Silane, rubber mixture containing the silane, vehicle tire comprising the rubber mixture in at least one component, and process for producing the silane

Abstract

The invention relates to a silane, to a rubber mixture comprising the silane and to a vehicle tire which comprises the rubber mixture in at least one component, and to a process for producing the silane. The silane of the invention has the following formula I)
(R.sup.1).sub.oSi—R.sup.2—S—R.sup.3—S—R.sup.3—S—X,  I)
which, according to the invention, comprises the —R.sup.2—S—R.sup.3—S—R.sup.3— unit in the spacer group. The rubber mixture of the invention comprises at least one silane of the invention.

Claims

1. A silane of formula I):
(R.sup.1).sub.oSi—R.sup.2—S—R.sup.3—S—R.sup.3—S—X  I) wherein o may be 1, 2 or 3 and the R.sup.1 radicals may be identical or different and are selected from alkoxy groups having 1 to 10 carbon atoms, cycloalkoxy groups having 4 to 10 carbon atoms, phenoxy groups having 6 to 20 carbon atoms, aryl groups having 6 to 20 carbon atoms, alkyl groups having 1 to 10 carbon atoms, alkenyl groups having 2 to 20 carbon atoms, alkynyl groups having 2 to 20 carbon atoms, aralkyl groups having 7 to 20 carbon atoms, halides, or alkyl polyether groups —O—(R.sup.6—O).sub.r—R.sup.5 wherein R.sup.6 are identical or different and are branched or unbranched, saturated or unsaturated, aliphatic, aromatic or mixed aliphatic/aromatic bridging C.sub.1-C.sub.30 hydrocarbon groups, preferably —CH.sub.2—CH.sub.2—, r is an integer from 1 to 30, preferably 3 to 10, and R.sup.5 are unsubstituted or substituted, branched or unbranched, terminal alkyl, alkenyl, aryl or aralkyl groups, preferably —C.sub.13H.sub.27 alkyl group; or two R.sup.1 form a cyclic dialkoxy group having 2 to 10 carbon atoms, in which case o is <3; or two or more silanes of formula I) may be bridged via R.sup.1 radicals; wherein R.sup.2 and R.sup.3 may be identical or different and are selected from the group consisting of linear or branched alkylene groups having 1 to 20 carbon atoms or cycloalkyl groups having 4 to 12 carbon atoms or aryl groups having 6 to 20 carbon atoms or alkenyl groups having 2 to 20 carbon atoms, alkynyl groups having 2 to 20 carbon atoms or aralkyl groups having 7 to 20 carbon atoms; wherein the X group is a hydrogen atom or a —C(═O)—R.sup.4 group or an —SiR.sup.7.sub.3 group, where R.sup.4 and R.sup.7 are selected from C.sub.1-C.sub.20-alkyl groups, C.sub.4-C.sub.10-cycloalkyl groups, C.sub.6-C.sub.20-aryl groups, C.sub.2-C.sub.20-alkenyl groups and C.sub.7-C.sub.20-aralkyl groups, and R.sup.7 is additionally selected from alkoxy groups having 1 to 10 carbon atoms, cycloalkoxy groups having 4 to 10 carbon atoms, phenoxy groups having 6 to 20 carbon atoms; and where the silane may also take the form of oligomers formed via hydrolysis and condensation of silanes of the formula I); wherein the silane modifies the surface of a silica; wherein a rubber mixture contains the silane; and, wherein the silane is prepared by a process which comprises at least the following process steps: a) providing a substance (R.sup.1).sub.oSi—R.sup.2—SH; b) providing a substance Cl—R.sup.3—Cl; c) reacting the substance from step a) with the substance from step b) in the presence of a base to give (R.sup.1).sub.oSi—R.sup.2—S—R.sup.3—Cl; d) reacting (R.sup.1).sub.oSi—R.sup.2—S—R.sup.3—Cl from step c) with a metallic hydrogensulfide (M-S—H) to give (R.sup.1).sub.oSi—R.sup.2—S—R.sup.3—SH, where M is metal; e) reacting (R.sup.1).sub.oSi—R.sup.2—S—R.sup.3—SH from step d) with a further portion of Cl—R.sup.3—Cl to give (R.sup.1).sub.oSi—R.sup.2—S—R.sup.3—S—R.sup.3—Cl; f) providing a substance M-S-X where the X group is a hydrogen atom or a —C(=0)—R.sup.4 group or an —SiR.sup.7.sub.3; group, where R.sup.4 and R.sup.7 are selected from C.sub.1-C.sub.20 alkyl groups, C.sub.4—C.sub.10—cycloalkyl groups, C.sub.6—C.sub.20—aryl groups, C.sub.2—C.sub.20—alkenyl groups and C.sub.7—C.sub.20—aralkyl groups, and R.sup.7 is additionally selected from alkoxy groups having 1 to 10 carbon atoms, cycloalkoxy groups having 4 to 10 carbon atoms, phenoxy groups having 6 to 20 carbon atoms and M is metal: g) reacting (R.sup.1).sub.oSi—R.sup.2—S—R.sup.3—S—R.sup.3—Cl with M-S—X to give the silane of formula I): (R.sup.1).sub.oSi—R.sup.2—S—R.sup.3—S—R.sup.3—S—X; h) optionally purifying the silane of formula I) obtained in step g), wherein the two instances of M in steps d) and f) may be identical or different.

