JP2015067720A - Method for producing terminal-modified polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a terminal-modified polymer which does not require many steps to introduce terminal functional groups for improving dispersibility of silica used as a compounding ingredient of an automotive pneumatic tire composition.SOLUTION: A terminal-modified polymer is produced by polymerizing a vinyl aromatic monomer, a conjugated diene monomer, or both of these under the presence of an anionic polymerization initiator and by thereafter terminating the polymerization by addition of 4-acyloxy-3-alkoxystyrene. The terminal-modified polymer obtained exhibits an interaction with silica and, when it is blended as an ingredient in a rubber composition for a silica-compounded pneumatic tire, dispersibility of the silica compounded in the rubber composition is improved and can sufficiently satisfy both of rolling resistance reduction inherent to silica and stability on a wet road surface.

Description

  The present invention relates to a method for producing a terminal-modified polymer. More specifically, the present invention relates to a method for producing a terminal-modified polymer that improves the dispersibility of silica used as a compounding agent for an automotive pneumatic tire composition.

  As various performances required for pneumatic tires for automobiles, reduction of rolling resistance, stability on wet road surfaces, and the like are required. As a method for achieving both of these properties, silica is compounded as a reinforcing filler in a tire rubber composition. However, even if silica is added to the rubber composition for tires, the dispersibility of silica in the composition is low, and even if a large amount of silica can be added, there is a problem that the effect cannot be sufficiently exhibited. It is done.

  Patent Document 1 discloses an elastomer / filling that is useful as a tire component and the like, in which a reinforcing filler is uniformly dispersed by forming the reinforcing filler in the elastomer host material in situ from its precursor. A method for producing a composite material is described, and in order to composite silica as a filler, a reaction from a filler precursor is required.

  In Patent Document 2, a filler precursor, a condensation reaction accelerator and an elastomer host (A) or (B) are blended in a closed mixer to start a condensation reaction of the filler precursor, and an elastomer host (A) And optionally for the elastomer host (B), the organosilane material and the filler / filler precursor are added and reacted in a closed mixer before the condensation reaction is complete and the resulting elastomer / filler composite is recovered. A method for producing an elastomer / filler composite is described. And it is stated that this composite material is used as an active ingredient of a rubber composition for tires, particularly a rubber composition for tire treads.

Here, the elastomer host (A) is a homopolymer of a conjugated diene or a copolymer of a conjugated diene and a vinyl aromatic monomer, and the elastomer host (B) is at least one alkoxy metal terminal functionalized diene-based elastomer. This diene-based elastomer has a general formula
Elastomer-X- (OR) n
Elastomer: Conjugated diene homopolymer or conjugated diene and vinyl
Copolymer with aromatic monomer
X: Metal made of Si, Ti, Al or B
R: alkyl group of C ₁ -C ₄
n: 3 for Si and Ti, 2 for Al and B
(Claim 5, paragraph [0014]).

  However, in each example of Patent Document 2, only the description that styrene and 1,3-butadiene are copolymerized in an organic solvent in the presence of a lithium-based catalyst and then the elastomer is recovered is used as an elastomer end group. There is no description regarding a method for producing a terminal-modified polymer into which an X- (OR) n group is introduced.

  In Patent Document 3, a polymer having a terminal diester group is produced by reacting a diester compound such as ditertiary alkyl maleate with an art complex composed of a living polymer and a compound containing a typical metal element such as aluminum. Then, a method for producing a terminal acid anhydride group-containing polymer in which the diester group is converted into an acid anhydride group is described.

The art complex used here will be described. First, when anionic polymerization of styrene is performed using butyllithium, the end of the polymer becomes ~ C ^- Li ⁺ unless the reaction is stopped. The -C ^- Li ⁺ in Li ⁺ belong to hard acid referred to HSAB theory, therefore of the pair -C ^- is as shown a high reactivity. In general, in this state, its high ~C showing reactivity (nucleophilic) ^- is a result of the attack to the carbonyl carbon, the introduction of the acid anhydride group is difficult, it is converted Therefore the hard acid soft acid Is done.

In this patent document, by using a trialkyl aluminum compound not containing leaving group as its method, i.e. -C ^- the Li ⁺ -C ^- by (AlR ₃ Li) ⁺ to changing, that allowed to lower the reactivity The technique is taken.

