JP2000159818A - Preparation of methacrylic polymer and preparation of plastic optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide methacrylic polymers excellent in optical quality and plastic optical fibers excellent in transmission performance. SOLUTION: In the method for preparing a methacrylic polymer which comprises the polymerization step of feeding starting materials containing methyl methacrylate or a monomer mixture having methyl methacrylate as the major component, a radical polymerization initiator, and a mercaptan compound as the chain transfer agent or the starting materials additionally containing a solvent to a complete mixing-type reactor to effect continuous bulk polymerization or solution polymerization and the volatiles removal step of separating and removing volatiles in the reaction mixture discharge from the reactor, the difference in temperature between the jacked part of the reactor in contact with the polymerization reaction solution and the polymerization reaction solution in the polymerization step is maintained within 30 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a methacrylic polymer having excellent optical properties and a method for producing a plastic optical fiber.

[0002]

2. Description of the Related Art A methacrylic polymer has been widely used in the optical field as a material for an optical disk substrate and a material for optical devices such as various lenses and plastic optical fibers, taking advantage of its outstanding transparency. Have been. Industrial production methods of such a methacrylic polymer include a suspension polymerization method, a bulk polymerization method, and a solution polymerization method. Above all, the method of continuously performing bulk polymerization or solution polymerization in a closed system has an advantage that a mixture of dust and dust is small, and a methacrylic polymer having high purity can be obtained because a dispersant or the like is not required.

[0003] In the continuous bulk polymerization method, for example,
In Japanese Patent No. 32665, the half-life and the amount of the radical polymerization initiator to be added at the polymerization temperature are specified, and the polymerization reaction temperature is set to 130.
A method is disclosed in which the polymer conversion at 50 ° C. to 160 ° C. is from 50% by weight to 78% by weight.

Japanese Patent Application Laid-Open No. 3-111408 discloses a method in which a monomer mixture containing methyl methacrylate as a main component is continuously bulk-polymerized by using a complete mixing type reactor. The average residence time is 0.5 to 120 kW per 1 m ^{3 of} the reaction solution while stirring with a stirrer having a stirring power of 0.5 to 20 kW. Is set to be 1/200 to 1/10000, and 13
There is disclosed a method for producing a methacrylic polymer which is polymerized at a temperature of 0 to 160 ° C. so as to have a polymer conversion of 45 to 70% by weight.

The continuous solution polymerization method is described in, for example,
Japanese Patent Application Laid-Open No. 3-57613 discloses a reaction raw material in which the amount of inert solvent is set to 10 to 25% by weight of the total reaction mixture (raw material), the dissolved oxygen content of the reaction raw material is reduced to 1 ppm or less, and then filtered through a filter of 0.5 μm or less. Is continuously supplied to the reaction zone to carry out polymerization at a temperature of 120 to 160 ° C. so that the polymerization conversion of the monomer is substantially constant within the range of 40 to 65%. Have been.

[0006]

However, the above-mentioned Japanese Patent Publication No. 52-32665 and Japanese Patent Application Laid-Open No. 3-111408 are not disclosed.
Although methacrylic polymers can be obtained by the prior art disclosed in Japanese Patent Application Laid-Open No. 63-57613 and Japanese Patent Application Laid-Open No. 63-57613, any of the techniques used for optical materials have extremely small optical distortion. Due to insufficient technical considerations for producing a coalesced polymer, the excellent optical properties inherently possessed by methacrylic polymers have not yet been sufficiently exhibited.

Accordingly, the present invention has been made in view of such conventional problems, and a method for producing a methacrylic polymer excellent in optical characteristics having truly small optical distortion and using this polymer. An object of the present invention is to provide a method of manufacturing a plastic optical fiber having excellent transmission performance.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above-mentioned object, and as a result, have found that the object can be achieved by performing a polymerization reaction under specific operating conditions. Thus, the present invention has been completed.

That is, the present invention relates to a completely mixed reactor comprising methyl methacrylate or a monomer mixture containing methyl methacrylate as a main component, a radical polymerization initiator, and a raw material containing a mercaptan compound as a chain transfer agent, or a raw material further containing a solvent. And a methacrylic polymer production method having a volatile removal step of separating and removing volatiles in a reaction mixture discharged from the reactor, and a polymerization step of continuously performing bulk polymerization or solution polymerization. In the polymerization step, the polymerization is carried out by maintaining the difference between the temperature of the jacket portion of the reactor in contact with the polymerization reaction solution and the temperature of the polymerization reaction solution within 30 ° C. The present invention relates to a method for producing a methacrylic polymer.

