Thermodynamic anomalies in the pressure-temperature phase diagram of poly-4-methyl pentene-1: Disordering of crystals on cooling

Abstract

We report on some highly unusual phase behavior of general implication for condensed matter in a polymer poly-4-methyl pentene-1. In situ x-ray studies, at the prerequisite pressure and temperature, reveal amorphization in this polymer, passing through a continuously varying sequence of mesomorphic states, at two widely separated temperature regions, the process being reversible. Present findigns invoke the possibility of the reentrant, widely separated disordered phases with temperature. Such possibility has arisen for the first time in a single-component system. The pressure-induced disordered phase, obtained at room temperature, converts into crystal with increasing temperature and reverts to a glassy disordered phase on lowering the temperature. Other unexpected findings include a new pressure-induced modification of poly-4-methyl pentene-1, with a one-way entry only. A few aspects of similar features found in other materials are also stated.