Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
METHOD FOR PRODUCING POLYMER
Document Type and Number:
WIPO Patent Application WO/2013/121894
Kind Code:
A1
Abstract:
A method for producing a polymer, including: (i) bringing a compressive fluid and raw materials containing a ring-opening polymerizable monomer into contact with each other at a mixing ratio represented by the following formula, to thereby allow the ring-opening polymerizable monomer to carry out ring-opening polymerization in the presence of a metal catalyst: 1 > {(Mass of the raw materials) / (Mass of the raw materials + Mass of the compressive fluid)} ≥ 0.5.

Inventors:
NEMOTO, Taichi (3-6, Nakamagome 1-chome, Ohta-k, Tokyo 55, 14385, JP)
TANAKA, Chiaki (3-6, Nakamagome 1-chome, Ohta-k, Tokyo 55, 14385, JP)
Application Number:
JP2013/052292
Publication Date:
August 22, 2013
Filing Date:
January 25, 2013
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
RICOH COMPANY, LTD. (3-6 Nakamagome 1-chome, Ohta-ku Tokyo, 55, 14385, JP)
NEMOTO, Taichi (3-6, Nakamagome 1-chome, Ohta-k, Tokyo 55, 14385, JP)
TANAKA, Chiaki (3-6, Nakamagome 1-chome, Ohta-k, Tokyo 55, 14385, JP)
International Classes:
C08G63/08; C08G85/00; C08L101/16
Foreign References:
JP2004277698A
JP2011208115A
JP2011208116A
JP2012188664A
Attorney, Agent or Firm:
HIROTA, Koichi (HIROTA, NAGARE & ASSOCIATES 4th Floor, TS Bldg., 1-24-10, Yoyogi, Shibuya-k, Tokyo 53, 15100, JP)
Download PDF:
Claims:
CLAIMS

1. A method for producing a polymer, comprising:

(i) bringing a compressive fluid and raw materials containing a ring-opening polymerizable monomer into contact with each other at a mixing ratio represented by the following formula, to thereby allow the ring-opening polymerizable monomer to carry out ring-opening

polymerization in the presence of a metal catalyst:

Mass of the raw materials

1 > > 0.5

Mass of the raw materials + Mass of the compressive fluid

2. The method for producing a polymer according to claim 1,

wherein the (i) bringing comprises-" after melting the ring-opening polymerizable monomer by bringing the compressive fluid and the raw materials containing the ring-opening polymerizable monomer into contact with each other, adding the metal catalyst to allow the

ring-opening polymerizable monomer to carry out the ring-opening polymerization.

3. The method for producing a polymer according to claim 1 or 2, wherein a polymerization rate of the ring-opening polymerizable monomer is 98 mol% or higher.

4. The method for producing a polymer according to any one of claims 1 to 3,

wherein the polymer has a number average molecular weight of

12,000 or greater.

5. The method for producing a polymer according to any one of claims 1 to 4, wherein the compressive fluid contains carbon dioxide.

6. The method for producing a polymer according to any one of claims 1 to 5,

wherein the ring-opening polymerizable monomer is a monomer having a ring structure containing an ester bond therein.

7. The method for producing a polymer according to any one of claims 1 to 6,

wherein a lower limit of a temperature during the ring-opening polymerization in the (i) is lower than a melting point of the ring-opening polymerizable monomer by 40°C, and an upper limit of the temperature during the ring-opening polymerization in the (i) is higher than the melting point of the ring-opening polymerizable monomer by 40°C.

Description:
DESCRIPTION

Title of Invention

METHOD FOR PRODUCING POLYMER Technical Field

The present invention relates to a method for producing a polymer through ring-opening polymerization of a ring-opening polymerizable monomer. Background Art

Conventionally known methods for producing polymers involve ring-opening polymerization of a ring-opening polymerizable monomer using a metal catalyst. For example, disclosed is a method for producing polylactic acid by allowing polymerization raw materials mainly containing lactide as a ring-opening polymerizable monomer to react for polymerization in a melted state (see PTL l). In accordance with the disclosed method, lactide is reacted in a melted state to polymerize using tin octylate as a metal catalyst and setting the reaction temperature to 195°C.

In the case where polylactic acid is produced in this method, however, more than 2% by weight of lactide remains in a produced polymer product (see PTL l). This is because an equilibrium

relationship between the ring-opening polymerizable monomer and a polymer is established in a reaction system of ring-opening

polymerization of polylactic acid or the like, and therefore a ring-opening polymerizable monomer tends to be generated by a depolymerization reaction, which is a reverse reaction of a ring-opening polymerization reaction, when it is polymerized at high temperature. The residual lactide acts as a catalyst for hydrolysis of the generated polymer product, or may impair thermal resistance of the polymer product.

As for a method for performing ring-opening polymerization of a ring-opening polymerizable monomer at low temperature, disclosed is a method for carrying out ring-opening polymerization of lactide in an organic solvent (see PTL 2). In accordance with the disclosed method, D-lactide is polymerized in a dichloromethane solution at 25°C, to thereby yield polyD-lactic acid with the polymerization of the monomer being 99.4%. In the case where the polymerization is carried out in an organic solvent, however, it is necessary to provide a step for drying the organic solvent after the polymerization, which raises a problem of being lowered in production efficiency.

