JPS58132002A - Continuous production of methacrylate copolymer - Google Patents

Abstract

PURPOSE:To produce the titled highly transparent, coloration-free copolymer at a low energy consumption, by polymerizing a methyl methacrylate monomer in two stages in the presence of methyl isobutyrate. CONSTITUTION:A mixture of a monomer component (A) consisting of above 50wt% methyl methacrylate and other copolymerizable monomers, 1-30wt% based on component A, methyl isobutyrate (B), two kinds of initiators (C) differing in 10-hour half life at least 40 deg.C, and a chain transfer agent (D) is introduced through a conduit 3 into a reaction vessel consisting of a homogeneous- phase reaction zone occupying 75-90% of the entire volume and a plug flow reaction zone 2 occupying the remaining volume. Then, the mixture is allowed to react under a pressure applied through a pressure line 4 and the heat of heating mdeium sent through a line 9, with agitation by an agitator blade 5, until 50-80mol% component B has been consumed, and then the reaction mixture is allowed to react further in the reaction zone 2, with agitation by a screw 6, until the amount of component B remaining has been lowered to below 5mol%. In this way, 50-90mol% of component A is converted into the copolymer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously producing a methacrylate copolymer. More specifically, by carrying out two-step polymerization of methyl methacrylate monomer and other copolymerizable monomers in the presence of methyl isobutyrate, a methacrylate copolymer with good transparency and no coloring can be produced. It relates to a continuous method that can provide a stable supply with low energy consumption.

Conventionally, suspension polymerization has been commonly used to polymerize methacrylate monomers, but this method uses water and suspending agents, making wastewater treatment troublesome and energy-consuming. This method is disadvantageous compared to other polymerization methods and cannot necessarily be said to be an industrially suitable method. Furthermore, suspension polymerization generally cannot be used when using water-soluble monomers due to the use of an aqueous medium, so its applicability is inevitably limited, and it also involves copolymerizing components with significantly different refractive indexes. In this case, there is also the disadvantage that the resulting copolymer often becomes cloudy. For these reasons, continuous bulk polymerization has recently attracted attention in the polymerization of methacrylate monomers, for example, using a stirred reactor.
A method of carrying out a homogeneous phase reaction at a relatively low polymerization conversion of 60 molar ratio or less has been proposed (Japanese Patent Application Laid-Open No. 147788/1983).
Publication No.). However, since this method has a low polymerization conversion rate, a large amount of remaining unreacted monomer must be recovered and recycled for reuse, but this recovery must be performed at high temperatures, which consumes a lot of energy. However, the disadvantage is that the production of by-products such as oligomers cannot be avoided, which causes coloring and deterioration of the product.

The present inventors have conducted extensive research to overcome the above-mentioned drawbacks of conventional methods and to develop a method for obtaining excellent quality methacrylate copolymers with low energy consumption. A material obtained by adding methyl isobutyrate to the polymer component is used as a raw material, and this is subjected to a two-stage reaction in a special reaction device, and the final amount is 90% by mole or more.
It has been discovered that the objective can be achieved by carrying out polymerization conversion to a range of less than 0 molar ratio, and based on this knowledge, the present invention has been completed.

That is, according to the present invention, when producing a methyl methacrylate copolymer containing at least 50 weight units of methyl methacrylate units by radical polymerization, the monomer component, 1 to 30]i% by weight based on the monomer component. A homogeneous phase reaction zone in which 75-90% of the total volume is agitated with a raw mixture of methyl isobutyrate, polymerization initiator and chain transfer agent in proportions, and the remaining part is formed by a plug flow reaction zone. , the radical polymerization initiator is fed to the homogeneous phase reaction zone of the two-stage polymerization reactor, where it is reacted in a column where 50 to 80 moles of the radical polymerization initiator is consumed, and then the remaining amount of the radical polymerization initiator is reduced in the plug flow reaction zone. The reaction is carried out until the amount becomes less than 5 molar of the initial addition amount, and finally 5
By polymerizing and converting 0 to 90 molar fractions, it is possible to produce high-quality methyl methacrylate copolymers with a narrow average molecular weight distribution without impairing the desirable properties of the methyl methacrylate polymers. It can be produced continuously under low energy consumption conditions.

