JP2024095202A - METHOD FOR PRODUCING POLYMER HAVING STRUCTURAL UNIT DERIVED FROM α-METHYL LACTONE - Google Patents

Abstract

To provide a method for producing a polymer having a structural unit derived from α-methylene lactone excellent in productivity.SOLUTION: A method for producing a polymer having a structural unit derived from α-methylene lactone includes: a suspension liquid producing step of stirring a mixture including α-methylene lactone monomer, a dispersion medium, and a first surfactant to obtain a suspension liquid; and a polymerization step of heating the suspension liquid to obtain a polymer. A second surfactant is added to the suspension liquid between the suspension liquid producing step and the polymerization step.SELECTED DRAWING: None

Description

This disclosure relates to a method for producing a polymer having structural units derived from α-methylene lactone.

Polymers (resins) containing structural units derived from α-methylene lactone are excellent in transparency, heat resistance, and optical isotropy, and are expected to be used in optical components. Such resins can be obtained by suspension polymerization, for example, as shown in Patent Document 1.

JP 2022-83035 A

The polymer particles obtained after suspension polymerization are usually recovered by filtration, centrifugation, etc. If the particle size of the polymer particles becomes too small, the recovery rate decreases and the recovery time increases, resulting in a decrease in productivity.

The present disclosure aims to provide a highly productive method for producing a polymer having structural units derived from α-methylene lactone.

The present disclosure provides a method for producing a polymer according to the following items [1] to [4].
[1] A method for producing a polymer having a structural unit derived from α-methylene lactone, comprising: a suspension production step of stirring a mixture containing α-methylene lactone monomer, a dispersion medium, and a first surfactant to obtain a suspension; and a polymerization step of heating the suspension to obtain the polymer, wherein a second surfactant is added to the suspension between the suspension production step and the polymerization step.
[2] The method for producing a polymer according to [1], wherein the first surfactant and/or the second surfactant includes an anionic surfactant.
[3] The method for producing a polymer according to [1] or [2], wherein the first surfactant and the second surfactant are the same surfactant.
[4] The method for producing a polymer according to any one of [1] to [3], wherein the peripheral speed of stirring in the suspension production step is 4 m/s or more and 15 m/s or less.

The present disclosure provides a highly productive method for producing a polymer having structural units derived from α-methylene lactone.

The following describes in detail the embodiments of the present disclosure. However, the present disclosure is not limited to the following embodiments. In the following description, "(meth)acrylic" is used as a term that includes both methacrylic and acrylic. Resin and polymer are used as synonymous terms. When a numerical range is indicated as X to Y, it means X or more and Y or less. For example, "5 to 60% by mass" means 5% by mass or more and 60% by mass or less.

[Method of producing polymer]
The method for producing a polymer having a structural unit derived from α-methylene lactone of the present embodiment includes a suspension production step of stirring a mixture containing α-methylene lactone monomer, a dispersion medium, and a first surfactant to obtain a suspension, and a polymerization step of heating the suspension to obtain a polymer, and further includes a step of adding a second surfactant to the suspension between the suspension production step and the polymerization step.

<Suspension manufacturing process>
The suspension of the present embodiment is obtained by stirring a mixture containing the α-methylene lactone monomer, a dispersion medium, and a first surfactant.

(Monomer)
The α-methylene lactone monomer is a general term for compounds in which a methylene group is bonded to the α-position carbon of a lactone ring. The number of ring members of the lactone is not particularly limited, but from the viewpoint of the stability of the compound, it is preferably a 5-membered ring (γ-lactone) or a 6-membered ring (δ-lactone).

Typical examples of α-methylene lactone monomers with five- or six-membered rings are α-methylene-γ-butyrolactone and α-methylene-δ-valerolactone.

The α-methylene lactone monomer is preferably, for example, a compound as shown in the following formula (1).

In formula (1), R ¹ to R ⁴ are each independently a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms.