As for a method for performing ring-opening polymerization of a ring-opening polymerizable monomer at low temperature without using an organic solvent, disclosed is a method for carrying out polymerization of L-lactide in supercritical carbon dioxide using a metal catalyst (see NPL 1). In accordance with the disclosed method, L-lactide in an amount of 10 w/v% relative to supercritical carbon dioxide is polymerized for 47 hours using tin octylate as a metal catalyst at a reaction

temperature of 80°C and a pressure of 207 bar, to thereby produce particles of polylactic acid at a yield of 85%. In this case, the

supercritical carbon dioxide used is turned into gas when the temperature and the pressure are returned to normal temperature and normal pressure after polymerization, and thus it is not necessary to perform a treatment of removing a solvent after polymerization.

Citation List

Patent Literature

PTL l: Japanese Patent Application Laid pen (JP-A) No. 08-259676 PTL 2: JP-A No. 2009-1614

Non-Patent Literature

NPL l: Ganapathy, H. S.;Hwang, H. S.; Jeong, Y. T.; LEE, W-T.; Lim, K. T. Eur Polym J. 2007, 43(1), 119-126.

Summary of Invention

Technical Problem

However, when a ring-opening polymerizable monomer is polymerized using a metal catalyst in a compressive fluid by a

conventional production method, there are problems that it takes a long time to complete polymerization reaction and production yield becomes low.

The present invention aims to solve the various problems in the art, and achieve the following object. An object of the present invention is to provide a method for producing a polymer, which can make time required for polymerization reaction shorter to produce a polymer at a higher yield than in the case where ring-opening polymerization of a ring-opening polymerizable monomer is performed using a metal catalyst in a compressive fluid by a conventional production method.

Solution to Problem

Means for solving the above problems are as follows.

That is, a method for producing a polymer of the present invention contains :

bringing a compressive fluid and raw materials containing a ring-opening polymerizable monomer into contact with each other at a mixing ratio represented by the following formula, to thereby allow the ring-opening polymerizable monomer to carry out ring-opening

polymerization in the presence of a metal catalyst- Mass of the raw materials

1 > > 0.5

Mass of the raw materials + Mass of the compressive fluid

Advantageous Effects of Invention

As described above, the method for producing a polymer of the present invention contains a polymerization step of bringing a

compressive fluid and raw materials containing a ring-opening

polymerizable monomer into contact with each other at a predetermined mixing ratio, to thereby allow the ring-opening polymerizable monomer to carry out ring-opening polymerization in the presence of a metal catalyst. The method of the present invention containing such a polymerization step can make time required for polymerization reaction shorter to produce a polymer at a higher yield than in the case where ring-opening polymerization of a ring-opening polymerizable monomer is performed using a metal catalyst in a compressive fluid by a conventional production method.

Brief Description of Drawings

FIG. 1 is a general phase diagram depicting the state of a substance depending on pressure and temperature conditions.

FIG. 2 is a phase diagram which defines a compressive fluid used in the present embodiment.

FIG. 3 is a system diagram illustrating one example of a

polymerization step used in the present embodiment.

Description of Embodiments

(Method for Producing Polymer)

One embodiment of the present invention will be specifically explained hereinafter.

The method for producing a polymer of the present embodiment contains at least a polymerization step, and may further contain appropriately selected other steps.

<Polymerization Step>

The polymerization step is a step of bringing a compressive fluid and raw materials containing a ring-opening polymerizable monomer into contact with each other at a mixing ratio represented by the following formula, to thereby allow the ring-opening polymerizable monomer to carry out ring-opening polymerization in the presence of a metal catalyst: Mass of the raw materials

1 > > 0.5

Mass of the raw materials + Mass of the compressive fluid

Raw Materials -

Substances, such as a ring-opening polymerizable monomer, as raw materials in the aforementioned production method will be explained.

In the present embodiment, the raw materials are materials for producing a polymer and are materials that become constitutional components of a polymer. Moreover, the raw materials contain at least a ring-opening polymerizable monomer, and may further contain

appropriately selected optional substances, such as an initiator, and additives.

--Ring-Opening Polymerizable Monomer-

The ring-opening polymerizable monomer for use in the present embodiment is appropriately selected depending on the intended purpose without any limitation, and the ring-opening polymerizable monomer is preferably a monomer having a ring structure containing a carbonyl bond, such as an ester bond. Examples of such ring-opening polymerizable monomer include cyclic ester, and cyclic carbonate.

The cyclic ester is not particularly limited, but it is preferably a cyclic dimer obtained through dehydration-condensation of an L-form and/or D form of a compound represented by General Formula 1.

