Phase transitions in single-crystalline polymerizing diacetylenes as seen by dielectric measurements

Abstract

This paper reports on results of measurements of low-frequency electric permittivity of mixed single crystals of solid-state polymerizable diacetylenes pTS and pFBS. The measurements were carried out on monomers and fully polymerized samples over the entire composition range, in the temperature range 80–330 K. The phase transitions in pure pTS and poly-pTS are visible on the ε(T) dependencies, whereas similar dependencies measured in pFBS and poly-pFBS are completely featureless, confirming absence of any phase transitions in that material within the accessible temperatures. In mixed crystals containing increasing amounts of pFBS, the transitions shift towards low temperatures, and their signatures become smeared and less pronounced. Such behavior can be explained by assuming that dipole-dipole interactions are responsible for the phase transitions.