WO2016058062A1

WO2016058062A1 - Cyclo-depolymerisation of polybutadiene

Info

Publication number: WO2016058062A1
Application number: PCT/BE2015/000053
Authority: WO
Inventors: Annelies DEWAELE; Tom RENDERS; Bert Sels
Original assignee: Katholieke Universiteit Leuven
Priority date: 2014-10-17
Filing date: 2015-10-19
Publication date: 2016-04-21
Also published as: GB201418395D0

Abstract

In general the present invention concerns a method for cyclo-depolymerisation of polybutadiene to large macrocycles by metathesis catalysts. More specifically this invention relates to a novel process for the degradation by olefin metathesis, forming unsaturated macrocycles, prepared by metathesis of a 1,3-butadiene polymer, such as polybutadiene, or of polymers containing such 1,3-butadiene polymer and of rubbers or rubber compositions or rubber nanocomposites, for instance comprising butadiene.

Description

CYCLO-DEPOLYMERISATION OF POLYBUTADIENE FIELD OF INVENTION

STATE OF THE ART

Polybutadiene is a large scale produced synthetic rubber resulting from butadiene polymerization. Different types exist, regarding the application. The most produced type is high molecular weight trans-polybutadiene, used for tire manufacturing. Another type, characterized by a larger amount of vinyl groups, is used for the modification of plastics, as for example high-impact polystyrene.

Since polybutadiene is produced on such a large industrial scale, waste streams are abundant and ready to be valorised. Metathesis offers a unique toolbox to rearrange carbon-carbon double bonds and can also serve as a process to degrade linear polyenes. A few metathesis degradation pathways towards linear compounds exist. Ethenolysis results in a mixture of α,ω- vinyl-terminated butadiene oligomers and unsaturated macrocylces (J. Polym. Sci. A. Polym. Chem. 37 (12): 1857-1861). WO2014031677A1 discloses the cross metathesis of polybutadiene with acrylates, resulting in a telechelic acrylate molecule that can be employed for condensation polymerization.

Previous degradation routes focus on the formation of telechelic compounds. However, polybutadiene has the potential to be used as a cheap source to produce unsaturated, macrocyclic structures. These macrocycles can be formed by only adding a metathesis catalyst, a second reagent is not needed. Macrocyclic structures exhibit unique physical and chemical properties due to a dense conformation and the absence of chain ends. Therefore, unsaturated cyclic butene oligomers with a regular structure could serve as valuable building blocks for lubricants, fragrances, star shaped polymers and other speciality materials. To fully exploit the potential of these cyclic molecules, there is a need for a commercially and practically feasible production method resulting in high macrocyclic yields.

Small, cyclic oligomers can be produced efficiently starting from a simple diene. For example c/^'s,fra/7s, a/7s-cyclo-dodecatriene (CDT), a cycle comprising 12 carbon atoms and 3 double bonds, is synthesized by the cyclotrimerisation of butadiene using a homogenous nickel catalyst. However, this strategy is more difficult for larger cycles, as shown in DE1906361; US3594435A and Russ. J. Org. Chem. 12(1) 44-46. Several articles (Macromol. Chem. Phys. 200(7): 1662-1671., Macromolecules 28(7):2147- 2154., Macromolecules 179(5): 1285-1290. and Polymerization of Cyclo-olefins, Some Mechanistic Aspects. Addition and Condensation Polymerization processes, Chapter 26, 399- 418.) show results from cyclo-depolymerization experiments with molybdenum and tungsten based metathesis catalysts. Reported results are contradictory in different ways, although all the authors claim to work under thermodynamically controlled conditions. Usually, the content of macrocycles, having more than 3 butene units, are generally low as CDT or large linear polymers are the main products.