R-C*-H(-OH)(-COOH) General Formula 1

In General Formula 1, R is a C1-C10 alkyl group, and "C

represents an asymmetric carbon. Specific examples of the compound represented by General Formula 1 include enantiomers of lactic acid, enantiomers of

2-hydroxybutanoic acid, enantiomers of 2-hydroxypentanoic acid, enantiomers of 2-hydroxyhexanoic acid, enantiomers of

2-hydroxyheptanoic acid, enantiomers of 2-hydroxyoctanoic acid, enantiomers of 2-hydroxynonanoic acid, enantiomers of

2 -hydroxy decanoic acid, enantiomers of 2-hydroxyundecanoic acid, and enantiomers of 2 -hydroxy dodecanoic acid. Among them, enantiomers of lactic acid are preferable since they are highly reactive and readily available. These cyclic dimers may be used independently or in combination.

Examples of the cyclic ester other than the compound represented by General Formula 1 include aliphatic lactone, such as β-propiolactone, β-butyrolactone, ybutyrolactone, γ-hexanolactone, γ-octanolactone, δ-valerolactone, δ-hexanolactone, δ-octanolactone, ε-caprolactone, δ-dodecanolactone, a-methyl-y-butyrolactone, 6-methyl'6-valerolactone, glycolide and lactide. Among them, ε-caprolactone is particularly preferable since it is highly reactive and readily available.

The cyclic carbonate is not particularly limited, and examples thereof include ethylene carbonate, and propylene carbonate. These ring-opening polymerizable monomers may be used independently, or in combination.

-Metal Catalyst-

The metal catalyst used in the production method of the present embodiment may be appropriately selected depending on the intended purpose without any limitation so long as it is a catalyst containing a metal atom. Examples thereof include: a tin compound, such as tin octylate, tin dibutylate, and tin di(2-ethylhexanoate); an aluminum compound, such as aluminum acetylacetonate, and aluminum acetate; a titanium compound, such as tetraisopropyl titanate, and tetrabutyl titanate; a zirconium compound, such as zirconium isopropoxide; and an antimony compound, such as antimony trioxide.

The amount of the metal catalyst added may be appropriately selected without any limitation depending on, for example, the type of the metal catalyst and the type of the ring-opening polymerizable monomer. For example, when ring-opening polymerization of lactide is performed using tin octylate, the amount of the tin octylate is preferably 0.005 mol% to 0.5 mol%, more preferably 0.01 mol% to 0.2 mol%, relative to 100 mol% of lactide.

- --Initiator- --

In the present embodiment, an initiator is suitable used for controlling a molecular weight of a polymer as obtained. As for the initiator, a conventional initiator can be used. The initiator may be, for example, aliphatic mono or di alcohol, or polyhydric alcohol, as long as it is alcohol-based, and may be either saturated or unsaturated. Specific examples of the initiator include : monoalcohol such as methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, nonanol, decanol, lauryl alcohol, myristyl alcohol, cetyl alcohol, and stearyl alcohol; dialcohol such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol,

1,4-butanediol, hexanediol, nonanediol, tetramethylene glycol, and polyethylene glycol; polyhydric alcohol such as glycerol, sorbitol, xylitol, ribitol, erythritol, and triethanol amine. ' and others such as methyl lactate, and ethyl lactate.

Moreover, a polymer having an alcohol residue at a terminal thereof, such as polycaprolactonediol and polytetramethylene glycol, may be used as the initiator. A use of such polymer enables to synthesize diblock copolymers or triblock compolymers.

An amount of the initiator may be appropriately adjusted depending on the intended molecular weight of a resulting polymer, but it is preferably 0.05 mol% to 5 mol%, relative to 100 mol% of the

ring-opening polymerizable monomer. In order to prevent a reaction from being initiated unevenly, the initiator is preferably sufficiently mixed with the monomer before the monomer is brought into contact with a polymerization catalyst.

■■ Additive---

Moreover, an additive may be added for the ring-opening polymerization, if necessary. Examples of the additive include a surfactant, an antioxidant, a stabilizer, an anticlouding agent, a UV ray-absorber, a pigment, a colorant, inorganic particles, various fillers, a thermal stabilizer, a flame retardant, a crystal nucleating agent, an antistatic agent, a surface wet improving agent, an incineration adjuvant, a lubricant, a natural product, a releasing agent, a plasticizer, and other similar components. If necessary, a polymerization terminator (e.g., benzoic acid, hydrochloric acid, phosphoric acid, metaphosphoric acid, acetic acid and lactic acid) may be used after completion of polymerization reaction. An amount of the additives varies depending on intended purpose for adding the additive, or a type of the additives, but it is preferably 0 parts by mass to 5 parts by mass, relative to 100 parts by mass of the polymer composition.

The surfactant for use is preferably a surfactant which is dissolved in the compressive fluid, and has compatibility to both the compressive fluid and the ring-opening polymerizable monomer. Use of such surfactant can give effects that the polymerization reaction can be uniformly preceded, and the resultant polymer has a narrow molecular weight distribution and be easily produced as particles. When the surfactant is used, the surfactant may be added to the compressive fluid, or may be added to the ring-opening polymerizable monomer. In the case where carbon dioxide is used as the compressive fluid, for example, a surfactant having groups having affinity with carbon dioxide and groups having affinity with the monomer can be used. Examples of such surfactant include a fluorosurfactant, and a silicone surfactant.