The hydrocarbon group is an aliphatic hydrocarbon group or an aromatic hydrocarbon group. The aliphatic hydrocarbon group is, for example, an alkyl group. The number of carbon atoms in the alkyl group is preferably 1 to 10, more preferably 1 to 8. The alkyl group may be linear or branched, or may be cyclic. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, a cyclopentyl group, and a cyclohexyl group.

Examples of aromatic hydrocarbon groups include phenyl, tolyl, and benzyl groups.

R ¹ to R ⁴ are preferably each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and more preferably all are a hydrogen atom.

The suspension may contain only one type of α-methylene lactone monomer, or may contain two or more types.

The suspension of this embodiment may contain any other monomer in addition to the α-methylene lactone monomer. The optional other monomer may be, for example, alkyl (meth)acrylate, benzyl (meth)acrylate, chloromethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, styrene, vinyl toluene, α-methylstyrene, acrylonitrile, methyl vinyl ketone, ethylene, propylene, vinyl acetate, etc. The suspension may contain only one type of the optional other monomer, or may contain two or more types.

Among the optional other monomers, from the viewpoint of further improving the heat resistance, transparency, etc. of the film obtained using the polymer of this embodiment, alkyl (meth)acrylate is preferred, alkyl (meth)acrylate having an alkyl group with 1 to 6 carbon atoms is more preferred, alkyl (meth)acrylate having an alkyl group with 1 to 3 carbon atoms is even more preferred, and methyl (meth)acrylate is even more preferred. The suspension may contain only one type of alkyl (meth)acrylate, or may contain two or more types.

In addition, examples of the alkyl group having 1 to 6 carbon atoms in the alkyl (meth)acrylate include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, a cyclopentyl group, and a cyclohexyl group.

From the viewpoint of further improving heat resistance, etc., the content of α-methylene lactone monomer contained in the suspension is preferably 5 to 60 mass %, more preferably 7.5 to 50 mass %, and even more preferably 10 to 45 mass %, of the total amount of monomers contained in the suspension.

The content of alkyl (meth)acrylate having an alkyl group with 1 to 6 carbon atoms in the suspension is preferably 40 to 95 mass %, more preferably 45 to 92.5 mass %, and even more preferably 50 to 90 mass %, of the total amount of monomers in the suspension.

The content of monomers other than α-methylene lactone monomer and alkyl (meth)acrylate having an alkyl group with 1 to 6 carbon atoms contained in the suspension is preferably 0 to 30 mass %, more preferably 0 to 25 mass %, and even more preferably 0 to 20 mass %, of the total amount of monomers in the suspension.

(Dispersion medium)
The dispersion medium is preferably an aqueous solvent. The aqueous solvent may contain a non-aqueous solvent (particularly a water-soluble organic solvent). Examples of the water-soluble organic solvent include alcohol solvents such as methanol, ethanol, propanol, butanol, 2-methylpropyl alcohol, and 2-methyl-2-propanol; ketone solvents such as acetone and methyl ethyl ketone; ester solvents such as ethyl acetate; and ether solvents such as dioxane, diethyl ether, and tetrahydrofuran.

The content of the dispersion medium in the suspension is, for example, 50 to 300 parts by mass, or 100 to 200 parts by mass, per 100 parts by mass of the total amount of monomer.

