Use of catalysts for the metathesis of nitrile rubber

Abstract

The present invention relates to the use of specific catalysts for the metathesis degradation of nitrile rubber (NBR). The invention further relates to a method for preparing nitrile rubber with reduced molecular weight using specific catalysts.

Claims

1. A method comprising a step of the use of at least one catalyst of the general formula (I) ##STR00036## wherein X and X.sup.1 in each case independently of one another are halogens, L is an uncharged ligand of the formula L.sup.1, L.sup.2, L.sup.3 or L.sup.4, ##STR00037## wherein R.sup.10 and R.sup.11 in each case independently of one another are a substituted or unsubstituted side chain comprising 1 to 30 carbon atoms and optionally comprising one or more functional groups, and wherein R.sup.12 and R.sup.13 in each case independently of one another are H, C.sub.1-6 alkyl, optionally substituted with an alkoxy radical OR.sup.15, or aryl optionally substituted with an alkoxy radical OR.sup.15, or form a 3- or 4-membered alkene bridge, and wherein R.sup.15 is selected from the group consisting of C.sub.1-20 alkyl, aryl and C.sub.7-18 aralkyl, and wherein g and g′ are in each case halogens, z is a methylene or carbonyl group, a, b and c are in each case H; R.sup.2 is selected from the group consisting of H, C.sub.1-12 alkyl; and R.sup.3 is selected from the group consisting of H, C.sub.1-12 alkyl, C.sub.5-12 cycloalkyl, C.sub.7-18 aralkyl, aryl, C.sub.1-12 haloalkyl, C.sub.1-12 ammonium alkyl, C.sub.1-12 pyridinium alkyl, C.sub.1-12 aldehyde alkyl, C.sub.1-12 nitroalkyl, nitrile or a radical selected from the group consisting of ketones COR.sup.4, esters CO.sub.2R.sup.4, oxalates COCO.sub.2R.sup.4, sulfones SO.sub.2R.sup.4 or amides CONHR.sup.4, where R.sup.4 is selected from the group consisting of H, C.sub.1-12 alkyl, C.sub.5-12 cycloalkyl, C.sub.7-18 aralkyl, aryl, C.sub.1-12 haloalkyl, C.sub.1-12 ammonium alkyl, C.sub.1-12 pyridinium alkyl, C.sub.1-12 aldehyde alkyl, C.sub.1-12 nitroalkyl and nitrile, or R.sup.3 is a side chain of the formula R.sup.3c, R.sup.3d, R.sup.3e, R.sup.3f, R.sup.3g, R.sup.3h, R.sup.3i, R.sup.3j, R.sup.3k, R.sup.3l, R.sup.3m, R.sup.3n, R.sup.3o or R.sup.3p: ##STR00038## ##STR00039## or, if z is methyl, R.sup.3 is a side chain of the formula R.sup.3a or R.sup.3b: ##STR00040## wherein A.sup.− is selected from the group consisting of F.sup.−, Cl.sup.−, Br, I.sup.−, tetrafluoroborate BF.sub.4.sup.−, hexafluorophosphate PF.sub.6.sup.− and bis(trifluoromethylsulfonyl)amide NTf.sub.2.sup.−, in a metathesis reaction of nitrile rubber.

2. The method of claim 1, wherein: R.sup.10 and R.sup.11 in each case independently of one another are C.sub.1-30 alkyl, optionally substituted with an alkoxy radical OR.sup.15, C.sub.2-30 alkenyl, optionally substituted with an alkoxy radical OR.sup.15, aryl, optionally substituted with an alkoxy radical OR.sup.15, aminoalkyl or aminocycloalkyl.

3. The method of claim 1 wherein: the ligand L in the catalyst of the general formula (I) has the following meanings (L.sup.1a), (L.sup.1b), (L.sup.1c), (L.sup.1d), (L.sup.1e), (L.sup.1f), (L.sup.1g): ##STR00041## ##STR00042##

4. The method of claim 1 wherein the ligand L of the general formula (I) is ##STR00043##

5. The method of claim 1 wherein the radical R.sup.3 in the catalyst of the general formula (I) is hydrogen or a side chain of the formula R.sup.3c, R.sup.3d, R.sup.3e, R.sup.3f, R.sup.3g, R.sup.3h, R.sup.3i, R.sup.3k, R.sup.3l, R.sup.3m, R.sup.3n, R.sup.3o or R.sup.3p.

6. The method of claim 1 wherein the radical R.sup.3 in the catalyst of the general formula (I) is hydrogen or a side chain of the formula R.sup.3c or R.sup.3e.

7. The method of claim 1 wherein the catalyst of the general formula (I) has the following meanings: X is Cl; L is L.sup.1g; z is carbonyl; a, b, c are H; R.sup.2 is C.sub.1-C.sub.12 alkyl, and R.sup.3 is H, R.sup.3c or R.sup.3e.

