LIQUID-CRYSTAL TRANSITION AND CRYSTALLIZATION KINETICS IN POLY(ESTER IMIDE)S

A series of monotropic liquid crystal poly(ester imide)s (PEIMs) was synthesized from N-[4-(chloroformyl)phenyl]-4-(chloroformyl)phthalimide and nine diols containing 4-12 methylene units (m). During cooling from their isotropic melts, all the polymers underwent a monotropic liquid crystal transition to form a smectic A phase, followed by a transition to a more ordered structure, which was examined with wide-angle X-ray diffraction, differential scanning calorimetry, and polarized light microscopy. The fact that the liquid crystal transition temperatures for some of the PEIMs were close to their glass transition temperatures provided an opportunity for the study of liquid crystal transition kinetics in temperature regions close to the glass transition temperature. It was found that when the temperature, and thus the molecular mobility decreased, the transition time increased despite the fact that this transition is close to equilibrium. The crystallization kinetics of PEIM(m)s from both the liquid crystal phase and the isotropic melt were also studied. In PEIM(m=even)s (except for m = 4), two different ordered structures can be formed. One is a crystalline phase formed directly from the isotropic melt, and the other is a highly ordered mesophase having a hexagonal-like packing develop from the liquid crystal state. Only one crystal structure in PEIM(m=odd)s is observed. Special attention has been paid to the effect of the presence of liquid crystal order on the crystallization kinetics. The pronounced acceleration of the crystallization was observed whenever this was preceded by liquid crystal formation, an effect pertaining within a wide temperature range from close to T(m) down to T(g).