JP2001172328A - Methacrylic polymer excellent in thermal stability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a methacrylic polymer which is excellent in thermal stability and exhibits satisfactory moldability when exposed to adverse molding conditions for achieving higher producibility. SOLUTION: In the methacrylic polymer which is obtained by the polymerization of a mixture of monomers comprising 90-100 mass % of methyl acrylate and 0-10 mass % of a 1-8C alkyl acrylate copolymerizable with the methyl acrylate, the rate of polymer end double bonds is so set as to be 5% or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a methacrylic polymer having excellent heat stability.

[0002]

2. Description of the Related Art Since methacrylic resins have excellent optical properties, weather resistance and high mechanical properties, they have recently been used in light guide plates and other parts such as automobile parts, lighting equipment and OA equipment parts. Widely used for various lenses. These parts and the like can be obtained by extrusion molding and injection molding of a methacrylic resin.
It is performed in the range of 0 to 280 ° C. However, the thermal decomposition reaction of the methacrylic resin tends to be remarkable when the temperature exceeds 250 ° C., and since the thermal decomposition temperature and the molding temperature are in the same range, the thermal decomposition of the polymer itself which is called a zipper reaction during the molding process is performed. Occurs, the monomer generated due to retention degradation remains in the molded product, and the heat resistance of the molded product is reduced,
Silver and the like are generated, and this is a factor that causes problems in molding processing, such as inviting poor appearance of the molded product and lowering the yield.

[0003] In order to solve the above-mentioned problems in the molding process and obtain a good molded product, it is desired to improve the thermal decomposition resistance of the methacrylic resin and improve the thermal stability.

As a technique for improving the thermal stability of a methacrylic resin, JP-A-10-87739 discloses a technique.
A method has been shown to increase the thermal stability of the polymer by increasing the number of mercaptan ends. In addition, there is known a method of suppressing thermal decomposition of a methacrylic resin by adding a small amount of a hindered phenol or a phosphorus-based antioxidant.

[0005]

However, in recent years, in response to the demand for higher productivity, high speed injection molding and long continuous operation in extrusion molding have been attempted. In order to reduce foreign substances or changes in fluidity due to polymer deterioration and to prevent the resin from deteriorating due to extrusion, development of a polymer having excellent thermal decomposition resistance has been increasingly demanded. The prior art described above cannot always sufficiently respond to such a request.

[0006] In addition, the method of adding an antioxidant may cause a decrease in transparency due to thermal coloring, and there is still room for improvement in this respect.

[0007] In view of the above circumstances, the present invention provides a methacrylic polymer having excellent heat stability and exhibiting good moldability even under severe molding conditions which realizes higher productivity than conventional ones. With the goal.

[0008]

It is known that a methacrylic resin depolymerizes from a polymer terminal at a high temperature and decomposes into a so-called zipper type. The present inventors have paid attention to this point, and as a result of investigating the polymerization conditions and the terminal structure of the molecule in detail, it has been clarified that the above decomposition reaction proceeds from a low temperature if a double bond is present at the molecular terminal, and completed the present invention. I let it.

The terminal double bond is quantified by the NMR method as described later. However, in the case of a polymer having a large molecular weight or a polymer having a small number of terminal double bonds, a quantification error increases. On the other hand, when a chain transfer agent such as mercaptan is used, an effect of suppressing the formation of a double bond due to the mercaptan residue bonding to the polymerization terminal can be expected. Since the quantification of sulfur contained in the mercaptan residue can be measured with high accuracy, the present inventors supplemented the region in which the amount of terminal double bonds, in which the quantification error increases in NMR, is small, with the quantification of sulfur. That is, the present invention was completed based on the understanding that the larger the amount of sulfur bonded to the polymer, the smaller the amount of terminal double bond.

That is, the present invention relates to a method for preparing 90 to 100% by mass of methyl methacrylate, which is an alkyl acrylate having 1 to 8 carbon atoms which is copolymerizable with methyl methacrylate.
A methacrylic polymer obtained by polymerizing a monomer mixture consisting of 10% by mass, wherein the ratio of polymer terminal double bonds is 5% or less. is there.

[0011] The present invention also relates to methyl methacrylate 90-
A monomer mixture comprising 100% by mass and 0 to 10% by mass of an alkyl acrylate having 1 to 8 carbon atoms copolymerizable with methyl methacrylate is used as a chain transfer agent in an alkyl mercaptan having 3 to 12 carbon atoms. A methacrylic polymer obtained by polymerization using a methacrylic polymer, wherein the amount of bound sulfur X (% by mass) in the polymer is in the range of the following formula (1): (Mass%) ≦ (X / 32) × Mn ≦ 100 (mass%) (1) (In the formula, Mn represents the number average molecular weight of the methacrylic polymer.)