(First Surfactant)
Examples of the first surfactant include fatty acid salts such as sodium oleate and potassium castor oil; alkyl sulfate salts such as sodium lauryl sulfate and ammonium lauryl sulfate; alkyl benzene sulfonates such as sodium dodecylbenzene sulfonate; alkyl naphthalene sulfonates; alkanesulfonates; dialkyl sulfosuccinates; alkyl phosphate salts; naphthalene sulfonate-formaldehyde condensates; polyoxyalkylene alkyl ether sulfates such as polyoxyethylene alkyl ether sulfates; polyoxyalkylene allyl ether sulfates such as polyoxyethylene phenyl ether sulfates; anionic surfactants such as polyoxyalkylene alkyl sulfate salts, alkyl amine salts such as laurylamine acetate and stearylamine acetate; cationic surfactants such as quaternary ammonium salts such as lauryl trimethyl alkyl ammonium chloride; amphoteric surfactants such as lauryl dimethylamine oxide; and nonionic surfactants such as polyoxyethylene alkyl ethers. The suspension may contain only one type of the first surfactant, or may contain two or more types. The first surfactant preferably contains an anionic surfactant, and in particular, it is preferable to contain a polyoxyethylene phenyl ether sulfate salt such as polyoxyethylene distyryl phenyl ether sulfate ammonium salt.

The content of the first surfactant in the suspension is preferably 0.01 to 20 parts by mass, more preferably 0.05 to 10 parts by mass, per 100 parts by mass of the total amount of monomer.

When dispersing the α-methylene lactone monomer, the first surfactant, etc. in the dispersion medium, the dispersion may be performed by stirring with a paddle blade or the like, or the dispersion may be performed using an emulsification and dispersion device such as a high-speed shear turbine type disperser, a high-pressure jet homogenizer, an ultrasonic type emulsification and dispersion device, a medium stirring disperser, or a forced gap passage type disperser.

From the viewpoint of increasing the productivity of the polymer, the stirring peripheral speed in the suspension production process is preferably 4 m/s or more and 15 m/s or less, more preferably 6 m/s or more and 13 m/s or less, and even more preferably 7 m/s or more and 12 m/s or less. The stirring peripheral speed may be appropriately adjusted within the above range depending on the scale of polymer production, and the time required for stirring may also be appropriately adjusted depending on the scale of polymer production.

In the suspension production process of this embodiment, additives such as a polymerization initiator, a chain transfer agent, and a dispersant may be added as necessary.

The polymerization initiator may be, for example, an organic peroxide such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, benzoyl peroxide, t-butylperoxyisopropylcarbonate, t-amylperoxy-2-ethylhexanoate, or t-butylperoxy-2-ethylhexanoate; or an azo compound such as 2,2'-azobis(isobutyronitrile), 1,1'-azobis(cyclohexanecarbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), or dimethyl-2,2'-azobis(2-methylpropionate). The amount of the polymerization initiator added may be adjusted as necessary, but is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, and even more preferably 0.1 to 2 parts by mass, relative to 100 parts by mass of the monomer.

Examples of chain transfer agents include monofunctional thiol compounds such as n-dodecyl mercaptan and β-mercaptopropionic acid; bifunctional thiol compounds such as polysiloxanes modified at both ends with mercapto groups; and side-chain multifunctional mercapto-modified polysiloxanes in which the side chains are modified with mercapto groups. The amount of chain transfer agent added may be adjusted as necessary, but is preferably 0.001 to 1 part by mass, more preferably 0.01 to 0.3 parts by mass, per 100 parts by mass of monomer.

Examples of dispersants include water-soluble polymer dispersion stabilizers such as polyvinyl alcohol (PVA), polyvinylpyrrolidone, cellulose, gelatin, sodium polyacrylate, and sodium polymethacrylate; alginate, zein, and casein; and inorganic dispersants such as barium sulfate, calcium sulfate, barium carbonate, magnesium carbonate, calcium phosphate, talc, clay, diatomaceous earth, bentonite, titanium hydroxide, thorium hydroxide, and metal oxide powder. The amount of dispersant added may be adjusted as necessary, but is preferably 0.1 to 3 parts by mass, and more preferably 0.2 to 1 part by mass, per 100 parts by mass of monomer.

