Melting and crystal structure: the melting parameters of some polyphenyls

Abstract Melting mechanisms have been studied for diphenyl, and o-, m- and p-terphenyl. The volume increase on melting is largest for the linear polyphenyls and smallest for branched molecules which can interlock in the melt. In no case will the volume increase permit the ‘onset of rotation’ on melting. Viscosity measurements give marked indications of the growth of cybotactic groups in the melts on approaching the freezing-points, especially in the case of o-terphenyl, where the , ratio Hvap /En reaches exceptionally low values near the freezing-point. Plots of fluidity against specific volume and the marked tendency of the melt of o-terphenyl to supercool give further indications of the presence of interlocked groups of molecules in the melt.