Thermodynamic Properties of Poly(irons-1,4-butadiene) Crystals. Relationship to Molecular Structure

Heat capacity measurements of melt crystallized poly(trans-1,4-butadiene) (PTBD) were carried out in the 50–130° region and the entropy change from 73° to the melting point, 139°, was calculated. A value of the entropy change obtained using the rotational isomeric state approximation is found to underestimate the experimental entropy change. Theoretical energy calculations were carried out using empirical potential energy-functions for a single PTBD chain, a unit cell and a lattice of cells. Minimization of the lattice energy with respect to two of the monoclinic cell constants for the low-temperature crystal form gave results in good agreement with X-ray diffraction data. The energy of transition from the low-temperature form was calculated and a theoretical heat capacity curve was obtained.