In Macromol. Chem. Phys. 200(7): 1662-1671 it was shown that the cyclo-depolymerization equilibrium is characterized by a large fraction of CDT (80 mol%), as in accordance with our own experience. Furthermore, it was concluded that the largest portion of CDT comprises the all-trans-isomer. This isomer is thermodynamically very stable because of the low ring strain. Since CDT is easily produced from butadiene and the all-rrans-isomer is economically less relevant, there is a need for bypassing the equilibrium distribution, but maintaining a high conversion of the polymer and a high macrocycle yield. The present invention addresses this need. SHORT DESCRIPTION OF THE INVENTION

The invention is directed to a method for the controlled cyclo-depolymerization of high molecular weight polybutadiene wherein the polyene is combined with an olefin metathesis catalyst to yield cyclic oligomers of butene units, larger than the trimer (CDT). The olefin metathesis catalyst comprises a Ru-complex lacking the well-known N-heterocyclic carbene ligand and containing at least one phosphine ligand.

According to one embodiment a process for cyclo-depolymerisation which is characterised in that in the presence of a olefin metathesis catalyst ruthenium complex of the general formula according to (I);

wherein Xi and X₂ are (identical) anionic ligands; A is an alkylidene ligand; Li and L₂ are neutral electron donor ligands, except for NHC-ligands; with at least one of them being a phosphine ligand so that a polybutadiene (co)polymer, is transformed to an unsaturated macrocyclic structure, having the following structure (a) :

wherein x > 1 and an integer,

to reach and yield of these cyclic structures of a of at least 80% from said cyclo- depolymerisation. According to the present invention there is provided this process of cyclo- depolymerisation whereby the catalyst of the general formula (I) in which Xi and X₂ are identical or different and are each hydrogen, halogen, pseudohalogen, Cl-C20-alkyl, aryl, Cl- C20-alkoxy, aryloxy, C3-C20-alkyldiketonate, aryldiketonate, Cl-C20-carboxylate, arylsulphonate, Cl-C20-alkylsulphonate, Cl-C20-alkylthiol, arylthiol, Cl-C20-alkylsulphonyl or Cl-C20-alkylsulphinyl radical. In more specific embodiments the catalyst uses in this process of cyclo-depolymerisation is a catalyst of the general formula (I) in which alkylidene ligand^'A is a benzylidene, 3-phenyl-lH-indene-l-ylidene, 3-methyl-2-butenylidene or (phenylthio)methylene. In yet another specific embodiment the catalyst used for this cyclo- depolymerisation of a polybutadiene (co)polymer is a catalyst of the general formula (I) in which Li or L₂ is triphenylphosphine, tricyclohexylphosphine, tricyclopentylphosphine, triisopropylphosphine, triio-tolyljphosphine, tri(o-xylyl)phosphine or trimesitylphosphine. In this cyclo-depolymerisation of a polybutadiene (co)polymer the olefin metathesis catalyst ruthenium complex can comprise a ruthenium complex according to general formula (I) wherein LI (or L2) comprises a heteroatom which is part of XI (or X2), as for example structure (II).

Alternatively in this process the olefin metathesis catalyst comprises a ruthenium complex according to general formula (I) wherein LI (or L2) comprises a heteroatom which is part of A, as for example structure (III).

In certain embodiments of the present invention, according to the above described process the initial polybutadiene concentration is less than 0.2M -CH2-CH=CH-CH2- monomer units. In yet another embodiment of the present invention, according to the above described process the polybutadiene is characterized by a high molecular weight in the range of 100000 to 1 000 000 g/mol (M_w). In yet another embodiment of the present invention, according to the above described process the polybutadiene is characterized by a low amount of vinyl groups (< 5%). In yet another embodiment of the present invention, according to the above described process the polybutadiene refers to the polymer as such, or as a part of the copolymers such as styrene-butadiene rubber and nitrile rubber. In yet another embodiment of the present invention, according to the above described process the catalyst concentration is in the range between 0.1 mM and 1 mM. In yet another embodiment of the present invention, according to the above described process the reaction temperature is in the range between 20° C and 130° C. In yet another embodiment of the present invention, according to the above described process the solvent is toluene, CHCI3, CH₂Cl2, chlorobenzene or methylcyclohexane. In yet another embodiment of the present invention, according to the above described process the formed macrocyclic oligomers comprise -CH₂-CH=CH-CH₂- monomer units.

