JPH0119402B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the production of acrylic polymers having terminal hydroxyl groups. Acrylic polymers having hydroxyl groups are widely used as coating resins because the hydroxyl groups can be crosslinked using a crosslinking agent such as an aminoplast resin or polyisocyanate. The so-called acrylic polyols traditionally used for this purpose are
For example, it is manufactured by copolymerizing an acrylic monomer having a hydroxyl group such as 2-hydroxyethyl acrylate. On the other hand, from the standpoint of saving resources and preventing pollution, there is a growing trend toward high-solid paints, and one method of achieving this is to lower the molecular weight of resins. In the case of the above-mentioned crosslinkable acrylic resin, when the molecular weight is lowered, the average number of crosslinkable monomers contained per molecule decreases accordingly, and the probability that a molecule does not contain a crosslinkable monomer increases, resulting in defects in the coating film. will occur. In addition, in the case of multi-component polymerization, due to the difference in the copolymerizability ratio of each monomer, the crosslinkable monomers in the polymer may be distributed, resulting in the formation of molecular chains that do not have crosslinkable functional groups, which may also cause coating film defects. It causes Therefore, there is a need for the development of a method that can reduce the molecular weight of a polymer and at the same time reliably introduce crosslinkable functional groups into each molecular chain. It is known that a polymer having a terminal hydroxyl group can be obtained by using hydrogen peroxide as a polymerization initiator in radical polymerization of monomers.
Examples of application to the polymerization of conjugated diene compounds such as butadiene can be found in JP-A-51-89589 and JP-A-50-86582. These methods use a commercially available aqueous hydrogen peroxide solution containing water, but it has been found that acrylic resins have various disadvantages. In other words, a dehydration process is necessary for polymerization, but as the polymerization progresses, the viscosity of the system increases and there is a risk of foaming, so dehydration is difficult, and the solvents that can be used are limited to those that are compatible with water. In addition, a gel appears due to extreme polymerization of monomers that are easily soluble in water due to the difference in polarity of the monomers. In order to overcome these disadvantages, the present invention relates to the use of hydrogen peroxide in the form of a solution of an acetate ester, for example an ethyl or butyl ester, as a polymerization initiator. The present invention involves using an acetate ester solution of hydrogen peroxide as a polymerization initiator when producing an acrylic polymer by polymerizing a mixture of acrylic monomers or a mixture of an acrylic monomer and other polymerizable monomers. This method of producing an acrylic polymer is characterized by introducing a hydroxyl group to the terminal end of the polymer produced simultaneously with polymerization. Acrylic monomers that can be used in the present invention include free acids of acrylic acid or methacrylic acid, alkyl esters such as methyl, ethyl, n-butyl, 2-ethylhexyl ester, hydroxyalkyl esters such as 2-hydroxyethyl,
Includes hydroxypropyl, hydroxybutyl esters, etc., tertiary aminoalkyl esters such as dimethylaminoethyl ester, amides and nitriles, and the like. Non-acrylic monomers include styrene and its derivatives such as α-methylstyrene, vinyltoluene, t-butylstyrene, α-olefins such as ethylene and propylene, dienes such as butadiene, isoprene, itaconic acid,
Crotonic acid, maleic acid, fumaric acid, allyl alcohol, methalyl alcohol, vinyl acetate, vinyl propionate, vinyl ether, divinylbenzene, diallyl phthalate, vinylpyridine,
Contains triallyl cyanurate, vinylidene chloride, vinylidene fluoride, etc. The monomer must contain at least one alkyl ester of acrylic acid or methacrylic acid. An acetate ester solution of hydrogen peroxide can be prepared by mixing a commercially available aqueous hydrogen peroxide solution, such as a 30% aqueous solution, and an acetate ester, such as butyl acetate, heating the mixture to the boiling point, and azeotropically removing water. The polymerization can be carried out in a conventional manner, except that an acetate solution of hydrogen peroxide is used as an initiator. It is desirable to add a cycloalkanone, such as cyclopentanone or cyclohexanone, to the reaction system. A portion of the cycloalkanone is oxidized by hydrogen peroxide to produce peroxide, which acts as a polymerization initiator for monomers, simultaneously consumes excess hydrogen peroxide, and also acts as a solvent for the polymer. In the present invention, the solvent for hydrogen peroxide must be acetic ester, but the solvent used as necessary to dilute the polymerization system is not limited to water-miscible solvents. For example, hydrocarbon, ester, alcohol, and ketone solvents can also be used. Further, a hydrogen peroxide acetate solution may be used in combination with other initiators. However, the mercaptan used as a chain transfer agent is oxidized in this system.
