JPH04356501A - Production of copolymer excellent in heat resistance - Google Patents

Abstract

PURPOSE:To obtain a copolymer having a low residual monomer content, a high heat distortion temperature, and improved heat decomposition resistance by heating a specific methyl methacrylate/maleic anhydride/styrene copolymer to remove volatile matters therefrom. CONSTITUTION:A monomer mixture consisting of (A) methyl methacrylate, (B) a 1-4C alkyl acrylate, (C) maleic anhydride, and (D) styrene is polymerized by bulk polymerization in the presence of a polymerization initiator and a chain transfer agent at 50-150 deg.C thereby to obtain a copolymer having a molecular structure made up units A to D respectively shown by formulae I to IV and bonded together in a random sequence. This copolymer is degassed and volatile matters are removed therefrom by passing it through the first polymerization zone at 40-80 deg.C, followed by the second polymerization zone at 10-130 deg.C and a cooling zone. Thus, a copolymer is obtained which has a unit A content of 41-97.5mol%, unit B content of 0-5mol%, unit C content of 1-26mol%, and unit D content of 1.5-58mol%, with the C/D molar ratio being 1/(1-5), and which has a molecular weight (as measured by gel permeation chromatography) of 80,000-250,000, a thermal decomposition index of 7 or less, and a residual monomer C content of 0.1wt.% or less.

Description

[Detailed description of the invention]

0001

[Field of Industrial Use] The present invention relates to a method for producing a copolymer having excellent heat resistance, and more specifically to a method for producing a copolymer having excellent heat deformation resistance, heat decomposition resistance, and water whitening resistance, which is extremely practical. This invention relates to a method for producing resin.

0002

[Prior Art] Generally, polymethyl methacrylate or a resin containing methyl methacrylate as a main component has transparency,
Due to its excellent properties such as surface gloss, mechanical strength, and moldability,
It is used in a wide range of fields such as automobile parts, electrical parts, and displays. However, its heat deformation resistance is not necessarily sufficient, and its use is limited in applications where shape stability at high temperatures is required.

[0003] Therefore, research has been widely conducted to improve the heat deformation resistance of methyl methacrylate resins, and several reports and proposals have been made. BACKGROUND ART Conventionally, methods for producing copolymers made of aromatic vinyl monomers, maleic anhydride, and other vinyl monomers have been known. (Tokuko Showa 40-15
No. 829, JP-A-55-102614, US Pat. No. 3,336,267, French Patent No. 147
6215 specification) However, although a polymer copolymerized with maleic anhydride has a high heat distortion temperature, it is of course resistant to water at high temperatures due to the presence of maleic anhydride monomer. It also undergoes chemical changes when exposed to heat and is easily decomposed. Therefore, injection molding or extrusion molding is severely restricted, and appearance defects such as silver streaks due to thermal decomposition occur, increasing the defective rate of the product. Furthermore, when the product is brought into contact with water or steam or exposed to high temperatures, there is a drawback that the product appearance may become white. Furthermore, a method has been proposed in which α-methylstyrene is further used in addition to methyl methacrylate, styrene, and maleic anhydride to improve heat deformation resistance. (Unexamined Japanese Patent Publication No. 5
6-81322)

0004

[Problems to be Solved by the Invention] The present invention provides a copolymer consisting of methyl methacrylate, styrene, and maleic anhydride that has a particularly high heat distortion temperature and significantly improved heat decomposition resistance without using such other components. The purpose is to produce polymers.

[0005]

[Means for Solving the Problems] The present inventor has conducted bulk polymerization using a specific initiator and chain transfer agent within a specific monomer composition range, and then thermally devolatilized the remaining monomer. It has been found that it is possible to obtain a methyl methacrylate-based resin that has a low heat deformation temperature, a high heat deformation temperature, and a markedly improved thermal decomposition property.

