Heat capacity of fluoropolymers

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.

Low-temperature measurements of the specific heat capacity of a thick ferroelectric copolymer film of vinylidene fluoride and trifluoroethylene

“…Another noteworthy aspect of our c p data is their overall agreement with independent estimates deduced from the sum of available c p data for the two constituents of the copolymer, [13][14][15][16] weighted with their molar representation. This agreement supports the principle of additivity, formerly used to estimate c p of linear fluoropolymers above ϳ40 K by adding contributions from their vibrational subunits.…”

“…Previous c p measurements of fluoropolymers 16 indicate that the three-dimensional interchain interaction decreases when hydrogen atoms are replaced by fluorine, with the exception of TrFE ͑CF 2 CHF͒ and PTFE ͑CF 2 CF 2 ͒. We have no explanation why two acoustic modes yield a ⌰ D that provides a superior scaling fit to c p data for PTFE.…”

“…͑5͒, with two rather than the four acoustic modes customarily assigned to fluoropolymers at low temperature. 16,59 The shape and vertical position of the scaled data for PTFE are only moderately sensitive to changes within the ϳ10% uncertainty in c D calculated from available velocity of sound data, but the horizontal position is visibly sensitive to differences in ⌰ D deduced for different numbers of acoustic modes. This latter sensitivity is readily apparent in the scaled data for PTFE, whose normalization factor c D was shifted to the lower range of its estimated uncertainty in order to facilitate comparison of its shape with the other data plotted in Fig.…”

“…͑3͒ for the copolymer, 61 using = 1.88 g / cm 3 , yields c D / T 3 = 1.01 mJ/ mol K 4 and ⌰ D = 137 K. The corresponding values, based on sound velocities for PVDF, 9 are, respectively, 0.877 mJ/ mol K 4 and 143.5 K. Some of the difference in the excess specific heat capacity observed for PVDF and PVDF/TrFE is undoubtedly due to differences in chemical composition which alters binding potentials of vibrating subunits. 16 Some compensation for such effects might be attained by scaling the specific heat capacity and temperature by their Debye values, as proposed by Sokolov et al 63 This scaling procedure was applied to plots of c p versus T in Fig. 2 for our PVDF/TrFE data and those for PVDF reported by Privalko et al 9 The overlap is surprisingly good even though the Debye normalizations, deduced from sound velocity data, do not include the Tarasov correction, 58 which approximates the presumed transition from 1D to 3D phonon propagation in polymer chains as they are cooled from intermediate temperatures to absolute zero.…”

Heat Capacity and Other Thermodynamic Properties of Linear Macromolecules. VII. Other Carbon Backbone Polymers

“…The heat capacity data from the two measurements Sochava (1960) [37J Lee and Choy (1975) [35] overlapJhe temperature range_from aO_tQ.120 K. The.daJa .. are in good agreement from 80 to 90 K, however, from 100 to 120 K the data of Socha va on sample 24 are somewhat lower (30/0-5%). Similar deviations in Sochava's data above 100 K have been observed for other polymers.…”