Method for improving catalytic SBS hydrogenation efficiency of titanocene catalyst

Abstract

The invention discloses a method for improving the catalytic SBS hydrogenation efficiency of a titanocene catalyst. The method comprises the following steps: obtaining a styrene / butadiene / styrene copolymer glue solution through an anionic polymerization method; carrying out hydrogenation reaction on the styrene / butadiene / styrene copolymer glue solution under the action of a siloxane cocatalyst, dicyclopentadiene titanium dichloride and lithium hydride to obtain a hydrogenated styrene / butadiene / styrene copolymer; by adopting the siloxane cocatalyst, the hydrogenation degree of the high-molecular-weight SBS can reach 98% or above, the problems of chromaticity and smell of the product can be solved, and in addition, a certain anti-sticking effect is achieved.

Description

A method to improve the efficiency of SBS hydrogenation catalysis by titanium holocata catalysts Technical Field

[0001] This invention relates to a method for hydrogenating SBS polymers using a dichlorodichlorotitanium / lithium hydride system, and particularly to a method for improving hydrogenation efficiency by using siloxane compounds as hydrogenation co-catalysts for the hydrogenation reaction of styrene / butadiene / styrene copolymers, belonging to the field of styrene / conjugated diene catalytic hydrogenation technology. Background Technology

[0002] Styrene / butadiene / styrene copolymer (SBS) thermoplastic elastomer is a block copolymer of styrene and butadiene. Due to its excellent elasticity and abrasion resistance, it is widely used in footwear materials, asphalt modification, adhesives, and other fields, and is hailed as the "third generation of synthetic rubber." However, because its butadiene blocks contain a large number of double bonds, they are prone to aging and bond breakage under the influence of oxygen, ultraviolet light, light, and heat, which significantly affects the product's application in outdoor environments. To address these shortcomings, a method of selective hydrogenation of the double bonds in the butadiene blocks has been proposed. Considering that hydrogen is very stable and difficult to polarize and break bonds, a catalyst is needed to advance the hydrogenation reaction.

[0003] Currently, catalysts used in existing technologies are generally classified as heterogeneous catalysts and homogeneous catalysts. Heterogeneous catalysts typically involve supporting heavy metals such as nickel, cobalt, platinum, palladium, and rhodium, and their compounds, on the surface of carriers such as activated carbon, diatomaceous earth, and alumina. Homogeneous catalysts mainly include Ziegler catalysts, metallocene catalysts, and noble metal catalysts such as platinum, rhodium, and palladium.

[0004] Heterogeneous catalysts are complex to prepare and tend to adhere to polymer surfaces. Due to the viscosity of the adhesive and steric hindrance of the polymer, they are difficult to access the active sites of unsaturated polymers, resulting in large dosages and difficult post-processing. Furthermore, the activity of these catalysts often decreases sharply during hydrogenation, necessitating high temperature and pressure for the hydrogenation reaction. This can lead to polymer decomposition, gel formation, or hydrogenation of the benzene ring. Therefore, heterogeneous catalysts have not been widely used in the hydrogenation industry.

[0005] Compared to heterogeneous catalysts, homogeneous catalysts have catalytically active species uniformly dispersed in the colloid, ensuring sufficient contact with the polymer. This results in lower dosage, milder reaction conditions, and better selectivity. Ziegler catalysts were first introduced to the market in 1970, but practical experience showed that they suffered from problems such as high dosage, poor reproducibility, and residue leading to unstable product performance. Therefore, metallocene catalysts, which offer higher activity, lower dosage, higher hydrogenation degree, better reproducibility, and lower residue, have been widely used, with titanocene catalysts being the most prevalent.