It causes a reduction reaction and is not effective. The resulting polymer has a hydroxyl group attached to the end, ie, the terminal carbon atom of the main carbon chain of the polymer, and has a number average molecular weight of about 700 to 7,000 and a weight average molecular weight of about 1,000 to 20,000. Even if these polymers have a low molecular weight, at least one hydroxyl group is reliably introduced into each molecule, so when crosslinked with an aminoplast resin or polyisocyanate compound, there will be no coating defects like in the past. It is particularly excellent as a resin for high solids paints. Other effects of the present invention are summarized as follows. 1. Foaming that occurs when water is included during polymerization can be prevented. 2. In the case of an aqueous solution system, the solvents that can be used are limited due to the difference in polarity between water and the solvent, but since it is an acetate ester solution, almost any solvent can be used as a polymerization solvent. 3. Since the molecular weight of hydrogen peroxide is small, the number of moles per unit weight is larger than that of other initiators, which is advantageous for lowering the molecular weight. 4. The polymerization rate is almost 100%, no dehydration step is required, and no harmful decomposition products are produced, so it can be used as is without purification. 6 Hydrogen peroxide in acetic acid solution is stable and can be stored for long periods of time. Examples of the present invention are shown below. Example 1 160 g of a 4.5% hydrogen peroxide/butyl acetate solution is charged into a 1-Kolben equipped with a stirrer, thermometer, nitrogen gas inlet tube, condenser, and dropping funnel, and the temperature is raised to 120°C. Styrene monomer 40g, n-butyl acrylate 14.32g, n-butyl methacrylate 317.88g,
A mixture of 27.8 g of 2-hydroxyethyl methacrylate and 200 g of a 4.5% hydrogen peroxide/butyl acetate solution were each added dropwise from a dropping funnel into a Kolben kept at 120 DEG C. over a period of 3 hours. 30 minutes after completion of dripping, add 40g of cyclohexanone to Kolben and leave for 1 hour and 30 minutes.
Hold at 120℃. Attach the decanter and
The temperature was maintained at 125° C. for 30 minutes to drive out a small amount of water generated during the reaction, and then the contents of the reactor were cooled, and the resulting polymer solution was taken out and its resin property values were investigated. The results are shown in Table 1. Example 2 A solution of an acrylic copolymer having the resin properties shown in Table 1 was obtained by repeating the same operation as in Example 1 except for changing the conditions below. Initial reaction charge 4.5% hydrogen peroxide/butyl acetate solution 160g Monomer mixture Methyl methacrylate 108g n-butyl acrylate 100g n-butyl methacrylate 100g 2-hydroxyethyl methacrylate 92g Initiator solution 4.5% hydrogen peroxide/butyl acetate Butyl acetate solution
200 g Post-added solution Cyclohexanone 40 g Example 3 The same operation as in Example 1 was repeated except for changing the conditions to obtain a solution of an acrylic copolymer having the resin properties shown in Table 1. Initial reaction charge 9.2% hydrogen peroxide/butyl acetate solution 80g Monomer mixture Styrene monomer 134.3g n-butyl acrylate 65.7g Initiator solution 9.2% hydrogen peroxide/butyl acetate solution
100 g Post-added solution Cyclohexanone 20 g Example 4 The same operation as in Example 1 was repeated except for changing the conditions to obtain a solution of an acrylic copolymer having the resin properties shown in Table 1. Initial reaction charge 9.2% hydrogen peroxide/butyl acetate solution 30g Monomer mixture Styrene monomer 201.5g n-butyl acrylate 98.5g Initiator solution 9.2% hydrogen peroxide/butyl acetate solution
37.5g Post-added solution Cyclohexanone 7.5g Example 5 The same operation as in Example 1 was repeated except for changing the conditions to obtain a solution of an acrylic copolymer having the resin properties shown in Table 1. Initial reaction filling: 12.0% hydrogen peroxide/butyl acetate solution 160g Monomer mixture Styrene monomer 40g Isobutyl methacrylate 305.6g 2-ethylhexyl methacrylate