Examples of additives other than the polymerization initiator, chain transfer agent, and dispersant include ultraviolet absorbers such as benzophenone compounds, salicylate compounds, benzoate compounds, triazole compounds, and triazine compounds; antioxidants such as phenols, phosphorus compounds, and sulfur compounds; polymerization inhibitors such as 4-tertiary butyl catechol (TBC), hydroquinone, and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4H-TEMPO); stabilizers such as light stabilizers, weather stabilizers, and heat stabilizers; reinforcing materials such as glass fibers and carbon fibers; near-infrared absorbers; flame retardants such as tris(dibromopropyl)phosphate, triallyl phosphate, and antimony oxide; phase difference adjusters such as phase difference increasers, phase difference reducers, and phase difference stabilizers; antistatic agents such as hydrophilic polymers and conductive fillers; colorants such as inorganic pigments, organic pigments, and dyes; organic and inorganic fillers; resin modifiers; organic and inorganic fillers; etc. The content ratio of these additives can be adjusted as necessary, but may be 0 to 5 parts by mass or 0 to 3 parts by mass per 100 parts by mass of monomer.

<Polymerization step>
The suspension is heated to initiate the polymerization reaction.

The method for heating the suspension may be selected as appropriate depending on the scale of polymer production. For example, the suspension may be heated to 50-90°C, the temperature may be kept constant for a while, and then the suspension may be heated to 70-100°C depending on the progress of the polymer reaction. The heating temperature and heating time may be adjusted as appropriate depending on the type of monomer, the scale of polymer production, etc.

In the polymerization step, the suspension may be heated while being stirred. The peripheral speed of stirring the suspension in the polymerization step is not particularly limited, but is preferably slower than the peripheral speed of stirring in the suspension production step. From the viewpoint of promoting the polymerization reaction, the peripheral speed of stirring in the polymerization step is, for example, 0.1 m/s or more and 3 m/s or less, or 1.0 m/s or more and 2.0 m/s or less.

<Step of adding a second surfactant to the suspension>
The method for producing a polymer according to the present embodiment includes a step of adding a second surfactant to the suspension between the suspension production step and the polymerization step, where "between the suspension production step and the polymerization step" means a step after stirring is stopped in the suspension production step and before heating is started in the polymerization step.

(Second Surfactant)
Specific examples of the second surfactant are the same as those of the first surfactant. Only one type of the second surfactant may be added to the suspension, or two or more types may be added. The first surfactant and the second surfactant may be the same type of surfactant, or different types of surfactant. In particular, from the viewpoint of ease of production, the first surfactant and the second surfactant may be the same surfactant. The second surfactant preferably contains an anionic surfactant, and in particular, preferably contains a polyoxyethylene phenyl ether sulfate salt such as polyoxyethylene distyryl phenyl ether sulfate ammonium salt.

The amount of the second surfactant added may be adjusted appropriately taking into account the content of the first surfactant in the suspension, but is preferably 0.01 to 20 parts by mass, and more preferably 0.05 to 10 parts by mass, relative to 100 parts by mass of the total amount of monomer. The amount of the second surfactant added is preferably 10 to 1000 parts by mass, and more preferably 20 to 800 parts by mass, relative to 100 parts by mass of the total amount of the first surfactant.

The second surfactant may be added by dissolving it in the above-mentioned dispersion medium. The amount of the dispersion medium may be adjusted appropriately depending on the type of the second surfactant and the amount added.

<Solid-liquid separation process>
After the polymerization step, the polymer can be recovered by solid-liquid separation. The solid-liquid separation method can be selected from, for example, filtration, centrifugation, and a combination thereof. The recovered polymer may be appropriately dried as necessary. The drying temperature is preferably 60° C. or higher, more preferably 70° C. or higher, and also preferably 90° C. or lower. The drying can be performed until the water content in the polymer is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less. The drying time is preferably 10 hours or more, more preferably 12 hours or more, and also preferably 20 hours or less, more preferably 18 hours or less.