[0006] US4501857 uses titanium dichlorophenocene as the main catalyst, adding alkyl lithium in a reducing atmosphere to form a hydrogenation catalytic system, achieving a hydrogenation degree of up to 98%. US4980421 utilizes titanium dichlorophenocene, lithium alkoxy (ROLi), and organometallic compounds (such as aluminum, zinc, and magnesium compounds) for hydrogenation reactions, exhibiting high activity, low dosage, easy handling, and mild conditions. Ennichem AG of Italy uses titanium dichlorophenocene ash as the main catalyst, and prepares a mixed reducing agent of triethylaluminum and dibutylmagnesium in a certain proportion, achieving a hydrogenation degree of up to 99%. CJ Gibler et al. developed a Terber reagent / sec-butyllithium catalytic system (Terber reagent refers to the addition of titanium dichlorophenocene and trimethylaluminum in the presence of hydroxyl and carbonyl groups), achieving a hydrogenation degree of up to 96.8%. US5039755 uses hydrogen to terminate the active chain of SBS to prepare lithium hydride as a reducing agent, then adds titanium dichlorophenocene to hydrogenate SBS, achieving a hydrogenation degree of up to 98%.

[0007] During the SBS hydrogenation process, the active lithium in the solution reacts with hydrogen to form reducing lithium hydride. Adding the main catalyst, titanium dichlorophenoxyacetate, generates the reactive [Cp₂TiH], which then reacts with conjugated diene polymers. However, the [Cp₂TiH] active body is unstable and prone to dimerization / polymerization, affecting the degree of hydrogenation. Therefore, stabilizing the active body or delaying its dimerization / polymerization is beneficial for the hydrogenation reaction. Titanium atoms have extra empty orbitals, exhibiting electron deficiency. When an electron-rich co-catalyst is added, it can undergo a complexation reaction with titanium, thereby stabilizing the active body [Cp₂TiH], maintaining high catalytic activity during hydrogenation, promoting the hydrogenation reaction, and shortening the reaction time.

[0008] In 1993, LR Chamberlain, based on US5039755, added methyl o-toluate to the original catalytic system, improving the hydrogenation efficiency of the diacenetimonate / lithium hydride catalytic system and achieving a hydrogenation degree of 98% with a lower main catalyst dosage. CN1166498A uses esters formed from phthalic acid, triphenylcarboxylic acid, tetraphenylcarboxylic acid, and hydroxybenzoic acid as co-catalysts, greatly promoting the catalytic activity of the co-catalyst. However, since ester co-catalysts gradually decompose, they must be replenished during the reaction to maintain reaction activity. In addition, the use of such co-catalysts can lead to problems such as poor product color and odor. US6461993B1 points out that aromatic esters have limited promoting effect on the diacenetimonate / lithium hydride catalytic system, and uses ethanol to consume excess lithium hydride, thereby inhibiting the formation of dimers / polymers of the active [Cp2TiH] and promoting the hydrogenation reaction. US4980421 utilizes BHT to generate BHT-Li compounds from butyllithium to promote the dichlorodicarboxylate / alkylaluminum system, achieving a hydrogenation degree of up to 98%. US6313230 and CN00107660.4 propose catalytic systems using dichlorodicarboxylate, compounds containing Si-H functional groups, and metal compounds. This catalytic system has a short storage time under nitrogen and is prone to deactivation; it must be used within a very short time after preparation, otherwise the hydrogenation efficiency is difficult to control. Furthermore, this system is prone to deactivation at high temperatures; therefore, the maximum temperature during the hydrogenation reaction must be kept below 60°C. Summary of the Invention

[0009] To address the problems of low efficiency, easy deactivation, poor product color, and odor in the hydrogenation of SBS by titanium-based catalysts in existing technologies, this invention provides a method to improve the efficiency of SBS hydrogenation by titanium-based catalysts. The method aims to stabilize the active body by using a siloxane co-catalyst to undergo a complexation reaction with the active [Cp2TiH], thereby inhibiting its dimerization / polymerization reaction, improving hydrogenation efficiency, improving product color and odor, and enhancing anti-sticking properties.

