Hydrogenation process of polymers

Abstract

The application discloses the technical field of polymer synthesis, and particularly discloses a hydrogenation method of a polymer, which comprises the following steps: obtaining an active polymer by using an anionic polymerization method; adding a terminating agent into a polymerization system and then performing hydrogenation reaction on the terminating reaction system to obtain a hydrogenated polymer. The application finds that the active polymer is terminated by the innovative terminating agent, which can effectively terminate the active molecular chain, maintain the activity of the catalyst in the hydrogenation process, improve the hydrogenation efficiency, and prevent the polymer from being degraded and broken in the high-temperature and high-pressure hydrogenation process.

Description

Technical Field

[0001] This invention belongs to the field of hydrogenation catalysis technology, specifically relating to a hydrogenation method for polymers containing benzene rings. Background Technology

[0002] Existing hydrogenation methods and catalysts for polymers, such as the common styrene-conjugated diene copolymer, can be broadly classified into two categories. One category comprises heterogeneous catalytic systems. The most typical such system involves supporting metals like nickel and cobalt, as well as noble metals like platinum, palladium, and rhodium, on supports such as diatomaceous earth and alumina, using fixed-bed or fluidized-bed hydrogenation processes under high temperature and pressure. Its main advantages are the absence of separation issues between hydrogenation products and catalysts, extended catalyst lifespan, high polymer hydrogenation degree, and the ability to hydrogenate both the benzene ring and the conjugated diene. However, it also has significant drawbacks: demanding hydrogenation conditions requiring high temperature and pressure, complex processes, high costs, and a tendency to polymer degradation and molecular chain breakage. The other category comprises homogeneous catalytic systems, typically including nickel or cobalt transition metal salt catalytic systems, platinum, palladium, rhodium, ruthenium, and other noble metal complex catalytic systems, and metallocene catalytic systems. These systems are characterized by simple processes, high hydrogenation efficiency, and high selectivity. However, they suffer from low benzene ring hydrogenation degrees and difficulties in separating the catalyst from the hydrogenation products.

[0003] Dow Chemical disclosed a highly hydrogenated styrene-conjugated diene block copolymer in its international patent WO0056782, using a heterogeneous supported catalyst under high temperature and pressure for hydrogenation. However, it did not address how to solve the problem of polymer degradation during hydrogenation. Chinese patent CN111085271A disclosed a homogeneous catalytic hydrogenation method using alkyl metals and transition metals nickel and / or cobalt alkoxides to obtain deeply hydrogenated styrene-conjugated diene copolymers, but this method also requires high reaction temperatures (170°C) and hydrogenation pressures (3 MPa), and does not solve the problems of difficult catalyst removal and easy polymer degradation and chain breakage under high temperature and pressure. Chinese patent CN109836525A disclosed a method for hydrogenating styrene-conjugated diene copolymers using a nickel / aluminum homogeneous catalyst. This method preferentially uses a phenolic anionic polymerization terminator, improving hydrogenation efficiency. However, the hydrogenation temperature and pressure are relatively low, resulting in selective hydrogenation and low hydrogenation degree of the benzene ring, and it does not address the problem of polymer molecular chain reduction. Currently, it is very difficult to achieve deep hydrogenation of styrene-conjugated diene copolymers using existing technologies without causing polymer degradation and chain breakage. Summary of the Invention

[0004] To address the problems of the prior art, the present invention aims to provide a method for polymer hydrogenation, particularly deep hydrogenation (e.g., hydrogenation of unsaturated bonds, especially aromatic unsaturated bonds, in polymers), which aims to improve the stability of polymer segments during hydrogenation, particularly deep hydrogenation, and reduce degradation through the innovative use of a terminating agent. Furthermore, it also improves the hydrogenation efficiency and effectiveness.

[0005] Polymers such as conventional styrene-conjugated diene copolymers can undergo selective hydrogenation of their non-aromatic unsaturated bonds under relatively mild conditions. However, aromatic unsaturated bonds, such as benzene rings, require harsh conditions, such as high temperature and high pressure, for deep hydrogenation. These harsh reaction conditions significantly affect chain stability, leading to chain degradation. Therefore, the present invention provides the following improvements:

[0006] A method for hydrogenating a polymer includes the following steps:

[0007] Step (1): Anionic polymerization

[0008] Anionic polymerization was used to obtain the active polymer (PLi);

[0009] Step: Terminating the reaction

[0010] Add a terminator of formula 1 to the polymerization system of step (1) to terminate the reaction;

[0011]

[0012] In R1 to R4, one of the substituents is a halogen, and the remaining substituents are individually C1 to C4. 20 Alkyl or aryl groups;

[0013] The alkyl and aryl groups are allowed to have substituents, and the substituents are at least one of C1-C3 alkyl, C1-C3 alkoxy, and phenyl groups;

[0014] Step (3): Hydrogenation reaction

[0015] The termination reaction system of step (2) is subjected to hydrogenation reaction to obtain hydrogenated polymer.