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The ratio of polymer terminal double bonds in the methacrylic polymer of the present invention is preferably 5% or less, more preferably 3% or less. The term "polymer terminal double bond" refers to an unsaturated bond (terminal double bond) present at the molecular terminal of a polymer, and the ratio of the polymer terminal double bond in the present invention refers to the ratio of the double bond in a plurality of polymer molecules. It refers to the ratio of the number of terminal double bonds to the total number of terminal molecules. For example, if there are 50 polymer molecules having two molecular terminals, the total number of polymer molecular terminals becomes 100, and when 5 of the 100 molecular terminals are terminal double bonds, the polymer terminal double bond Is 5%. 5% polymer double bond ratio
By the following, sufficient thermal decomposition resistance can be obtained even in the forming process at around 280 ° C., and the forming process of a product free from defects such as silver at a high temperature becomes possible, and the forming process time can be shortened. . This will be described later in the Examples section.

In the present invention, the amount of bound sulfur in the polymer X
(% By mass) is preferably in the range of the following formula (1). 90 (% by mass) ≦ (X / 32) × Mn ≦ 100 (% by mass) (1) In the formula, Mn represents a number average molecular weight of the methacrylic polymer. “32” is the molecular weight of sulfur. (X / 3
2) When the value of × Mn is 100 (% by mass), it means that 100 sulfur atoms are bound per 100 polymer molecules when 100 polymer molecules are taken as an example. This means that a polymer molecule having two molecular ends is a polymer molecule 10
Of 0, 100 molecular terminals are S-terminals, 100 molecular terminals are H-terminals, and there are no terminal double bonds. The amount X of bound sulfur in the polymer can be measured by X-ray fluorescence analysis as described below.

The value of (X / 32) × Mn is more preferably 95 (% by mass) or more. In this case, the thermal stability of the polymer is further improved.

When the amount X of bound sulfur in the polymer is within the above range, the thermal decomposition resistance of the polymer is remarkably improved. When the amount X of bound sulfur in the polymer is less than 90%, sufficient thermal decomposition resistance may not be obtained, and it is particularly difficult to obtain a molded article having good appearance and the like under severe molding conditions. It may be.

As described above, the ratio of the double bond at the terminal of the polymer is set to 5% or less, and the amount X of bound sulfur in the polymer is 90 to 90%.
In order to achieve 100% by mass, it is necessary to adjust the amounts of the initiator and the chain transfer agent, and to carefully control the polymerization temperature and the polymerization time. In general, it is preferable that the amount of the initiator is small, the amount of the chain transfer agent is increased, and the polymerization is carried out at a low temperature for a long period of time. In the polymerization, there is a method using a catalyst composed of a metal complex as an initiator, but there is a disadvantage that a metal atom remains in the polymer and the resin is easily colored. Therefore, polymerization is preferably performed using various initiators that generate radicals by heat. For example, an azo compound such as 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), dimethyl 2,2′-azobisisobutyrate, or tert-butylperoxy Laurate, tert-butyl peroxyisobutyrate, tert-butyl peroxy 2-ethylhexanate, tert-butyl peroxy-3,5
An initiator such as an organic peroxide such as 5-trimethylhexanate can be preferably used.

The alkyl acrylate having 1 to 8 carbon atoms constituting the methacrylic polymer of the present invention includes:
Methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and the like can be given, and one kind or a combination of two or more kinds can be used. Of these, it is preferable to use one of methyl acrylate, ethyl acrylate and n-butyl acrylate.

In the present invention, the proportion of the alkyl acrylate having 1 to 8 carbon atoms in the methacrylic resin in the monomer is 0 to 10% by mass. From the viewpoints of heat resistance, chemical resistance, and fluidity of the methacrylic resin, it is preferable that the amount used is small. When the use amount of the above-mentioned alkyl acrylate is 0%, it means 100% of methyl methacrylate, that is, a homopolymer.

In the present invention, as the chain transfer agent, for example, an alkyl mercaptan can be used, and among them, an alkyl mercaptan having 3 to 12 carbon atoms is preferably used. Examples of such mercaptans include n-butyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, tert-dodecyl mercaptan, and the like. Mercaptans are preferred. 100% by mass of monomer
The lower limit of the amount of the chain transfer agent to be added is preferably 0.1.
05% by mass or more, more preferably 0.1% by mass or more,
Most preferably, it is at least 0.24% by mass. If the addition amount is too small, it may be difficult to sufficiently increase the amount of bound sulfur in the polymer, and it may be difficult to sufficiently reduce the ratio of the polymer terminal double bond. On the other hand, the upper limit of the amount of the chain transfer agent is preferably 1.0% by mass or less, more preferably 0.5% by mass or less. If the amount is too large, the molecular weight of the polymer may be too low to obtain sufficient strength.

