“Liquid Crystallization” Mechanism of Liquid Crystalline Polymers

Abstract

Morphology of the liquid crystals of thermotropic main chain liquid crystalline polymers isothermaly formed at atmospheiric pressure from the melt and their formation mechanism was studied. Materials used were a copolyether based on 1,2-Bis (4-hydroxy phenyl) ethane (BPE-8/12) and poly [bis (trifluoro ethoxy) phosphazenel, (PBFP). Morphology of liquid crystals observed by polarizing microscopy and that of the quenched liquid crystals into crystalline phase oberved by transmission electron microscopy was very similar to that of extended chain crystals (ECCs) of crystalline polymers, such as polyethylene (PE). Therefore it is concluded that extended chain liquid crystals (ECLCs) are formed from the melt, which suggests that lamellar thikening growth is fast within the liquid crystalline phase. The lateral growth rate (V) of an ECLC showed the same degree of supercooling (ΔT) dependence as has been observed on crystalline polymers, that is V ∝ exp(\( - \frac{C} {{\Delta T}} \)) where C is a constant This indicates that the lateral growth of the liquid crystals is a nucleation controlled process, as has been proposed by Papkov et al. Combination of these two results leads to a conclusion that the liquid cyrstals are formed by the coupling of the thickening growth and the nucleation controlled lateral growth, which we proposed to term “liquid crystallization” mechanism.