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

Highly unusual phase behavior, of general implication for condensed matter, is reported for the title polymer. In situ x-ray studies, at the prerequisite pressure and temp., reveal amorphization in this polymer, passing through a continuously varying sequence of mesomorphic states, at 2 widely sepd. temp. regions, the process being reversible. Present findings invoke the possibility of the reentrant, widely sepd. disordered phases with temp. Such possibility has risen for the 1st time in a single-component system. The pressure-induced disordered phase, obtained at room temp., converts into crystal with increasing temp. and reverts to a glassy disordered phase on lowering the temp. Other unexpected findings include a new pressure-induced modification of the polymer, with a 1-way entry only. A few aspects of similar features found in other materials are also stated. [on SciFinder (R)]