Molecular order and phase transitions in smectic poly(ester imide)s based on trimellitimide

Abstract

Poly(ester imide)s have been derived from aminobenzoic acid (PEI 1), respectively, aminocinnamic acid (PEI 2), trimellitic acid, and α,ω-dihydroxyalkanes to form various smectic liquid-crystalline (LC) and smectic-crystalline phases, dependent on the type of mesogen, spacer length, and thermal treatment. In this study, the phase behaviour and molecular structure of these PEI has been investigated by polarising microscopy, DSC, X-ray scattering, light scattering and solid-state NMR.The temperature gap of the monotropic LC-phase becomes narrower with increasing spacer length. If the LC-phase is lost completely, the smectic-crystalline phase develops directly from the isotropic melt with a three-dimensional spherulitic superstructure of several μm diameter. In contrast, the Avrami-evaluation of the crystallisation from the LC-phase indicates two-dimensional crystal growth starting from disclination centres. The development of a long period reflection in the small angle X-ray scattering reveals a lamellar superstructure of 100–400Å. Each lamella contains a number of smectic-crystalline layers, while the interlamellar regions are amorphous.X-ray fibre patterns demonstrates that the PEI 1 form orthogonal smectic phases (SA, SB, SE), unlike PEI 2, which form tilted phases (SC,SH). The 13C NMR results indicate a uniform spacer conformation in the LC-phase corresponding to an alternate-trans model, while the smectic-crystalline phase contains ordered trans–trans-conformations, as well as completely disordered sequences.