Quantitative study of the annealing of poly(vinyl chloride) near the glass transition

Abstract

Abstract Poly(vinyl chloride) displays a normal DSC of DTA curve for the glass transition when quenched from above its T g . However if cooled slowly or annealed near the glass transition temperature, a peak appears on the DSC or DTA curve at the T g . 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 at more than 50°C below T g . The energy difference between the quenched and annealed forms is small. For a PVC homopolymer annealed 2 hr at 68°C, which is T g −10°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 g curve for a polymer when annealed near the glass temperature appears to be a general phenomenon.