Thermal studies on isotactic polypropylene. Measurements of Tg, Tm and ΔHf

Measurements of the glass transition temperature Tg, the melting temperature Tm and the enthalpy of fusion ΔHf were made with three types of polypropylene with different orientation by means of differential scanning calorimetry and dynamic mechanical analysis. The difference in the Tg values determined with the two techniques is ca. 30 K. Tm and ΔHf increase with increase of the draw ratio of the filaments. These increases indicate an increase in the crystallinity between the undrawn and drawn specimen as the result of better chain alignment, and hence the cooperative resistance of the main chain segments of thermal motions.