8. The method of claim 1 wherein the catalyst of the general formula (I) is a catalyst of the formulae (I.A), (I.B) or (I.C): ##STR00044##

9. The method of claim 8 wherein the amount of catalyst used is 0.002 phr to 0.1 phr.

10. The method of claim 1, wherein the amount of catalyst used is 0.001 phr to 1 phr, based on the nitrile rubber used.

11. The method of claim 1, wherein the metathesis reaction is carried out without, or in the presence of, a co-olefin.

12. The method of claim 11, wherein the co-olefin is a straight-chain or branched C.sub.2-C.sub.16 olefin.

13. The method of claim 1 wherein the nitrile rubbers ares based on copolymers or terpolymers comprising repeat units of at least one conjugated diene, at least one α,β-unsaturated nitrile and optionally one or more further copolymerizable monomers.

14. The method of claim 13, wherein the copolymerizable monomers, are based on α,β-unsaturated mono- or dicarboxylic acids, or alkyl esters thereof, or alkoxyalkyl esters thereof, or PEG acrylate of the general formula (J) ##STR00045## wherein R is hydrogen or branched or unbranched C.sub.1-C.sub.20 alkyl, n is 1 to 8, and R.sup.1 is hydrogen or CH.sub.3—, and also mixtures of the abovementioned copolymerizable monomers.

15. The method of claim 1 wherein the nitrile rubbers used in the metathesis reaction have a Mooney viscosity (ML 1+4 at 100° C.) in the range from 30 to 70 MU.

16. The method of claim 1 wherein the metathesis reaction takes place in a reaction mixture and wherein the concentration of the nitrile rubber in the reaction mixture is in the range from 1 to 20 wt % of the reaction mixture.

17. The method of claim 1, wherein the metathesis reaction is carried out in a solvent.

18. The method of claim 1, wherein the metathesis reaction is carried out at a temperature in the range from 10° C. to 150° C.

19. The method of claim 1, wherein the metathesis reaction is a method of reducing the molecular weight of nitrile rubber, wherein a nitrile rubber is subjected to a metathesis degradation in the presence of a catalyst of the general formula (I).

20. The method of claim 1, wherein the metathesis reaction is a method of preparing hydrogenated nitrile rubbers, wherein a nitrile rubber is subjected to a metathesis degradation in the presence of a catalyst of the general formula (I), and the resultant nitrile rubber obtained is subsequently subjected to a hydrogenation.

Description

EXAMPLES

(1) Metathesis degradation of nitrile rubber in the presence of different catalysts

(2) The following examples show that the catalysts of the formulae (I.A), (I.B.) and (I.C) have metathesis activity in the metathesis degradation of nitrile rubber, in each case at the same dose.

(3) The following catalysts were used:

(4) “Grubbs II catalyst” (comparative example 1): [1,3-bis-(2,4,6-trimethylphenyl)-2-imidazolidinylidene3]dichloro(phenylmethylene)(tricyclohexylphosphine)ruthenium (CAS number: 246047-72-3), C.sub.46H.sub.65Cl.sub.2N.sub.2PRu weight: 848.97 g/mol; the Grubbs II catalyst was obtained from the company Materia Inc.

(5) ##STR00031##

(6) “Hoveyda-Grubbs II catalyst” (comparative example 2): [1,3-Bis-(2,4,6-trimethylphenyl)-2-imidazolidinylidene]dichloro(o-isopropoxyphenylmethylene)ruthenium (CAS number 301224-40-8); C.sub.31H.sub.38Cl.sub.2N.sub.2ORu, weight: 626.62 g/mol; the Hoveyda-Grubbs II catalyst was obtained from the company Materia Inc.

(7) ##STR00032##

(8) Catalyst (I.A) (inventive example (I)): [1,3-Bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene]{2-ethyl-3-oxo-3,4-dihydro-2H-benzo[b][1,4]oxazin-8-yl]methylene}ruthenium(II) dichloride; C.sub.38H.sub.50Cl.sub.2N.sub.3O.sub.2Ru; molecular weight: 752.23 g/mol; green powder. The catalyst of the formula (I.B) can be prepared according to the method disclosed in WO-A-2012/013208.

(9) ##STR00033##

(10) Catalyst (I.B) (inventive example (II)): [1,3-Bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene]{(2-ethyl-4-(isobutoxycarbonyl)-3-oxo-3,4-dihydro-2H-benzene[b][1,4]oxazin-8-yl)methylene}ruthenium(II) dichloride; C.sub.43H.sub.58Cl.sub.2N.sub.3O.sub.4Ru; molecular weight: 852.28 g/mol; green powder. The catalyst of the formula (I.B) can be prepared according to the method disclosed in WO-A-2012/013208.

(11) ##STR00034##

(12) Catalyst (I.C) (inventive example (III)): [1,3-Bis(2,6-di-isopropylphenyl)imidazolidin-2-ylidene]{(2-ethyl-3-oxo-4-(perfluorophenylcarbonyl)-3,4-dihydro-2H-benzo[b][1,4]oxazin-8-yl)methylene}ruthenium(II) dichloride C.sub.45H.sub.49Cl.sub.2F.sub.5N.sub.3O.sub.3Ru; molecular weight: 946.21° g/mol; green powder. The catalyst of the formula (I.C) can be prepared according to the method disclosed in WO-A-2012/013208.