The present invention also provides a polymer obtained by the above method,
The present invention relates to a method for producing a plastic optical fiber in which this polymer and another polymer having a different refractive index are supplied to a composite spinning nozzle and spun.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The production method of the present invention is applied to the production of a methacrylic polymer, that is, a homopolymer or a copolymer of methyl methacrylate. As the copolymer,
It is preferably applied to the production of a copolymer containing not less than 80% by weight of a methyl methacrylate unit and not more than 20% by weight of another monomer unit copolymerizable with methyl methacrylate.

The above-mentioned homopolymer and copolymer are obtained by homopolymerization of methyl methacrylate or copolymerization of a monomer mixture containing methyl methacrylate and another monomer, respectively. Hereinafter, methyl methacrylate or a monomer mixture is referred to as “raw material monomer”.

The other monomers to be copolymerized are not particularly limited, but, for example, (meth) acrylates such as methyl acrylate, ethyl acrylate, n-butyl acrylate, fluoroalkyl methacrylate and benzyl methacrylate are preferably used.

In the present invention, first, an inert gas such as nitrogen is introduced into a raw material monomer or, in the case of solution polymerization, a reaction raw material containing the raw material monomer and an inert solvent, or is maintained under reduced pressure for a certain period of time. Dissolved oxygen is set to 2 ppm or less. If the dissolved oxygen is more than 2 ppm, not only the polymerization reaction is not stable, but also the coloring is easily performed by keeping the high temperature for a long time in the polymerization step. It is preferably at most 1 ppm.

The raw material monomer or reaction raw material from which dissolved oxygen has been removed as described above is mixed with a mercaptan compound as a radical polymerization initiator and a chain transfer agent, and is continuously supplied to a complete mixing type reactor. Polymerization of the supplied raw material is started in the reactor, and becomes a polymerization reaction liquid.

The mercaptan compound used in the present invention is not particularly limited, but n-butyl, n-octyl, n-dodecyl, tert-butyl mercaptan and the like are preferably used.

The polymer terminated by a mercaptan chain transfer reaction is excellent in thermal decomposition resistance. As the ratio of the number of mercaptan terminated terminals to the total number of polymer terminals increases,
A polymer having excellent thermal decomposition resistance is obtained. However,
If the amount is too large, the degree of polymerization of the polymer decreases and the strength of the polymer decreases. Therefore, an appropriate degree of polymerization capable of forming and processing while maintaining the strength (in the present invention, the polymer after finally removing volatile components) Is preferably in the range of 70,000 to 150,000) and a polymer having excellent thermal decomposition resistance is desirably produced. For this purpose, the amount of the mercaptan used is 1.0 × 10 ⁻⁴ to 1.0.
0 × 10 ⁻² mol is preferred, and 5.0 × 10 ^{−4 to} 5.0 ×.
^10-3 mol is more preferred.

The radical polymerization initiator used in the present invention is:
It is possible to select from known organic peroxides or azo compounds, for example, as a specific polymerization initiator,
1,1,3,3-tetramethylbutylperoxy-2-
Ethyl hexanate, 1-cyclohexylperoxy-
2-ethylhexanate, t-hexylperoxy-2
-Ethylhexanate, t-butylperoxy-2-ethylhexanate, 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, t-
Organic peroxides such as butylperoxy-3,5,5-trimethylhexanate and di-t-butyl peroxide;
Or 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile,
2,2′-azobis (2-methylbutyronitrile), dimethyl-2,2 ′ (2-methylpropionate), 1,2
Azo compounds such as 1′-azobis (cyclohexane-1-carbonitrile) and 2,2′-azobis (2,4,4-trimethylpentane) are exemplified.

One of these polymerization initiators may be used alone, or two or more thereof may be used in combination. However, when two or more polymerization initiators are used, the polymerization becomes complicated. Single use is preferred.

The amount of the polymerization initiator used depends on the polymerization temperature, the reactor
Average residence time of the polymerization reaction solution at
Depending on the content, the amount of terminal double bonds in the polymer is small.
In order to obtain a polymer with excellent thermal decomposition resistance,
The upper limit of the dose is 1.0 × 10^-FourMo
The lower limit is 5.0 × 10 in consideration of industrial productivity. ^-6
It is preferable to supply in a molar range.