In the method of the present invention, a mixture of methyl methacrylate and a monomer copolymerizable with it is used as the monomer component of the raw material. Examples of monomers copolymerizable with methyl methacrylate include alkyl esters of acrylic acid or methacrylic acid in which the alkyl group is derived from an alcohol having 1 to 20 carbon atoms, such as methyl acrylate, ethyl acrylate, butyl acrylate, ethyl Methacrylate, propyl methacrylate, butyl methacrylate and n-chloroalkyl esters include cyclohexyl methacrylate, but others include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, maleic acid monoester, maleic diester 1 N-methylmaleic acid imide, fumaric acid, acrylamide, methacrylamide,
N-methylacrylamide, N-4-3-butylacrylamide, acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-cyanoacrylic acid and hiso ester, styrene, α-methylstyrene, α-cyanostyrene, etc. can also be used. .

These may be used alone or in combination of two or more. In the present invention, methyl methacrylate 100
A mixture of 0.5 to 30 parts by weight of the above copolymerizable monomer per part by weight is used.

Next, in the method of the present invention, methyl isobutyrate is added in an amount of 1 to 30% by weight, preferably 5 to 2% by weight, based on the monomer components.
It is necessary to add it in a proportion of 0% by weight. This methyl isobutyrate reduces the viscosity of the polymer mixture and
It plays a role in alleviating the so-called gel effect, which is an abnormal reaction acceleration phenomenon that accompanies an increase in the polymerization rate, and thereby allows the homogeneous mixing reaction to proceed to a high polymerization conversion rate (Japanese Patent Laid-Open No. 48-86990). Public bulletin). In the present invention, by using methyl isobutyrate, although the polymerization conversion rate is high, hard polymer parts with a high polymerization rate are locally generated, and therefore, smooth stirring is prevented. can be carried out to obtain a homogeneous product. In addition, when recovering unreacted monomers from the polymer mixture, the presence of methyl isobutyrate, which does not have polymerizability, suppresses the production of by-products and enables stable operation. There is an effect.

By the way, if methyl isobutyrate is present in the polymerization system, a chain transfer reaction will naturally occur, and methyl isobutyrate will enter some of the polymer molecules, but other substances, such as solvents, can be used for purposes such as solvents. Surprisingly, the quality of the polymer does not deteriorate, nor is it colored or lowered in heat resistance. This is believed to be because the molecular structure of methyl imbutyrate is similar to that of methyl methacrylate polymers.

It is necessary to use this methyl isobutyrate within the range of 1 to 30% by weight based on the total monomer, and within this range, the amount of the chain transfer agent used in combination can be controlled to reduce the molecular weight. It is possible to correct for the effect. If this amount is less than 1% by weight, the effect of adding methyl isobutyrate described above will be insufficient;
If the amount exceeds 0% by weight and 1%, it becomes difficult to form the molecular needles, making it impossible to obtain the desired copolymer.

Next, as the polymerization initiator used in the method of the present invention, when the temperature of the homogeneous phase reaction zone is selected to be relatively low, for example in the range of 70 to 110°C, tributyl peroxyacetate,
tert-butylperoxy7 (2-ethylhexanony)),
1.1-bis(tert-butylperoxy) -3,3,5
Peroxides such as -IJ methylcyclohexane, 1,1-bis(tert-butylperoxy)-/chlorohexane, dimethyl-2,2'-azobisinobutyrate, azobisisobutyronitrile, 2. 2'-azobis-2,4
-Azo compounds such as -dimethylvaleronitrile, 1.1'-7zobiscyclohexanecarbonitrile, etc. also raise the temperature of the homogeneous phase reaction zone to relatively high temperatures, e.g. 120-170°C.
When selecting within the range of , dicumyl peroxide, 2.5-
Dimethyl-2,5-di(tert-butylperoxy)-hexane, tert-butyl cumyl peroxide, diinopropylbenzene hydroperoxide, di-tert-butyl peroxide, tert-butyl hydroperoxide, 2,5 -dimethyl-2,5-di(tert-butylperoxy)-hexyne-3
Peroxides such as 2-77/-2-propylazoformamide, 2-phenylazo-2,4-dimethyl-4-methoxyvaleronitrile, azobisisobutanol diacetate, azoditertiary butane and other azo compounds are suitable. It is.