2. The silane as claimed in claim 1, wherein the R.sup.3 radicals are identical and are linear alkylene radicals having 1 to 20 carbon atoms, preferably 2 to 10 carbon atoms, more preferably 4 to 8 carbon atoms.

3. The silane as claimed in claim 1, wherein the X group is a —C(═O)—R.sup.4 group and wherein R.sup.4 is selected from C.sub.1-C.sub.20-alkyl groups.

4. The silane as claimed in claim 1, wherein the R.sup.1 radicals are identical or different and are alkoxy groups having 1 to 6 carbon atoms or halides.

5. The silane as claimed in claim 1, wherein the R.sup.2 radical is a linear or branched alkylene group having 2 to 8 carbon atoms.

6. The silane as claimed in claim 1, wherein the silane has the following formula II): ##STR00006##

7. A vehicle tire comprising the rubber mixture as claimed in claim 1 in at least one component.

Description

(1) The invention will be explained in detail hereinafter with reference to working examples. The silane of formula III), as an example according to the invention, was prepared in the following way:

1. Preparation of (3-((6-chlorohexyl)thio)propyl)triethoxysilane; (EtO).SUB.3.Si(CH.SUB.2.).SUB.3.S(CH.SUB.2.).SUB.6.Cl According to the Synthesis Scheme for Formula III)

(2) ##STR00002##

(3) To a solution of sodium ethoxide (12.84 g, 189.0 mmol, 1.0 eq.) in ethanol (60 mL) was added 3-(mercaptopropyl)triethoxysilane (45.6 mL, 45.00 g, 189.0 mmol, 1.0 equivalent (eq.).) dropwise at 60° C. under an argon atmosphere over the course of 5 min. Subsequently, the orange reaction mixture was heated under reflux for 3 h in order to complete the deprotonation, and then allowed to cool back down to room temperature (RT). The ethanolic solution of the thiolate was transferred to a dropping funnel and added dropwise to 1,6-dichlorohexane (110.0 mL, 117.0 g, 755.0 mmol, 4.0 eq.) at 80° C. over 30 min. The resulting suspension was then stirred at 80° C. overnight. The resultant white solid (NaCl) was filtered off by means of a Buchner funnel, and the target molecule was purified by means of fractional distillation. The target compound was isolated as the second fraction (at about 140° C., 0.3 mbar) in the form of a pale yellow liquid (34.3 g, 96.0 mmol, 51%).

(4) .sup.1H NMR (nuclear magnetic resonance) (500 MHz, DMSO-d.sub.6) δ 3.75 (q, J=7.0 Hz, 6H, —SiOCH.sub.2CH.sub.3), 3.62 (t, J=6.6 Hz, 2H, —CH.sub.2C.sub.1), 2.47 (dd, J=14.9, 7.5 Hz, 4H, —SCH.sub.2—), 1.71 (dq, J=8.0, 6.6 Hz, 2H, —SiCH.sub.2CH.sub.2CH.sub.2—), 1.62-1.49 (m, 4H, —CH.sub.2—), 1.42-1.33 (m, 4H, —CH.sub.2—), 1.15 (t, J=7.0 Hz, 9H, —SiOCH.sub.2CH.sub.3), 0.70-0.64 (m, 2H, —SiCH.sub.2CH.sub.2CH.sub.2—).

