Heat Capacity and Thermodynamic Properties of Poly(chlorotrifluoroethylene) from 2.5 to 620 K.

Heat capacities and thermodynamic properties of a number of poly(chlorotrifluoToethylene) samples subjected to various thermal treatments, to achieve crystallinities ranging from approximately 10 to 90%, have been studied from 2.5 to 370 K by automated adiabatic calorimetiy and from 250 to 620 K by differential scanning calorimetry. Small heat capacity discontinuities in the temperature range from 320 to 350 K were observed in all samples with crystallinities greater than 40%. Spontaneous adiabatic temperature drifts associated with these anomalies were prasitive (exothermic) for quenched samples and negative (endothermic) for annealed samples. Therefore these anomalies were believed to be associated with a relaxation phenomenon similar to that of a glass transition. For highly quenched low crystallinity films, a much larger heat capacity discontinuity of greater than 15% was observed, amidst a crystallization exotherm. In addition to the above phenomena, annealing of the sample at any temperature between 240 to 400 K would produce a shift in the population distribution of crystallites from reorganization or melting and recrystallization. As a result, the apparent heat capacity became somewhat lowered at the annealing temperature and somewhat raised at about 20 K above the annealing temperature.

The Intensity as a Function of Temperature of the Low-Angle X-Ray Diffraction Maxima of the n-Paraffins: Hexatriacontane, Tetratetracontane, and Tetranonacontane.

The diffraction of x-rays by the crystalline n-paraffins, C36H74, C44H90, and C94H190, was examined at small angles - below seven degrees 2θ - as a function of temperature. The Bragg maxima (00l) that occur at these angles result from a lamellar repeat distance which depends on the molecular length. In general the intensity of these maxima was found to increase with increasing temperature in an approximately reversible manner. All the samples experienced solid-solid phase transitions in the temperature range of observation. Several possible mechanisms consistent with the temperature dependence of the intensity are considered.

Heats of Reaction of Natural Rubber With Sulfur.

An adiabatic copper calorimeter was used to determine the heats of vulcanization of pale crepe natural rubber with sulfur for mixtures varying in composition from 0 to 32 percent added sulfur. The side reaction that produces hydrogen sulfide was avoided by using reaction temperatures near 155 °C. Heats of reaction at 25 °C and at 155 °C are reported. The enthalpy change at 25 °C for compounds containing up to about 18 percent sulfur is given in joules per gram of vulcanizate by the equation, ΔH 25 = -21.1 · S with a standard deviation of 11 J/g. Here S is the percentage of combined sulfur. Above 18 percent sulfur the heat of reaction at 25 °C remains approximately constant at 380 ±8 J/g. A comparison is made between the heat of vulcanization and the volume change on vulcanization, both as functions of combined sulfur, by making use of data in the literature.