JPH05132521A - Production of acrylic polymer - Google Patents

Abstract

PURPOSE:To obtain a high-molecular acrylic polymer having excellent heat resistance through the solution polymerization of a (meth)acrylic ester by adding an organic mercapto compound immediately before the completion of the reaction. CONSTITUTION:A (meth)acrylic ester (e.g., ethyl acrylate) is polymerized by solution polymerization conducted, for example, in the presence of a polymerization initiator using methyl ethyl ketone as a reaction medium at about 50-70 deg.C. Immediately before the completion of the reaction, an organic mercapto compound (e.g. butyl mercaptan) is added. Compared with the polymer obtained by a process in which the mercapto compound is added at the beginning of the polymerization reaction, the acrylic polymer obtained by this process has better heat resistance and a higher mol.wt., even though the two polymers have almost the same bonded mercapto compound content. In addition, the excellent transmitting properties inherent in acrylic polymers are not substantially impaired.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing an acrylic polymer. More specifically, it relates to a method for producing a high molecular weight acrylic polymer having excellent heat resistance.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication (Kokai) No. 55-5950 discloses a method of obtaining a methacrylic resin by carrying out a polymerization reaction using a mercaptan as a chain transfer agent, but for the purpose of improving heat resistance. However, if a large amount of mercaptans is added from the start of the polymerization reaction, only a low molecular weight polymer can be obtained. Therefore, in order to obtain a high-molecular weight polymer, it is necessary to reduce the amount of mercaptans added. However, in this case not only sufficient heat resistance is not obtained, but especially when the side chain has a crosslinking site. Has a problem that gelation occurs.

Similarly, when producing an acrylic elastomer having a crosslinkable group in its side chain by a solution polymerization method, it has been proposed by the present applicant to add a mercapto chain transfer agent from the beginning of the polymerization reaction. (Japanese Patent Laid-Open No. 63-2101
No. 13), the acrylic elastomer obtained in this case is excellent in vulcanization physical properties and transparency, but is still insufficient in heat resistance.

Further, Japanese Patent Publication No. 38-14491 and Japanese Patent Laid-Open No. 50-1
44745 discloses a method of adding mercaptans to a methacrylic resin with a blender or the like to improve thermal stability, but increasing the number of steps, increasing the chances of contamination with foreign substances, and complicating work, etc. There are some difficulties.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing an acrylic polymer having a high heat resistance and a high molecular weight by modifying the polymer itself.

[0006]

The object of the present invention is as follows.
This can be achieved by adding an organic mercapto compound immediately before the termination of the polymerization reaction during the solution polymerization of an acrylic acid ester or a methacrylic acid ester to produce an acrylic polymer.

Examples of the acrylic acid ester or methacrylic acid ester used for the polymerization reaction include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, dicyclopentenyl acrylate,
One or more of dicyclopentenyloxyethyl acrylate, ethylene glycol diacrylate, propylene glycol diacrylate, polyethylene glycol diacrylate or their corresponding methacrylates are used, and when two or more are used, they are generally used. Alkyl (meth) acrylate as the main component,
Other (meth) acrylates are used in the form of copolymerization therewith. Furthermore, other vinyl compounds having copolymerizability with these can be copolymerized.

The polymerization reaction is carried out at about 50 to 70 ° C. by the solution polymerization method in the presence of a polymerization initiator. As the reaction solvent, methyl ethyl ketone, acetone, acetonitrile,
Chloroform, toluene and the like are generally used. Immediately before the termination of this polymerization reaction, specifically, the number average molecular weight of the polymer produced in the polymerization solution is measured in advance, and the process of the change is monitored by the stirring torque of the polymerization solution, that is, the torque value. The relationship between the number average molecular weight and the number average molecular weight is obtained in advance, and when the torque corresponding to the desired number average molecular weight is reached during the polymerization reaction, the organic mercapto compound is added,
By continuing stirring for about 1 to 30 minutes, the organic mercapto compound is bonded to the produced polymer.

As the organic mercapto compound, for example, butyl mercaptan, octyl mercaptan, dodecyl mercaptan, lauryl mercaptan, mercaptoethanol and the like are contained in an amount of about 0.05 to 3 mol%, preferably about 0.5 to 1 mol% based on the raw material monomer. Used in proportion. If it is less than this, sufficient heat resistance cannot be obtained, and if it is added in a proportion higher than this, coloring and odor become problems.

After completion of the reaction, a poor solvent for the produced polymer is added to the reaction mixture for reprecipitation, and then reprecipitation with a good solvent and a poor solvent is repeated to obtain a purified acrylic polymer.