(5) .sup.13C NMR (126 MHz, DMSO-d.sub.6) δ 57.72, 45.34, 34.03, 31.98, 30.85, 29.11, 27.47, 25.90, 18.23, 9.24.

(6) ESI-MS (electrospray ionization mass spectrometry) m/z (%): 311.13 [M+H−EtOH].sup.+ (100).

2. Preparation of (3-((6-mercaptohexyl)thio)propyl)triethoxysilane; (EtO).SUB.3.Si(CH.SUB.2.).SUB.3.S(CH.SUB.2.).SUB.6.SH According to the Synthesis Scheme for Formula IV)

(7) ##STR00003##

(8) To a solution of anhydrous sodium hydrogensulfide (NaHS) (3.77 g, 67.2 mmol, 1.2 eq.) in dimethylformamide (DMF) (40 mL) was added dropwise, at 60° C. under an argon atmosphere, (3-((6-chlorohexyl)thio)propyl)triethoxysilane (20.00 g, 56.0 mmol, 1.0 eq.) over a period of 10 min. The resulting suspension was then stirred at 60° C. overnight.

(9) After cooling to RT, the solvent was removed under reduced pressure, and the residue was taken up in demineralized water (50 mL) and extracted with ethyl acetate (3×50 mL). The combined organic phases were washed with demineralized water (50 mL) and dried over sodium sulfate, and the solvent was removed under reduced pressure.

(10) After column chromatography purification on silica gel (120 g, cyclohexane/ethyl acetate 0% 5%), it was possible to isolate the target compound as a colourless liquid (11.15 g, 31.4 mmol, 56%).

(11) .sup.1H NMR (500 MHz, DMSO-d.sub.6) δ 3.74 (q, J=7.0 Hz, 6H, —SiOCH.sub.2CH.sub.3), 2.49-2.43 (m, 6H, —SCH.sub.2—), 2.19 (t, J=7.7 Hz, 1H, —SH), 1.60-1.46 (m, 6H, —CH.sub.2—), 1.36-1.29 (m, 4H, —CH.sub.2—), 1.15 (t, J=7.0 Hz, 9H, —SiOCH.sub.2CH.sub.3), 0.69-0.63 (m, 2H, —SiCH.sub.2CH.sub.2CH.sub.2—).

(12) .sup.13C-NMR (126 MHz, chloroform-d) δ 58.48, 35.25, 33.98, 31.94, 29.65, 28.42, 28.06, 24.67, 23.32, 18.42, 9.99.

(13) ESI-MS m/z (%): 309.14 [M+H−EtOH].sup.+ (100).

3. Preparation of 1-(1-thio-3-(triethoxysilyl)propyl)-6-(1-thio-6-chlorohexyl)hexane; (EtO).SUB.3.Si(CH.SUB.2.).SUB.3.S(CH.SUB.2.).SUB.6.S(CH.SUB.2.).SUB.6.Cl According to the Synthesis Scheme for Formula V)

(14) ##STR00004##

(15) To a solution of sodium ethoxide (0.77 g, 11.3 mmol, 1.0 eq.) in ethanol (40 mL) was added (3-((6-mercaptohexyl)thio)propyl)triethoxysilane (4.00 g, 11.3 mmol, 1.0 eq.) at 60° C. under an argon atmosphere. Subsequently, the reaction mixture was heated at 80° C. for 3 h in order to complete the deprotonation, and then allowed to cool back down to RT.

(16) The ethanolic solution of the thiolate was transferred to a dropping funnel and added dropwise to 1,6-dichlorohexane (19.7 mL, 20.99 g, 135.0 mmol, 12.0 eq.) at 80° C. over 15 min. The resulting suspension was then stirred at 80° C. overnight.

(17) The resultant white solid (NaCl) was filtered off by means of a Buchner funnel, and excess 1,6-dichlorohexane was removed under reduced pressure.

(18) After column chromatography purification on silica gel (80 g, cyclohexane/ethyl acetate 0% 5%), it was possible to isolate the target compound as a colourless oil (2.30 g, 4.9 mmol, 43%).