Particularly suitable are two types with a 10-hour half-life that differ by 40°C or more.
Species polymerization initiators such as tert-butyl peroxy-2-ethylhexanoate (10 hour half-life 72°C) and di-tert-butyl peroxide (10 hour half-life 124°C) are used in combination. .

This polymerization initiator is usually used in a proportion of 0.0005 to 0.05 parts by weight per 100 parts by weight of monomer components.

In addition, as the chain transfer agent of the present invention, various mercaptans commonly used as chain transfer agents in ordinary polymerization reactions, such as n-butyl mercaptan, isobutyl mercaptan, tert-butyl mercaptan, n-hexyl mercaptan, n- Octyl mercaptan, 2-ethylhexyl mercaptan, 1 n-dodecyl mercaptan, and the like can be used.

The amount of this chain transfer agent used depends on the type of mercaptan, the amount of methyl isobutyrate used together, etc., but is usually 0.05 to 0.5 per 100 parts by weight of monomer components.
Selected within the range of parts by weight. Generally, the molecular weight can be properly controlled by increasing the amount of methyl isobutyrate and decreasing the amount of chain transfer agent.

In the method of the present invention, it is necessary to conduct the reaction so that the polymerization conversion rate of the raw material monomer components is in the range of 50 mol% or more and less than 90 mol%. Using a reactor configured with a homogeneous phase reaction zone where ~90% is stirred and the remaining 10~25% is a plug flow reaction zone, 50~80 mol% of the radical polymerization initiator is in the homogeneous phase reaction zone. After reacting the raw material mixture until it is consumed, it is necessary to send it to the plug flow reaction zone 1 where it is reacted until the residual amount of the radical polymerization initiator becomes 5 mol % or less.

Next, the measurement method of the present invention will be explained according to the attached drawings.
The drawing is a schematic cross-sectional view showing one example of a reactor suitable for carrying out the present invention, and this reactor is composed of a homogeneous core section 1 and a plug flow reaction section 2. The raw material mixture is continuously fed to the homogenizing core 1 via a conduit 3 and is passed through a stirring blade 5 under pressure applied via a pressure line 4.
React while stirring. Reference numeral 9 is a heating medium feed line for adjusting the gas phase temperature, and 10 is a refrigerant line for removing the heat of polymerization reaction.

The reaction mixture that has reacted to a predetermined degree is then transferred to the plug flow reaction section 2, where it undergoes one more reaction while being mixed by a screw 6 having no rearward stirring vector, and then taken out from the discharge port 8. 11 is a heating medium supply line for heating the plug flow reaction section 2. In this figure, the stirring blades 5 and the screw 6 are attached to the same rotating shaft 7, but they are separate rotating shafts. Needless to say, it may also be attached to. The reactor is advantageously constructed vertically as shown in the figure, but if desired the reactor can be constructed horizontally by connecting the homogeneous core and the plug flow reactor laterally. It can also be configured.

In this reactor, the homogeneous phase core 1 has a total internal volume of 75 to 90%.
%, and the remaining 10 to 25% is the plug flow reaction section 2.
This is usually achieved by making the inner diameter of the plug flow reaction section 2 smaller than the inner diameter of the homogeneous reciprocal core section 1. Also, the average
A screw whose diameter gradually changes along the shape of the reactor may be provided between the reciprocal core section 1 and the plug flow reaction section 2 to facilitate movement of the reaction mixture.

