Compositional and Temperature Dependence of Free Volume in Segmented Copolymer PET/PEO Studied by Positron Annihilation Lifetime Measurement

Positron lifetime measurements were performed for segmented copolymer poly(ethylene oxide)–poly(ethylene terephthalate) (PEO/PET) as a function of the hard segment content (PET) and the temperature, which is used to study the free volume properties, structural transition and miscibility behaviour of segmented copolymer PEO/PET. From the variation of the ortho-positronium (o-Ps) lifetimes with changes in the hard segment content, we find that the free volume decreases with increase of the hard segment, this fact means that the hard segment microdomains act as physical cross-links that suppress movement of the chains and that the interactions between the hard segment (PET) and soft segment (PEO) also plays an important role. On the other hand, the temperature dependence of positron lifetimes reveals the existence of two glass transition temperatures. This experimental results show that the hard segment PET is immiscibility with soft segment PEO in segmented copolymer PEO/PET (PEO molecular weight 4000, PET content 30 wt.%). The maximum entropy lifetime method (MELT) is used to detect the distributions of the free volume holes. Large differences in width of the free volume hole distributions as a function of temperature are observed.