(19) .sup.1H NMR (500 MHz, DMSO-d.sub.6) δ 3.75 (q, J=7.0 Hz, 6H, —SiOCH.sub.2CH.sub.3), 3.62 (t, J=6.6 Hz, 2H, —CH.sub.2Cl), 2.49-2.43 (m, 8H, —SCH.sub.2—), 1.71 (dq, J=7.9, 6.5 Hz, 2H, —SiCH.sub.2CH.sub.2CH.sub.2—), 1.61-1.46 (m, 8H, —CH.sub.2—), 1.42-1.31 (m, 8H, —CH.sub.2—), 1.15 (t, J=7.0 Hz, 9H, —SiOCH.sub.2CH.sub.3), 0.69-0.63 (m, 2H, —SiCH.sub.2CH.sub.2CH.sub.2—).

(20) .sup.13C NMR (126 MHz, DMSO-d.sub.6) δ 57.64, 45.21, 34.03, 31.93, 31.04, 30.99, 30.89, 29.11, 29.02, 28.97, 27.75, 27.40, 25.83, 22.90, 18.14, 9.21.

(21) ESI-MS m/z (%): 427.19 [M+H−EtOH].sup.+ (100), 490.26 [M+Na].sup.+ (10).

4. Preparation of the silane of formula II) 1-(1-thio-3-(triethoxysilyl)propyl)-6-(1-thio-6-thioacetylhexyl)hexane; (EtO).SUB.3.Si(CH.SUB.2.).SUB.3.S(CH.SUB.2.).SUB.6.S(CH.SUB.2.).SUB.6.SAc According to the Synthesis Scheme for Formula VI)

(22) ##STR00005##

(23) To a solution of potassium thioacetate (1.20 g, 10.5 mmol, 1.5 eq.) in DMF (20 mL) was added 1-(1-thio-3-(triethoxysilyl)propyl)-6-(1-thio-6-chlorohexyl)hexane (3.19 g, 6.7 mmol, 1.0 eq.) dropwise at 50° C. over a period of 10 min.

(24) The resultant yellowish suspension was stirred at 50° C. overnight, then cooled down to RT, and the white solid (NaCl) was filtered off by means of a Buchner funnel. Ethyl acetate (50 mL) was added to the filtrate, and the organic phase was washed with demineralized water (2×50 mL) and saturated NaCl solution (2×50 mL), and dried over Na.sub.2SO.sub.4. The solvent was removed under reduced pressure. There was no column chromatography purification on silica gel since the crude product showed sufficiently high purity and the yield would otherwise be much lower.

(25) After drying under high vacuum, the target compound was isolated as a pale yellow oil (3.13 g, 6.1 mmol, 91%).

(26) .sup.1H NMR (500 MHz, DMSO-d.sub.6) δ 3.74 (q, J=7.0 Hz, 6H, —SiOCH.sub.2CH.sub.3), 2.81 (t, J=7.2 Hz, 2H, —CH.sub.2SC(O)CH.sub.3), 2.49-2.42 (m, 8H, —SCH.sub.2—), 2.31 (s, 3H, —SC(O)CH.sub.3), 1.60-1.52 (m, 2H, —SiCH.sub.2CH.sub.2CH.sub.2—), 1.53-1.45 (m, 8H, —CH.sub.2—), 1.33 (td, J=7.1, 3.4 Hz, 8H, —CH.sub.2—), 1.14 (t, J=7.0 Hz, 9H, —SiOCH.sub.2CH.sub.3), 0.69-0.62 (m, 2H, —SiCH.sub.2CH.sub.2CH.sub.2—). .sup.13C NMR (126 MHz, DMSO-d.sub.6) δ 195.10, 57.64, 34.01, 31.01, 30.98, 30.88, 30.48, 29.11, 29.00, 28.93, 28.23, 27.74, 27.67, 27.61, 22.89, 18.14, 9.20.

(27) ESI-MS m/z (%): 467.21 [M+H−EtOH].sup.+ (61), 530.28 [M+NH.sub.4].sup.+ (100).

