JPH0827202A - Star polymer synthesis method - Google Patents

Abstract

PURPOSE:To surely synthesize a star-type polymer having a low molecular weight and a functional group at each branched part by synthesizing a living polymer in the presence of a specific anion polymerization initiator, further reacting the obtained living polymer with a coupling agent and then introducing functional groups. CONSTITUTION:A living polymer is synthesized by using an anion polymerization initiator of the formula (R1, R2 and R4 are each a hydrocarbon; R3 is an alkylene or a phenylene; M is an alkali metal). A star-type prepolymer is synthesized by reacting plural molecules of the obtained living polymer with a coupling agent having plural conjugated double bonds. The O-Si bonds in the obtained star-type prepolymer are broken by unmasking and functional groups are introduced. Thus, the objective polymer is produced through these reactions carried out in serial order. Preferably, R1 and R2 in the formula are each a t-butyl or a phenyl, R3 is a propylene in the case where M is lithium and R4 is a phenyl. As an unmasking agent, tetrabutylammonium fluoride or hydrogen chloride is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synthesizing a star polymer having a structure in which a plurality of branches are radially extended from a center. The star polymer obtained in the present invention is extremely useful for high solid paints.

[0002]

2. Description of the Related Art From the viewpoint of protecting the global environment, paints and
In the field of painting, reducing organic solvent emissions is a major issue. In addition, there are high-solid paints, water-based paints, and powder paints as paints, which have been put into practical use. However, in the case of powder coating and water-based coating, there is a problem that the coating equipment needs to be modified and the coating conditions become strict, while the high solid coating has the advantage that existing coating equipment can be used as it is. Therefore, research on high solid paints has been actively conducted in recent years.

The high solid coating material is a coating material having a higher non-volatile content at the time of coating as compared with the conventional coating material. Generally, if the non-volatile content is increased, the viscosity becomes high and the coating becomes difficult.
Therefore, it is necessary to reduce the viscosity of the resin, but a sufficient reduction in viscosity has not yet been achieved. Furthermore, it is necessary for the paint resin to react with a crosslinking agent to form a tough coating film having a three-dimensional network structure. For that purpose, it is necessary to have two or more functional groups in one molecule of the resin. However, since conventional acrylic resins for paints are polymerized by radical polymerization, it is difficult to reliably synthesize a polymer having a low molecular weight and having two or more functional groups. Therefore, if a low molecular weight is used to obtain a high solid, a polymer having one functional group or a polymer having no functional group is inevitably included, which causes deterioration of physical properties of the coating film.

Therefore, it may be considered to synthesize a coating resin by utilizing ionic polymerization. For example, Japanese Patent Laid-Open No. 62-3215.
Japanese Unexamined Patent Publication (Kokai) No. 6 discloses synthesizing a methacrylic acid ester polymer for paint by an anionic polymerization method using an alkali metal alcoholate as a polymerization initiator. In addition, JP-A-6
Although not specified for paints in JP-A 1-179210, it is described that a methyl methacrylate polymer is synthesized using an anionic polymerization initiator composed of a Grignard reagent represented by the following formula (2). .

[0005]

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(However, R ₅ , R ₆ and R ₇ are hydrocarbon groups having 1 to 10 carbon atoms and may be the same or different.)

[0007]

The conventional acrylic resin for paint has a linear molecular structure. However, it is known that, by adopting a star-shaped structure in which multiple branches are radially extended from the center, the viscosity is lower than that of the linear structure due to the large radius of gyration when the molecular weight is the same. Has been. However, the technology for surely synthesizing star polymers has not been developed yet.

If a functional group is introduced at the end of each branch of the star polymer, the crosslink density in the case of a coating film can be dramatically improved. For that purpose, it is necessary to have a synthetic technique to reliably introduce a functional group with a low molecular weight, but in the conventional anionic polymerization, the initiator remains bound to the end of the obtained polymer molecule, or the bound initiator is attached. May be desorbed early in the reaction and chain transfer may occur,
It was difficult to surely introduce a functional group with a low molecular weight.

The present invention has been made in view of the above circumstances, and an object thereof is to reliably synthesize a star-shaped polymer having a low molecular weight and having a functional group at the end of each branch extending from the center. .

[0010]

The method for synthesizing a star polymer according to the present invention, which solves the above-mentioned problems, comprises an anionic polymerization step of synthesizing a living polymer using an anionic polymerization initiator represented by the following general formula (1): A coupling step of synthesizing a star-shaped prepolymer by reacting a living polymer having a plurality of molecules with a coupling agent having a plurality of conjugated double bonds, and a functional group by cleaving the O—Si bond in the star-shaped prepolymer And a deprotection step of introducing.

