Electrical properties of certain high polymer materials

In the course of an investigation of the electrical properties of pure high polymer materials, measurements of the dielectric constant and loss factor of Poly-vinybutyral (Butvar), Polystyrene, Methyl methacrylate, and a copolymer of the latter two materials were made over a frequency range from 60 c/s to 1000 Mc/s. An effort was made to improve the accuracy of these determinations to facilitate the analysis of the data and its correlation with other factors. In the frequency range from 60 c/s to 200 kc/s, where three-terminal bridge measurements may be made, the accuracy of the determination of the dielectric constant is usually limited by the accuracy with which the thickness of the sample and the area of the measuring electrode can be measured. In order to permit the highest possible precision in the determination of the average thickness, a precision molding technique was developed in the Plastics Section of the National Bureau of Standards for producing disk specimens with improved uniformity of thickness and diameter and with square edges. This permitted the use of a travelling microscope in measuring the diameter. The volume of the disk was determined by hydrostatic weighings. The thickness was computed from these determinations.