GPC of methacrylic polymer according to the present invention
The number average molecular weight by (gel permeation chromatography) is preferably 30,000 to 100,000, more preferably 40,000 to 80,000. By setting such a range,
A molded product having sufficient strength can be obtained while maintaining good moldability.

The methacrylic polymer according to the present invention can be used in combination with other components such as a releasing agent, an antioxidant, an ultraviolet absorber, a dye and a pigment, if necessary. The method of addition may be any of a method of dissolving in a monomer pair before polymerization and polymerizing, or a method of blending with the obtained polymer and then pelletizing.

The method for producing the methacrylic resin of the present invention may be a known radical polymerization method, and is not particularly limited.
The reaction is carried out at 170 ° C., and as the method, a suspension polymerization method, a continuous bulk polymerization method, a solution polymerization method, or a back polymerization method is applied.

[0023]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples. In the Examples and Comparative Examples, “parts” means “parts by weight (parts by weight)” unless otherwise specified. The measurement and evaluation of various physical properties in the following Examples and Comparative Examples were measured and evaluated by the following methods.

(1) Measurement of Number Average Molecular Weight (Mn) of Polymer The resin was dissolved in acetone, reprecipitated in n-hexane, and dried under vacuum.
After dissolving at 1 ° C. for 1 hour, a liquid chromatography HLC-8020 manufactured by Tosoh Corporation was used, the separation column was two TSK-Gel GMHXL series, and the solvent was TH.
F (tetrahydrofuran), flow rate 1.0 ml / min, detector is a differential refractometer, measurement temperature 40 ° C., injection amount 0.1 m
1. Polymethacrylic resin was used as a standard polymer.

(2) Terminal Double Bond Amount (Polymer Terminal Double Bond) A 15 to 20% by mass deuterated dimethyl sulfoxide solution of a sample reprecipitated with n-hexane was prepared, and was collected by JEOL ( It was measured at the H nucleus using GSX400 type FT-NMR manufactured by Co., Ltd. In this case, the integration is performed for 12 hours or more, and the integrated intensity of the obtained terminal double bond (resonance frequency 5.5 ppm and 6.1 ppm) and the integrated intensity of the methoxy group of the methyl methacrylate main chain (resonance frequency 3.6 ppm) are obtained. Further, the ratio was determined from the equation (2) using the number average molecular weight determined from GPC.

[0026]

(Equation 1)

(3) Sulfur content in polymer Amount of residual monomer A sample was dissolved in acetone in advance, reprecipitated with n-hexane, and vacuum dried at 60 ° C for 24 hours. The dried sample was molded under high pressure at room temperature, and the concentration of sulfur contained in the polymer was measured by a measurement using a system 3080E2 type fluorescent X-ray analyzer manufactured by Rigaku Denki Kogyo KK.

(4) Amount of residual monomer After the sample was dissolved in acetone, gas chromatography HP-6890 manufactured by Hewlett-Packard Company was used, the separation column was HP-Wax (0.25 mm diameter x 30 m length), and the measurement temperature was Quantification was performed at 40 ° C. using a detector FID and methyl isobutyl ketone as an internal standard.

(5) Measurement of thermal stability Using an injection molding machine 125 / 75MS (manufactured by Mitsubishi Heavy Industries, Ltd.), a spiral mold was attached, and a nozzle temperature of 240
℃, 260 ℃, 280 ℃, 300 ℃, mold temperature 60 ℃,
Injection molding was carried out under the conditions of a molding cycle of 55 seconds, the appearance of the obtained molded product (e.g., generation of silver and foaming) and the amount of remaining monomer were determined, and the amount of the monomer in the molded product was increased. It was compared with the residual monomer in the inside.

Example 1 Production of Copolymer (b-1) 1,1-bis (t-butylperoxy) was added to 100 parts of a monomer mixture of 98% of methyl methacrylate and 2% of methyl acrylate. 3,3,5-trimethylcyclohexane 0.0
05 parts, n-octyl mercaptan 0.25 parts and stearyl alcohol 0.10 parts were continuously supplied to the polymerization reactor, and polymerization was carried out at a polymerization temperature of 130 ° C. and a kettle residence time of 5 hours.
The polymerization rate was 40% by mass. The polymerization liquid was taken out of the polymerization reactor, and after devolatilizing the unpolymerized raw material with a devolatilizing extruder, the pellets were formed. After evaluation by the above-mentioned method, the residual monomer in the pellets was 0.14%. Average molecular weight (M
n) is 57500, the ratio of polymer terminal double bonds is 2%,
Further, the sulfur content in the polymer was 0.055%, the value represented by the formula (1) was 99, and the result of thermal stability measurement was as follows:
The increase in monomer in the molded product at 240 ° C was 0.1%, 0.22% at 260 ° C, 0.38% at 280 ° C, and 0.76% at 300 ° C. Furthermore, there was no defect in appearance at each molding temperature in 10 shots, and the appearance was good.