(13) ##STR00035##

(14) The degradation reactions described below were carried out using a nitrile rubber from ARLANXEO with 34 wt % acrylonitrile content; a Mooney viscosity (ML 1+4 @100° C.) of 34 MU and a residual double bond content (RDB) of 100%. This nitrile rubber is abbreviated to NBR below.

(15) General Description of the Metathesis Reactions Carried Out:

(16) 425 g of chlorobenzene (MCB; Aldrich) were used in each case for the metathesis degradation. 75 g of NBR were dissolved therein over a period of 24 h at room temperature.

(17) TABLE-US-00001 TABLE 1 Analytical data for the NBR solution before the metathesis reaction Analytical data NBR solution Mw [g/mol] 282 066 Mn [g/mol]  78 392 PDI 3.6

(18) In each case 3.1 g (4 phr) of 1-hexene were added to the NBR-containing solution and mixed to homogenize for 120 min on an agitator.

(19) The 0.0049 g (0.0065 phr) of ruthenium-containing catalyst were in each case dissolved in 5 ml of MCB at room temperature. The catalyst solutions were added to the NBR solutions in MCB immediately after the catalyst solutions were prepared.

(20) After 24 hours at room temperature on an agitator, the metathesis reaction stopped and in each case 5 ml of the reaction solution were used for the GPC.

(21) The molecular weight is determined by gel permeation chromatography (GPC) according to DIN-55672-1 Version 2007. A modular system was used, having a Shodex RI-71 differential refractometer, S 5200 autosampler (from SFD), column oven (ERC-125), Shimadzu LC 10 AT pump and a column combination of 3 PLgel 10 μm Mixed B 300×7.5 mm columns from Agilent.

(22) The solvent used was tetrahydrofuran; the molecular weights present are based on polystyrene standards from PSS (Mainz). The finished THF sample solutions are filtered through syringe filters having 0.45 μm PTFE membranes and diameter 25 mm. The measurements were conducted at 40° C. and a flow rate of 1 ml/min in tetrahydrofuran.

(23) The molecular parameters such as number-average molecular weight Mn, mass-average molecular weight Mw and the resulting polydispersity index PDI are determined from the RI signal by means of the “Empower 2 data base” software from Waters.

(24) GPC analysis was used to determine the following characteristic variables both for the original NBR rubber (prior to degradation) and the degraded nitrile rubbers:

(25) Mw [g/mol]: weight-average molecular weight

(26) Mn [g/mol]: number-average molecular weight

(27) PDI: width of the molecular weight distribution (Mw/Mn)

(28) Comparison of the Activity of the Tested Catalysts in the Presence of 4 Phr of 1-Hexene

(29) The activity of the comparative catalysts “Grubbs II catalyst” (V1) and “Hoveyda-Grubbs II catalyst” (V2) with the catalysts of the formulae (I.A), (I.B) and (I.C) was compared at a catalyst concentration of 0.0065 phr (0.0049 g) and a dose of 4.0 phr (3.1 g) of the cocatalyst 1-hexene.

(30) TABLE-US-00002 TABLE 2 Molecular weight and PDI of the nitrile rubbers after 24 h of metathesis in the presence of the comparative catalysts V1 and V2 and also the inventive catalysts (I.A), (I.B) and (I.C) compared to the initial values at the start Start V1 V2 (I)* (II)* (III)* Analytica ldata 0 h 24 h 24 h 24 h 24 h 24 h Mw [g/mol] 282 066 155 368 120 560 108 864 106 482 121 723 Mn [g/mol]  78 392  57 467  46 641  42 768  42 342  47 581 PDI 3.6 2.7 2.6 2.5 2.5 2.6 *Inventive examples

(31) The use of the catalysts (I.A), (I.B) and (I.C) leads to a metathesis degradation of nitrile rubber without noticeable gel formation.

(32) The comparison of the decrease in the weight-average molecular weight Mw of the nitrile rubber in the inventive examples (I)* and (II)* shows that the activity of the catalysts (I.A) and (I.B) is considerably greater than in the comparative catalysts used in the comparative examples V1 and V2, Grubbs II catalyst and Hoveyda-Grubbs II catalyst. For in each case identical reaction times, lower molar masses are achieved with the catalysts (I.A) and (I.B) than with the comparative catalysts V1 and V2 and also the further inventive catalyst (I.C). The inventive catalyst (I.C) exhibits greater reduction in the weight-average molecular weight Mw and the PDI after 24 hours of metathesis reaction than the comparative catalyst Grubbs II and virtually the same reduction in the weight-average molecular weight Mw and the PDI after 24 hours of metathesis reaction as the comparative catalyst Hoveyda-Grubbs II. The inventive catalysts (I.A), (IB) and (I.C) are thus suitable for use in a method for the metathesis of nitrile rubber.

(33) The metathesis degradation of nitrile rubber using the catalysts of the formula (I.A), (I.B) and (I.C) takes place without noticeable gel formation (<3 wt %).