As for the stabilizer, used are epoxidized soybean oil, and carbodiimide. As for the antioxidant, 2,6-di-t"butyl-4-methyl phenol, and butylhydroxyanisol are used. As for the anticlouding agent, glycerin fatty acid ester, and monostearyl citrate are used. As for the filler, a thermal stabilizer, a flame retardant, an internal mold release agent, and inorganic additives having an effect of a crystal nucleus agent (e.g., clay, talc, and silica) are used. As for the pigment, titanium oxide, carbon black, and ultramarine blue are used.

-Compressive Fluid- Next, a compressive fluid for use in the method for producing a polymer of the present embodiment is explained with reference to FIGs. 1 and 2. FIG. 1 is a phase diagram depicting the state of a substance depending on pressure and temperature conditions. FIG. 2 is a phase diagram which defines a compressive fluid used in the present

embodiment. In the present embodiment, the term "compressive fluid" refers to a state of a substance present in any one of the regions (l), (2) and (3) of FIG. 2 in the phase diagram of FIG. 1.

In such regions, the substance is known to have extremely high density and show different behaviors from those shown at normal temperature and normal pressure. Note that, a substance is a

supercritical fluid when it is present in the region (l). The supercritical fluid is a fluid that exists as a noncondensable high-density fluid at temperature and pressure exceeding the corresponding critical points, which are limiting points at which a gas and a liquid can coexist. When a substance is in the region (2), the substance is a liquid, but in the present embodiment, it is a liquefied gas obtained by compressing a substance existing as a gas at normal temperature (25°C) and ambient pressure (l atm). When a substance is in the region (3), the substance is in the state of a gas, but in the present invention, it is a high-pressure gas whose pressure is 1/2 or higher than the critical pressure (Pc), i.e. l/2Pc or higher.

Examples of a substance that can be used in the state of the compressive fluid include carbon monoxide, carbon dioxide, dinitrogen oxide, nitrogen, methane, ethane, propane, 2,3-dimethylbutane, and ethylene. Among them, carbon dioxide is preferable because the critical pressure and critical temperature of carbon dioxide are respectively about 7.4 MPa, and about 31°C, and thus a supercritical state of carbon dioxide is easily formed. In addition, carbon dioxide is non-flammable, and therefore it is easily handled. These compressive fluids may be used independently, or in combination.

<Polymerization Reaction Device>

A polymerization reaction device suitably used in the method for producing a polymer of the present embodiment will be explained with reference to FIG. 3 next. FIG. 3 is a system diagram illustrating one example of the polymerization step in the present embodiment. The polymerization step in the present embodiment may be a polymerization step of a batch-type, or a polymerization step of a continuous-type. Next, an example of the polymerization step of a batch-type will be explained.

In the system diagram of FIG. 3, the polymerization reaction device 100 contains- ' a tank 7, a metering pump 8, an addition pot 11, a reaction vessel 13 and valves (21, 22, 23, 24, 25). The above devices are connected with each other via a pressure resistant pipe 30 as depicted in FIG. 3. The pipe 30 is provided with connectors (30a, 30b).

The tank 7 stores the compressive fluid. Note that, the tank 7 may store a gas or solid that becomes a compressive fluid by application of heat or pressure in the path through which it is supplied to the reaction vessel 13, or in the reaction vessel 13. In this case, the gas or solid stored in the tank 7 may be formed in the state of (l), (2), or (3) depicted in the phase diagram of FIG. 2, within the reaction vessel 13 upon application of heat or pressure.

The metering pump 8 supplies the compressive fluid stored in the tank 7 to the reaction vessel 13 with constant pressure and flow rate. The addition pot 11 stores the metal catalyst to be added to the raw materials in the reaction vessel 13. By opening and closing each of the valves (21, 22, 23, 24), the path is switched between a path for supplying the compressive fluid stored in the tank 7 to the reaction vessel 13 via the addition pot 11, and a path for supplying the compressive fluid to the reaction vessel 13 without passing through the addition pot 11.

The reaction vessel 13 has been charged with the ring-opening polymerizable monomer and the initiator in advance. The reaction vessel 13 is a pressure resistant vessel configured to bring the previously charged ring-opening polymerizable monomer and initiator into contact with the compressive fluid supplied from the tank 7 and the metal catalyst supplied from the addition pot 11, to thereby carry out

ring-opening polymerization of the ring-opening polymerizable monomer.

Note that, the reaction vessel 13 may be provided with a gas outlet for releasing evaporated materials. Moreover, the reaction vessel 13 contains a heater for heating the raw materials and the compressive fluid.

Further, the reaction vessel 13 contains a stirring device for stirring the raw materials and the compressive fluid. The stirring device prevents sedimentation of generated polymer by stirring when there is a difference in concentration between the raw materials and the polymer product.

Therefore, the polymerization reaction can be carried out more uniformly and quantitatively. The valve 25 discharges the compressive fluid and the polymer product (polymer) in the reaction vessel 13 by opening after the completion of the polymerization reaction.

