Method of removing low molecular weight substance from polymide precursor or polymide containing low molecular weight substance

Abstract

A method of efficiently removing a low molecular weight substance from a polyimide precursor or polyimide in which the low molecular weight substance is dispersed as micro-domains, without using a large amount of an organic solvent. The method of removing a low molecular weight substance comprises subjecting either a polymer composition having a micro-domain structure made up of a continuous phase comprising a polyimide precursor and, dispersed therein, a discontinuous phase comprising a low molecular weight substance or a polyimide composition obtained from the polymer composition by converting the polyimide precursor into a polyimide to extraction with a combination of supercritical carbon dioxide and a co-solvent to thereby remove the low molecular weight substance. The co-solvent is preferably an aprotic polar solvent, more preferably a nitrogen compound solvent or a sulfur compound solvent.

Description

[0001] The present invention relates to a method of removing a low molecular weight substance by extraction from a polyimide precursor or polyimide in which the low molecular weight substance is dispersed as micro-domains and to processes for producing a porous polyimide by utilizing the method. This porous polymer is extremely useful as, for example, circuit substrates for electronic appliances, etc.DESCRIPTION OF THE RELATED ART[0002] Polyimide resins have conventionally been used widely as parts or members required to have reliability, such as circuit substrates for electronic / electrical appliances and other electronic parts, because of their features such as high insulating properties, dimensional stability, moldability, and lightweight properties. Especially in recent years, there is a desire for higher-speed information transmission with the trend toward performance and function advancement in electrical / electronic appliances, and members for use in these appliances also are r...

AI Technical Summary

Benefits of technology

[0010] Another object of the invention is to provide processes by which a porous polyimide having a small cell size and a low dielectric constant can be efficiently produced.

[0041] According to the above-described method of removing a low molecular weight substance, since an extraction operation is conducted with a combination of supercritical carbon dioxide and a co-solvent, the low molecular weight substance constituting the discontinuous phase as well as the residual solvent and the like can be removed in a relatively short period of time. Furthermore, since there is no need of using a large amount of an organic solvent, the method is preferred from the standpoint of environmental preservation. In addition, the method is effective in easily removing oligomers having a relatively high molecular weight and in greatly improving the efficiency of removal of low molecular weight substances.

[0043] As described above, according to the method of the invention for removing a low molecular weight substance, the low molecular weight substance present as a discontinuous phase in a polyimide precursor or polyimide can be efficiently removed because extraction is conducted with a combination of supercritical carbon dioxide and a co-solvent. Even oligomers having a relatively high molecular weight can be removed. This method is advantageous also from an environmental standpoint.

[0044] According to the porous polyimide production processes of the invention, a porous polyimide having a small cell diameter and a low dielectric constant can be efficiently obtained.

Problems solved by technology

However, in view of the fact that the dielectric constants of polyethylene and polytetrafluoroethylene, which are regarded as low dielectric constant polymers, are about 2.3 and about 2.1, respectively, there are limitations in the technique of controlling dielectric constant based on skeleton modifications.

In addition, the above technique poses problems, for example, that a skeleton modification results in changes in properties such as film strength and coefficient of linear expansion.

However, these techniques have problems, for example, that a sufficiently small cell size cannot be obtained and there are limitations on the formation of finer patterns in circuit formation.

However, these methods have a drawback from the standpoint of production process because of the necessity of a prolonged time period and further pose an environmental problem because of the use of a large amount of an organic solvent.

With respect to the removal of oligomers having a relatively high molecular weight of 1,000 or above, there has been no technique proved to be effective in this purpose.

If a low molecular weight substance having a weight average molecular weight lower than 100 is used, there are cases where the low molecular weight substance is completely compatibilized with the polyimide precursor, making it impossible to obtain a porous object.

On the other hand, if a low molecular weight substance having a weight average molecular weight exceeding 10,000 is used, there are cases where the removal thereof in a later step is difficult.

This drying may result in porosity.