Creation of porous polyimide membrane by viscoelastic phase separation

If we can define the word "functionality" as the special interaction between materials, the large surface is regarded as one of the most basic physical properties. Hence, the need of a porous material is very high. Especially the creation of multi porous structures by using the macromolecular self-organization mechanism has a feature of providing uniform structure efficiently, and is a very leading technique. And it is well known that the structure created by self-organization mechanism depends on the molecular weight very much. In the present work, we investigated the relation between the polymerization concentration of polyamic acid (PAA), the pre-polymer of polyimide (PI) and molecular weight, and clarified a technique of obtaining high molecular weight PAA. We also clarified that the interaction between PAA molecules was very strong in the N-methyl-2-pyrrolidone (NMP) solution. Then, as described in a previous report, a film adjusting solvent substitution speed was used and formation of multi porous membrane was tried by the solvent replacing method in a state where a molecular weight was high and where interaction was strong, by using the visco-elastic phase separation phenomenon. As the result, we succeeded in obtaining a porous membrane with a very sufficient continuity of a pore. The structure of this membrane was not collapsed by heat treatment. The obtained PI porous membrane was excellent in gas and liquid permeability, and was excellent also in heat resistance.