[0016] This invention has discovered that the innovative use of Formula 1 to terminate active polymers can not only effectively terminate active molecular chains, maintain catalyst activity during hydrogenation, and improve hydrogenation efficiency, but also prevent polymer degradation and chain breakage during high-temperature and high-pressure hydrogenation.

[0017] The technical solution of this invention can be used for the selective hydrogenation of non-aromatic unsaturated bonds, and also for the deep hydrogenation of unsaturated bonds containing aromatics. In particular, in terms of deep hydrogenation, it has greater advantages over the prior art in improving polymer stability, hydrogenation efficiency and effect during the deep hydrogenation process.

[0018] In this invention, the desired active polymer can be obtained by using existing and well-known anionic polymerization methods.

[0019] For example, by polymerizing alkyl lithium and polymeric monomers, active polymers (PLi) can be obtained.

[0020] In this invention, the active polymer is an active polymer containing a benzene ring;

[0021] Preferably, the active polymer is an active polymer obtained by polymerizing styrene monomers.

[0022] More preferably, the polymer is an active polymer comprising random or block copolymerization of styrene and conjugated diene;

[0023] Preferably, the conjugated diene includes at least one of 1,3-butadiene, isoprene, isoprene, and methylpentadiene.

[0024] Taking the active polymer as an active SBS block polymer as an example, the anionic polymerization method is as follows:

[0025] In a polymerization reactor purged with high-purity nitrogen, a polymerization solvent and reaction aids (such as structure modifiers tetrahydrofuran (50–1000 mg / kg), tetrahydrofurfural ethyl ether (5–100 mg / kg), etc.) are added. Alkyl lithium (e.g., C1–C6 alkyl lithium) and styrene monomer are added for a first-stage polymerization (polymerization temperature, for example, 60–65 °C). Then, a conjugated diene is added for a second-stage polymerization (polymerization temperature, for example, 60–75 °C). Finally, styrene is added for a third-stage polymerization (polymerization temperature, for example, 60–65 °C) to obtain the active polymer (SBS-Li).

[0026] In this invention, the structure of Formula 1 is innovatively used to terminate the active polymer. Studies have found that it not only effectively terminates the polymer but also unexpectedly improves the stability of the chain segments in subsequent hydrogenation, especially deep hydrogenation, avoiding degradation of the polymer chain segments by the reaction conditions. Moreover, it helps to improve the hydrogenation efficiency and effect.

[0027] In this invention, the alkyl group is, for example, a straight-chain or branched alkyl group, more preferably a C1-C6 straight-chain or branched alkyl group. The aryl group is, for example, a benzene ring, or a five- or six-membered heterocyclic aryl group. In R1-R4, the non-halogenated substituent can also be a substituted alkyl group or a substituted aryl group, wherein the substituent is, for example, a C1-C3 alkyl group, a C1-C3 alkoxy group, or a phenyl group; for example, it can be benzyl, benzyloxy, etc.

[0028] Preferably, in R1 to R4, one of the substituents is a halogen, and the remaining substituents are C1 to C6 alkyl, phenyl, or benzyl groups.

[0029] In this invention, the halogen is Cl, Br, or I.

[0030] In this invention, the total molar ratio of the terminator to the active chain end of the active polymer is 0.5-2.0:1; preferably 0.9-1.3:1.

[0031] Preferably, the reaction is terminated at 40-60°C.

[0032] Preferably, the reaction termination time is 2-20 min.

[0033] In this invention, hydrogenation can be carried out using methods known in the industry.

[0034] Preferably, the hydrogenation in step (3) is a deep hydrogenation that hydrogenates the benzene ring in the polymer. The present invention preferably uses deep hydrogenation, but does not exclude its application in selective hydrogenation. Its preference for deep hydrogenation is only because deep hydrogenation has greater advantages in terms of structural stability and hydrogenation effect compared to existing methods.

[0035] In this invention, the catalyst used in the hydrogenation stage can be one that is known in the industry.

[0036] Preferably, the catalyst added during the hydrogenation process is a composite catalyst of organonitrile-IIIA cluster metal alkylates or alkoxides; more preferably, it is a Ziegler-type nickel / aluminum catalyst.

[0037] Preferably, the hydrogenation pressure is 2.5-3.2 MPa during the hydrogenation process.