  Furthermore, as a method for improving the dispersibility of silica in a diene rubber, it is known that it is effective to introduce a functional group such as a phenolic hydroxyl group having an interaction with silica at the end of the diene rubber. However, when introducing a phenolic hydroxyl group, a multi-step process such as introduction of a protective group with a functional group such as a tertiary butyl group or trimethoxysilyl group and deprotection of the acid or tetrabutylammonium fluoride with a tetrahydrofuran solution. Need. In addition to these protection and deprotection steps, the phenol-terminated polymer is synthesized by cationic polymerization using a fluoroborane cationic initiator and terminated by Friedel-Crafts reaction using a phenol compound. (Patent Document 4) is not suitable for synthesizing modified polymers for tires because of the low molecular weight and wide molecular weight distribution caused by frequent chain transfer reactions.

JP 2000-273191 A JP 2000-143881 A JP 2007-084711 A JP 2008-189745 A

  The object of the present invention is to provide a method for producing a terminal-modified polymer that does not require multiple steps when introducing a terminal functional group that improves the dispersibility of silica used as a compounding agent for an automotive pneumatic tire composition. There is to do.

  The object of the present invention is to polymerize a vinyl aromatic monomer, a conjugated diene monomer, or both in the presence of an anionic polymerization initiator, and then add 4-acyloxy-3-alkoxystyrene to perform polymerization. This is achieved by a method in which the reaction is stopped to produce a terminally modified polymer.

  In the terminal-modified polymer produced by the method of the present invention, a phenolic hydroxyl group can be easily introduced into the polymer end in one step by using 4-acyloxy-3-alkoxystyrene as a polymerization reaction terminator. .

  Since the obtained terminal-modified polymer exhibits an interaction with silica, when compounded as one component in the rubber composition for silica-containing pneumatic tires, the dispersibility of the silica compounded in the rubber composition is improved, The problem of reducing the rolling resistance inherent to silica and the stability on wet road surfaces can be fully satisfied.

  The polymer whose end groups are modified is formed as a vinyl aromatic monomer, a conjugated diene monomer, or a polymer of both. Examples of the vinyl aromatic monomer include styrene, α-methylstyrene, p-methylstyrene, 2,4,6-trimethylstyrene, vinyltoluene, 1-vinylnaphthalene, and preferably styrene is used. Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 1,3-hexadiene, chloroprene, and preferably 1,3-butadiene or isoprene. Used. Both of these vinyl aromatic monomers and conjugated diene monomers can be used in combination, and preferably both styrene and 1,3-butadiene or isoprene are used. When both of these are used, the resulting polymer is generally a random copolymer, but it may be a block copolymer.

  The polymerization reaction is performed by an anionic polymerization method using an anionic polymerization initiator. As the anionic polymerization initiator, an organic lithium compound, preferably alkyl lithium or aryl lithium is used.

  Examples of the alkyl lithium include methyl lithium, ethyl lithium, propyl lithium, n-butyl lithium, secondary butyl lithium, tertiary butyl lithium, isobutyl lithium, hexyl lithium, octyl lithium, tetramethylene dilithium, and m-diisopropenylbenzene. Examples of the aryllithium include phenyllithium and tolyllithium. These may be used singly or in combination of two or more, and from the viewpoints of handleability and industrial economy, n-butyllithium, secondary butyllithium, and tertiary butyllithium are preferable. From the viewpoint of reactivity, n-butyl lithium and secondary butyl lithium are more preferable.

  These organolithium compounds are generally used in a proportion of about 0.0001 to 10 mol%, preferably about 0.0005 to 6 mol%, based on the amount of monomer (mixture) charged.

  In the polymerization reaction system, 2,2-ditetrahydrofurylpropane, N, N, N ′ used in a proportion of about 10 to 300 mol%, preferably about 40 to 200 mol%, relative to the molar amount of initiator used. , N′-tetramethylethylenediamine, diethyl ether, monoglyme, diglyme, dimethoxyethane, tetrahydrofuran and the like are used. These compounds act as a randomizer in an anion initiator and a growth species activator or copolymerization when a nonpolar solvent such as cyclohexane or methylcyclohexane is used in the polymerization reaction.

  The polymerization reaction is carried out using a hydrocarbon solvent such as cyclohexane, methylcyclohexane, toluene, tetrahydrofuran and the like at about -100 to 100 ° C, generally about 0 to 70 ° C for about 1 to 5 hours, and thereafter 4-Acyloxy-3-alkoxystyrene is added to the polymerization reaction system to stop the polymerization reaction. The amount of 4-acyloxy-3-alkoxystyrene is an amount sufficient to introduce the end group of the resulting polymer, for example, about 33 to 1000 mol%, preferably about 33 to 1000 mol%, based on the molar amount of the anionic polymerization initiator used. Is used in a proportion of about 100 to 400 mol%.