That is, the present invention provides a methyl methacrylate unit (MMA) represented by the following chemical formula (1),

000
7]

[C5]

[0008] Alkyl acrylate unit (RA) represented by the following chemical formula (2),

[0009]

[C6]

Maleic anhydride unit (MAH) represented by the following chemical formula (3),

[0011]

[C7]

[0012] Styrene unit (ST) represented by the following chemical formula (4)

[0013]

[Chemical formula 8]

After producing a copolymer having a molecular structure in which the following are irregularly arranged and bonded by bulk polymerization, 41 to 97.5 mol% of methyl methacrylate is produced by heating and devolatilizing the copolymer.
, 0 to 5 mol% of alkyl acrylate having 1 to 4 carbon atoms,
Maleic anhydride 1-26 mol% and styrene 1.5-5
8 mol%, and the ratio of styrene to maleic anhydride has a molar ratio of 1:1 to 1:5, and the molecular weight measured by gel permeation chromatography (GPC) is 8.
This is a method for producing a copolymer having a thermal decomposition index α of 7 or less and a residual amount of maleic anhydride monomer in the polymer of 0.1 or less.

Generally, polymethacrylate is a transparent resin that has particularly excellent weather resistance. However, one or two other copolymer components are added to increase the heat deformation resistance, which is the drawback of this method.
Generally, a method of introducing a combination of more than one species is carried out,
In order to obtain satisfactory heat deformation resistance, it was impossible to avoid the disadvantage that the excellent properties of polymethyl methacrylate would be impaired. Therefore, when introducing other copolymer components such as maleic anhydride and styrene, the amount thereof is severely limited, and sufficient improvement effects cannot be obtained.

In the present invention, in such a methyl methacrylate resin, particularly for a copolymer containing maleic anhydride and styrene as copolymerization components, maleic anhydride and styrene are selected within a specific molar range, and the copolymerization By configuring the components in proportions within a specific range, it retains the excellent properties of polymethyl methacrylate and also has significantly improved heat deformation resistance.

The resin of the present invention comprises methyl methacrylate 4
1 to 97.5 mol%, C1 to 4 alkyl acrylate 0 to 5 mol%, maleic anhydride 1 to 26 mol%, preferably 12 to 22 mol%, and styrene 1.5 to 58 mol%. It is a copolymer consisting of If the amount of the component deviates from this range, the improvement effect of the present invention cannot be obtained. In the above structure, it is extremely important that the molar ratio of maleic anhydride to styrene is in the range of 1:1.5 to 1:5, and even if it deviates from this range, the object of the present invention will not be achieved. If the ratio of styrene to maleic anhydride is less than the above range, the effect of improving heat deformation resistance will be insufficient, and if it exceeds the ratio, physical properties, especially mechanical strength such as tensile strength, will deteriorate, which is not preferred. A particularly preferred ratio of styrene to maleic anhydride is 2 to 3 moles.

Under these conditions of introduction of maleic anhydride and styrene, if the methyl methacrylate content is less than 41 mol%, the mechanical strength will be low, and if it exceeds 97.5 mol%, high heat deformation resistance will not be obtained. . Preferably 41-70
It is mole%. Alkyl acrylate is 0 to 5 mol%
It is preferable to use it, and the heat decomposition resistance can be improved by using it. If it exceeds 5 mol %, the heat deformation resistance decreases, which is not preferable. As the alkyl acrylate, methyl acrylate, ethyl acrylate, butyl acrylate, etc. can be used. Alkyl acrylate may be added if necessary, and when added, it is required in an amount of 0.5 to 5 mol%, preferably 1 to 5 mol%. If it is less than 0.5 mol%, there will be no effect. When the maleic anhydride content is less than 1 mol% or the styrene content is less than 1.5 mol%, the effect of improving heat deformation resistance is small, and when the maleic anhydride content exceeds 26 mol%, the mechanical strength becomes low.
The strength of the resin also decreases when styrene exceeds 58 mol%. Preferably, maleic anhydride is 12-22 mol% and styrene is 18-40 mol%.

Furthermore, in the present invention, it is important that the amount of monomer remaining in such a copolymer is 1.5% by weight or less, preferably 1.0% by weight or less. If this amount exceeds 1.5% by weight, it is not preferable because its plasticizing effect lowers heat deformation resistance and causes problems such as a significant deterioration of appearance due to foaming caused by volatile matter during heat processing.