[0010] To achieve the above-mentioned technical objectives, the present invention provides a method for improving the catalytic hydrogenation efficiency of SBS using a titanium staphylocumerode catalyst. This method involves obtaining a styrene / butadiene / styrene copolymer solution via anionic polymerization. The styrene / butadiene / styrene copolymer solution is then subjected to a hydrogenation reaction with a siloxane co-catalyst and dicyclopentadiene titanium dichloride and lithium hydride to obtain a hydrogenated styrene / butadiene / styrene copolymer. The siloxane co-catalyst includes at least one of cyclohexylmethyldimethoxysilane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and decamethylcyclopentasiloxane.

[0011] The key to this invention lies in the use of siloxane-based cocatalysts. In the dicyclopentadiene titanium dichloride / lithium hydride catalytic system, the active lithium in the colloid reacts with hydrogen to form reducing lithium hydride. Adding dicyclopentadiene titanium dichloride generates reactive [Cp₂TiH], but the [Cp₂TiH] active form is unstable and prone to dimerization / polymerization reactions, affecting the degree of hydrogenation. The siloxane-based cocatalyst provided by this invention exhibits both electron-donating and electron-withdrawing electronic properties. In siloxanes, oxygen atoms surrounding silicon atoms can attract electrons from the silicon atoms through π bonds, generating a stable resonance structure, thus exhibiting electron-donating properties. Simultaneously, silicon atoms can also attract surrounding electrons through π-conjugated structures, demonstrating electron-withdrawing properties. Therefore, this invention, by adding siloxane cocatalysts, can, on the one hand, utilize their electron-donating properties to undergo complexation reactions with titanium atoms possessing excess empty orbitals, thereby stabilizing the active body [Cp2TiH], inhibiting its dimerization / polymerization reactions, and improving hydrogenation efficiency; on the other hand, utilizing their electron-withdrawing properties, when olefin molecules and hydrogen molecules in the system come into contact with the catalyst surface, they are attracted by the electronic structure of the catalyst surface and adsorbed onto the surface. Moreover, the special electronic structure of the catalyst makes it easier for olefin molecules to accept the addition of hydrogen atoms, thus completing the hydrogenation of olefins. In addition, traditional ester cocatalysts are slightly yellow and have an aromatic odor, while the siloxane cocatalysts in this invention are white, odorless solids, exhibit low viscosity at room temperature and pressure, and are stable. These properties make them effective as cocatalysts in improving product color and odor problems, and also give the product superior anti-sticking properties.

[0012] The preferred siloxane cocatalyst of this invention can react with some lithium hydride to reduce the lithium hydride concentration. It can also inhibit the dimerization / polymerization reaction of active [Cp2TiH], promote the hydrogenation reaction, and shorten the reaction time. At the same time, it can reduce the amount of butyllithium to be added to a certain extent, thus saving costs.

[0013] The inventors discovered that replacing siloxane-based cocatalysts with silane cocatalysts could not achieve the same effect as the present invention. The reason is that silicon atoms in silanes have strong nucleophilicity and can donate electrons to react with electron-deficient atoms or molecules. Therefore, in the hydrogenation reaction, they can only play the role of electron donation.

[0014] The anionic polymerization method used in this invention is a conventional anionic polymerization method.

[0015] As a preferred embodiment, the siloxane cocatalyst is hexamethylcyclotrisiloxane.

[0016] As a preferred embodiment, the siloxane cocatalyst is added in three stages. After the first addition, the reaction time is 20-30 minutes; after the second and third additions, the reaction time is 30-60 minutes each time.

[0017] As a preferred embodiment, the molar ratio of the amount of the siloxane co-catalyst added for the first time to the dicyclopentadiene titanium dichloride is (0.5-1.5):1.

[0018] Due to the unique electron-donating properties of siloxane co-catalysts, they can combine with titanium atoms in the main catalyst, thereby hindering the polymerization of the active centers. Therefore, in this invention, the siloxane catalyst is added in three stages. A portion of the co-catalyst can be added simultaneously with the main catalyst. When the amount added is too low, its inhibitory effect on the main catalyst is weak. When the amount added reaches a certain value, the degree of hydrogenation tends to stabilize, thereby improving the interaction between the co-catalyst and the main catalyst.