Example 2 Production of copolymer (b-2) 2,100'-azobisisobutyronitrile was added to 100 parts of a monomer mixture of 98% of methyl methacrylate and 2% of methyl acrylate. .10 parts, n-octyl mercaptan 0.2
6 parts, a monomer mixture consisting of 0.15 parts of stearyl alcohol, 0.3 part of a suspension stabilizer and 250 parts of distilled water are charged into a polymerization reactor, polymerized at 70 ° C., and an exothermic peak is obtained after about 3 hours. Polymerized in profile. After completion of the polymerization, a beaded polymer was obtained through cooling, filtration, washing and drying. Further, after pelletizing with an extruder, evaluation was made by the above-mentioned method. As a result, the residual monomer in the pellet was 0.16%, the number average molecular weight (Mn) was 58500, and the ratio of polymer terminal double bonds was 4. 8% and the sulfur content in the polymer is 0.05%
3%, the value represented by the formula (1) was 97, and as a result of thermal stability measurement, the monomer increase of the molded article at 240 ° C. was 0.1%, 260
0.25% at ℃, 0.55% at 280 ° C, 300 ° C
Was 0.99%. Furthermore, there was no defect in appearance at each molding temperature in 10 shots, and the appearance was good.

Comparative Example 1 The procedure of Example 1 was repeated, except that the polymerization temperature was changed from 130 ° C. to 170 ° C., and the amounts of the polymerization initiator and mercaptan were modified so as to obtain the same molecular weight as in Example 1. Was polymerized with a methacrylic resin. As a result of evaluating the obtained polymer by the method described above, the residual monomer in the pellet was 0.29%, and the number average molecular weight (M
n) is 57600, the ratio of polymer terminal double bonds is 6%,
Further, the sulfur content in the polymer was 0.043%, the value represented by the formula (1) was 77, and the thermal stability measurement showed that:
The increase in monomer in the 240 ° C molded article was 0.19%, 0.41% at 260 ° C, 0.82% at 280 ° C, and 1.50% at 300 ° C. Further, as a defect in appearance at each molding temperature, foaming of 6 sheets was observed in 10 shots at 300 ° C.

Comparative Example 2 In Example 1, the polymerization temperature was changed from 130 ° C. to 105 ° C., and 30 parts of toluene was added to perform solution polymerization. The amounts of the polymerization initiator and mercaptan were adjusted to the same molecular weight as in Example 1. Example 1 except for correction
The methacrylic resin was polymerized in the same manner as in the above. As a result of evaluating the obtained polymer by the above-mentioned method, the residual monomer in the pellet was 0.31%, and the number average molecular weight (Mn) was 5820.
0, the ratio of polymer terminal double bonds was 16%, the sulfur content in the polymer was 0.029%, the value represented by the formula (1) was 53, and the thermal stability was measured. 0.12% increase in monomer of product, 0.33% at 260 ° C, 2%
It was 0.70% at 80 ° C and 1.49% at 300 ° C. Further, the appearance defect at each molding temperature was such that three foams were observed in 10 shots at 300 ° C.

[0034]

As described above, the methacrylic polymer of the present invention has excellent thermal stability because the ratio of the polymer terminal double bond and the amount X of the bonded sulfur in the polymer are within the appropriate ranges. In addition, defects (silver generation, foaming, etc.) during molding can be effectively prevented. For this reason, it is very useful for solving the problems in molding automotive parts, lighting equipment, louvers, lenses and optical parts that require long-time heating and stagnation, and lowering the incidence of product defects.

Claims (3)

[Claims] 1. 90 to 100% by weight of methyl methacrylate
And 1 to 8 carbon atoms copolymerizable with methyl methacrylate
A methacrylic polymer obtained by polymerizing a monomer mixture comprising 0 to 10% by mass of an acrylic acid alkyl ester, wherein the ratio of polymer terminal double bonds is 5% or less. Methacrylic polymer. 2. Methyl methacrylate 90 to 100% by mass
And 1 to 8 carbon atoms copolymerizable with methyl methacrylate
A methacrylic polymer obtained by polymerizing a monomer mixture comprising 0 to 10% by mass of an acrylic acid alkyl ester with an alkyl mercaptan having 3 to 12 carbon atoms as a chain transfer agent. Characterized in that the amount X (% by mass) of the bonded sulfur of the above is in the range of the following formula (1). 90 (% by mass) ≦ (X / 32) × Mn ≦ 100 (% by mass) (1) (In the formula, Mn represents the number average molecular weight of the methacrylic polymer.) 3. The methacrylic polymer according to claim 2, wherein the ratio of the polymer terminal double bond is 5% or less.