cut off and discarded.

(21) The measurement subsequently lasts 6 hours5 min, during which the product is left in the oven. At the end of the 6 hours, the extruded product sample has to be recovered by cutting it flush with the surface of the base. The result of the test is the weight of rubber, weighed in grams.

(22) 2) Preparation of a Copolymer a Functionalized with SiOH at the Chain End

(23) Cyclohexane, butadiene, styrene and tetrahydrofurfuryl ethyl ether are introduced continuously, according to respective flow rates by weight of 100/11/3.2/0.037, into a 32.5 l reactor equipped with a stirrer of turbine type. 200 micromol of n-butyllithium (n-BuLi) per 100 g of monomers are introduced at the line inlet in order to neutralize the protic impurities introduced by the various constituents present in the line inlet. 530 mol of n-BuLi per 100 g of monomers are introduced at the inlet of the reactor.

(24) The various flow rates are adjusted so that the mean residence time in the reactor is 40 min. The temperature is maintained at 80 C.

(25) The degree of conversion, which is measured on a sample withdrawn at the reactor outlet, is 98%.

(26) Finally, at the reactor outlet, 265 micromol of hexamethylcyclotrisiloxane, in solution in cyclohexane, per 100 g of monomers are added to the living polymer solution (on an in-line static mixer). The copolymer is then subjected to an antioxidizing treatment using 0.8 phr of 2,2-methylenebis(4-methyl-6-(tert-butyl)phenol and 0.2 phr of N-(1,3-dimethylbutyl)-N-phenyl-p-phenylenediamine.

(27) The copolymer thus treated is separated from its solution by a steam stripping operation and is then dried on an open mill at 100 C. for 20 min, in order to obtain the copolymer functionalized with SiOH at the chain end.

(28) The ML viscosity of this copolymer A is 53. The molecular weight of the copolymer, determined by conventional SEC, is 123 000 g/mol and the PI is 2.0.

(29) The microstructure of this copolymer A is determined by .sup.13C NMR.

(30) The SBR block of this copolymer A comprises 25% of styrene (by weight) and, for its butadiene part, 58% of vinyl units, 21% of cis-1,4-units and 21% of trans-1,4-units.

(31) The 2D .sup.1H-.sup.29Si NMR analysis allows it to be concluded that there exists a chain-end functional group SER(CH.sub.3).sub.2SiOH. The content of (CH.sub.3).sub.2Si functional groups, determined by .sup.1H NMR, for the copolymer A is 5.85 mmol/kg.

(32) 3) Preparation of a Copolymer B Star-Branched by Tin:

(33) The synthesis of the copolymer B is carried out according to the operating conditions described in Test 1, except that tin tetrachloride is added in place of the hexamethylcyclotrisiloxane, 265 micromol of tin tetrachloride in solution in cyclohexane per 100 g of monomers.

(34) The ML viscosity of the copolymer B is 104. The molecular weight of the copolymer, determined by conventional SEC, is 209 000 g/mol and the PI is 2.1.

(35) The microstructure of this copolymer B is determined by .sup.13C NMR.

(36) The SBR block of this copolymer B comprises 25% of styrene (by weight) and, for its butadiene part, 58% of vinyl units, 21% of cis-1,4-units and 21% of trans-1,4-units.

(37) 4) Preparation of Elastomer Matrices, Mixtures of the Copolymer A and Copolymer B:

(38) 5 kg of cyclohexane, 285 g of polymer A and 15 g of polymer B are added to a 10 litre reactor and this mixture is placed at 60 C. for 5 hours. The copolymer thus treated is separated from its solution by a steam stripping operation and is then dried on an open mill at 100 C. for 20 min, in order to obtain the copolymer C.

(39) TABLE-US-00002 Copolymer Copolymer B Cold Copolymer A (g) (g) Mn SEC PI flow C 285 15 119 000 2.0 1.83 D 270 30 119 000 2.1 1.40 E 240 60 125 000 2.0 0.84 F 210 90 129 000 2.1 0.41

(40) II Comparative examples of rubber compositions

(41) 1) Measurements and tests used (h) The Mooney viscosity ML (large) and MS (small) (1+4) at 100 C.: measured according to Standard ASTM: D-1646, entitled Mooney in the tables. The results are in relative data: an increase with respect to the control at 100 indicates an increase in the viscosity and thus a detrimentally affected processing. (i) The Shore A hardness: measurements carried out according to Standard DIN 53505. The results are in relative data: an increase with respect to the control at 100 indicates an increased stiffness. (j) The dynamic properties G* and tan()max are measured on a viscosity analyser (Metravib VA4000) according to Standard ASTM D 5992-96. The response of a sample of vulcanized composition (cylindrical test specimen with a thickness of 2 mm and with a cross section of 79 mm.sup.2), subjected to a simple alternating sinusoidal shear stress, at a frequency of 10 Hz, under the standard temperature conditions (23 C.) according to Standard ASTM D 1349-99, is recorded. A peak-to-peak strain amplitude sweep is carried out from 0.1% to 50% (outward cycle) and then from 50% to 0.1% (return cycle). The results made use of are the complex dynamic shear modulus (G*) and the loss factor tan . The maximum value of tan observed (tan()max), and the difference in complex modulus (G*) between the values at 0.1% and 50% strain (Payne effect), are shown for the return cycle. The results are in relative data: an increase with respect to the control at 100 indicates an increase in the hysteresis.

