| Abstract: | The heat capacities of poly(vinyl fluoride), poly(vinylidene fluoride), and polytrifluoroethylene have been measured between 80 and 340°K. The results can be expressed as the sum of two terms: the optical contribution calculated from the vibrational band assignments in the literature and the acoustical contribution calculated according to the Tarasov continuum model. Combining our data with those for polyethylene and polytetrafluoroethylene, it is concluded that the force constant for one-dimensional intrachain interaction is approximately constant for all polymers with carbon backbones. The force constant for three-dimensional interchain interaction is one order of magnitude smaller than the one-dimensional force constant, and decreases when the hydrogen atoms in polyethylene are replaced by fluorine atoms. The thermodynamic functions for the three polymers have been evaluated. Glass transitions at 228°K and 305°K have been found in poly(vinylidene fluoride) and polytrifluoroethylene, respectively. |
