Rigid Amorphous Fraction in Poly(phenylene Oxide) Detected by Temperature-modulated Calorimetry

摘要

Poly(oxy-2,6-dmethyl-1,4-phenylene),PPO,is an exampleofapolyiner which has the glass transition of the rigid-amorphous fraction above the melting temperature of the crystals. Semicrystalline PPO is analyzed by temperature-modulated calorimetry with a modulation amplitude of 0.5 K, a 60 s modulation period and also by standard DSC. In the standard DSC trace of an as-received sample of PPO with about 30% crystallinity, a single melting peak appears at about 515 K, but no glass transition can be seen at 482 K, which is known as the T_g of the amorphous PPO. The reversing heat capacity of the semicrystalline PPO shows no melting peak, but a glass transition at about 503 K. Annealing at 496 K causes development of a glass transition at 482 K and a decrease in crystallinity. After 600 min of annealing at 496 K, the irreversible melting peak and the glass transition at 503 K disappear and only the glass transition at 482 K remains which is also seen in quenched PPO. The rigid amorphous fraction was calculated from the deficiency between the measured reversing heat capacity and the expected heat capacity based on the crystallinity. It was about 76% at 489 K and decreased to 4% at 509 K.