Studies of phase separated copolymer blends using thermally stimulated currents and dielectric spectroscopy

Abstract

Thermally stimulated currents (t.s.c.s) and a.c. dielectric spectroscopy were used to study poly(butylene terephthalate) (PBT) and blends of PBT with segmented copoly(ester-ether) elastomers. The high sensitivity of t.s.c. and a.c. dielectric techniques as compared to d.s.c. was useful for the study of these blends where the elastomer phase was present at only 20%. The techniques together cover a frequency range of ∼5 × 10 −3–10 5 Hz allowing detailed characterization of amorphous relaxations in these phase separated blends. Two separate glass transitions for the PBT/copoly(ester-ether) blends were observed, unchanged from the original pure components, indicating that they are immiscible and that ester exchange during processing was minimal. Peak assignments are made using a new analysis scheme by comparing activation energies ( E a) determined by the t.s.c. thermal sampling technique with predicted values using the activated states equation. With this method all values of E a agree with the zero activation entropy prediction except those measured in the vicinity of glass transitions.