«Polymerization Method»

Next, a batch-type polymerization method of a ring-opening polymerizable monomer using the polymerization reaction device 100 will be explained. In this case, first, the metering pump 8 is operated and the valves (21, 22) are open to thereby supply the compressive fluid stored in the tank 7 to the reaction vessel 13 without going through the addition pot 11. As a result, the previously charged ring-opening polymerizable monomer and initiator are brought into contact with the compressive fluid supplied from the tank 7 in the reaction vessel 13, and the mixture is stirred by the stirring device so that the raw materials, such as the ring-opening polymerizable monomer, are melted. In the present embodiment, the term "melt" means that raw materials or a generated polymer is plasticized or liquidized with swelling as a result of the contact between the raw materials or generated polymer, and the compressive fluid.

In this case, a ratio (mixing ratio) of the raw materials to the compressive fluid in the reaction vessel 13 is within the ratio represented by the following formula (i).

Mass of the raw materials

1 > > 0.5

Mass of the raw materials + Mass of the compressive fluid

Formula (i)

In the present embodiment, the raw materials in the formula above contain the ring-opening polymerizable monomer and the initiator. The mixing ratio is appropriately selected depending on the intended purpose without any limitation, provided that it is 0.5 or more but less than 1. The mixing ratio is preferably 0.65 to 0.99, more preferably 0.80 to 0.95. When the mixing ratio is less than 0.5, an amount of the compressive fluid for use increases and thus not economical, and moreover as the density of the ring-opening polymerizable monomer becomes low, polymerization speed may be slow down.

The range of the mixing ratio is applied to both the polymerization step of a batch type and the polymerization step of a continuous type. In the case of the polymerization step of a continuous type, the range of the mixing ratio is expressed by the following formula (ii).

Feeding speed of the raw materials (g/min)

^ > Feeding speed of the raw materials (g/min) + > 0.5

Feeding speed of the compressive fluid (g/min)

Formula (ii)

The temperature and pressure at which the ring-opening polymerizable monomer is melted in the reaction vessel 13 is controlled to the temperature and pressure at least equal to or higher than the triplet point of the compressive fluid to thereby prevent the fed compressive fluid from transforming into gas. This is controlled by adjusting output of a heater of the reaction vessel 13 or a degree of opening or closure of the valves (21, 22). In the present embodiment, the temperature at which the ring-opening polymerizable monomer is melted may be temperature equal to or lower than the melting point of the ring-opening polymerizable monomer under atmospheric pressure. The internal pressure of the reaction vessel 13 becomes high in the presence of the compressive fluid, and thus the melting point of the ring-opening polymerizable monomer becomes low. As a result, the ring-opening polymerizable monomer melts in the reaction vessel 13 even the state where the amount of the compressive fluid is small and the value of the mixing ratio is large.

Moreover, the timing for applying heat to or starting stirring each of the raw materials and the compressive fluid in the reaction vessel 13 may be adjusted so as to sufficiently melt each of the raw materials. In this case, heat or stirring may be applied or started after or during each of the raw materials is brought into contact with the compressive fluid. Moreover, the ring-opening polymerizable monomer and the compressive fluid may be brought into contact with each other after heat having temperature equal to or higher than the melting point of the ring-opening polymerizable monomer is applied to the ring-opening polymerizable monomer to melt in advance.

Subsequently, the valves (23, 24) are open to thereby supply the metal catalyst stored in the addition pot 11 to the reaction vessel 13. The metal catalyst supplied to the reaction vessel 13 is optionally sufficiently stirred by the stirring device of the reaction vessel 13, and is heated to the predetermined temperature by the heater. As a result, the ring-opening polymerizable monomer is proceeded to ring-opening polymerization in the presence of the metal catalyst in the reaction vessel 13, to thereby generate a polymer.

As for a range of temperature during ring-opening polymerization of the ring-opening polymerizable monomer (polymerization reaction temperature), the lower limit is preferably temperature lower than a melting point of the ring-opening polymerizable monomer by 40°C. The upper limit is preferably temperature higher than the melting point of the ring-opening polymerizable monomer by 40°C. When the polymerization reaction temperature is lower than the temperature lower than the melting point of the ring-opening polymerizable monomer by 40°C, the reaction speed may be low during the polymerization, by which the polymerization reaction may not be able to progress quantitatively.

When the polymerization reaction temperature is higher than the temperature higher than the melting point of the ring-opening

polymerizable monomer by 40°C, a depolymerization reaction, which is a reverse reaction of ring-opening polymerization, tends to occur

equilibrately, by which the polymerization reaction may not be

progressed quantitatively. Note that, the ring-opening polymerizable monomer may be subjected to ring-opening polymerization at

temperature outside the aforementioned range, depending on a

combination of the compressive fluid, ring-opening polymerizable monomer, and metal catalyst. In the case where a ring-opening monomer having low melting point, such as a ring opening polymerizable monomer that is liquid at room temperature, is used, the polymerization reaction temperature may be temperature that is higher than the upper limit of the above range to enhance the activity of the catalyst. In this case, however, the polymerization reaction temperature is preferably

150°C or lower.