The amount of water in the polymer can be measured using a water content measuring device. For example, a method of measuring with a water content measuring device is to disperse about 0.5 g of dried polymer in a methanol solution, and measure the amount of water carried over by the polymer into the methanol solution using a Karl Fischer volumetric titrator (automatic water content measuring device "AQV-300" manufactured by Hiranuma Sangyo Co., Ltd.). Aquamicron SS-Z 3 mg (manufactured by Mitsubishi Chemical Corporation) is used as the titrant, and deionized water can be used to test the titrant's potency.

The average particle size of the polymer obtained by the above method is preferably 1.1 μm or more, more preferably 1.5 μm or more, and even more preferably 2.0 μm or more, from the viewpoint of facilitating the solid-liquid separation process after polymerization. Also, from the viewpoint of obtaining a uniform polymer, it is preferably 50 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less.

According to the above-described method for producing a polymer having structural units derived from α-methylene lactone, a portion of the surfactant used in suspension polymerization is added to the suspension after production of the suspension. This allows the particle size of the polymer obtained by the polymerization step of suspension polymerization to be optimized. As a result, the efficiency of the solid-liquid separation step is improved.

Conventionally, the entire amount of surfactant used in suspension polymerization is added to the mixture used to produce the suspension. This can lead to the particle size of the polymer obtained by the polymerization process of suspension polymerization becoming excessively small. Furthermore, if the amount of surfactant used is reduced in consideration of the particle size, the dispersion state of the monomers in the suspension can become insufficient.

In contrast, according to the method of producing a polymer having structural units derived from α-methylene lactone according to the present disclosure, the surfactant content in the mixture for producing the suspension is reduced compared to conventional methods, and the particle size of the polymer obtained by the polymerization step of suspension polymerization is optimized. In addition, because a surfactant is added to the produced suspension, the dispersion state of the monomers in the suspension is well maintained.

The present disclosure will be explained in more detail below with reference to examples, but the present disclosure is not limited to these examples. In addition, various physical properties were measured and evaluated as follows.

[Average particle size of polymer]
The average particle size of the polymer was determined by irradiating the suspension after the completion of the polymerization reaction with ultrasonic waves to disperse the polymer, measuring the particle sizes of 30,000 particles using a precision particle size distribution measuring device ("Coulter Multisizer III" manufactured by Beckman Coulter, Inc.), and calculating the average particle size per volume.

The materials used in the examples are described below. Methyl methacrylate (MMA) and α-methylene-γ-butyrolactone (ML) are commercially available products manufactured by Tokyo Chemical Industry Co., Ltd. Peroyl L (dilauroyl peroxide, LPO) is a commercially available product manufactured by NOF Corporation. Polyoxyethylene distyrylphenyl ether sulfate ester ammonium salt (product name "Hitenol (registered trademark) NF-08") is a commercially available product manufactured by Daiichi Kogyo Seiyaku Co., Ltd. t-Amylperoxy 2-ethylhexanoate (product name "Luperox (registered trademark) 575 (R575)") is a commercially available product manufactured by Arkema Yoshitomi Co., Ltd. Polyoxyethylene 2-ethylhexyl ether (product name "Newcol (registered trademark) 1020") is a commercially available product manufactured by Nippon Nyukazai Co., Ltd.

Example 1
A reactor equipped with a stirring device (three-one motor, anchor-type stirring blade, manufactured by Shinto Chemical Industry Co., Ltd.), a temperature sensor, a cooling tube, and a nitrogen introduction tube was prepared. 150 parts by mass of deionized water in which 0.25 parts by mass of Hitenol (registered trademark) NF-08 was dissolved as a first surfactant was charged into the vessel. A liquid containing 75 parts by mass of MMA, 25 parts by mass of ML, 0.5 parts by mass of LPO, and 0.01 parts by mass of nDM (n-dodecyl mercaptan) that had been prepared in advance was charged therein. Then, the mixture in the reactor was stirred for a predetermined time at a stirring peripheral speed of 12 m/s using a T. K. homogenizer MARK II model 2.5 (manufactured by Primix Corporation) to form a uniform suspension.