[0020] In particular, the amount of residual maleic anhydride must be 0.1% by weight or less, because if a large amount of maleic anhydride remains, it will affect the thermal decomposition of the polymer, causing the polymer to take on a yellow color. It is necessary to reduce this as much as possible. The thermal decomposition index α of the copolymer needs to be 7 or less; if it exceeds 7, silver etc. will be generated during injection molding, which is not preferable. When the amount of residual maleic anhydride in the copolymer exceeds 0.1% by weight, the thermal decomposition index is 7.
Exceeding, and the molar ratio of maleic anhydride and styrene,
It is difficult to reduce the thermal decomposition index to 7 or less unless the type and amount of the initiator and the type of chain transfer agent are specified.

The molecular weight of the copolymer of the present invention must be 80,000 to 250,000 as measured by GPC. If the molecular weight is less than 80,000, mechanical properties such as tensile strength are significantly reduced, which is not preferable. Moreover, if it exceeds 250,000, the viscosity during melting becomes high and injection molding becomes difficult, which is not preferable. In the method for producing the copolymer of the present invention, bulk polymerization using a radical initiator is suitable for polymerization. In the copolymerization, the initiators used are, for example, azobisisobutyronitrile, 2,2'-azobis(2,4-
Azo initiators such as dimethylvaleronitrile), peroxides such as benzoyl peroxide, and t-butylperoxy 2-ethylhexanoate can be used. In particular, it is preferable to use lauroyl peroxide or decanoyl peroxide because they have excellent transparency and hot water whitening resistance.

As the chain transfer agent used, alkyl mercaptans such as butyl mercaptan and octyl mercaptan can be used. Next, in order to reduce the residual amount of maleic anhydride in the copolymer, it is very important that the molar ratio of styrene to maleic anhydride is in the range of 1:1 to 1:5. The amount of maleic anhydride remaining in the copolymer is reduced to 0.0 by removing volatile components from the copolymer polymerized in such a state using a vented extruder or the like.
It became possible to reduce the amount to 1% by weight or less.

However, according to the conventional methods, it is difficult to reduce the residual amount of maleic anhydride. For example, according to the method of Example 1 disclosed in French Patent No. 1,476,215, the residual amount of maleic anhydride in the copolymer obtained is 0.2% by weight, and the object of the present invention cannot be achieved. A particularly preferred method for producing the resin of the present invention is to form the resin using two endless belts made of surface-treated steel that run opposite each other and a pair of continuous soft vinyl chloride gaskets that run at the same speed on both sides of the belts. A space was formed, the thickness of the resulting cast polymer was made constant, and the degassed partial polymer of the above constituent monomers was continuously injected and passed through the first polymerization zone at 40°C to 80°C. After, 11
A colorless and transparent plate can be obtained by passing through a second polymerization zone and an annealing zone at temperatures of 0°C to 130°C. This plate is pulverized and pellets are obtained while removing volatile components using a vented extruder.

In order to obtain a copolymer with a small residual amount of maleic anhydride in this production method, it is very important that the molar ratio of styrene to maleic anhydride is in the range of 1:1 to 1:5. However, if the molar ratio is lower than 1:1, a transparent plate with a low residual amount of maleic anhydride cannot be obtained. In addition, when the plate is crushed and the volatile matter is removed using a vented extruder, if the amount of maleic anhydride remaining in the transparent plate is 0.5% by weight or more, the resulting pellets will be colored yellow. However, it cannot be put to practical use.

Another preferred method of production is continuous bulk polymerization. 30% by weight to 7% in the first reactor where the homogeneous polymerization reaction is carried out at a constant temperature in the range of 50°C to 150°C.
Polymerization is carried out to a polymerization rate of 0% by weight, and then the polymerization rate is further increased to 10% to 30% by weight in a second reactor consisting of a flow reactor.
the second reactor by increasing the weight percent and ensuring that the molar ratio of styrene to maleic anhydride in the copolymer chain obtained in the process for obtaining the polymer is in the range of 1:1 to 1:5. After reacting so that the concentration ratio of maleic anhydride in the volatile components of the monomers remaining in the resulting polymer mixture becomes 2.5% by weight or less, maleic anhydride is removed by sending it to a degassing step. A polymer having an acid concentration of 0.1% by weight or less can be obtained. If the molar ratio of styrene to maleic anhydride is 1:1 or less, it is difficult to reduce the ratio of maleic anhydride to 2.5% by weight or less in the polymerization mixture sent to the degassing step. In such cases, the resulting pellets are markedly yellow and cannot be put to practical use.

