JPS62143911A - Prevention of maleimide from polymerization - Google Patents

Abstract

PURPOSE:To effectively prevent a maleimide from polymerization without discoloration of the maleimide itself when stored for a long period, by the use of an alkyl-substituted hydroxybenzene as a polymerization inhibitor. CONSTITUTION:The objective prevention of a maleimide from polymerization can be attained by incorporating it with, as a polymerization inhibitor, an alkyl- substituted hydroxybenzene (e.g. 2,4-dimethyl-6-tert-butylphenol, 4-tert- butylcatechol). The incorporation may be carried out at any time, e.g. during its production (in the raw material, amide-modification, imide-modification, purification), storage, transfer, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for preventing polymerization of maleimides. Specifically, the present invention is a method for inhibiting the polymerization of maleimides using an alkyl-substituted hydroxybenvin as a polymerization inhibitor, such as a process of producing maleimides from maleic anhydride and amines, or a process of producing crude maleimides by distillation or the like. The present invention provides a method of significantly preventing the polymerization of maleimides by using this specific polymerization inhibitor in the purification process, storage or transportation process of maleimides, and the like.

Conventional technology Maleimides are extremely unstable compounds that easily undergo polymerization reactions due to their molecular structure. Therefore, various methods have been proposed to suppress polymerization in the process of producing maleimides from maleic anhydride and amines, the process of purifying crude maleimides, and the like. For example, during the production of maleimides, in order to prevent polymerization of maleimides during the reaction, maleamic acid is heat-treated under reduced pressure, and the generated maleimides are quickly distilled out of the reaction system. is JP-A-47-2
It is disclosed in Japanese Patent No. 7974. Also, JP-A-53-
Publication No. 137956 discloses that umaleimide is produced by adding hydrogen halide in advance to the double viscosity of maleic anhydride as a raw material to eliminate the polymerization reactivity of the double viscosity, and then dehydrating and ring-closing it with amines. A method of manufacturing is disclosed.

However, none of these methods has disclosed a method for producing maleimides in good yield by preventing polymerization of maleimides.

Furthermore, methods for purifying crude maleimides with as little heat as possible have been disclosed, for example, in JP-A-58-96066 and JP-A-60-100.
No. 554, etc., purification is carried out by recrystallization at a relatively low temperature of 4 degrees using a solvent such as methanol, toluene, or isopropanol.

However, even if purified under these conditions, polymerization will proceed while the maleimide is being stored, rendering it almost useless as a commercial product.

For example, if a homopolymer of maleimides is contained in maleimides, for example, if these 7 reimides and styrene, or styrene and acrylonitrile are copolymerized, maleimides will be present in the copolymer. Because the homopolymer of maleimide is included, the heat resistance and strength may not be as high as expected, and the appearance, especially the transparency, of the copolymer may be extremely poor because it is insoluble in the monopolymer of maleimide. This will lead to a significant decrease in the commercial value of the copolymer.

Purpose of the Invention As described above, although preventing the polymerization of maleimide compounds during manufacturing, purification, storage, and transportation processes is a very important issue, until now there has been no effective method for preventing polymerization. Almost never proposed.

SUMMARY OF THE INVENTION In view of the current situation, an object of the present invention is to provide a polymerization prevention method that effectively prevents the polymerization of maleimides without coloring the maleimides themselves.

Means for Solving the Problems In order to achieve the above object, the inventors of the present invention have made intensive studies and found that alkyl-substituted hydroxybenzenes such as 2,4-dimethyl-6-tert-butylphenol, 2,4-dimethyl-6-tert-butylphenol, 4-tert-butylcatecholtyl-p-cresol, 2,5-di-tert-butylhydroquinone, 2-tert-butylhydroquinone, 4,4'-thio-bis(6-tert-butyl-m-
The present invention was completed based on the discovery that polymerization can be efficiently prevented without coloring the maleimides themselves by using polycresol (cresol) or the like. It is clear from the following examples and comparative examples that the alkyl-substituted hydroxybenzenes specified by the present invention have a polymerization-inhibiting effect on maleimides compared to p-methoxyphenol, hydroquinone, etc. that are generally used as polymerization inhibitors. A huge difference can be seen.

Examples of maleimides to which the polymerization prevention method of the present invention can be applied include maleimide, N-methylmaleimide, N-ethylmaleimide, N-hexylmaleimide, N-octylmaleimide, N-dodecylmaleimide, N-benzylmaleimide, N- Cyclohexylmaleimide, N-phenylmaleimide, N-nitrophenylmaleimide, N-
Methoxyphenylmaleimide, N-methylphenylmaleimide, N-carboxyphenylmaleimide, N-hydroxyphenylmaleimide, N-chlorphenylmaleimide, N-dimethylphenylmaleimide, N-dichlorophenylmaleimide, N-bromphenylmaleimide,
N-dibromphenylmaleimide, N-trichlorophenylmaleimide, N-tribromphenylmaleimide, etc., and solutions containing one or more of these, such as acrylonitrile, styrene, maleic anhydride, (meth)acrylic Examples include solutions of acid esters and mixed solutions thereof, but are not limited thereto.

Alkyl-substituted hydroxybenzenes can be used in any step in the maleimide production process, such as in raw materials, during amidation reactions, during imidization reactions, during purification, during storage, and during transportation, and are excellent polymerization prevention agents. give effect. In particular, when maleimides are stored for a long period of time, they can be stored stably without causing changes in the hue of the maleimides.

The amount of alkyl-substituted hydroxybenzenes to be used is appropriately determined depending on the temperature, time, pressure, gas phase gas composition, liquid phase composition, etc. of each step, but in general, it is 0.0001 to 1% by weight based on the raw material or maleimide. , preferably o, o
o i ~ 0.1 overlap % is used. Further, these alkyl-substituted hydroxybenzenes can also be used in combination with other polymerization inhibitors such as hydroquinone and p-methoxyphenol. Furthermore, regarding the addition method, these polymerization inhibitors may be added as they are in liquid or powder form, or may be added after being dissolved in a solvent, raw material, etc.

Hereinafter, this will be explained in detail using examples.

Examples 1 to 12 and Comparative Examples 1 to 7 Maleimides and polymerization inhibitors were inserted into test tubes under various conditions such as the type of maleimide, the type of polymerization inhibitor, and the amount added. Put it in the oil bath of C, 3
heated for an hour. At this time, nitrogen gas was introduced into the gas phase portion of the sealed tube. After heating for 3 hours, the sealed tube was removed from the oil bath, and the maleimides in the sealed tube were cooled and crushed, analyzed by high performance liquid chromatography to measure purity, and
The results shown in the table were obtained.

Example 13 Yellow N-phenylmaleimide 1 with 99.8% purity by weight
Kg and 4-tert-butylcatechol 0.2q
was heated from the outer shell in a stainless steel container having a diameter of 10 cIn and a height of 20 cIII and equipped with a heating outer shell to bring the internal temperature to 100°C.

At this time, N-phenylmaleimide was a yellow liquid. Note that the gas phase part of the container was replaced with nitrogen gas.

When kept in this state for 30 days, the color of N-phenylmaleimide after 30 days remained the same as the initial color.
Analysis of this product by high performance liquid chromatography revealed that the purity was 99.7% by weight, with almost no change.

Claims (1)

[Claims] (1) A method for inhibiting the polymerization of maleimides, which comprises using an alkyl-substituted hydroxybenzene as a polymerization inhibitor.