250 parts by mass of deionized water in which 1.75 parts by mass of Hitenol NF-08 was dissolved as a second surfactant was added to the suspension, and then the suspension was transferred to a reactor. After the transfer, nitrogen gas was blown in while stirring, and the suspension was heated to 70°C. The point at which the internal temperature reached 70°C was set as the reference time, and the reactor was kept at 70°C until the internal temperature reached a peak temperature due to self-heating, after which it was kept at 75°C. Two hours after the reference time, the suspension was heated to 90°C and stirred for four hours to complete the polymerization reaction. The reaction liquid (suspension) was then cooled and centrifuged for 10 minutes at 4000 rpm using a tabletop centrifuge H-36α (manufactured by Kokusan Co., Ltd.), and the solid-liquid separation was performed to obtain a polymer, which was then dried using a hot air dryer to obtain a polymer (powder).

(Examples 2 to 3, Comparative Example 1)
A polymer (powder) was obtained in the same manner as in Example 1, except that the amount of surfactant added and the stirring speed were changed as shown in Table 1.

Example 4
A reactor equipped with a stirring device (three-one motor, anchor-type stirring blade, manufactured by Shinto Chemical Co., Ltd.), a temperature sensor, a cooling tube, and a nitrogen inlet tube was prepared. 0.15 parts by mass of Newcoal (registered trademark) 1020 as a first surfactant and 150 parts by mass of deionized water in which 0.1 parts by mass of sodium lauryl sulfate were dissolved were charged into the vessel. A liquid containing 75 parts by mass of MMA, 25 parts by mass of ML, 0.5 parts by mass of LPO, and 0.01 parts by mass of nDM, which had been prepared in advance, was charged therein. Then, the mixture in the reactor was stirred for a predetermined time at a stirring peripheral speed of 7.5 m/s using a T. K. homogenizer MARK II model 2.5 (manufactured by Primix Corporation) to form a uniform suspension.

0.15 parts by mass of Newcol 1020 as a second surfactant and 250 parts by mass of deionized water in which 0.1 parts by mass of sodium lauryl sulfate was dissolved were added to the suspension, and then the suspension was transferred to a reactor. After the transfer, nitrogen gas was blown in while stirring, and the suspension was heated to 70°C. The point at which the internal temperature reached 70°C was set as the reference time, and the reactor was kept at 70°C until the internal temperature reached the peak temperature due to self-heating, and then the temperature was kept at 75°C. After 2 hours from the reference time, the suspension was heated to 90°C and stirred for 4 hours to complete the polymerization reaction. The reaction liquid (suspension) was then cooled and centrifuged for 10 minutes at 4000 rpm using a tabletop centrifuge H-36α (manufactured by Kokusan Co., Ltd.), and the polymer was obtained by solid-liquid separation, and further dried using a hot air dryer to obtain a polymer (powder).

The average particle size and recovery rate of the obtained polymer are shown in Table 1. The recovery rate of the polymer is calculated based on the theoretically obtained polymer mass being 100% by mass.

Claims (4)

A method for producing a polymer having a structural unit derived from α-methylene lactone, comprising the steps of:
a suspension producing step of stirring a mixture containing an α-methylene lactone monomer, a dispersion medium, and a first surfactant to obtain a suspension;
A polymerization step of heating the suspension to obtain the polymer,
A method for producing a polymer, comprising adding a second surfactant to the suspension between the suspension production step and the polymerization step. The method for producing a polymer according to claim 1, wherein the first surfactant and/or the second surfactant includes an anionic surfactant. The method for producing a polymer according to claim 1, wherein the first surfactant and the second surfactant are the same surfactant. The method for producing a polymer according to any one of claims 1 to 3, wherein the stirring peripheral speed in the suspension production process is 4 m/s or more and 15 m/s or less.