[0038] The hydrogenation reaction takes place at a temperature of 160-170℃.

[0039] Preferably, the hydrogenation reaction takes 1-2 hours.

[0040] The present invention discloses a preferred method for deep hydrogenation of styrene-conjugated diene copolymer, which includes anionic polymerization of styrene and conjugated diene to form an active base adhesive (active polymer PLi), followed by the addition of a formula 1 terminator to terminate the active molecular chain, and finally hydrogenation to prepare hydrogenated styrene-conjugated diene copolymer using a composite catalyst of organonitrile / IIIA cluster metal alkylate or alkoxide.

[0041] The beneficial effects of this invention are:

[0042] This invention is the first to discover that the compound of Formula 1 can be used as an active polymer terminator in anionic polymerization. It not only prevents polymer degradation and chain scission, but also unexpectedly improves the reaction efficiency and hydrogenation effect of subsequent hydrogenation, and improves the stability of chain segments under high temperature and high pressure hydrogenation conditions.

[0043] The technical solution of this invention is simple in process and low in cost, and has a better hydrogenation effect, which is conducive to the development and application of high-performance polymers. Detailed Implementation

[0044] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0045] In the examples and comparative examples:

[0046] The molecular weight and molecular weight distribution of styrene-conjugated diene copolymers were determined by gel permeation chromatography. The instrument used was a Shimadzu LCD-10ADvp gel chromatograph, with a RID-10A differential refractive index detector. The separation columns were GPC804 and 805, the flow rate of the mobile phase THF was 1 mL / min, and the test temperature was room temperature. Monodisperse polystyrene was used for calibration, and data were processed by a Shimadzu CR-7A.

[0047] The degree of hydrogenation was calculated based on the 1H NMR spectrum and measured at room temperature using a Bruker AV400 spectrometer (400MHz). CDCl3 was used as the solvent.

[0048] Hydrogenation degree % = [(moles of double bonds in the styrene-conjugated diene copolymer - moles of double bonds in the product after hydrogenation) / moles of double bonds in the styrene-conjugated diene copolymer] × 100%, which represents the degree of double bond saturation in the hydrogenation product. The degree of hydrogenation of the benzene ring and the diene is calculated separately for the double bonds of the benzene ring and the double bonds of the diene, respectively.

[0049] The following examples and comparative examples were all performed according to the following steps:

[0050] In a 5L polymerization reactor purged with high-purity nitrogen, pure cyclohexane (water value <20 mg / kg) was added as a solvent, and block or random styrene-butadiene copolymers were synthesized by anionic polymerization. Immediately after polymerization, a metered terminator was added to terminate the active chain, and the mixture was stirred at 40-60℃ for 5-20 min. The polymer was then pressed into a 5L hydrogenation reactor, and hydrogen was added using a Ziegler-type nickel / aluminum catalyst. The hydrogenation temperature was 160-170℃, and the pressure was 2.5-3.2 MPa. After 1-2 hours of reaction, samples were taken for GPC and NMR testing. The hydrogenated polymer solution was acidified to form water-soluble salts. The acidic aqueous phase of the solution was separated by centrifugation to remove metal ions from the polymer. After purification, an antioxidant was added, and the mixture was stirred until homogeneous. Water vapor was then condensed, and the mixture was dried to obtain the final sample.

[0051] The hydrogenation catalyst described in this invention can be a known homogeneous catalyst. For example, in the following cases, unless otherwise stated, the aluminum-nickel catalyst is a nickel isooctanoate / triethylaluminum cyclohexane solution, wherein the molar ratio of nickel to aluminum is 1:3.

[0052] Example 1

[0053] Step (1-a): Polymer synthesis

[0054] In a 5L polymerization reactor purged with high-purity nitrogen, 3000 mL of pure cyclohexane (water value < 20 mg / kg), tetrahydrofuran (equivalent to 200 mg / kg solvent), and 30 mg / kg tetrahydrofurfural ethyl ether were added. Stirring was started, and the temperature was raised to 60°C. In the first stage, 5.0 mmol of n-butyllithium and 60 g of styrene monomer were added and polymerized for 30 minutes. Then, 180 g of butadiene monomer was added in the second stage. The reaction temperature was controlled below 80°C using a jacketed water cooling method. After reacting for 40 minutes, 60 g of styrene monomer was added in the third stage, and the reaction was carried out at a temperature of 60–65°C for 30 minutes.

[0055] use As a terminator, it was stirred at 50°C for 10 min. The molar ratio of the amount added to the active chain was 1.2.