DETAILED DISCLOSURE OF THE INVENTION Definitions

Rubber is in the meaning of elastomers produced by improving the properties of natural rubber or by synthetic means. Natural rubber, also called India rubber or caoutchouc, as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds plus water. Forms of polyisoprene that are used as natural rubbers are classified as elastomers. Polybutadiene is a synthetic rubber that is a polymer formed from the polymerization process of the monomer 1,3-butadiene. Diene rubber component comprises 20 to 80% by weight of a butadiene rubber. A rubber composition can comprise parts (flake-like) graphite or graphite particle (for instance with a diameter of 2 to 80 μιη ) in diene rubber. Polybutadiene rubber is formed by the polymerization of 1,3-butadiene, whereby fhe composition of the polybutadiene chain (cis/trans ratio, vinyl %) is determined by the catalyst. For the purpose of the present invention, the term polybutadiene refers to polybutadiene rubber as such, or as a copolymer of other rubbers, the most important being styrene- butadiene rubber (SBR) and nitrile rubber (NBR).

Illustrative embodiments of the invention

For the purposes of the present invention, the term yield refers to the yield of macrocycles, originating from the polybutadiene part, and the macrocycles being larger than the trimer (CDT), and is expressed in wt . CDT and cyclooctadiene are excluded in this way; these oligomers are readily synthesized from butadiene and are not in our main interest.

The process of the invention yields a mixture of macrocyclic structures comprising -CH₂- CH=CH-CH₂- monomeric units larger than CDT, with a yield of at least 80%. This mixture comprises 1,5,9,13-cyclohexadecatetraene; 1,5,9,13,17-cycloeicosapentaene; 1,5,9,13,17,21- cyclotetracosahexaene; 1,5,9,13,17,21,25-cyclooctacosaheptaene; 1,5,9,13,17,21,25,29- cyclodotriacontaoctaene; 1,5,9,13,17,21,25,29,33-cyclohexatriacontanonaene and larger analogues.

The invention accordingly provides a process for the degradation of polybutadiene rubbers by metathesis, comprising subjecting the polybutadiene rubber to a metathesis reaction in the presence of a catalyst of the general formula (I)

wherein

Xi and X₂ are (identical) anionic ligands;

A is an alkylidene ligand; Li and L₂ are neutral electron donor ligands, except for N-heterocyclic carbene (NHC) ligands; with at least one of them being a phosphine ligand.

In the catalysts of the general formula (I), XI and X2 can be identical or different and are each, for example, hydrogen, halogen, Cl-C20-alkyl, aryl, Cl-C20-alkoxy, aryloxy, C3-C20- alkyldiketonate, aryldiketonate, Cl-C20-carboxylate, arylsulphonate, Cl-C20-alkylsulphonate, Cl-C20-alkylthiol, arylthiol, Cl-C20-alkylsulphonyl or Cl-C20-alkylsulphinyl.

In the catalysts of the general formula (I), A comprises an alkylidene ligand. A can comprise, but is not restricted to, benzylidene, 3-phenyl-lH-indene-l-ylidene, 3-methyl-2-butenylidene and (phenylthio)methylene.

In the catalysts of the general formula (I), Li and L₂ can be identical or different and comprises no NHC-ligand. Li and L₂ include, but are not restricted to, triphenylphosphine, tricyclohexylphosphine, tricyclopentylphosphine, triisopropylphosphine, tri(o- tolyl)phosphine, tri(o-xylyl)phosphine and trimesitylphosphine.

The process of the invention is preferably carried out with high molecular weight 1,4- polybutadiene, in the range of 100 000 - 1 000 000 g/mol (M_w).

The process of the invention is preferably carried out with linear polybutadiene containing less than 10% vinyl groups; preferably less than 5%. Higher vinyl contents result in more side products, for example due to cross-linking. In the process of the invention, the olefin metathesis catalyst can comprise a ruthenium complex according to general formula (I), wherein Li (or L₂) comprises a heteroatom which is part of XI (or X2), as for example structure (II).