In the method of the present invention, the ratio of the homogeneous phase reaction zone to the plug flow reaction zone is determined by keeping the volume of the plug flow reaction zone constant, instead of configuring the reactor itself to a desired ratio in advance as described above. It can also be adjusted by changing the liquid level. Generally, if it is desired to increase the polymerization conversion rate, the volume of the homogeneous phase reaction zone may be made as small as possible within a predetermined range.

When carrying out the method of the present invention, it is necessary to remove the polymerization heat generated in the homogeneous phase reaction zone of the polymerization reactor by appropriate cooling means, but the plug flow reaction zone must be completely insulated from the outside. to raise the temperature by the heat of reaction, or
It is necessary to supply heat from the outside as necessary to maintain the temperature in the range of 70 to 200°C. The reaction in this plug flow reaction zone proceeds with the radical polymerization initiator remaining in the homogeneous phase reaction zone, so the type and amount of polymerization initiator to be used is selected in advance by considering the polymerization reaction temperature and residence time of each zone. is advantageous.

The consumption rate of the polymerization initiator in the homogeneous phase reaction zone is chosen to be 50 to 80 mol % of the total added radical polymerization initiator acid, with the remainder being at least 95%, preferably 99.5%, in the plug flow reaction zone. React until % or more is consumed. These conditions are controlled by means of average residence time, initiator half-life, and polymerization temperature for the homogeneous phase reaction zone and by controlling the polymerization temperature for the plug flow reaction zone.
Each can be realized by controlling the polymerization temperature.

In addition, in the method of the present invention, two
In the homogeneous phase reaction zone, 70 to 1
The reaction is carried out at a relatively low temperature of 10°C, and in the plug flow reaction zone, the polymerization reaction is carried out at a relatively high temperature of 200°C or less to control the formation of oligomers by increasing the polymer production rate in the low crystallization. , the syndiotactic proportion of the polymer can be increased.For such purposes, a radical polymerization initiator with a half-life of 40°C for 10 hours is used.
It is advantageous to prepare a combination of two different types. If this difference is less than 40° C., it is not preferable because a runaway reaction may occur in the homogeneous phase reaction zone. Furthermore, if only a polymerization initiator with a high optimum operating temperature is added later into the plug flow reaction zone, non-uniform polymerization occurs and a homogeneous polymer cannot be obtained. In this way,
According to the method of the present invention, the conversion rate in the homogeneous phase reaction zone is 50-7.
0 mol % and a conversion of 65 to 90 mol % can be achieved in the plug flow reaction zone. Moreover, approximately 20% of the polymerization reaction heat can be effectively recovered, and therefore an energy-saving process with low energy consumption can be realized.

Normally, if the catalyst remains in the polymerization product, when unreacted monomers are recovered from the polymer, they will be mixed into the monomers, causing problems that will impede the long-term operation of the recovery equipment. However, in the present invention, since the residual amount of the catalyst is 5 mol% or less, preferably 0.5 mol% or less of the pre-added amount, there is no risk of such trouble. In method 2 of the present invention, 50 mol % or more and less than 90 mol % of the raw material monomer components are polymerized and converted in up to 10 reactors. In general, lowering the polymerization conversion rate facilitates the homogeneous phase reaction, but since the amount of monomer recovered increases, the process becomes an energy-intensive process, which is economically disadvantageous. Moreover, in the continuous bulk polymerization of methyl methacrylate, a homogeneous phase reaction is possible at most up to a conversion rate of 60 mol%, and to increase the conversion further, it is necessary to raise the polymerization temperature and lower the viscosity. This is not preferable because a large amount of oligomers and oligomers are produced as by-products, causing deterioration in the quality of the polymer. If a curved blade or screw type reactor is used, 9
Although it is possible to polymerize to a high conversion rate of about 0 mol%, the composition of the resulting polymer changes over time and ultimately a mixture of many different polymers with different compositions is obtained. It will be done. In such a mixture, there is a difference in the folding index between the initial product and the final product, so if the two products lack compatibility during melting, the polymer The degree of light scattering increases and turbidity becomes visible.