Example 1

Tg=25 C.

(42) The elastomers SBR C, SBR D, SBR E and SBR F were used for the preparation of rubber compositions C, D, E and F of tread type, each comprising silica as reinforcing filler.

(43) Each of these compositions C, D, E and F exhibits the following formulation (expressed as phr: parts per hundred parts of elastomer):

(44) TABLE-US-00003 BR (1) 23 SBR 77 Silica (2) 85 Carbon black (3) 4 Plasticizer (4) 12 Plasticizer (5) 18 Silane (6) 6.8 Stearic acid 2 DPG (7) 1.6 Antiozone wax 1.5 ZnO 1.5 6PPD (8) 1.9 Sulphur 1.2 Accelerator 1.9 (1) = BR with 4.3% of 1, 2 units; 2.7% of trans-1,4-units; 93% of cis-1,4-units (Tg = 106 C.) (2) = Zeosil 1163 MP silica from Rhodia (3) = N234 (4) = MES oil (Catenex SNR from Shell) (5) = polylimonene resin (Dercolyte L120 from DRT) (6) = TESPT coupling agent (Si69 from Degussa) (7) = diphenylguanidine (Perkacit DPG from Flexsys) (8) = N-(1,3-dimethylbutyl)-N-phenyl-para-phenylenediamine (Santoflex 6-PPD from Flexsys) (9) = CBS (Santocure from Flexsys)

(45) Each of the following compositions is produced, in a first step, by thermomechanical working and then, in a second finishing step, by mechanical working.

(46) The following are successively introduced into a laboratory internal mixer of Banbury type, the capacity of which is 400 cm.sup.3, which is 70% filled and which has a starting temperature of approximately 90 C.: the elastomer, two thirds of the silica, the black, the coupling agent and the diphenylguanidine, then, approximately one minute later, the remainder of the reinforcing filler, the MES oil, the resin, the antioxidant, the stearic acid and the antiozone wax and then, approximately two minutes later, the zinc oxide.

(47) The stage of thermomechanical working is carried out for 4 to 5 minutes, up to a maximum dropping temperature of approximately 160 C.

(48) The first abovementioned step of thermomechanical working is thus carried out, it being specified that the mean speed of the blades during this first step is 50 rev/min.

(49) The mixture thus obtained is recovered and cooled and then, in an external mixer (homofinisher), the sulphur and the accelerator are added at 30 C., the combined mixture being further mixed for a time of 3 to 4 minutes (second abovementioned step of mechanical working).

(50) The compositions thus obtained are subsequently calendered, either in the form of plaques (with a thickness ranging from 2 to 3 mm) or fine sheets of rubber, for the measurement of their physical or mechanical properties, or in the form of profiled elements which can be used directly, after cutting and/or assembling to the desired dimensions, for example as semifinished products for tyres, in particular for treads.

(51) The crosslinking is carried out at 150 C. for 40 min.

(52) TABLE-US-00004 TABLE 1 Composition A C D E F (% star branching) (0%) (5%) (10%) (20%) (30%) Elastomer SBR A SBR C SBR D SBR E SBR F ML 1 + 4 at 50 53 53 56 59 100 C. elastomer Cold flow 2.17 1.83 1.4 0.84 0.41 elastomer Properties in the noncrosslinked state ML (1 + 4) at 100 99 105 104 101 100 C. Properties in the crosslinked state Shore A 100 103 106 104 102 Dynamic properties as a function of the strain tan()max at 100 105 105 106 107 23 C.

(53) It is found that the cold flow resistance of the functionalized diene elastomer is significantly improved by increasing the content of copolymer star-branched by tin in the rubber composition, with respect to composition A in which it is not present. In addition, it is found, for the compositions C, D and E, that tan()max is maintained at acceptable values, despite the increase in the content of copolymer star-branched by tin at the expense of the copolymer functionalized at the chain end by a silanol functional group.

(54) The cold flow of the elastomershysteresis of the composition compromise is entirely satisfactory for the compositions C, D and E according to the invention respectively comprising, in their elastomer matrix, 5%, 10% and 20% of a copolymer star-branched by tin.