In the process of the invention, the olefin metathesis catalyst can comprise a ruthenium complex according to general formula (I), wherein Li (or L₂) comprises a heteroatom which is attached to A, as for example structure (III). Li (or L₂) include, but are not restricted to (substituted) isopropoxybenzylidene or pyridinyl propylidene. The process of the invention is preferably carried out using a substrate concentration less than 0.2 M. The concentration (M) is defined in mol monomer -CH₂-CH=CH-CH₂- units per liter. Higher substrate concentrations lead to lower product yields as more linear polymers are formed.

In the process of the invention, the amount of the catalyst of the general formula (I) depends on the nature and catalytic activity of the specific catalyst. The amount of catalyst used is preferably between 0.1 mM and 1 mM, but lower concentrations are possible as well.

In the process of the invention, the reaction temperature depends on the nature and catalytic activity of the specific catalyst, on the thermal stability of the specific catalyst and on the boiling point of the solvent. The reaction temperature is usually carried out between 20°C and 130°C; preferably between 30°C and 90°C.

The metathesis reaction can be carried out in a suitable solvent which does not deactivate the catalyst nor adversely affects the reaction in any other way. Oxygen-containing solvents will coordinate to the Ru-center and will lead to a decreased activity. The solvent choice depends furthermore on the reaction temperature, the catalyst solubility and the polymer solubility in the specific solvent. Preferred solvents include, but are not restricted to, toluene, CHCI3, CH₂CI₂, chlorobenzene and methylcyclohexane.

REFERENCE EXAMPLE 1

45.9 mg (0.17 M) polybutadiene (Sigma Aldrich, M_w 200 000 - 300 000 g/mol, 98% c/s; 2% vinyl) was dissolved in 5 ml CH₂Cl2 (VWR, > 99.8%), to which 4.0 mg of Umicore Ml complex (dichloro-(3-phenyl-lH-indene-l-ylidene)bis(tricyclohexylphosphine)ruthenium, Strem Chemicals) was added. The mixture was magnetically stirred at 35°C. After 3h, a sample (0.1 ml) was taken and quenched with potassium-2-isocyanoacetate (Sigma Aldrich, 85%). The measured yield of aimed macrocycles by gas chromatography was 83%. Addition of an extra amount of catalyst (4.0 mg) to the same reaction mixture did not significantly influence the yield, nor the macrocycle distribution. REFERENCE EXAMPLE 2

The process according to reference example 1, but with Grubbs 1^st generation complex (Benzylidene-bis(tricyclohexylphosphine)dichlororuthenium, Sigma Aldrich , 97%). The yield of aimed macrocycles was 80%.

REFERENCE EXAMPLE 3

The process according to reference example 1, but with Hoveyda-Grubbs 1^st generation complex ((Dichloro(o-isopropoxyphenylmethylene)(tricyclohexylphosphine)ruthenium, Sigma Aldrich) and a reaction time of 72h. The yield of aimed macrocycles was 81%.

REFERENCE EXAMPLE 4

The process according to reference example 1, but with an indenylidene Schiff base Ru- complex (structure (III), UGent) and a reaction time of 72h. The measured yield of aimed macrocycles was 80%.

