A Room-Temperature Transition in Polytetrafluoroethylene

IN the course of determinations of the variation of the specific volume of polytetrafluoroethylene with temperatures between = 30° and + 360° C., a phenomenon was observed at about 20° C. which is, to the best of our knowledge, unique in the polymer field. Below 15° and above 25° C., the cubical coefficients of expansion are roughly the same and of the order of 3 × 10-4 c.c./c.c./° C., but at about 20° C. there is a 1 per cent increase in volume; data for five different samples of polytetrafluoroethylene are presented in the accompanying curves. The results for any single sample are reproducible, and the same curve is obtained on approaching the transition region from low and high temperatures.