In the present invention, known polymerization conditions can be employed for the polymerization temperature. Generally, in the case of continuous polymerization containing methyl methacrylate as a main component, 110 to 170 ° C.
It is said that it is preferable to carry out the polymerization while stirring so as to maintain a certain temperature in the range described above, and the same applies to the present invention.

However, in order to suppress the by-product of the dimer, the reaction temperature is more preferably 140 ° C. or lower.

The most important point of the present invention is that, in the complete mixing type reactor, the temperature difference between the temperature of the jacket portion of the reactor in contact with the polymerization reaction solution and the temperature of the polymerization reaction solution (polymerization temperature) is 30 ° C. or less. The polymerization is performed while maintaining such that

It is generally known that the methacrylic polymer has a difference in the stereoregularity of the polymer depending on the temperature at which the monomer is polymerized. The lower the polymerization temperature, the more the polymer having many syndiotactic portions. can get.

On the other hand, the present inventors have found that silver is generated when polymethyl methacrylate obtained by melt-kneading two types of polymethyl methacrylate obtained by polymerizing methyl methacrylate at different polymerization temperatures generates silver, and remarkable molding occurs. It was empirically known that it would cause a defect. In view of such a phenomenon, the present inventors hypothesized that steric regularity due to a difference in polymerization temperature is involved, and based on the hypothesis that the steric regularity due to the temperature irregularity in the polymerization reactor is sufficiently different. It is thought that coalescence may be produced, and by improving this point, it is possible to produce a methacrylic polymer having excellent optical properties with small optical distortion compared to the conventional continuous polymerization method. It was just.

The temperature unevenness in the complete mixing type reactor may be the temperature unevenness in the entire polymerization reaction solution, but generally, the temperature unevenness is very small in a sufficiently stirred and mixed reactor. "Chemical Factory," Volume 12, Volume 4
No. p59 (1968), it has been found that there is almost no temperature unevenness in a complete mixing type reactor which is stirred and mixed so as to satisfy the following equation (1).

Pv · gc / μ> 100 [1 / (sec) ² ] (1) where Pv: power required for stirring [kg · m / sec / m ³ ] gc: gravity conversion coefficient [m / (sec) ² μ: Reaction solution viscosity [Pa · sec] Normally, the reactor generates heat such as reaction heat and stirring heat. To keep the polymerization temperature constant, the heat balance is satisfied by adjusting the jacket temperature and other factors. Driven to be. Therefore, when the polymer content increases, the calorific value also increases, and it becomes difficult to maintain a constant temperature unless the jacket temperature is significantly reduced. On the other hand, when the polymer content decreases, the temperature of the jacket increases. Therefore, a temperature atmosphere different from the temperature of the polymerization reaction liquid is formed near the inner surface of the jacket of the reactor. As a result, the polymer polymerized under the temperature atmosphere near the inner surface of the jacket becomes a polymer having a different stereoregularity, and the polymer is mixed therein to separate and remove volatile components in the reaction mixture discharged from the reactor. It is considered that the resulting methacrylic polymer has an increased optical strain and a reduced optical property.

As a result of intensive research based on the above ideas,
The polymerization reaction is carried out by maintaining the temperature difference between the temperature of the jacket portion of the reactor in contact with the polymerization reaction solution and the temperature of the polymerization reaction solution at 30 ° C. or less, and then the volatile components in the reaction mixture are separated. When an optical fiber was manufactured using the removed polymer as a core material, an optical fiber with extremely small optical transmission loss was surprisingly manufactured. If the temperature difference between the temperature of the jacket portion of the reactor in contact with the polymerization reaction solution and the temperature of the polymerization reaction solution (polymerization temperature) exceeds 30 ° C., as described above, the optical distortion increases and the light transmission property increases. No good optical fiber was obtained. In particular, when the temperature of the jacket portion is lower than the polymerization temperature by more than 30 ° C., the optical transmission loss increases, and a coating layer of a polymer having a high degree of polymerization is formed so as to cover the inner surface of the jacket portion. The problem of unstable driving is likely to occur. Preferably, the difference between the temperature of the jacket portion and the polymerization temperature is no greater than 20 ° C, and most preferably, there is substantially no temperature difference.