COUNTER EXAMPLE 1

146.9 mg (0.17 M) polybutadiene (Sigma Aldrich, M_w 200 000-300 000 g/mol, 98% c/^'s; 2% vinyl) was dissolved in 16 ml CH₂CI₂, to which 11.7 mg of Grubbs 2^nd generation catalyst ((1,3- Bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene)dichloro(phenylmethylene)(tricyclo- hexylphosphine)ruthenium, Sigma Aldrich) was added. After 20 minutes, the yield of macrocycles reached a maximum of 61% and dropped significantly afterwards. CDT is formed in almost equal amounts during the decrease. Similar behaviour was observed using a catalyst comprising Hoveyda-Grubbs 2^nd generation complex (l,3-Bis-(2,4,6-trimethylphenyl)-2- imidazolidinylidene)dichloro(o-isopropoxyphenylmethylene)ruthenium, Sigma Aldrich, 97%), Umicore M2 complex ((l,3-Bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene)dichloro(3- phenyl-lH-inden-l-ylidene)(tricyclohexylphosphine)-ruthenium, Umicore AG & Co. KG), Grubbs 3^rd generation complex (Dichloro(l,3-bis(2,4,6-trimethylphenyl)-2- imidazolidinylidene)(benzylidene)bis(3-bromopyridine)ruthenium, Di-chloro[l,3-bis(2,6- isopropylnaphthyl)-2-imidazolidinylidene](2-isopropoxyphenylmethylene)-rut (UGent), Umicore M73 SIMes ((l,3-Bis(2,4,6-trimethylphenyl)-2- imidazolidinylidene]dichloro[5-(isobutoxycarbonylamido)-2-isopropoxybenzylidene]- ruthenium, Umicore AG & Co. KG) and Umicore M73 SIPr ((l,3-Bis(2,6-diisopropylphenyl)-2- imidazolidinylidene]dichloro[5-(isobutoxycarbonylamido)-2-isopropoxybenzylidene]- ruthenium, Umicore AG & Co. KG) . This example shows the influence of catalyst properties, and more specifically the effect of the replacement of a phosphine ligand by an N-heterocyclic carbene ligand (figure 1). COUNTER EXAMPLE 2

73.5 mg (0.17 M) polybutadiene (Sigma Aldrich, M_n 1530-2070 g/mol, 72% c/s; 27% trans; 1% vinyl) was dissolved in 8 ml CH₂CI₂, to which 6.4 mg of Umicore Ml complex was added. The mixture was magnetically stirred at 35°C. After 8 h, a sample (0.1 ml) was taken and quenched with potassium-2-isocyanoacetate. The measured yield by gas chromatography was 30%, showing the influence of substrate properties, more specifically the chain length.

COUNTER EXAMPLE 3

73.5 mg (0.17 M) polybutadiene (M_w 500 000 g/mol, 48% c/s; 42 % trans; 10% vinyl) was dissolved in 8 ml CH₂CI₂, to which 5.7 mg of Grubbs 1^st generation complex (dichloro- (benzylidene)bis(tricyclohexylphosphine)ruthenium, Sigma Aldrich, 97%) was added. The mixture was magnetically stirred at 35°C. After 8h, a sample (0.1 ml) was taken and quenched with potassium-2-isocyanoacetate. The measured yield by gas chromatography was 36%, showing the influence of substrate properties, more specifically the amount of vinyl substituents.

COUNTER EXAMPLE 4

135.0 mg (0.5 M) polybutadiene (Sigma Aldrich, M_w 200 000-300000 g/mol, 98% cis; 2% vinyl) was dissolved in 5 ml CH₂CI₂ (VWR, > 99,8%), to which 4.0 mg of Umicore Ml complex was added. The mixture was magnetically stirred at 35°C. After 3h, a sample (0.1 ml) was taken and quenched with potassium-2-isocyanoacetate. The measured yield by gas chromatography was 52%, showing the influence of an increased initial polybutadiene concentration. COUNTER EXAMPLE 5

45.9 mg (0.17 M) polybutadiene (Sigma Aldrich, Mw 200 000 - 300 000 g/mol, 98% c/s; 2% vinyl) was dried under reduced pressure (10 mbar) for 12 h before starting the reaction. The dried polymer was dissolved in 5 ml anhydrous toluene (Sigma Aldrich, 99.8%), to which 5.0 mg of a Schrock complex (2,6-diisopropylphenylimidoneophylidene molybdenum(VI) bis(hexafluoro-t-butoxide) (Mo(CioHi2)(Ci2Hi7N)[OC(CH₃)(CF₃)₂]₂, Strem Chemicals) was added. The mixture was magnetically stirred at 40 °C. After 48h, a sample (0.1 ml) was taken and quenched with potassium-2-isocyanoacetate (Sigma Aldrich, 85%). The measured yield of macrocycles by gas chromatography was 59%, whereby the fraction of aimed macrocycles was only 4%. 96% of the cyclic oligomer fraction consisted of the cyclic trimer of butadiene CDT, showing the influence of the type of metathesis catalyst, and more specifically the use of Molybdenum alkylidenes instead of Ruthenium alkylidenes.