[0011]

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However, R ₁ , R ₂ and R ₄ are hydrocarbon groups, R
₃ is at least one of an alkylene group and a phenylene group,
M represents an alkali metal.

[0013]

[Action]

 [Anionic polymerization step] Initiation of anionic polymerization used in the present invention
In the agent, the carbon atom that is ionically bonded to the alkali metal
At least one phenyl group is attached. Accordingly
Initiation occurs extremely quickly due to electron resonance effect
it is conceivable that. In this sense, R _FourIs also a phenyl group
Which aromatic group is preferred.

On the other hand, during the polymerization reaction, the group of the following general formula (3) is bonded to the end of the carbanion opposite to the active end group. Since this group has a t-Bu group (tertiary butyl group) and an alkyl group, it is bulky and is likely to cause steric hindrance during the reaction, which is considered to suppress the carbanion reaction to some extent.

[0015]

[Chemical 4]

As a result of these two actions, the ionic bond strength of the alkali metal is moderated, and the initiation reaction is much faster than the growth reaction and the chain transfer reaction is suppressed, so that the living body having an extremely narrow molecular weight distribution. Polymer 1
(See FIG. 1). At the end opposite to the active end of this living polymer 1, the bulky group 10 of the general formula (3) is attached.
Are combined. [Coupling process] Then, after the living polymer 1 having a degree of polymerization determined by the concentration ratio of the monomer and the initiator is quantitatively polymerized, it has a plurality of conjugated double bonds such as 1,6-hexanediol dimethacrylate. React with coupling agent 2. As a result, the active end of the living polymer reacts with the coupling agent 2 to stop the polymerization reaction, and the star-shaped prepolymer 3 in which the active ends of a plurality of living polymers are bonded to one molecule of the coupling agent is produced. [Deprotection Step] The Si—O bond of the bulky group 10 bonded to the end of each branched portion 30 radially extending from the center of the star-shaped prepolymer 3 is a deprotection agent such as tetrabutylammonium fluoride or HCl. By the addition of 4, the star polymer 5 having the functional group 11 such as a hydroxyl group and the like, and having the functional group 11 at the end of each of the plurality of branched portions 30 radially extending from the center is synthesized.

The Si of the group represented by the general formula (3) is t
-Bu group is bonded, and further R₁, R ₂The hydrocarbon groups of
I am fit. Therefore, S during the polymerization reaction due to steric hindrance
Attack on i-O bond is suppressed and deprotection agent is added
The Si-O bond is retained up to. This enables deprotection
Ensure deprotection reaction at the end of each branch 30
Can be done. In this sense, R₁And R₂of
At least one, preferably both, is a t-Bu group or
Use a bulky group such as a phenyl group that causes steric hindrance.
Is desirable.

[0018]

EXAMPLES The present invention will be specifically described below with reference to examples. Formula (4) shows the chemical structural formula of the anionic polymerization initiator used in this example.

[0019]

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This anionic polymerization initiator was synthesized as follows. First, γ-butyrolactone represented by the formula (5) and the phenylgrine reagent represented by the formula (6) are
The reaction was performed overnight at room temperature using THF as a solvent, and the ring-opened reaction product was recrystallized in an aqueous hydrochloric acid solution. The obtained compound (1,1-diphenyl 1,4-butanediol) was represented by the formula (7), and the yield thereof was 63%.

[0021]

[Chemical 6]

[0022]

[Chemical 7]

[0023]

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This 1,1-diphenyl 1,4-butanediol 5
4 g and 50 g of the compound represented by the formula (8) were reacted in THF overnight at room temperature to give 4,4-diphenyl 1-t- represented by the formula (9).
Butyldiphenylsiloxy n-butanol was synthesized. The yield was 99%.

[0025]

[Chemical 9]

[0026]

[Chemical 10]

Next, the compound of the formula (9) was charged into a flask with methylene chloride and (C ₂ H ₅ ) ₃ and then added with S at 0 ° C. and 0 ° C.
OCl ₂ was slowly added dropwise. After completion of the dropping, the temperature was gradually raised to room temperature and stirred overnight to obtain 1,1-diphenyl-4-t-butyldiphenylsiloxy 1-butene represented by the formula (10). The yield was 94%.

[0028]

[Chemical 11]

The compound of the formula (10) is reacted with hydrogen gas in methanol using Pd as a catalyst to obtain the compound of the formula (11)
1,1-diphenyl 1-t-butyldiphenylsiloxy n-
Butane The yield was 90%.

[0030]

[Chemical 12]

By mixing the compound of formula (11) with t-butyllithium, the anionic polymerization initiator represented by formula (4) is obtained. In this embodiment, R in the formula (1)
₁ and R ₂ are phenyl groups, R ₃ is an n-propylene group, R ₄ is a phenyl group, and M
Lithium is selected as. However, the present invention is not limited to this, and various hydrocarbon groups can be selected and used as R ₁ , R ₂ and R ₄ . However, a group that easily causes steric hindrance is desirable, and a phenyl group, a t-Bu group and the like are desirable.