The average residence time of the polymerization reaction solution in the complete mixing type reactor is preferably in the range of 1 to 6 hours. When the content is within this range, the polymerization control can be stabilized, and a polymer which is difficult to thermally decompose and has excellent transparency can be produced. If the residence time is too short, it is necessary to increase the amount of the polymerization initiator, and it becomes difficult to control the polymerization reaction due to the increase in the polymerization initiator,
Since the amount of terminal double bonds in the polymer increases, thermal decomposition during the molding process tends to cause thermal decomposition, and a polymer having excellent transparency cannot be obtained. More preferably, it is 2 hours or more. on the other hand,
If the average residence time is too long, productivity is reduced and the production of dimers is increased, which is not preferable. More preferably, it is 5 hours or less.

In carrying out the solution polymerization in the present invention, known solvents such as toluene, xylene, acetone, methyl ethyl ketone, methanol, ethanol, ethyl benzene, methyl isobutyl ketone and n-butyl acetate can be used. Methyl ethyl ketone, methanol, ethylbenzene, n-butyl acetate and the like are particularly preferred. The content of the solvent with respect to the total amount of the monomer, the radical polymerization initiator, the mercaptan compound and the solvent is preferably 20% by weight or less,
More preferably, the content is 10% by weight or less.

The temperature control in the reactor can be performed by a known method. For example, jackets, heat transfer heat removal or heating by circulating a heating medium to a draft tube or a coil installed in a reaction zone, or the like, a method of cooling and supplying a raw material, reflux cooling of a monomer vapor, and the like can be adopted.
In the present invention, since it is important not to carry out polymerization in an atmosphere having a temperature difference exceeding 30 ° C., in a complete mixing type reactor, a method such as cooling supply of raw materials, reflux cooling of monomer vapor, or the like is used. It is preferable to employ it.

The polymer content in the reactor of the present invention is:
It is preferably in the range of 30 to 60% by weight. If the polymer content is too large, the viscosity is so high that the polymerization speed is greatly accelerated by the gel effect, and the polymerization temperature fluctuates greatly, making stable operation difficult. On the other hand, when the polymer content is too small, the cost is increased due to the separation of volatiles mainly composed of unreacted monomers, and the industrial merit is reduced. Furthermore, the conditions for producing more stably and economically advantageously are preferably such that the polymerization temperature is in the range of 120 to 140 ° C. and the polymer content is in the range of 40 to 55% by weight.

As the complete mixing type reactor used in the present invention, a tank type reactor having a supply port, a discharge port and a stirrer can be used, and the stirrer can have mixing performance over the entire reaction zone. desirable. Preferred stirring devices include a double helical ribbon blade, a Max Blend blade (Sumitomo Heavy Industries, Ltd.) and the like.

The polymerization is carried out by pressurizing the gas phase in the reactor with an inert gas such as nitrogen. The pressure to apply is
Maintain above the vapor pressure of methyl methacrylate at the higher of the polymerization temperature and the temperature of the reactor jacket. If the pressure in the gas phase is lower than the vapor pressure of methyl methacrylate, a uniform polymer cannot be obtained because foaming of the polymerization reaction liquid occurs. Preferably, the pressure is 2 kg /
Preferably, the pressure is maintained at a level higher than cm ² .

In the present invention, after such a polymerization step,
An unreacted monomer, or having a step of separating volatiles mainly composed of unreacted monomer containing a solvent, the reaction mixture having a predetermined polymer content continuously sent, under reduced pressure Preferably heated to 170-290 ° C,
Most of the volatiles are continuously separated and removed so that the residual monomer content in the obtained polymer is preferably 1.0% by weight or less, more preferably 0.3% by weight or less.

In the volatile matter separation step, dimers are also removed. The dimer is preferably smaller because it causes coloring during the heat molding of the polymer and lowers the heat distortion temperature. The residual dimer content in the obtained polymer is preferably adjusted to 0.1% by weight or less, more preferably 0.05% by weight or less.