17.6g 2-hydroxyethyl methacrylate 36.8g Initiator solution 12.0% hydrogen peroxide/butyl acetate solution
208 g Post-added solution Cyclohexanone 32 g Reference example The same operation as in Example 1 was repeated except for changing the conditions to obtain a solution of an acrylic copolymer having the resin properties shown in Table 1. Initial reaction charge 11.2% hydrogen peroxide/butyl acetate solution 80g Monomer mixture Styrene monomer 200g Initiator solution 11.2% hydrogen peroxide/butyl acetate solution
100g Post-filling solution Cyclohexanone 20g Comparative Example 1 340g of xylene is charged into a 1-kolben equipped with a stirrer, thermometer, nitrogen inlet tube, condenser, and dropping funnel, and the temperature is raised to 135°C. 40g of styrene monomer,
22.92g n-butyl acrylate, n methacrylate
- A mixed solution of 301.28 g of butyl, 27.8 g of 2-hydroxyethyl methacrylate, and 8 g of methacrylic acid, and an initiator solution of 20 g of tert-butyl peroxy 2-ethylhexanoate (Perbutyl-O manufactured by NOF Co., Ltd.) and 60 g of xylol, respectively. From the dropping funnel
Drop into a Kolben kept at 135℃ for 3 hours.
After completion of dropping, maintain temperature at 135°C for 1 hour and 30 minutes. Thereafter, the contents of the reactor were cooled and the resulting polymer solution was taken out and its resin properties were investigated. The results are shown in Table 1. Comparative Example 2 A solution of an acrylic copolymer having the resin properties shown in Table 1 was obtained by repeating the same operation as in Comparative Example 1 except for changing the conditions below. Reaction temperature 135℃ Initial reaction charge Xylol 340g Monomer mixture Styrene monomer 40g n-butyl acrylate 31.68g n-butyl methacrylate 264.72g 2-hydroxyethyl methacrylate 55.6g methacrylic acid 8g Initiator solution tert-butyl peroxy 2-ethylhexanoate 20g Xylol 60g Comparative Example 3 The same operation as Comparative Example 1 was repeated except for changing the conditions below. Reaction temperature 150°C Initial reaction charge Aromatic hydrocarbon solvent (Solbetsuso 100 manufactured by Etsuso) 170g Monomer mixture Styrene monomer 130.3g n-butyl acrylate 65.7g Methacrylic acid 4.0g Initiator solution Tertiary-butylperoxy-2-ethylhexanoate 14g Aromatic hydrocarbon solvent (Solbetsuso 100 manufactured by Etsuso) 30g Comparative example 4 The same operation as in Comparative Example 1 was repeated except for changing the conditions below. Reaction temperature 120℃ Reaction initial charge Butyl acetate 240g Monomer initiator mixture Methyl methacrylate 100g n-Butyl acrylate
100g n-butyl methacrylate
100g 2-hydroxyethyl methacrylate 92g Methacrylic acid 8g 2,2'azobisisobutyronitrile 16g Initiator solution Butyl acetate 160g 2,2'azobisisobutyronitrile
8g Comparative Example 5 The same operation as in Comparative Example 1 was repeated except for changing the conditions below. Reaction temperature 135℃ Initial reaction charge Aromatic hydrocarbon solvent (Solbetsuso 100 manufactured by Etsuso) 170g Monomer mixture n-butyl acrylate 116g 2-hydroxyethyl acrylate
80g Acrylic acid 4g Initiator solution Tertiary butyl peroxy 2-ethylhexanoate 18g Aromatic hydrocarbon solvent (Solbetsuso 100 manufactured by Etsuso) 30g Comparative example 6 (1) Stirrer, thermometer, nitrogen inlet tube, cooler , a decanter, and a 1-kolben equipped with a dropping funnel.
Charge 200g of butyl acetate and raise the temperature to 125℃. Styrene monomer 200g, 30% hydrogen peroxide solution 13.4
g was added dropwise from the dropping funnel into a Kolben kept at 125°C over 3 hours. The water in the reaction system was added dropwise while being removed using a decanter. 30 minutes after the end of dripping, add 30 minutes as a post-initiator.
During dropwise addition of 6.7 g of % hydrogen peroxide solution over 1 hour, foaming became intense and bumping occurred, so the reaction was stopped. (2) Pour 200 g of butyl acetate into a 1-kolben equipped with the same equipment as in (1) and raise the temperature to 95°C. Styrene monomer 200g, 30% hydrogen peroxide solution 13.4
g was added dropwise from a dropping funnel into a Kolben kept at 95°C over 3 hours. 30 minutes after the completion of dropping, add 30% hydrogen peroxide solution 6.7 as a post-initiator.
g was added dropwise over 1 hour. In order to remove the water in the reaction system, the temperature was raised to 125°C, and the reaction was stopped because foaming during dehydration became intense and bumping occurred.

