Successive phase transitions of partially and fully polymerized crystals of 2,4-Hexadiyne-1,6-Diol bis (p-toluene sulfonate)

The specific heat capacity is measured in both partially and fully polymerized crystals of 2,4-hexadiyne-1,6-diol bis (p-toluene sulfonate). A new intermediate phase is found in partially polymerized crystals; its lower and upper transition temperatures lie at 157 and 193 K, respectively. Fully polymerized crystals undergo a structural phase transition at 190 K, in good agreement with reported values. The critical exponents, α and α', of the specific heat capacity are calculated from the experiments to be 0.71 ± 0.09, which is extremely large in comparison with that of simple model systems. The excess entropy is estimated to be about 1 Jmol–1K–1. This means that the motion of the side groups attached to the polymer chain is highly anharmonic.