In a conventional production method of a polymer using

supercritical carbon dioxide, polymerization of a ring-opening polymerizable monomer is carried out using a large amount of

supercritical carbon dioxide as supercritical carbon dioxide has low ability of dissolving a polymer. In accordance with the polymerization method of the present embodiment, ring-opening polymerization of a ring-opening polymerizable monomer is performed with a high concentration, which has not been realized in a conventional art, in the course of production of a polymer using a compressive fluid. In the present embodiment, the internal pressure of the reaction vessel 13 becomes high under the influence of the compressive fluid, and thus glass transition temperature (Tg) of a polymer product becomes low. As a result, the produced polymer product has low viscosity, and therefore a ring-opening reaction uniformly progresses even in the state where the concentration of the polymer is high.

In the present embodiment, the polymerization reaction time is appropriately set depending on a target molecular weight of a polymer product to be produced. When a target molecular weight is 3,000 to 100,000, the polymerization reaction time is 2 hours to 24 hours.

The pressure for the polymerization, i.e., the pressure of the compressive fluid, may be the pressure at which the compressive fluid supplied by the tank 7 becomes a liquid gas ((2) in the phase diagram of

FIG. 2), or high pressure gas ((3) in the phase diagram of FIG. 2), but it is preferably the pressure at which the compressive fluid becomes a supercritical fluid ((l) in the phase diagram of FIG. 2). By making the compressive fluid into the state of a supercritical fluid, melting of the ring-opening polymerizable monomer is accelerated to uniformly and quantitatively progress a polymerization reaction. In the case where carbon dioxide is used as the compressive fluid, the pressure is 3.7 MPa or higher, preferably 5 MPa or higher, more preferably 7.4 MPa or higher, which is the critical pressure or higher, in view of efficiency of a reaction and polymerization rate. In the case where carbon dioxide is used as the compressive fluid, moreover, the temperature thereof is preferably 25°C or higher from the same reasons to the above.

The moisture content in the reaction vessel 13 is preferably 4 mol% or less, more preferably 1 mol% or less, and even more preferably 0.5 mol% or less, relative to 100 mol% of the ring-opening polymerizable monomer. When the moisture content is greater than 4 mol%, it may be difficult to control a molecular weight of a resulting product as the moisture itself acts as an initiator. In order to control the moisture content in the polymerization reaction system, an operation for removing moistures contained in the ring-opening polymerizable monomer and other raw materials may be optionally provided as a pretreatment.

To the polymer obtained through polymerization of the

ring-opening polymerizable monomer, a urethane bond or ether bond can be introduced. Similarly to the ring-opening polymerizable monomer, the urethane bond or ether bond can be introduced by carrying out a polyaddition reaction in a compressive fluid with addition of an

isocyanate compound or glycidyl compound. In this case, a preferable method thereof for controlling a resulting molecular structure is a method in which the aforementioned compound is separately added after completion of a polymerization reaction of the ring-opening polymerizable monomer.

The isocyanate compound used in the polyaddition reaction is not particularly limited, and examples thereof include a polyfunctional isocyanate compound, such as isophorone diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, xylene diisocyanate, tolylene

diisocyanate, diphenylmethane diisocyanate, and cyclohexane

diisocyanate. The glycidyl compound is not particularly limited, and examples thereof include a polyfunctional glycidyl compound, such as diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, and diglycidyl terephthalate.

The polymer product P completed the ring-opening polymerization reaction in the reaction vessel 13 is discharged from the valve 25 to sent outside of the reaction vessel 13.

In the production method of the present embodiment, the polymerization rate of the ring-opening polymerizable monomer through ring-opening polymerization is 96 mol% or higher, preferably 98 mol% or higher. When the polymerization rate is less than 96 mol%, the polymer product does not have satisfactory thermal characteristics to function as a polymer product, and moreover it may be necessary to separately provide an operation for removing a ring-opening polymerizable monomer. Note that, in the present embodiment, the polymerization rate is a ratio of the ring opening polymerizable monomer contributed to generation of a polymer, relative to the ring-opening polymerizable monomer of the raw materials. The amount of the ring-opening polymerizable monomer contributed to generation of a polymer can be obtained by deducting the amount of the unreacted ring-opening polymerizable monomer

(ring-opening polymerizable monomer residues) from the amount of the generated polymer.

The number average molecular weight of the polymer product obtained in the present embodiment can be adjusted by adjusting an amount of the initiator. The number average molecular weight thereof is not particularly limited and can be adjusted depending on the intended use, but it is generally 12,000 to 200,000, preferably 100,000 to 200,000. Note that, in the present embodiment, the number average molecular weight is calculated based on a measurement of gel permeation

chromatography (GPC). When the number average molecular weight thereof is greater than 200,000, productivity is low because of the increased viscosity, which is not economically advantageous. When the number average molecular weight thereof is smaller than 12,000, it may not be preferable because a polymer product may have insufficient strength to function as a polymer. The value (Mw/Mn) obtained by dividing the weight average molecular weight Mw of the polymer product obtained by the present embodiment with the number average molecular weight Mn thereof is preferably in the range of 1.0 to 2.5, more preferably 1.0 to 2.0. When the value thereof is greater than 2.0, it is not preferable as the polymerization reaction may have progressed non-uniformly to produce a polymer product, and therefore it is difficult to control physical properties of the polymer.