  As 4-acyloxy-3-alkoxystyrene, a compound in which the acyloxy group is an acetoxy group, a benzoyloxy group or the like, and the alkoxy group is an alkoxy group having 1 to 10 carbon atoms, preferably 4-acetoxy-3-methoxystyrene is used. Used. As 4-acetoxy-3-methoxystyrene, commercially available products such as those manufactured by Tsukino Food Industry Co., Ltd. can be used as they are.

The anionic polymerization used here is a polymerization method that proceeds in the following process.
1) Growth species are generated by the nucleophilic attack of the initiator on the monomer.
2) The growing species further undergoes a nucleophilic attack on the monomer, and the process is repeated to produce a polymer having a growing end.
3) The growing species at the end of the polymer undergoes nucleophilic attack on the terminator and the polymerization stops.
As a result, one start end and one stop end are introduced into each polymer chain. Therefore, ideally, the stopper is used at a ratio of 1: 1, that is, 100%, ideally with respect to the initiator. Further, the amount of alcohol used to form the alkoxyl group is sufficient to completely convert the halogen group or (meth) acryl group to the alkoxyl group.

本発明で用いられている4-アセトキシ-3-メトキシスチレン(停止剤)のアセトキシ基のオルト位にメトキシ基が存在することがこのような反応を可能にしているものと考えられる。メトキシ基が存在しない4-アセトキシスチレンで同様の重合を行った場合には全く赤変せず、ビニル部位とアセトキシ部位の両方が存在するだけの条件では、カルバアニオンのアセトキシ基に対する求核反応が優先するようになる。 The phenolic hydroxyl group is considered to be generated according to the following scheme.

The presence of a methoxy group at the ortho position of the acetoxy group of 4-acetoxy-3-methoxystyrene (terminator) used in the present invention is considered to enable such a reaction. When the same polymerization is performed with 4-acetoxystyrene having no methoxy group, the nucleophilic reaction to the acetoxy group of the carba anion does not change at all. Priority will be given.

  When 4-acetoxy-3-methoxystyrene is homopolymerized in the presence of an anionic polymerization initiator, it consists of, for example, an n-hexane solution of cyclohexane, 2,2-ditetrahydrofurylpropane and n-BuLi. When 4-acetoxy-3-methoxystyrene is dropped into the solution, the solution turns red, and after a while, the red color disappears and becomes colorless and transparent.

  This styrene derivative does not undergo anionic polymerization, but when a styrene derivative is added to an n-hexane solution of BuLi, it turns red, and after a while, the phenomenon returns from red to a colorless solution. This means that a benzyl anion is generated, and the benzyl anion nucleophilically attacks the carbonyl carbon to stop the reaction.

  However, also by this polymerization reaction, as shown in the results of Reference Examples described later, in addition to a fraction (raw material) having a molecular weight comparable to the molecular weight 168 of 4-acetoxy-3-methoxystyrene, Mn is 300, 480 or 4310 fractions are produced at a rate of about 30%, about 20% or about 10%, respectively.

Next, the present invention will be described with reference to examples.
Example 1
In a two-necked flask with a volume of 100 ml,
Cyclohexane (Kanto Chemicals) 7ml
2,2-ditetrahydrofurylpropane (Tokyo Kasei product) 0.268 g (1.45 mmol)
n-BuLi in 1.64 mol / L n-hexane solution (Kanto Chemicals) 2 ml (3.28 mmol)
Was added at room temperature, and 5.86 g (56.3 mmol) of styrene (Kanto Chemical) was added to the solution.
Was added dropwise at 0 ° C. and stirred at room temperature for 3 hours.
4-acetoxy-3-methoxystyrene 1.01 g (5.25 mmol)
(Tsukino Food Industry Co., Ltd.)
Was added to stop the polymerization reaction.

After filtering the reaction mixture with filter paper, the volatile components were distilled off from the filtrate, and a solution in which the residue was dissolved in 30 ml of tetrahydrofuran was dropped into 200 ml of methanol (Kanto Chemicals) to dissolve the soluble components and insoluble components. Separated into ingredients. After repeating the same operation twice, the volatile component was distilled off to obtain 5.51 g (yield 94%) of a brownish solid as terminal-modified polystyrene.
Mn: 4920
Mn (number average molecular weight) is measured by SEC (size exclusion chromatography), and the value is estimated as the molecular weight in terms of polystyrene.
PDI: 1.2
PDI (polydispersity) is calculated as Mw / Mn using Mw (weight average molecular weight) and Mn values measured by SEC, and the molecular weight distribution was controlled as the PDI value was closer to 1. Shows that a polymer can be obtained.
R _f : 0.81
The R _f value is measured using TLC (thin layer chromatography) on a silica plate with toluene as the eluent. The smaller the value, the higher the affinity with silica.
¹ H-NMR (CDCl ₃ , 20 ° C.): δ = 7.3 to 6.9 (br)
6.9-6.7 (br)
6.7 ~ 6.2 (br)
2.7 ~ 2.2 (br)
2.1 ~ 1.2 (br)
1.2 ~ 0.9 (br)
0.8 ~ 0.7 (br)