Legend to the graphics

Figure 1: Influence of the ligand properties, more specifically the effect of a phosphine ligand (reference example 1) compared to the effect of a N-heterocyclic carbene ligand (counter example 1) on the macrocycles yield.

Claims

CYCLO-DEPOLYMERISATION OF POLYBUTADIENE CLAIMS What is claimed is:

1. A process for cyclo-depolymerisation of a polybutadiene (co)polymer to an unsaturated macrocyclic structure, having the following structure (a):

wherein x > 1 and an integer, characterised in that the cyclo- depolymerisation is in the presence of a olefin metathesis catalyst ruthenium complex of the eneral formula according to (I);

wherein Xi and X₂ are (identical) anionic ligands; A is an alkylidene ligand; Li and L₂ are neutral electron donor ligands, except for NHC- ligands; with at least one of them being a phosphine ligand

to reach and yield the cyclic structures of a of at least 80% from said cyclo- depolymerisation.

2. The process according to claim 1, wherein a catalyst of the general formula (I) in which XI and X2 are identical or different and are each hydrogen, halogen, pseudohalogen, Cl-C20-alkyl, aryl, Cl-C20-alkoxy, aryloxy, C3-C20-alkyldiketonate, aryldiketonate, Cl- C20-carboxylate, arylsulphonate, Cl-C20-alkylsulphonate, Cl-C20-alkylthiol, arylthiol, Cl-C20-alkylsulphonyl or Cl-C20-alkylsulphinyl radical, is used.

3. The process according to any one of the claims 1 to 2, wherein a catalyst of the general formula (I) in which alkylidene ligand A is a benzylidene, 3-phenyl-lH-indene-l-ylidene, 3-methyl-2-butenylidene or (phenylthio)methylene, is used.

4. The process according to any one of the claims 1 to 3, wherein a catalyst of the general formula (I) in which LI or L2 is triphenylphosphine, tricyclohexylphosphine, tricyclopentylphosphine, triisopropylphosphine, tri(o-tolyl)phosphine, tri(o- xylyl)phosphine or trimesitylphosphine, is used.

5. The process according to claim 1, wherein the olefin metathesis catalyst comprises a ruthenium complex according to general formula (I) wherein LI (or L2) comprises a heteroatom which is part of XI (or X2), as for example structure (II).

6. The process according to claim 1, wherein the olefin metathesis catalyst comprises a ruthenium complex according to general formula (I) wherein LI (or L2) comprises a heteroatom which is part of A, as for example structure (III).

7. The process according to any one of the previous claims 1 to 6, wherein the initial polybutadiene concentration is less than 0.2M -CH2-CH=CH-CH2- monomer units.

8. The process according to any one of the previous claims 1 to 7, wherein polybutadiene is characterized by a high molecular weight in the range of 100 000 to 1 000 000 g/mol (Mw).

9. The process according to any one of the previous claims 1 to 8, wherein polybutadiene is characterized by a low amount of vinyl groups (< 5%).

10. The process according to any one of the previous claims 1 to 9, wherein polybutadiene refers to the polymer as such, or as a part of the copolymers such as styrene-butadiene rubber and nitrile rubber.

11. The process according to any one of the previous claims 1 to 10, wherein the catalyst concentration is in the range between 0.1 mM and 1 mM.

12. The process according to any one of the previous claims 1 to 11, wherein the reaction temperature is in the range between 20° C and 130° C.

13. The process according to any one of the previous claims 1 to 12, wherein the solvent is toluene, CHCI3, CH2CI2, chlorobenzene or methylcyclohexane.

14. The process according to any one of the previous claims 1 to 13, wherein the formed macrocyclic oligomers comprise -CH2-CH=CH-CH2- monomer units.