In contrast, in the present invention, by adding methyl isobutyrate and using both a homogeneous phase reaction zone and a plug flow reaction zone, the final amount is 50 mol% or more.
Since the polymerization conversion rate is less than 0 mol %, preferably 65 to 85 mol %, it has high transparency and 3. lW/λ
It is possible to obtain a methacrylate-based copolymer with excellent properties such that In (where Mw is the weight molecular weight and 2, !11 is the number average molecular acid) is 2.1 or less, that is, the molecular weight distribution range is narrow.

Next, the present invention will be explained in more detail with reference to Examples. The average molecular weight distribution in each example was determined by gel filtration chromatography (GPC).

Example 1 A polymerization reactor having the structure shown in the drawings and a homogeneous core part of 6.4 tons and a plug flow part of 1.61 tons was used.
To 100 parts by weight of a monomer mixture consisting of 4.8% by weight of methyl isobutyrate, 0.0025 parts by weight of tert-butyl peroxide as a polymerization initiator and 0.21 parts by weight of n-octyl mercaptan as a chain transfer agent. was added at a rate of 2 tons per hour. This is evenly
After reacting at 145°C for 3.2 hours in the reciprocal core, the temperature was increased from 145°C to 190°C during 08 hours in the plug flow part.
The temperature was raised linearly in a °C trench to allow continuous polymerization. The consumption rate of the polymerization initiator in one homogeneous phase reaction section is 62
The amount of polymerization initiator remaining at the final point of Plugflo was approximately 1 mole. The obtained polymer, still containing unreacted monomers, was introduced into an extruder equipped with a flash vent, and the volatile components were separated and the polymer was continuously converted into a berent. When the system was operated continuously for 50 hours in this manner, both the polymerization reactor and the extruder could be operated stably, and a transparent and uncolored methyl methacrylate copolymer was obtained.

The final reaction rate was 78.0 molar, and the dimer content in the pellets was 2000 ppm.

Also, the weight average molecular weight (Mw) is 11.06 x 10
4. Number average molecular weight (Mn) is 5.8 x 10', M
w/Mn was 1.91.

Example 2 Using the same apparatus as in Example 1, 100 parts by weight of a monomer mixture consisting of 78.8% by weight of methyl methacrylate, 1.2% by weight of methyl acrylate and 20% by weight of methyl imbutyrate was added as a polymerization initiator. 0.0044 parts by weight of tert-butyl peroxide and 0.17 parts by weight of n-octyl mercaptan as a chain transfer agent were added, and this mixture was fed at a rate of 1.5 tons/hour. This was reacted at 145°C for 4.3 hours at the bottom of the homogeneous phase, and then the temperature was raised linearly from 145°C to 185°C in 1.1 hours in the plug flow part, and polymerization was continued for 50 hours. went. At this time, the consumption rate of the polymerization initiator at the bottom of the homogeneous phase was 69
The remaining amount of the initiator was 1 molar or less. In addition, the final reaction rate of the obtained polymer was 84 molar, and when it was pelletized, the dimer content in it was 1500.
It was ppm. In addition, the front W is 11.5 x 104, M
n was 5.8 x 10', and Mw/Mn was 1.98.

Example 3 Using the same apparatus as in Example 1, methyl methacrylate L/-door 8.8% by weight, methyl methacrylate 1.2% by weight,
0.19 parts by weight of n-octyl mercaptan as a chain transfer agent and tert-butyl peroxy (2-ethylhexanoate) as a low temperature active polymerization initiator to 100 parts by weight of a monomer mixture consisting of 20 parts by weight of )
0.0186 parts by weight of ditert-butyl peroxide as a high temperature active polymerization initiator were added and continuously fed.