Further, as R ₃ , a propylene group is particularly desirable when M is lithium from the viewpoint of certainty of synthesis,
In addition, various alkylene groups or aphenylene groups may be used. And as M, Na, K, C other than Li
Alkali metals such as s can be used. [Anionic Polymerization Step] Using the obtained compound of formula (4) as an anionic polymerization initiator, MMA is subjected to anionic polymerization.

The structure of the polymerization apparatus used is shown in FIG. In the polymerization vessel 6, a dropping funnel 60 with a first cock containing 5.64 g of MMA monomer (THF solution) was added.
Second dropping funnel 61 with a second cock containing 24 × 10 ^-2 mol of 1,6-hexanediol dimethacrylate (THF solution) and 1.24 × 10 ^-3 mol of the initiator of formula (4) (THF). A dropping funnel 62 with a third cock in which a solution) is put is provided. These three kinds of raw materials were transferred into each dropping funnel in a dry box under an argon gas atmosphere.

Prior to the synthesis, about 500 ml of THF in the container 7 was first transferred to the polymerization container 6 by distillation. Then, while cooling the reaction system to -78 ° C with dry ice / methanol, the initiator was dropped from the dropping funnel 62 with the third cock, and the dropping funnel with the first cock 6 was vigorously stirred.
The total amount of the monomer is dropped from 0, and stirring is continued at -78 ° C for about 0.5 hours.

The reaction at this time is as shown in the following formula (12), and the carbanions react one after another to produce a living polymer.

[0036]

[Chemical 13]

The living polymer produced by the formula (12) is abbreviated as the following formula (13).

[0038]

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[Coupling Step] Thereafter, 1,6-hexanediol dimethacrylate was dropped from the dropping funnel 61 with the second cock, and stirring was continued at -78 ° C for about 1 hour. As a result, the reaction is stopped as in formula (14), and a star-shaped prepolymer is produced.

[0040]

[Chemical 15]

[Deprotection Step] Next, the reaction solution was added with 2.10 ×.
A THF solution containing 10 ⁻³ mol of tetrabutylammonium fluoride was added dropwise, and the mixture was reacted overnight at room temperature. As a result, the Si—O bond is broken and a hydroxyl group is formed at the end of each branch of the star prepolymer as shown in formula (15), and the star polymer is synthesized. In this deprotection step, the star prepolymer can be isolated, redissolved and reacted.

[0042]

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The reaction solution was poured into a large amount of hexane to precipitate and collect the star polymer. Then, the star-shaped polymer powder was isolated by dissolving in benzene and freeze-drying. The number average molecular weight of the branched portion calculated from the number average molecular weight of the living polymer before the coupling step is about 4500,
Since the number average molecular weight of the star-shaped polymer was about 32000, it is considered that the obtained star-shaped polymer has about 7 branched portions.

[0044]

According to the method for producing a star polymer of the present invention, a star polymer having a functional group at the end of a branched portion can be reliably synthesized. Moreover, since the branched portion of this star-shaped polymer can be easily and surely made to have a low molecular weight, if the obtained star-shaped polymer is used for a high solid coating, it is a high solid coating which has low viscosity and crosslinks at a high crosslink density. Thus, the non-volatile content at the time of coating becomes higher than that of the present high solid paint, and a coating film having extremely excellent physical properties can be formed.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing the synthesis method of the present invention.

FIG. 2 is a structural explanatory view of an anionic polymerization apparatus used in one example of the present invention.

[Explanation of symbols]

1: Living Polymer 2: Coupling Agent 3: Star Prepolymer 4: Deprotection Agent 5: Star Polymer 10: Bulky Group 11: Functional Group 30: Branching Part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Mitsuru Nagasawa 3-1, Mukoyama, Showa-ku, Nagoya, Aichi Prefecture Nomura Mukoyama Hills 204

Claims (1)

[Claims] 1. An anionic polymerization step of synthesizing a living polymer using an anionic polymerization initiator represented by the following general formula (1) and a coupling agent having a plurality of molecules of the living polymer and a plurality of conjugated double bonds. A star-shaped structure characterized by sequentially performing a coupling step of reacting to synthesize a star-shaped prepolymer and a deprotection step of cleaving an O—Si bond in the star-shaped prepolymer to introduce a functional group. Polymer synthesis method. Embedded image However, R ₁ , R ₂ and R ₄ are hydrocarbon groups, R ₃ is at least one of an alkylene group and a phenylene group, and M is an alkali metal.