The resin of the present invention may contain a small amount of a copolymerizable monomer such as acrylonitrile or a crosslinking agent such as divinylbenzene, or may contain colorants, stabilizers, plasticizers, etc. during its production. They may be used in combination to the extent that the effects of the present invention are not impaired.

[0027]

[Example] Composition analysis of copolymer a) Analysis by infrared absorption spectrum -C=O absorption attributed to MMA unit, 1710 cm-
1. Attributed to MAH unit

[0028]

[Chemical formula 9]

Absorption of 1760 cm −1 , assigned to ST units

[0030]

[Chemical formula 10]

The copolymer composition was analyzed using absorption at 690 cm-1. b) Analysis of MAH units by acid value quantitative analysis MAH units were analyzed using the acid value quantitative method applied in oil and fat analysis. 1 g of polymer was dissolved in 50 cc of acetone, and titrated using a normal solution prepared by dissolving KOH in a mixture of acetone/methanol at a weight ratio of 1/1. Since the obtained MAH value was in good agreement with the above method a), the values of method a) are shown in the examples. c) Molecular Weight Measurement by GPC Molecular weight measurement by GPC is generally carried out as described in the literature "Gel Chromatography (Basic Edition)" (written by Takeda et al., published by Kodansha, pp. 97-122).

For example, the molecular weight of the copolymer of the present invention was measured as follows. HSG-20,5 as column
0 (manufactured by Shimadzu Corporation) and a standard polystyrene manufactured by Pressure Chemical Co., Ltd. to prepare a calibration curve. The elution curve obtained using a sample solution in which 75 mg of the copolymer was dissolved in 30 ml of methyl ethyl ketone was divided into equal parts, the height of the curve at the dividing points was measured, and the weight average molecular weight Mw was determined by the following formula. The carrier solvent used was methyl ethyl ketone at a flow rate of 1 to 1.5 ml/mi.
n, measurements are taken at 30°C.

[0033]

[Math 1]

where Hi is the height of the elution curve at dividing point i, Mi(p) is the molecular weight of standard polystyrene at dividing point i, and QM and QP are the Q factors of the copolymer and polystyrene, which are 40 and 41, respectively. be. d) Measurement of thermal decomposition index α Pyrolysis gas chromatography (DY-I manufactured by Shimadzu Corporation)
A, G (6A)), the copolymer was heated to 450°C with N2
The detection and integration of all the decomposed gases decomposed and generated in 60 minutes after decomposition in the atmosphere is set as x, the detection and integration of the gases decomposed and generated in 30 minutes at 290°C is set as y, and the thermal decomposition index α=y/ α was calculated as x×100. e) Pyrolysis weight loss measurement method Dai-ni Seikosha, differential thermogravimetry simultaneous measurement device (SSC/5
60GH). Sample 40-45mg
After preheating at 150° C. for 10 minutes under N2 atmosphere, measurements at the experimental temperature were started.

[0035] The invention will be specifically explained below with reference to Examples. The heat deformation resistance was evaluated by measuring HDT as defined in ASTM-D648. (No heat treatment)
The residual monomer was measured by a conventional GC method. Melt index is ASTM-D1238 (
The bending strength was measured according to the AST
Measured according to M-D790.

[0036]

[Example 1] Using a device in which the molding space was formed by two Teflon-coated endless belts running oppositely and a pair of continuous soft vinyl chloride gaskets running at the same speed on both sides of the belt, a heavy Obtained union. Raw materials: 90% methyl methacrylate, 5% styrene,
A monomer consisting of 5% by weight of maleic anhydride and a monomer of 10% by weight
A monomer mixture consisting of 0.3 parts by weight of lauryl peroxide and 0.12 parts by weight of octyl mercaptan was put into a prepolymerization tank equipped with a stirrer and degassed for 15 minutes at a temperature of 20 to 30°C. The mixture was reacted at 45° C. for about 10 hours to obtain a prepolymer with a polymerization rate of 30%. This prepolymer was injected into the above-mentioned molding space adjusted to a plate thickness of 4 mm to obtain a continuous transparent plate.