«Use of Polymer Product» The polymer product obtained by the method for producing a polymer of the present embodiment is excellent in safety and stability because it is produced by the method which does not use an organic solvent, and there are hardly any monomer residues therein.

Accordingly, the polymer obtained by the production method of the present embodiment is widely applied for various uses, such as an electrophotographic developer, a printing ink, paints for building, cosmetic products, and medical materials.

«Effects of Present Embodiment»

In a conventional melt polymerization method of a ring-opening polymerizable monomer, a reaction is generally performed at high temperature, i.e., 150°C or higher, and therefore unreacted monomer residues remain in a resulting polymer product. Therefore, in some cases, it is necessary to provide a step for removing the unreacted monomers. Moreover, a solution polymerization is performed using a solvent, it is necessary to provide a step for removing the solvent in order to use a resulting polymer as a solid. Accordingly, any of these conventional methods cannot avoid increased cost due to increase in the number of steps in the production, or decrease in yield.

In accordance with the method for producing a polymer of the present embodiment, it is possible to provide a polymer having excellent mold formability and thermal stability at low cost, with low

environmental load, energy saving, and resource saving for the following reasons.

(l) A reaction proceeds at low temperature compared to a melt polymerization method.

(2) As the reaction proceeds at low temperature, a side reaction hardly occurs, and thus a polymer can be obtained at high yield relative to an amount of the ring-opening polymerizable monomer added (namely, an amount of unreacted ring-opening polymerizable monomer is small).

Accordingly, a purification step for removing unreacted ring-opening polymerizable monomer, which is performed for attaining a polymer having excellent mold formability and thermal stability, can be simplified, or omitted.

Examples

The present embodiment will be more specifically explained through Examples and Comparative Examples, but Examples shall not be construed as to limit the scope of the present invention in any way. Note that, molecular weights and polylmerizarion rates of polymer products obtained in Examples and Comparative Examples were determined in the following manners.

<Measurement of Molecular Weight of Polymer Product>

The molecular weight was measured through gel permeation chromatography (GPC) under the following conditions.

Apparatus: GPC-8020 (product of TOSOH CORPORATION)

Column: TSK G2000HXL and G4000HXL (product of TOSOH

CORPORATION)

Temperature: 40°C

Solvent: Tetrahydrofuran (THF) Flow rate- ' 1.0 mL/min

First, a calibration curve of molecular weight was obtained using monodispersed polystyrene serving as a standard sample. A polymer sample (1 mL) having a polymer concentration of 0.5% by mass was applied and measured under the above conditions, to thereby obtain the molecular weight distribution of the polymer. The number average molecular weight Mn and the weight average molecular weight Mw of the polymer were calculated from the calibration curve. The molecular weight distribution is a value calculated by dividing Mw with Mn.

<Polymerization Rate of Monomer (mol%) = 100% - Amount of Unreacted Monomer (mol %)>

Nuclear magnetic resonance (NMR) spectroscopy of polylactic acid of the polymer product or complex was performed in deuterated

chloroform by means of a nuclear magnetic resonance apparatus

(JNM-AL300, of JEOL Ltd.). In this case, a ratio of a quartet peak area attributed to lactide (4.98 ppm to 5.05 ppm) to a quartet peak area attributed to polylactic acid (5.10 ppm to 5.20 ppm) was calculated, and an amount of the unreacted monomer (mol%) (an amount of ring-opening polymerizable monomer residues) was determined by multiplying the obtained value from the calculation with 100. The polymerization rate is the value obtained by deducting the calculated amount of the unreacted monomer from 100.

[Example l]

Ring-opening polymerization of a mixture (mass ratio: 90/10, manufacturer: Purac, melting point: 100°C) of L-lactide and D-lactide was performed by means of the polymerization reaction device 100 of FIG. 3. The configuration of the polymerization reaction device 100 was as follows.

Tank 7 : Carbonic acid gas cylinder

Addition pot 11 ' ·

A 1/4-inch SUS316 pipe was sandwiched with valves 23, 24, and the resultant was used as an addition pot.

The addition pot was charged with 4 mg of tin

di(2-ethylhexanoate) (also called "tin 2-ethylhexanoate," CAS-" 301-10-0) in advance.

Reaction vessel 13:

A 100 mL SUS316 pressure resistant vessel

This pressure resistant vessel was charged with 108 g of a mixture (a molar ratio 100/3) of (a) fluid lactide (a mixture (mass ratio-' 90/10) of L-lactide and D-lactide) as the ring-opening polymerizable monomer, and (b) lauryl alcohol as the initiator, in advance.

