The direct current conductivity of three different forms of polyethylene terephthalate was studied over a wide temperature and voltage range to determine the structural dependence of the conduction process. From the films in the amorphous, crystallized, and oriented and crystallized forms it was determined that crystallization reduces the conductivity by more than one order of magnitude. Orientation results in a sixfold decrease in conductivity. The conductivity does not change over a wide range of molecular weight or carboxyl end group concentration. As shown from model polymers and copolymers, disruption of chain symmetry and molecular packing, introduction of side chains, or any other modification which reduces the crystallinity and order, results in greater conductivity. The structural dependence of conductivity, the temperature dependence, and the current–voltage relationships of polyethylene terephthalate are consistent with a proposed ionic mechanism for the conduction process.

The dielectric constant and dissipation factor of Teflon were measured at frequencies from 10 2 to 10 5 cis and from room temperature to temperatures j ust below the first-order t.ransition point occurring at 327 0 O. Measurements of the d-c conductivity were made over the same temperature int.erval. R esult s show t hat the dielectric constant decreases somewhat with increasing temperature. T he relation between thermal-expansion coeffi cient and temperature coeffi cient of t he dielectric constant is roughly as predicted by the Clausius-Mossotti equation. Val ues of dissipation factor ann d-c eonductivity at all temp eratures are v~ry low (less than 2 X 10-4 and 2 X 10-15 mho /em, respectively), and the dielectric constant is independent of frequency at all temperatures.

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The inability of polymer chains to deform the required amount within the time allowed by a stress‐to‐failure event results in brittle failure. Factors related to brittle behavior of films were investigated. By both conventional and novel testing techniques, stress–time–temperature relationships were studied to determine the brittle point. From high‐speed tensile tests at strain rates up to 106%/min., the critical strain rate (incipient brittleness as indicated by failure accompanied by a marked decrease in ductility) was determined for representative films. High‐speed motion pictures (6,000 frames/sec.) of film failure in rice bag drop tests, were used to ascertain the time of deformation to be related to brittleness. Deformation rates were calculated to be of the order of 130 to 230 × 103%/min.