[0011]

[Effects of the Invention] In solution polymerization of acrylic acid ester or methacrylic acid ester, by adding the organic mercapto compound immediately before the termination of the polymerization reaction, compared with the case where the organic mercapto compound is added from the beginning of the polymerization reaction. While the amount of the organic mercapto compound bonded is almost the same, an acrylic polymer having higher heat resistance and higher molecular weight can be obtained. Moreover, the excellent permeability inherent in the acrylic polymer is hardly impaired.

Therefore, the acrylic polymer of the present invention having such characteristics can be effectively used in the field of optical communication such as a highly flexible light guide and a lens, and the field of optical parts.

[0013]

EXAMPLES The present invention will now be described with reference to examples.

Example 1 Ethyl acrylate was placed in a polymerization kettle equipped with a stirring torque detector.
200.2g (2.0mol), azobisisobutyronitrile 0.164g
And a mixture of methyl ethyl ketone (144.2 g) were heated to 54 ° C., and when the stirring torque reached a value corresponding to a number average molecular weight = 9 × 10 ⁴ (2 hours and 40 minutes after the initiation of the polymerization reaction), 2.93 g (0.02 g) of octyl mercaptan Mol) was added and stirred for 10 minutes to terminate the polymerization reaction.

A polymer obtained by adding 70% by weight aqueous methanol solution to the reaction mixture for reprecipitation and reprecipitating with methyl ethyl ketone and aqueous methanol solution three times has a number average molecular weight of 1.2 × 10 ⁵ , while the reaction From the quantitative value (2.02 g) of unreacted octyl mercaptan in the mixture solution, it is considered that 31% of the octyl mercaptan used at the polymer end is bound.

COMPARATIVE EXAMPLE 1 In Example 1, the mixture containing octyl mercaptan from the beginning was heated to 53 ° C. and polymerized for 12 hours.
A polymer having a number average molecular weight = 5.7 × 10 ⁴ was obtained. The polymerization reaction was continued at this temperature for a further 12 hours in order to obtain a higher molecular weight polymer, but only a polymer having a number average molecular weight of 6.3 × 10 ⁴ was obtained.

As in Example 1, the amount of unreacted octyl mercaptan was determined to be 1.93 g, and from this result, it is considered that 34% of the octyl mercaptan used was bound to the polymer terminal.

Example 2 In the polymerization kettle of Example 1, 241.0 g of n-butyl acrylate
(1.88 mol), dicyclopentenyl acrylate 24.5 g (0.
(12 mol), 0.164 g of azobisisobutyronitrile and 144.2 g of methyl ethyl ketone are heated to 56 ° C., and when the stirring torque reaches a value corresponding to number average molecular weight = 1.1 × 10 ⁵ (2 1.25 g (0.016 mol) of 2-mercaptoethanol was added and stirred for 15 minutes to terminate the polymerization reaction.

The copolymer obtained by reprecipitation from the reaction mixture with an aqueous solution of methyl ethyl ketone-methanol had a number average molecular weight of 1.5 × 10 ⁵ , and was used based on the quantitative value (0.71 g) of unreacted 2-mercaptoethanol. It is considered that 43% of the obtained 2-mercaptoethanol is bound to the end of the copolymer.

With respect to the polymers obtained in each of Examples 1 to 2 and Comparative Example 1 above, changes in the number average molecular weight when kept in air at 130 ° C. were measured with time.
The results shown in Fig. 2 were obtained, and the results shown in Figs. 2 to 3 were obtained by measuring the light transmission spectrum. These results show that the polymers obtained in each example are excellent in both heat resistance and light transmission.

Further, visible light transmittance (JIS R-3106) before and after the heat resistance test when kept in air at 130 ° C. for 100 hours.
The values of were:

Comparative Example 2 In Example 2, the mixture containing 2-mercaptoethanol from the beginning was heated to 55 ° C. and polymerized for 3 hours and 35 minutes to give a copolymer having a number average molecular weight of 8.8 × 10 ^4. Was obtained.
When the polymerization reaction was further continued at this temperature in order to obtain a higher molecular weight copolymer, it rapidly gelled, and a copolymer which could be used as a molding material or the like could not be obtained.

[Brief description of drawings]

FIG. 1 is a graph showing the heat resistance of the polymers obtained in Examples 1 and 2 and Comparative Example 1, respectively.

FIG. 2 is light transmission spectra of the polymers obtained in Example 1 (solid line) and Comparative Example 1 (dotted line), respectively.

FIG. 3 is a light transmission spectrum of the polymer obtained in Example 2.

Claims (1)

[Claims] 1. A method for producing an acrylic polymer, which comprises adding an organic mercapto compound immediately before the termination of the polymerization reaction during solution polymerization of an acrylic acid ester or a methacrylic acid ester.