Example 2
In Example 1, the amount of 2,2-ditetrahydrofurylpropane was changed to 0.272 g (1.48 mmol), the amount of 4-acetoxy-3-methoxystyrene was changed to 0.646 g (3.36 mmol), respectively, and instead of styrene, By using 17.1 g (47.4 mmol) of a 15 wt% n-hexane solution of 1,3-butadiene (product of Aldrich), 2.26 g (yield 88%) of a brown viscous liquid as a terminal modified polybutadiene was obtained.
Mn: 3730
PDI: 1.1
R _f : 0.77
¹ H-NMR (CDCl ₃ , 20 ° C.): δ = 7.1 to 6.7 (br)
5.9 ~ 5.7 (br)
5.6-5.2 (br)
5.1 ~ 4.8 (br)
2.7 ~ 1.7 (br)
1.6-1.0 (br)
0.8 ~ 0.7 (br)

Example 3
In Example 1, the amount of 2,2-ditetrahydrofurylpropane was 0.287 g (1.56 mmol), the amount of 4-acetoxy-3-methoxystyrene was 1.29 g (6.71 mmol), and the amount of styrene was 3.76 g (36.1 mmol). In addition, 14.5 g (40.2 mmol) of a 15% by weight n-hexane solution of 1,3-butadiene was used as a mixed solution with styrene, and 5.17 g of a brownish viscous liquid as a terminally modified poly (styrene-butadiene) ( Yield 87%).
Mn: 5630
PDI: 1.2
R _f : 0.80
¹ H-NMR (CDCl ₃ , 20 ° C.): δ = 7.4 to 6.9 (br)
6.9-6.2 (br)
5.9-5.0 (br)
5.0 ~ 4.4 (br)
2.7 to 0.9 (br)
0.9-0.7 (br)

Reference Example In Example 1, instead of styrene, 4-acetoxy-3-methoxystyrene [Mw: 168] 7.71 g (40.1 mmol) was used, and when it was added dropwise, the solution turned red and was about 10 minutes. After the lapse of time, the red color disappeared and a colorless transparent solution was obtained. The solution was stirred at room temperature for 3 hours, and volatile components were distilled off from the solution. The red color of the initiator solution due to the dropwise addition of 4-acetoxy-3-methoxystyrene indicates that the vinyl group of 4-acetoxy-3-methoxystyrene has reacted to form a benzyl anion, and in that state The change from red to colorless due to continued stirring is considered to indicate that the generated benzyl anion reacted with the acetoxy group and the benzyl anion disappeared.

  The residue was dissolved in 30 ml of tetrahydrofuran and then dropped into 200 ml of methanol, and the volatile component was distilled off from the soluble component to obtain 7.02 g of colorless liquid (yield 91%). Here, almost no insoluble components were obtained.

The obtained colorless liquid (4-acetoxy-3-methoxystyrene polymer) was confirmed to be a mixture of the following components A to D4 by Mn measurement by SEC.
Component Mn PDI mixing ratio (%)
A 6310 1.3 10
B 480 1.0 20
C 300 1.0 30
D 170 (raw material) 1.0 40

Claims (6)

  It is characterized by polymerizing a vinyl aromatic monomer, a conjugated diene monomer, or both in the presence of an anionic polymerization initiator and then adding 4-acyloxy-3-alkoxystyrene to stop the polymerization reaction. A method for producing a terminal-modified polymer.   The method for producing a terminal-modified polymer according to claim 1, wherein styrene or a derivative thereof is used as the vinyl aromatic monomer.   The method for producing a terminal-modified polymer according to claim 1, wherein 1,3-butadiene or isoprene is used as the conjugated diene monomer.   The method for producing a terminal-modified polymer according to claim 1, wherein an organolithium compound is used as the anionic polymerization initiator.   The method for producing a terminal-modified polymer according to claim 1, wherein 4-acetoxy-3-methoxystyrene is used as 4-acyloxy-3-alkoxystyrene.   The method for producing a terminal-modified polymer according to claim 1, wherein a polymer having a phenolic hydroxyl group at a terminal site is formed.