[0019] As a preferred approach, the molar ratio of the second and third additions of the siloxane-based co-catalyst to dicyclopentadiene titanium dichloride is (1–5):1. As the hydrogenation reaction proceeds, the co-catalyst gradually decomposes, causing a rapid decrease in the hydrogenation rate. To maintain the reaction rate, additional co-catalyst needs to be added. Insufficient addition will make it difficult to prevent polymerization of the catalytically active sites and to deassociate already polymerized active sites.

[0020] As a preferred embodiment, the hydrogenation reaction conditions are: temperature of 65–95°C, total reaction time of 1.5–2.5 h, and reaction pressure of 1.5–1.8 MPa. With increasing hydrogenation reaction temperature, the degree of hydrogenation of the product initially increases and then decreases. This is because excessively high reaction temperatures may reduce catalyst activity; a further preferred temperature is 65–75°C. Conversely, with increasing pressure, the degree of hydrogenation of the product also increases; however, the hydrogenation reaction pressure should not be too high, otherwise there may be safety hazards.

[0021] As a preferred embodiment, the amount of dicyclopentadiene titanium dichloride added is calculated as 0.075g / 250g styrene / butadiene / styrene copolymer to 0.11g / 250g styrene / butadiene / styrene copolymer.

[0022] As a preferred embodiment, the lithium-titanium ratio is measured as a molar ratio of active lithium in lithium hydride to dicyclopentadiene titanium dichloride of (7–8.5):1. Dicyclopentadiene titanium dichloride (Cp₂TiCl₂) reacts with lithium hydride (LiH) to generate an active catalyst species. This active species plays a crucial role in the hydrogenation of double bonds in styrene / butadiene / styrene copolymer (SBS). As the lithium-titanium ratio increases, the amount of lithium hydride in the reaction system increases, and the participation of more lithium hydride in the reaction leads to an increase in the number of active catalytic sites, thus increasing the degree of hydrogenation of the product.

[0023] Compared with the prior art, the present invention has the following technical effects:

[0024] 1) In the process of preparing hydrogenated styrene / butadiene / styrene copolymer by hydrogenation of styrene / butadiene / styrene copolymer in the dicyclopentadiene titanium dichloride / lithium hydride system, this invention employs a siloxane cocatalyst that can undergo a complexation reaction with active [Cp2TiH], stabilizing the active body, inhibiting its dimerization / polymerization reaction, and improving hydrogenation efficiency. Furthermore, one of cyclohexylmethyldimethoxysilane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and decamethylcyclopentasiloxane as a cocatalyst can react with some lithium hydride, reducing the lithium hydride concentration, which can also inhibit the dimerization / polymerization reaction of active [Cp2TiH], promote the hydrogenation reaction, and shorten the reaction time.

[0025] 2) The siloxane cocatalyst used in this invention can reduce the amount of active lithium to be added to a certain extent, thus saving costs.

[0026] 3) The hydrogenation reaction time of the present invention is short, which can make the degree of hydrogenation of the polybutadiene block in the polymer greater than 98%; and the hydrogenation reaction conditions are mild and gentle, which is conducive to the heat transfer of the reaction.

[0027] 4) The yellowness index and odor grade of the SEBS products prepared by the method of the present invention are significantly reduced, and they are less prone to clumping, thus improving the appearance quality of existing SEBS. Attached Figure Description

[0028] Figure 1 is a comparison of the products prepared in Example 6 using an ester catalyst (b) and a hexamethylcyclotrisiloxane catalyst (a).

[0029] Figure 2 is a comparison of the agglomeration degree of the products prepared in Example 7 using ester catalyst (a) and hexamethylcyclotrisiloxane catalyst (b), respectively. Detailed Implementation

[0030] To better understand the technical solution of the present invention, the present invention will now be described in further detail with reference to specific embodiments. However, those skilled in the art should understand that the following description is only for illustrating some preferred embodiments of the present invention and should not be considered as a limitation of the present invention. Any modifications or substitutions based on the present invention should be included within the protection scope of the present invention without departing from the spirit and scope of the present invention.