The obtained sheet-like resin is pulverized with a cutter mill, and then extruded into pellets through a strand die using a 30 mm twin-screw extruder with a vent at a vent part of 150 Torr and a resin temperature of 250°C. The pellets thus obtained can be molded in a 3-ounce injection molding machine in the same way as a normal methacrylic resin molding material (Delpet 80N manufactured by Asahi Kasei K.K.), and the physical properties were measured using the obtained physical property test piece. do.

The monomers remaining in the pellets include 0.15% by weight of MMA, 0.01% by weight of MAH or less, and 0.01% by weight of ST.
01% by weight or less, the molecular weight measured by gel permeation chromatography is 150,000, and the thermal decomposition index α
is 3.3 and HDT is 98°C.

[0039]

[Examples 2 to 8 and Comparative Examples 1 to 5] Using the same equipment and conditions as in Example 7, polymerization was carried out with various compositions, and the results shown in Tables 1 and 2 were obtained.

[0040]

[Comparative Example 6] In a container equipped with a stirrer, 75 parts of methyl methacrylate (MMA) and 10 parts of maleic anhydride (MAH)
and 15 parts of styrene (ST) were mixed so that the total amount was 200 g, and to this was added 0.6 g of benzoyl peroxide.
, 0.6 g of lauryl mercaptan was added and dissolved to prepare a monomer blend solution.

Separately, the outer edges of two glass plates measuring 250 x 300 mm and 6 mm in thickness were covered with a flexible vinyl chloride gasket, and the distance between the two glass plates was 3.5 mm. The cell is assembled and prepared in such a manner that the cell is immediately poured into the prepared glass cell to fill it. Then, it was kept in a heated water tank with a temperature of 50 to 60°C for 18 hours.
After that, it was kept in a hot air circulation oven whose temperature was controlled at 105 to 110°C for 3 hours, and then left to cool indoors, and the glass plate was removed to obtain a sheet-shaped resin.

The obtained sheet-like resin is pulverized with a cutter mill and extruded into pellets through a strand die using a 30 mm twin-screw extruder with a vent at a vent part of 150 Torr and a resin temperature of 250°C. The pellets thus obtained can be molded in a 3-ounce injection molding machine in the same way as a normal methacrylic resin molding material (Delpet 80N manufactured by Asahi Kasei K.K.), and the physical properties were measured using the obtained physical property test piece. do.

The monomers remaining in the pellet are 0.35% by weight of MMA, 0.2% by weight of MAH, and 0.1% by weight of ST, the molecular weight measured by gel permeation chromatography is 100,000, and the thermal decomposition index is α. is 8.0, H
DT is 90°C.

[Table 1]

[Table 2]

According to the method of the present invention, a methacrylate resin can be obtained which has a small amount of residual monomer, a high heat deformation temperature, and a markedly improved thermal decomposition property.

Claims (1)

[Claims] [Claim 1] Methyl methacrylate unit (MMA) represented by the following chemical formula (1), [Chemical 1] Alkyl acrylate unit (RA) represented by the following chemical formula (2), [Chemical 2] Represented by the following chemical formula (3) maleic anhydride unit (MA
H), [Chemical 3] A copolymer having a molecular structure in which styrene units (ST) [Chemical 4] shown by the following chemical formula (4) are arranged and bonded in an irregular manner is produced by bulk polymerization, and then heated and devolatilized. By this, methyl methacrylate 41-97.5 mol%, carbon number 1-
4, alkyl acrylate 0 to 5 mol%, maleic anhydride 1 to 26 mol%, and styrene 1.5 to 58 mol%, and the ratio of styrene to maleic anhydride is 1:1 to 1.
:5, the molecular weight measured by gel permeation chromatography is 80,000 to 250,000, the thermal decomposition index α is 7 or less, and the remaining amount of maleic anhydride monomer in the polymer is 0.1% by weight. A method of producing a copolymer that is: