SynopsisPoly(viny1 chloride) displays a normal DSC or DTA curve for the glass transition when quenched from above its T,. However if cooled slowly or annealed near the glass transition temperature, a peak appears on the DSC or DTA curve a t the T,. In this paper quantitative studies of the time and temperature effects on the production of this endothermal peak during the annealing of PVC homopolymer and an acetate copolymer are presented. The phenomenon conforms to the Williams, Landell, and Ferry equation for the relaxation of polymer chains, the rate of the peak formation becoming negligible a t more than 50°C below T,. The energy difference between the quenched and annealed forms is small. For a PVC homopolymer annealed 2 hr a t 68OC, which is Z ' , -lO"C, the difference is 0.25 cal/g. For a 13% acetate copolymer of PVC similarly annealed, the difference is 0.36 cal/g. The measured rates of the process give a calculated activation energy of 13-14 kcal/mole for PVC homopolymer and copolymer.This appearance of a peak on the T, curve for a polymer when annealed near the glass temperature appears to be a general phenomenon.

SynopsisA difference has been observed in the DTA and DSC curves for the glass transition of both PVC homopolymer and acetate copolymer, depending on the rate of quenching or annealing below the glass transition temperature. The difference has the appearance of an endothermal peak added to the glass transition curve and is attributed to an.alignmerit of stereoregular chain segments of adjacent polymer molecules. The lengths of chain segments are assumed to be so short that no x-ray evidence of crystallinity was obtained. The orientation process involved has an activatiop energy of 47.8 kcal./mole in the homopolymer and 43.6 kcal./mole in the copolymer. The measured rate of the process agrees with the principle of time-temperature superposition, the rates becoming equal for homopolymer and copolymer at equal temperatures below their glass transition temperatures.

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This thermal degradation study reports the application of “time‐resolved” pyrolysis gas chromatography (PGC) in addition to derivative thermogravimetric analysis (DTGA) to a series of PVC homopolymers with differing branch content and to a model copolymer series with low amounts of propylene in an otherwise vinyl chloride chain. Benzene and toluene generation and decay envelopes were determined during the controlled thermal degradation and related to the derivative TGA experiments. These data allowed interpretation as to the microstructure of the respective polymers and its effect on the degradative pathways. It was concluded that the branch content was not a dominant factor in the initiation of thermal degradation, although it was a factor in other stages of the complex mechanism. A unique fragmentation step was noted only under oxidative thermal exposures, which gave additional support for the theory of low‐level unsaturation sites as being significant triggers in the decomposition mechanism.

synopasDifferential thermal analysis methods have been used to investigate the kinetics of oxidation of isotactic polypropylene. The interpretation of results is based on an oxidation mechanism that emphasizes the role of hydroperoxide production. The mechanism has been simulated by computer methods, and the rate constants for the abstraction of labile hydrogen atoms as well M an apparent energy of activation are obtained.