The metering pump 8 was operated and the valves (21, 22) were open to thereby supply carbon dioxide stored in the tank 7 to the reaction vessel 13 without going through the addition pot 11. After replacing the atmosphere of the reaction vessel 13 with carbon dioxide, the reaction vessel 13 was charged with carbon dioxide until the internal pressure of the reaction vessel 13 reached 15 MPa. After heating the internal temperature of the reaction vessel 13 to 110°C, the valves (23, 24) were open to supply tin di (2-ethylhexanoate) stored in the addition pot 11 to the reaction vessel 13. Thereafter, lactide was allowed to proceed to a polymerization reaction for 12 hours in the reaction vessel 13. After completing the reaction, the valve 25 was open, and the internal temperature and pressure of the reaction vessel 13 were gradually returned to room temperature and ambient pressure. Three hours later, a polymer product (polylactic acid) in the reaction vessel 13 was taken out. The physical properties (Mn, Mw/Mn, polymerization rate) of the polymer product were measured by the aforementioned methods. The results are depicted in Table 1. Note that, the mixing ratio in Table 1 was

calculated by the following formula.

Spatial volume of supercritical carbon dioxide: 100 mL - 108 g/1.27 (specific gravity of raw materials) = 15 mL

Mass of supercritical carbon dioxide'- 15 mL x 0.303 (specific gravity at

110°C, 15 MPa) = 4.5

Mixing ratio: 108 g/(l08 g + 4.5 g) = 0.96

[Examples 2 to 4]

Polymers of Examples 2 to 4 were produced in the same manner as in Example 1, provided the amount of the initiator for use was changed to those as depicted in the columns thereof for Examples 2 to 4 of Table 1. Physical properties of the obtained polymers were measured by the aforementioned manners. The results are presented in Table 1.

[Examples 5 to 7]

Polymers of Examples 5 to 7 were produced in the same manner as in Example 1, provided that the mixing ratio and the reaction

temperature were respectively changed to those as depicted in the columns thereof for Examples 5 to 7 of Table 1. Physical properties of the obtained polymers were measured by the aforementioned manners. The results are presented in Table 1.

[Examples 8 to 10]

Polymers of Examples 8 to 10 were produced in the same manner as in Example 1, provided that the mixing ratio, the amount of the initiator, and the reaction pressure were respectively changed to those as depicted in the columns for Examples 8 to 10 of Table 2. Physical properties of the obtained polymers were measured by the

aforementioned manners. The results are presented in Table 2.

[Examples 11 to 14, and Comparative Example l]

Polymers of Examples 11 to 14 and Comparative Example 1 were produced in the same manner as in Example 1, provided that an amount of the raw materials added to the reaction vessel 13 was changed to 90 g (Example 11), 70 g (Example 12), 50 g (Example 13), 30 g (Example 14), and 10 g (Comparative Example l) and that the reaction time was changed as depicted in the columns for Examples 11 to 14 of Table 2 and Comparative Example 1 of Table 3. Physical properties of the obtained polymers were measured by the aforementioned manners. The results are presented in Tables 2 and 3.

[Examples 15 to 17]

Polymers of Examples 15 to 17 were produced in the same manner as in Example 1, provided that the reaction temperature and the reaction time were respectively changed to those as depicted in the columns for

Examples 15 to 17 of Table 3. Physical properties of the obtained polymers were measured by the aforementioned manners. The results are presented in Table 3

Table 1

Table 2

Table 3

Aspects of the present invention are as follows, for example. <1> A method for producing a polymer, including:

(i) bringing a compressive fluid and raw materials containing a ring-opening polymerizable monomer into contact with each other at a mixing ratio represented by the following formula, to thereby allow the ring-opening polymerizable monomer to carry out ring-opening polymerization in the presence of a metal catalyst:

Mass of the raw materials

1 > > 0.5

Mass of the raw materials + Mass of the compressive fluid

<2> The method for producing a polymer according to <1>,

wherein the (i) bringing includes- ' after melting the ring-opening polymerizable monomer by bringing the compressive fluid and the raw materials containing the ring-opening polymerizable monomer into contact with each other, adding the metal catalyst to allow the ring-opening polymerizable monomer to carry out the ring-opening polymerization.

<3> The method for producing a polymer according to <1> or <2>, wherein a polymerization rate of the ring-opening polymerizable monomer is 98 mol% or higher.

<4> The method for producing a polymer according to any one of <1> to <3>,

wherein the polymer has a number average molecular weight of 12,000 or greater.

<5> The method for producing a polymer according to any one of <1> to <4>,

wherein the compressive fluid contains carbon dioxide.

<6> The method for producing a polymer according to any one of <1> to <5>,

wherein the ring-opening polymerizable monomer is a monomer having a ring structure containing an ester bond therein.

<7> The method for producing a polymer according to any one of <1> to <6>,

wherein a lower limit of a temperature during the ring-opening polymerization in the (i) is lower than a melting point of the ring-opening polymerizable monomer by 40°C, and an upper limit of the temperature during the ring-opening polymerization in the (i) is higher than the melting point of the ring-opening polymerizable monomer by 40°C.

Reference Signs List

7: tank 8'· metering pump

11: addition pot

13 ' · reaction section

21, 22, 23, 24, 25: valve

100: polymerization reaction device