[0031] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available products or products that can be prepared by known methods.

[0032] Example 1

[0033] 2500 mL of cyclohexane was pressurized into a 5L polymerization reactor as a solvent. The temperature was raised to 60°C under stirring. 41 mL of styrene, 1.2 mL of tetrahydrofurfuryl ethyl ether (a structure modifier), and 2.6 mL of butyllithium were added to the polymerization reactor. After reacting for 30 minutes, 282 mL of butadiene was added to carry out the polymerization reaction. The reaction temperature was set to 60°C and the reaction time was 45 min. After the reaction was completed, 41 mL of styrene was added to the polymerization reactor to carry out the polymerization reaction. The reaction temperature was set to 55°C and the reaction time was 30 min to obtain the polymerized resin.

[0034] The adhesive was pumped into a hydrogenation reactor and heated to 70°C. Based on a lithium-to-titanium ratio of 7.5, the required amount of butyllithium was calculated and added, followed by a 30-minute reaction with hydrogen gas. Then, 0.4 mmol of hexamethylcyclotrisiloxane and 0.1 g of dicyclopentadiene titanium dichloride catalyst were added, and the reaction was continued with hydrogen gas for 40 minutes. The hydrogenation reaction temperature was controlled at 70°C, and the reaction pressure at 1.8 MPa. After a 30-minute high-temperature reaction, hexamethylcyclotrisiloxane was added twice, at a rate of 0.4 mmol each time. After 2 hours of reaction, a sample was taken for analysis, and the degree of hydrogenation of the double bonds in the polybutadiene segments of the polymer was found to be 99.34%.

[0035] Example 2

[0036] The implementation process was the same as in Example 1, except that the molar ratio of active lithium to the main catalyst dicyclopentadiene titanium dichloride was changed during the experiment. The experimental results are shown in Table 1.

[0037] Table 1. Effect of Lithium-Titanium Ratio

[0038]

[0039]

[0040] Note: Main catalyst: 0.4 mmol / 250 g SBS; Mn of SBS: 180,000-200,000; Reaction time: 2 h; Reaction start temperature: 70 °C; Co-catalyst: hexamethylcyclotrisiloxane; Passivation amount of co-catalyst / addition amount of main catalyst and co-catalyst / main catalyst are 1 and 2 respectively; co-catalyst is added twice.

[0041] Example 3

[0042] The implementation process was the same as in Example 1, except that the molar ratio of the co-catalyst hexamethylcyclotrisiloxane to the main catalyst dichlorotitanium was changed during the experiment. The experimental results are shown in Table 2.

[0043] Table 2 Effect of co-catalyst

[0044]

[0045] Note: Main catalyst: 0.4 mmol / 250 g SBS; Mn of SBS: 180,000-200,000; Reaction time: 2 h; Reaction start temperature: 70 °C; Co-catalyst: hexamethylcyclotrisiloxane; Lithium-titanium molar ratio: 7.5; Co-catalyst added twice, where passivation refers to the first addition of co-catalyst, and replenishment refers to the second and third additions; Co-catalyst number 3 was added once.

[0046] Table 2 shows that neither adding a co-catalyst for passivation in the early stages nor adding a co-catalyst in the later stages is conducive to the hydrogenation reaction. This is because the amount of active lithium in the system is 7.5 times (molar ratio) that of the titanium catalyst. The catalytically active [Cp2TiH] is prone to self-polymerization in this system, therefore, a stepwise addition of a co-catalyst is necessary to prevent the polymerization of the active material. As shown in numbers 2-3, the number of times the catalyst is added has little effect on the reaction, while the amount added has a crucial influence on the hydrogenation reaction.

[0047] Example 4

[0048] The implementation process was the same as in Example 1, except that the starting temperature of the hydrogenation reaction was changed during the experiment. The experimental results are shown in Table 3.

