Synthesis and phase transition of liquid crystalline homopoly(ester–imide) and copoly(ester–imide)s with different lengths of methylene spacers

A homopoly(ester–imide) was prepared from N-(10-carboxydecanyl) trimellitic imide and hydroquinone diacetate via melt transesterification condensation. The phase transition behavior was checked with DSC, rheometry, and polarized light microscopy experiments. The homopoly(ester–imide) showed only crystallization transition when it was cooled from isotropic melt. Nevertheless it showed thread-like texture when quenched below crystallization temperature. In order to check mesophase formation, copoly(ester–imide)s containing both 10 and 4 methylene units were made varying the mole ratio of N-(10-carboxydecanyl) trimellitic imide to N-(4-carboxybutyl) trimellitic imide. All copoly(ester–imide)s exhibited nematic phase transition and, in particular, they showed monotropic nematic transition, when they had large portion of 10 methylene unit. The nematic to isotropic phase transition temperature of homopoly(ester–imide) was obtained extrapolating those of copoly(ester–imide)s and matched well with the crystallization temperature of the homopoly(ester–imide).