Paper Title
WATER ABSORPTION AND ELECTRIC PROPERTIES FOR HEAT RESISTANT POLYMERS

Abstract
A number of aliphatic biobased polymers have been developed thus far, however, their low glass transition temperature and only a small percentage of their substitutes limited their use for various applications. We have developed so far biobased polyimides (PIs) from bioavailable aromatic diamines, which were photodimers of 4-aminocinnamic acid (4ACA) derived from genetically manipulated Escherichia coli. In order to apply the biopolyimide to electrical materials, the electrical resistivity and dielectric constant of polyimide films under high electric fields have been studied. In this study, the effects of water absorption on the electric resistivity and dielectric constant of polyimide (PI), biopolyimide, and poly(ethylene terephthalate) (PET) were investigated and the deterioration mechanism of the electrical insulation properties is discussed. The critical volume fraction of the percolation threshold of electric conductivity due to water absorption was 0.034 for both PMDA-ODA and BPDA-PDA. On the other hand, PET did not show a significant decrease in the resistivity. For both PIs and PET, the dielectric constant observed could be explained by a series model of the respective capacitances of pure water and polymer. Actually, the resistivity of samples cut from the edges of the film after water absorption was almost the same value as that in the dry state. These results suggest that the absorbed water molecules are not uniformly dispersed in the film, but are localized at the edges in the film even after the absorption equilibrium have reached.