[0049] Table 3 Effect of Starting Temperature

[0050]

[0051] Note: Main catalyst: 0.4 mmol / 250 g SBS; Mn of SBS: 180,000-200,000; reaction time: 2 h; lithium-titanium ratio / mol: 7.5; co-catalyst: hexamethylcyclotrisiloxane; passivation amount of co-catalyst / main catalyst and co-catalyst replenishment amount / main catalyst: 1 and 2 respectively; co-catalyst replenishment was performed twice.

[0052] Example 5

[0053] The implementation process was the same as in Example 1, except that the hydrogen pressure of the hydrogenation reaction was changed during the experiment. The experimental results are shown in Table 4.

[0054] Table 4. Effect of Hydrogen Pressure

[0055]

[0056] Note: Main catalyst: 0.4 mmol / 250 g SBS; Mn of SBS: 180,000-200,000; reaction time: 2 h; initial reaction temperature: 70 °C; lithium-titanium ratio / mol: 7.5; co-catalyst: hexamethylcyclotrisiloxane; passivation amount of co-catalyst / main catalyst and co-catalyst replenishment amount / main catalyst: 1 and 2 respectively; co-catalyst replenishment was performed twice.

[0057] Example 6

[0058] The implementation process was the same as in Example 1, except that the type of co-catalyst was changed to explore its effect on the color and odor of the product. The results are shown in Table 5 and Figure 1.

[0059] Table 5. Effect of co-catalyst type on product color

[0060]

[0061] Note: The odor rating in the table is based on standard GB / T12761.

[0062] Example 7

[0063] The implementation process was the same as in Example 1, except that the type of co-catalyst was changed to explore its effect on the product's anti-sticking properties. The results are shown in Table 6 and Figure 2.

[0064] Table 6. Effect of co-catalyst type on product anti-sticking properties

[0065]

Claims

1. A method for improving the efficiency of SBS hydrogenation catalyzed by a titanocene catalyst, characterized in that: Styrene / butadiene / styrene copolymer solution is obtained by anionic polymerization; the styrene / butadiene / styrene copolymer solution is then subjected to hydrogenation reaction in the presence of a siloxane cocatalyst and dicyclopentadiene titanium dichloride and lithium hydride to obtain hydrogenated styrene / butadiene / styrene copolymer; the siloxane cocatalyst includes at least one of cyclohexylmethyldimethoxysilane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane.

2. The method for improving the efficiency of SBS hydrogenation catalyzed by a titanocene catalyst according to claim 1, characterized in that: The siloxane cocatalyst is hexamethylcyclotrisiloxane.

3. A method for improving the efficiency of SBS hydrogenation catalyzed by a titanocene catalyst according to claim 1 or 2, characterized in that: The siloxane-based cocatalyst was added in three stages. After the first addition, the reaction time was 20–30 min; after the second and third additions, the reaction time was 30–60 min each time.

4. The method for improving the efficiency of SBS hydrogenation catalyzed by a titanocene catalyst according to claim 1, characterized in that: The molar ratio of the first addition of the siloxane cocatalyst to the dicyclopentadiene titanium dichloride is (0.5-1.5):1; the molar ratio of the second and third additions of the siloxane cocatalyst to the dicyclopentadiene titanium dichloride is (1-5):

1.

5. The method for improving the efficiency of SBS hydrogenation catalyzed by a titanocene catalyst according to claim 4, characterized in that: The conditions for the hydrogenation reaction are: temperature of 65–95°C, total reaction time of 1.5–2.5 h, and reaction pressure of 1.5–1.8 MPa.

6. The method for improving the efficiency of SBS hydrogenation catalyzed by a titanocene catalyst according to claim 1, characterized in that: The amount of dicyclopentadiene titanium dichloride added is calculated as 0.075g / 250g styrene / butadiene / styrene copolymer to 0.11g / 250g styrene / butadiene / styrene copolymer.

7. A method for improving the efficiency of SBS hydrogenation catalyzed by a titanocene catalyst according to claim 1 or 6, characterized in that: The lithium-titanium ratio is measured as a molar ratio of (7-8.5):1 between active lithium in lithium hydride and dicyclopentadiene titanium dichloride.

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