Synthesis and investigation of the effect of nematic phases on the glass-transition behavior of novel cycloaliphatic liquid-crystalline poly(ester amide)s

Abstract

We designed and developed novel cycloaliphatic liquid-crystalline (LC) poly(ester amide)s to investigate the effects of nematic LC phases and hydrogen-bonding interactions on the glass-transition behavior. Three series of poly(ester amide)s based on commercially important poly(1,4-cyclohexanedimethylene terephthalate) were synthesized with two new cycloaliphatic diamines {3,8-bis(aminomethyl)-tricyclo [5.2.1.0.(2,6)]decane (tricyclic) and 1,3-cyclohexane bismethylene amine (monocyclic)} and a linear counterpart (1,6-hexamethylene diamine). The compositions of the ester/ amide units in the copolymers were varied up to 50% by the adjustment of the amounts of the diol and diamine in the feed. The structures of the polymers were confirmed with NMR and Fourier transform infrared, and their inherent viscosities were measured at 30 degrees C with an Ubbelohde viscometer. Thermal analysis revealed that the poly(ester amide)s having less than 25 mol % amide linkages were thermotropic and LC, and threadlike nematic phases were observed under a polarizing microscope. The introduction of nematic, LC phases drastically affected the glass-transition temperatures of the copolymers, and a plot of the composition versus the glass-transition temperature passed through a maximum for lower amide incorporation, regardless of the structural differences of the amide units (cyclic or linear). This nonlinear Flory-Fox trend was correlated to the cooperative effect of the strong alignment of polymer chains in the nematic phases and intermolecular packing induced by the hydrogen bonding in the poly(ester amide)s.