Further, usually, the polymerization step and the volatile matter separation step are connected by a pipe via a liquid feed pump. In the present invention, the polymerization reaction substantially occurs during the transfer in the pipe. It is preferable not to proceed. Generally, the temperature of the pipe and the polymerization temperature are different, so the progress of the polymerization reaction in the pipe is due to the fact that a polymer having a different polymerization temperature from the polymer polymerized in the complete mixing reactor is generated. In addition, as described above, polymers having different stereoregularities are mixed, which is disadvantageous in optical characteristics. For this reason, it is preferable to reduce the concentration of the residual initiator in the reaction mixture continuously discharged from the complete mixing type reactor, and for that purpose, it is desirable to use a polymerization initiator having a high decomposition rate. The half life of the radical polymerization initiator at the polymerization temperature in the complete mixing type reactor is preferably 1 minute or less. When the methacrylic polymer thus produced is used as a molding material, a lubricant such as a higher alcohol or a higher fatty acid ester can be added. Also, if necessary, an ultraviolet absorber, a heat stabilizer,
You may add a coloring agent, an antistatic agent, etc.

When an optical fiber is manufactured using the polymer obtained as described above, an optical fiber having excellent transmission performance can be obtained.

The structure of the optical fiber is not particularly limited. For example, an SI type optical fiber in which a core / sheath is laminated concentrically and the refractive index changes rapidly at the interface, the refractive index continuously increases from the center toward the outer layer. Examples include a GI optical fiber that changes, and an optical fiber whose refractive index changes stepwise from the center to the outer periphery. Since the polymer produced according to the present invention has excellent optical properties, it is preferably used as a component constituting a core in a portion through which light passes when light is transmitted through an optical fiber, for example, in an SI type optical fiber. .

In producing an optical fiber, it is preferable to spin a plurality of materials by using a composite spinning nozzle which concentrically stacks and discharges the materials. As the composite spinning nozzle, two or more layers are appropriately used. For example, when manufacturing an optical fiber whose refractive index changes stepwise from the center to the outer periphery, a composite spinning nozzle having three or more layers is used. When producing an SI type optical fiber, the core component is supplied to the inner layer of the two-layer composite spinning nozzle, and the sheath component is supplied to the outer layer, and the fiber is spun. The method for producing an optical fiber is not limited to a method using a composite spinning nozzle. For example, when producing an SI type optical fiber, a method of spinning only a core component and melt-coating a sheath component on an outer layer thereof is used. Is used.

As the sheath component for producing the SI type optical fiber, for example, a copolymer of vinylidene fluoride and fluoroalkyl vinyl ester, methacrylic ester, acrylate ester, tetrafluoroethylene, hexafluoropropene, or vinyl acetate is used. Polymers and the like can be used. Further, a copolymer of a fluorinated alkyl methacrylate, a fluorinated alkyl acrylate, or the like with a methacrylate, an acrylate or the like can also be used. Preferred is a polymer containing vinylidene fluoride units as a main component. As the polymer, for example, a copolymer of vinylidene fluoride and tetrafluoroethylene containing 75 to 99% by weight of vinylidene fluoride unit, 75 to 95% by weight of vinylidene fluoride and tetrafluoroethylene 4 to
Copolymer of 20% by weight and 1 to 10% by weight of hexafluoropropene, 75 to 95% by weight of vinylidene fluoride
And a copolymer of 4 to 20% by weight of tetrafluoroethylene and 1 to 5% by weight of vinyl fluoride.

[0042]

The present invention will be described in more detail with reference to the following examples. In addition, the evaluation of the physical properties of the polymers of the examples was performed by the following methods.

<Measurement of Molecular Weight> The molecular weight was measured by gel permeation chromatography (GPC). The measuring device used was HLC-8020 manufactured by TOSOH, and two GMHXL (manufactured by TOSOH) were used as columns. A calibration curve was prepared using THF as a solvent and TSKOH standard polystyrene manufactured by TOSOH, and a sample was used as a stationary solution having a concentration of 0.1 g / dl.

The weight average molecular weight Mw, and the weight average molecular weight and the number average molecular weight (Mw / Mn) were measured using a commercially available GPC data processor (TOSOH data unit SC-8010).
Asked by.

<Measurement of Tacticity> NMR of polymer
The spectrum was measured, and α-
The ratio of the area assigned to the syndiotactic and heterotactic ones in the methyl group signal (S /
H).

