Effects of Annealing upon Molecular Orientation and Microwave Dielectric Anisotropy in Polyimide Films

Abstract

ABSTRACT:Molecular orientation and dielectric anisotropy of polyimide films before and after annealing for 2 h at 250°C were studied by use of the microwave method. The annealing made the dielectric constant e' and loss e" decrease markedly while gave a little change in the orientation pattern and then in the direction and degree of molecular orientation in the polyimide films. On the other hand, the direction of maximal thermal shrinkage corresponded to that in which the polyimide molecules are, on an average, aligned in the maximum dielectric loss and minimum transmitted microwave intensity. The results suggest that the orientation pattern reflects the thermal shrinkage and that the decrease in e" due to the annealing is ascribed to an increase in crystallinity of polyimide molecules in the amorphous region but gives a bit change in orientation of macromolecules.KEY WORDS Annealing / Polyimide / Molecular Orientation / Dielectric Anisotropy / Microwave / Aromatic polyimide films exhibit excellent physical, electrical, and mechanical properties over a wide temperature range. Because of the good electrical properties in dielectric strength and dissipation factor over a wide range of temperature and frequency, the films are useful for heat-resistive insulating materials such as printed circuit board and electric cable. In the practical application to the electronic engineering field, the information on the thermal shrinkage and the mechanical and microwave dielectric properties is very important.As for polyimide films, the molecular orientation has been roughly estimated from the data on the viscoelastic modulus 1 • 2 and the complex dielectric constant has been measured only at audio frequencies. 3 .4 But, the molecular orientation affecting thermal shrinkage data and microwave dielectric data on polyimide films had not yet been reported in details in the literature.The microwave method developed by the author 5 -7 has overcome such difficulty in the time-consuming. The microwave method made it possible to determine quickly and accurately the molecular or fiber orientation and the microwave dielectric anisotropy without contact. It was applied to the paper sheets, 8 -11 polymer films such as poly(ethylene terephthalate) (PET) and poly(vinylidene fluoride), 12 -2 0 human blood vessels, 21 cow skins, 22 and nonwoven fabrics. 23 In a previous paper, 24 we reported the molecular orientation of polyimide films determined by the microwave method, and compared the results with those by the mechanical and infrared methods.The present paper describes effects of annealing upon the molecular orientation and the microwave dielectric anisotropy in polyimide films and compares the results with the thermal shrinkage. EXPERIMENT AL SamplesSamples used here were commercially available polyimide Kapton l00H (Du Pont) films with 26 µm thick which were prepared by the cast method. Measurement of Orientation PatternA given film is inserted into the cavity resonator system. 12 • 15 Polarized microwaves are incident perpendicularly to...

High-performance solution-processed polymer ferroelectric field-effect transistors

“…P(VDF/TrFE) is a wide-bandgap insulator and a ferroelectric material 17 . Its annealing temperature is 140 °C, which is compatible with fl exible substrate materials such as polyimide 18 . MEH-PPV is a p-type semiconductor whose charge transport is characterized by site-to-site hopping 19 .…”