(28) The prepared silane of formula II) is mixed into an inventive rubber mixture comprising at least one diene rubber and at least one silica as filler. To this end, the silane of formula II) is preferably adsorbed onto a silica beforehand and subsequently added in this form to the rubber mixture.

(29) Adsorption onto silica is carried out, for example, as follows:

(30) To a suspension of silica, for example pelletized silica, in DMF is added, at room temperature, a solution of the silane of formula II) in the desired silica/silane ratio dissolved in DMF. For example, silica (VN3, Evonik) and 14.4 phf of silane of formula II) are used.

(31) The resulting suspension is for example stirred overnight at 120° C. and the solvent is subsequently removed under reduced pressure. After drying for one day under high vacuum at 40° C., the modified silica thus obtained is comminuted by means of a mortar, possibly according to the fineness desired. It is then for example dried under high vacuum for a further day at 40° C.

(32) The rubber mixture of the invention is by way of example applied to a green tire in the form of a preformed tread of a vehicle tire (as described above) and subsequently vulcanized therewith.

(33) The invention will be further illustrated in detail by comparative examples and working examples of rubber mixtures which are summarized in table 1. The comparative mixtures are labeled V, the inventive mixtures E. The amount of the silanes in phf is based on the respective amount of silica.

(34) The mixtures were produced under customary conditions in multiple stages in a twin-screw extrusion mixer. Test specimens were produced by vulcanization from all of the mixtures, and these test specimens were used to determine material properties typical for the rubber industry.

(35) The described tests on test specimens were carried out by the following test methods: Standard: ISO 868, DIN 53 505; Shore A hardness at room temperature and 70° C. Standard: ISO 4662, DIN 53 512; resilience at room temperature and 70° C. Standard: DIN 53 513; maximum loss factor tan δmax at 55° C. as the maximum over the strain sweep from dynamic-mechanical measurement Standard: ASTM D6601; loss factor tan δ (10%) and dynamic storage modulus (G′(1%), G′(100%)) of the second strain sweep at 1 Hz and 70° C. Standard: ISO 37, ASTM D 412, DIN 53 504; elongation at break at room temperature and fracture energy density at room temperature determined by a tensile test, the fracture energy density being the work required for fracture, based on the volume of the sample.
a) NR TSR: natural rubber.
b) SSBR: solution-polymerized styrene-butadiene copolymer from the prior art having hydroxyl groups, Nipol® NS 612, from Zeon Corporation.
c) Silica: VN3, from Evonik.
d) Silane in the appropriate amount was presilanized/reacted with the silica mentioned in a separate step. Silica and silane were fed to the mixing process together as modified filler.
e) Further additives: zinc oxide/aging stabilizer/antiozonant/stearic acid

(36) Inventive mixture E1 (comprising the inventive silane of formula II)), by comparison with reference mixture V1 (comprising the silane TESPD), shows reduced RT resilience and elevated 70° C. resilience. This increase in the differential (70° C. resilience—RT resilience) is advantageous in terms of the trade-off between rolling resistance and grip characteristics, and the maximum loss factor for E1 is additionally lower than for V1. These properties show the person skilled in the art an improvement in rolling resistance in the application of tires.

(37) A predictor for increased stiffness observed for E1 compared to V1 is an increase in Shore A hardness at RT and 70° C.

(38) Moreover, in the case of E1, elevated elongation at break and fracture energy density compared to V1 are observed.

(39) These different properties lead to improved service life and tear resistance with simultaneous improvement in rolling resistance characteristics, and clearly show the benefit of the silanes of the invention over the prior art.

(40) TABLE-US-00001 TABLE 1 Unit V1 E1 Constituents NR TSR a) phr 20 20 SSBR b) phr 80 80 Silica c) phr 95 95 Silane TESPD d) phf 7.2 — Silane of formula II phf — 15.6 d) TDAE phr 35 35 Further additives e) phr 9 9 DPG phr 2 2 CBS phr 1.6 1.6 Sulfur phr 2 2 Physical measurements Shore A hardness RT ShA 75.9 76.2 Shore A hardness 70° C. ShA 71.7 73.5 Resilience RT % 18.2 18.0 Resilience 70° C. % 46.4 47.6 Tan d (max) — 0170 0163 Elongation at break % 117 151 RT (S3) Fracture energy J/cm.sup.3 5 8 density (S3)