(Example 1) Purified dissolved oxygen was adjusted to 1 ppm
Dimethyl 2,2'-azobi
(2-methylpropionate) (Wako Pure Chemical V-60)
1.95% by weight)^-Five(mol) / thing
Normal butyl mercaptan (E
LF ATOCHM NORTH AMERICA INC, purity 99.5 wt%)
1.75 × 10 ^-3(mol) / 1 monomer (mol)
Each added raw material is continuously supplied to the complete mixing reactor.
Was. The temperature of the polymerization reaction solution was measured using a thermocouple inserted in the bottom of the reactor.
And controlled to be constant at 130 ° C.
The raw material supplied to the reactor is supplied by double helical ribbon blades.
At 75 rpm. Gas phase in the reactor
Is 7 kg / cm with nitrogen^TwoAdjust the pressure to maintain G
Was.

The polymerization was carried out with the average residence time of the polymerization reaction solution in the reactor being 4 hours. At this time, the reactor jacket temperature was 130 ° C., and the polymerization temperature was controlled by adjusting the temperature of the feedstock in the range of 0 to 10 ° C.

The reaction mixture was continuously taken out of the reactor, fed with a pump, and continuously supplied to a vent extruder extruder to separate and remove volatiles to obtain a polymer. The polymer content of the reaction mixture immediately after being taken out of the reactor was 46% by weight, and the dimer content was 0.05% by weight. The polymer obtained by separating volatiles from the reaction mixture had a residual monomer content of 0.1% by weight and a residual dimer content of 0.03% by weight or less.

Further, Mw of the polymer measured by GPC was 95,000, Mw / Mn was 2.0, and the polymer had a narrow molecular weight distribution. The tacticity of this polymer was 1.30 in S / H ratio.

In the polymerization step of the present example, the polymerization reaction was extremely stable even in the continuous operation for 360 hours, and even if the inside of the reactor was observed after the operation was completed, the adhesion of the polymer to the apparatus and the foreign matter No formation was observed.

Subsequently, using a two-layer composite spinning nozzle,
This polymer is supplied as a core component to the inner layer of a two-layer composite spinning nozzle, and a separately produced polymer of 2,2,2-trifluoroethyl methacrylate is supplied to the outer layer of the composite spinning nozzle as a sheath component to form a composite spinning nozzle. The outer diameter is 1000 μm by performing melt composite spinning with the nozzle temperature set to 210 ° C.
m, a plastic optical fiber having a core-sheath structure with a sheath thickness of 10 μm was obtained.

As a result of evaluating the light transmission performance of the obtained plastic optical fiber, it was found that the wavelength was 520 nm, 570 nm, and 65 nm.
The light transmission loss at 0 nm is 70 dB / km and 6
The transmission loss was as small as 1 dB / km and 133 dB / km, and the optical characteristics were extremely excellent.

(Comparative Example 1) The jacket temperature of the reactor was 9
Polymerization was carried out under the same conditions as in Example 1 except that the temperature of the raw material was adjusted to 5 ° C and the temperature of the feedstock was adjusted in the range of 20 ° C to 30 ° C.

The polymer content of the reaction mixture immediately after being taken out of the reactor was 46% by weight, and the dimer content was 0.05% by weight. Further, the polymer obtained by separating volatiles from the reaction mixture had a residual monomer content of 0.1% by weight and a residual dimer content of 0.03% by weight or less, which was the same as that of the example. was gotten. Further, Mw of this polymer is 96,000, and Mw / Mn is 2.2.
The polymer had a slightly wider molecular weight distribution than that of Example 1. The tacticity of this polymer was 1.33 in terms of the S / H ratio.

After 100 hours of continuous operation, when the inside of the reactor was observed, a thin coating layer of a polymer was formed so as to cover the inner surface of the jacket. When the city was measured, the weight average molecular weight Mw was 110,000, Mw / Mn was 3.2, and the tacticity was 1.45 in S / H ratio. Subsequently, a plastic optical fiber having a core-sheath structure was obtained in the same manner as in Example 1, and its light transmission performance was evaluated. The light transmission loss at wavelengths of 520 nm, 570 nm and 650 nm is 80 dB / km and 73 dB / k, respectively.
m, 140 dB / km, transmission loss increased as compared with the first embodiment.

[0056] (Example 2) 2,2'-azobis (2-methyl propionate) feed concentration of 1.6 × 10 of ^{- 5} (mo
l) / monomer 1 (mol), and the polymerization temperature was controlled under the same conditions as in Example 1 except that the temperature of the feedstock was adjusted in the range of 40 to 50 ° C.