[0056] Step (1-b): Hydrogenation of the polymerized gel

[0057] The polymer solution was introduced into a 5L hydrogenation reactor, hydrogen gas was introduced, and 3 mmol / 100g of aluminum-nickel catalyst was added for catalytic hydrogenation. The hydrogenation pressure was controlled at 3.0 MPa, the temperature was 165℃, and the reaction was carried out for 2 hours. GPC and NMR were analyzed every hour. The specific data are shown in Table 1.

[0058] Example 2

[0059] The hydrogenated polymer was synthesized according to the method of Example 1, except that the terminator used was... See Table 1 for specific data.

[0060] Example 3

[0061] The hydrogenated polymer was synthesized according to the method of Example 1, except that the terminator used was... See Table 1 for specific data.

[0062] Example 4

[0063] The hydrogenated polymer was synthesized according to the method in Example 1, except that the molar ratio of the terminator to the active chain was 0.5. Specific data are shown in Table 1.

[0064] Example 5

[0065] The hydrogenated polymer was synthesized according to the method in Example 1, except that the molar ratio of the terminator to the active chain was 1.5. Specific data are shown in Table 1.

[0066] Example 6

[0067] The hydrogenated polymer was synthesized according to the method in Example 1, except that the molar ratio of the terminator to the active chain was 2.5. Specific data are shown in Table 1.

[0068] Comparative Example 1

[0069] The hydrogenated polymer was synthesized according to the method in Example 1, except that isopropanol was used as the terminator. Specific data are shown in Table 1.

[0070] Comparative Example 2

[0071] The hydrogenated polymer was synthesized according to the method in Example 1, except that methanol was used as the terminator. Specific data are shown in Table 1.

[0072] Comparative Example 3

[0073] The hydrogenated polymer was synthesized according to the method in Example 1, except that 2,6-diisobutyl-p-pentylphenol was used as the terminator. Specific data are shown in Table 1.

[0074] Comparative Example 4

[0075] The hydrogenated polymer was synthesized according to the method in Example 1, except that water was used as the terminator. Specific data are shown in Table 1.

[0076] Table 1. Data on different terminators and dosages in relation to polymer molecular weight and degree of hydrogenation.

[0077]

[0078]

[0079] Table 1 (continued)

[0080]

[0081] As shown in Table 1, adding Formula 1 as a terminator can inhibit the molecular chain degradation and scission of the styrene-butadiene copolymer during deep hydrogenation. After 2 hours of hydrogenation, the polymer does not degrade. When other terminators are used, the content of small molecular weights generated after deep hydrogenation is greater than 10%, and the polymer molecular chain degradation is obvious. Moreover, this type of terminator can improve the catalytic hydrogenation activity and hydrogenation efficiency. Compared with other terminators, Formula 1 as a terminator generally increases the degree of hydrogenation of benzene ring by more than 10% after 2 hours of hydrogenation.

Claims

1. A method for hydrogenating a polymer, characterized in that, Includes the following steps: Step (1): Anionic polymerization Anionic polymerization was used to obtain an active polymer; the polymer was an active polymer comprising random or block copolymers of styrene and conjugated diene. The conjugated diene includes at least one of 1,3-butadiene, isoprene, isoprene, and methylpentadiene; Step (2): Termination of reaction Add a terminator of formula 1 to the polymerization system of step (1) to terminate the reaction; Formula 1 In R1~R4, one of the substituents is a halogen, and the remaining substituents are C1~C6 alkyl, phenyl or benzyl; the molar ratio of the terminator to the total molar ratio of the active chain end of the active polymer is 0.5~2.0:1; Step (3): Hydrogenation reaction The termination reaction system of step (2) is subjected to hydrogenation reaction to obtain hydrogenated polymer; The hydrogenation described herein is a deep hydrogenation that hydrogenates the benzene ring in the polymer; The catalyst added during hydrogenation is a composite catalyst of organonitrile-IIIA group metal alkylates or alkoxides; During hydrogenation, the pressure for adding hydrogen is 2.5~3.2 MPa; The hydrogenation reaction takes place at a temperature of 160~170℃; The hydrogenation reaction takes 1 to 2 hours.

2. The method for hydrogenating the polymer as described in claim 1, characterized in that, The ratio of the molar amount of the terminator to the total molar amount of the active chain ends of the active polymer is 0.9~1.3:

1.

3. The method for hydrogenating the polymer as described in claim 1, characterized in that, The reaction is terminated at a temperature of 40-60℃.

4. The method for hydrogenating the polymer as described in claim 1, characterized in that, The reaction is terminated in 2 to 20 minutes.

5. The method for hydrogenating the polymer as described in claim 1, characterized in that, The catalyst added during hydrogenation is a Ziegler-type nickel / aluminum catalyst.

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