Two types of aggregation structure formed in a thermotropic aromatic polyester

The aggregation structures of the enantiotropic liquid crystalline polyester, K145N213 (°C), were investigated using polarizing optical microscope (POM), wide-angle X-ray diffraction (WAXD) and scanning electron microscope (SEM). Depending on annealing temperature, two types of aggregation structure (AS), I and II, were formed. AS I was grown directly from nematic melt, while AS II was formed from supercooled liquid crystalline state. By comparing AS I and AS II it was found that there was much difference between them, such as the morphology, the melting behaviour and the pattern of WAXD. The experimental results showed that the aggregation behaviour of AS II was more like that of the conventional crystalline polymers, while AS I made conspicuous difference. A sketch map of the formation mechanism of AS I was suggested, which showed that the particular AS I was composed of nematic domains.