The polymer content of the reaction mixture immediately after being taken out of the reactor was 38% by weight, and the dimer content was 0.07% by weight. The polymer obtained by separating volatiles from the reaction mixture had a residual monomer content of 0.1% by weight and a residual dimer content of 0.03% by weight or less.

Further, Mw of the polymer was 95,000, Mw / Mn was 2.0, and the polymer had a narrow molecular weight distribution. The tacticity of this polymer was 1.30 in S / H ratio.

A plastic optical fiber having a core-sheath structure was obtained in the same manner as in Example 1, and its light transmission performance was evaluated. The light transmission losses at wavelengths of 520 nm, 570 nm, and 650 nm are 72 dB / km, 62 dB / km, respectively.
The transmission loss was as small as 132 dB / km, and the optical characteristics were extremely excellent.

(Comparative Example 2) The jacket temperature of the reactor was 1
Polymerization was carried out under the same conditions as in Example 2 except that the temperature of the feed was adjusted to 65 ° C and the temperature of the feedstock was adjusted in the range of 20 to 30 ° C.

The polymer content of the reaction mixture immediately after being taken out of the reactor was 38% by weight, and the dimer content was 0.1% by weight. The polymer obtained by separating volatiles from the reaction mixture had a residual monomer content of 0.1% by weight and a residual dimer content of 0.03% by weight or less, which was almost the same as in Example 2. A polymer was obtained. Further, the Mw of this polymer is 95,000, and the Mw / Mn is 2.0
As in Example 2, the polymer had a narrow molecular weight distribution. The tacticity of this polymer is 1.28 in S / H ratio.
Met.

After 100 hours of continuous operation, when the inside of the reactor was observed, no deposit was found on the inner surface of the jacket.

Subsequently, a plastic optical fiber having a core-sheath structure was obtained in the same manner as in Example 1, and its light transmission performance was evaluated. The light transmission losses at wavelengths of 520 nm, 570 nm and 650 nm are 81 dB / km and 75 dB / km, respectively.
km and 140 dB / km, the transmission loss was larger than in Examples 1 and 2.

[0064]

According to the present invention, it is possible to produce a methyl methacrylate polymer sufficiently excellent in optical characteristics with small optical distortion and a plastic optical fiber excellent in transmission performance.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) D01F 8/10 D01F 8/10 A G02B 6/00 366 G02B 6/00 366 (72) Inventor Koji Ishizaka Toyama No. 3, Kaigan-dori, Toyama-shi, Japan Mitsubishi Rayon Co., Ltd. Toyama Works (72) Inventor Takeshi Kitayama No. 3, Kaigan-dori, Toyama City, Toyama Pref. AB08 AB09 DB16 DB28 FB04 FB05 FB07 FB09 FB11 HB01 HB02 HB03 HB05 HB07 4J100 AL03P AL03Q AL08Q BB10Q BC43Q CA01 CA04 FA03 FA04 FA18 FA19 FA47 GC26 4L041 AA07 BA02 BA05 BA21 BA23 BA46 BC06 DD20 DD47 CA55

Claims (5)

[Claims] A raw material containing methyl methacrylate or a monomer mixture containing methyl methacrylate as a main component, a radical polymerization initiator, and a mercaptan compound as a chain transfer agent, or a raw material further containing a solvent is supplied to a complete mixing type reactor. A method for producing a methacrylic polymer, comprising: a polymerization step of continuously performing bulk polymerization or solution polymerization; and a volatile removal step of separating and removing volatiles in a reaction mixture discharged from the reactor. In the polymerization step, the polymerization is carried out while maintaining the difference between the temperature of the jacket portion of the reactor in contact with the polymerization reaction solution and the temperature of the polymerization reaction solution within 30 ° C. to carry out the polymerization. Manufacturing method. 2. The method for producing a methacrylic polymer according to claim 1, wherein the temperature of the polymerization reaction solution is adjusted by the temperature of the feed material and the temperature of the jacket. 3. The polymer content in the reactor is 30.
3. The method for producing a methacrylic polymer according to claim 1, wherein the amount is from 60 to 60% by weight. 4. 4. The method for producing a methacrylic polymer according to claim 3, wherein the average residence time of the polymerization reaction solution in the reactor is 1 to 6 hours. 5. A plastic light for obtaining a polymer by the method according to claim 1, and supplying the polymer and another polymer having a different refractive index to a composite spinning nozzle for spinning. Fiber manufacturing method.