After reacting at 95°C for 3.9 hours at the bottom of the homogeneous phase, the plug flow was heated from 95°C to 190'C for 1.9 hours.
The temperature was increased linearly for 0 hours to further polymerize. After 50 hours of continuous operation in this way, the reaction rate was 70.
A methyl methacrylate copolymer which was molar transparent and free from coloration was obtained. At this time, the consumption rate of the polymerization initiator at the bottom of the homogeneous phase was 67 moles, and the polymerization initiator content of the product taken out from the plug flow part was 1 mole. Moreover, when this material was pelletized, its dimer content was 800 ppm. In addition, Mw is 13.8
10', Mn? , OX 10 XMw/Mn is 1.
It was 97.

Comparative Example 1 Using the same equipment as in Example 1, methyl methacrylate 98
．． 0.0025 parts by weight of ditert-butyl peroxide as a polymerization initiator and 0.21 parts by weight of n-octyl mercaptan as a chain transfer agent were added to 100 parts by weight of a monomer mixture consisting of 5% by weight and 1.5% by weight of methyl acrylate. ,
This was delivered at a rate of 2 tons per hour. The polymerization conditions were the same as in Example 1, but after 4 hours of continuous operation, stirring became difficult and the operation had to be stopped.

Thus, if methyl isobutyrate is not added, the reaction will not proceed smoothly.

Comparative Example 2 The structure is similar to that of Example 1, but the homogeneous phase bottom is 2.
Using a device with a plug flow reaction section of 4 tons and a plug flow reaction section of: 61, 100 parts by weight of a seven-mer mixture consisting of 75.8% by weight of methyl methacrylate, 1,1% by weight of methyl acrylate and 23.1% by weight of methyl isobutyrate were added. 0.006 parts by weight of di-tert-butyl peroxide as a polymerization initiator and 0.16 parts by weight of n-octyl mercaptan as a chain transfer agent were added, and these were fed at a rate of 0.8 t/hour. In this case, the reaction was carried out continuously at 145° C. for 3 hours at the bottom of the homogeneous phase and at 145° C. to 180° C. for 2 hours at the plug flow reaction section. After continuous operation for 50 hours, the operation was stable and a copolymer was obtained with a reaction rate of 91 moles, but this product had an Mw/Mn of 2.15.
Therefore, the width of the molecular weight distribution became wide.

As described above, when a reactor in which the homogeneous phase reaction zone is 75% by volume is used, it is not possible to obtain a copolymer with a narrow molecular weight distribution.

[Brief explanation of the drawing]

The drawing is a schematic cross-sectional view of one example of a reactor used to carry out the method of the present invention. In the figure, numeral 1 is a homogeneous phase conversion section, 2 is a plug flow reaction section,
5 is a stirring blade, 6 is a screw, and 7 is a rotating shaft. Patent applicant: Asahi Kasei Industries Co., Ltd. Agent: Akira Agata

Claims (1)

[Scope of Claims] 1. In producing a methyl methacrylate copolymer containing at least 50 methyl methacrylate units by weight of 1 radical, 1 monomer component, 1 methyl methacrylate unit per monomer component.
A raw material mixture of methyl isobutyrate, polymerization initiator and chain transfer agent in a proportion of ~30% by weight is added to 75% to 90% of the total volume.
The mixture is fed to a homogeneous phase reaction zone of a two-stage polymerization reactor formed of a homogeneous phase reaction zone in which the mixture is stirred, the remainder being a plug flow reaction zone, where 50 to 80 molar fractions of radical polymerization initiator are After reacting until consumption, the remaining amount of the radical polymerization initiator is reacted in a plug flow reaction zone until it becomes less than 5 mol of the initial addition amount, and finally 50 mol of the raw material monomer component or more. A method for producing a methacrylate copolymer, which comprises polymerizing and converting less than 90 moles. 2. The method according to claim 1, wherein the radical polymerization initiator is a mixture of two types of polymerization initiators whose 10-hour half-life differs by 40° C. or more. 3. The plug flow reaction zone is stirred by a screw that does not have a stirring vector backward in the direction of movement of the contents.
The method according to claim 1 or 2, wherein