[Table] Comparison of physical property values Using Example 1 and Comparative Examples 1 and 2, the physical property values of the coating films were compared. As a curing agent, butyl etherified melamine-formaldehyde resin (Yuban, manufactured by Mitsui Toatsu Chemical Co., Ltd.)
20SE−60) and conducted a test. Table 2 shows the tensilon measurement results of a clear coating film mixed with an acrylic resin/melamine resin ratio of 8/2 and baked at 140°C for 30 minutes. We also compared the physical properties of white coated plates that were baked at 140°C for 30 minutes with a P/V = 1/1, an acrylic resin/melamine resin ratio of 8/2, and a white pigment (rutile-type titanium oxide) dispersed in each resin. Summer. The results are shown in Table 2.

【table】

[Table] The varnishes produced in Example 2 and Comparative Example 4 were irradiated with ultraviolet rays and their colorability was compared. Put 60g of each sample into a quartz reaction container,
Light irradiation was performed for 4 hours using a photochemical reaction device equipped with a 300W high-pressure mercury lamp manufactured by Eikosha, and the number of colors was measured using APHA. The results are shown in Table 3.

[Table] Gel fraction measurement Gel fraction was measured using the varnishes produced in Example 3 and Comparative Example 3. Hexamethylene diisocyanate biuret (Desmodyur L-manufactured by Bayer) was used as a curing agent.
2291) was selected, 9.6 g of curing agent was mixed with 100 g of acrylic resin solution, and the gel fraction of the coating film was measured by baking at 100°C for 4 hours + 120°C for 12 hours. Extraction solvent: acetone, extraction temperature: acetone reflux temperature, extraction time: 3 hours

[Table] From the above results, the following facts are clear. By comparing Example 1 and Comparative Examples 1 and 2,
Polymers made in accordance with the present invention have approximately twice the hydroxyl number than polymers made with perbutyl-O using the same monomer composition, and with increased amounts of the polymer and 2HEMA. It has better pencil hardness, stain resistance, impact resistance, solvent resistance, acid resistance, and light resistance than polymers with similar hydroxyl values manufactured using the same method. In addition, when comparing the physical properties of clear coatings, Young's modulus is high,
It has excellent hardening properties (Table 2). Comparing Example 2 and Comparative Example 4, it was found that when 2,2'-azobisisobutyronitrile was used to obtain the same molecular weight, yellowing was more significant than when an acetate solution of hydrogen peroxide was used. This shows that (Table 3). A comparison of Example 3 and Comparative Example 3 shows that hydroxyl groups are introduced into the polymer obtained by using the hydrogen peroxide/acetate solution. This is also clear from the physical properties of the reference polystyrene, which clearly shows an absorption band for hydroxyl groups in its infrared absorption spectrum. Comparing Example 5 and Comparative Example 5, the molecular weight
In order to obtain a polymer with a molecular weight of 1000 or less, the conventional method requires a high reaction temperature of 155°C and the usable solvents are limited, but in the method of the present invention, the reaction temperature is only 120°C.
It has been shown that there are many solvents to choose from, and that it also saves thermal energy. Example 4 shows that the method of the present invention is applicable not only to the production of low molecular weight acrylic polymers but also to medium to high molecular weight acrylic polymers.

Claims (1)

[Claims] 1. In producing an acrylic polymer by polymerizing a mixture of acrylic monomers or a mixture of acrylic monomers and other polymerizable monomers,
A method for producing an acrylic polymer, characterized in that a hydroxyl group is introduced at the end of a polymer produced simultaneously with polymerization by using an acetate ester solution of hydrogen peroxide as a polymerization initiator. 2. The method according to claim 1, wherein a polymerized hecycloalkanone is further added. 3. The method of claim 1, wherein the acetate is selected from ethyl acetate and butyl acetate. 4 Weight average molecular weight having at least one hydroxyl group in the molecule bonded to the terminal carbon atom of the polymer main chain
1000 to 25000 liquid acrylic polymer.