Ordered structures in a series of liquid-crystalline poly(ester imides)

Abstract

A series of poly(ester imide)s (PEIMs) has been synthesized from N-[4-(chloroformyl)phenyl] -4-(chloroformyl)phthalimide and different diols with methylene units of 4 to 12 (n). PEIMs with both even and odd methylene units exhibit a monotropic mesophase behavior during cooling due to the supercooling necessary for crystallization. Identification of this mesophase as a monotropic liquid crystal with smectic A order has been carried out via differential scanning calorimetry, wide angle X-ray diffraction (WAXD), small angle X-ray scattering, polarized light microscopy, and transmission electron microscopy. It is found that the methylene units in these chain molecules are also largely responsible for the formation of this liquid crystal phase. After investigating different types of main chain mesogen-nonmesogen liquid crystal polymers, a general concept considering the contributions to enthalpy aind entropy changes during the liquid crystal transitions may be associated with the relative rigidity, linearity, and regularity of the mesogenic groups compared to the methylene units. Detailed WAXD study of fiber and powder patterns indicates that the degree of orientation and the order correlation lengths along and perpendicular to the direction of chain molecules (chain lateral packing and layer structure) not only increase with the number of methylene units but also show an even-odd alternation. A possible chain packing model is suggested. The morphology and defects of this smectic A liquid crystal phtwe are also discussed.

The double melting behavior of a liquid crystalline polyimide derived from PMDA and 1,3-bis[4-(4′-aminophenoxyl) cumyl] benzene

“…To our knowledge the liquid crystalline polyimide used in this study is the only PMDA-based aromatic polyimide that exhibits liquid crystallinity, although a number of liquid crystalline polyimides have been reported. [37][38][39][40][41] The diamine group used for this liquid crystalline polyimide synthesis seems to be a poor unit for molecular tight packing owing to the metaconnection and the methyl groups. Most polyimides derived from this diamine are amorphous.…”

Structures and phase transformations of odd-numbered asymmetric main-chain liquid crystalline polyesters

“…For the high-temperature transition, the heat of transition and the onset transition temperature at the high-temperature side do not exhibit cooling rate dependence. This indicates that the high-temperature transition takes place close to thermodynamic equilibrium, and it may be associated with the transitions between an isotropic melt (I) and a low ordered LC phase [28][29][30][31][32][33][34][35]. In contrast, the heat of transition (6.5 kJ/mol) at the lower transition temperature and its onset transition temperature are cooling rate dependent, which is often observed during polymer crystallization processes.…”

A solid-state13C-NMR study of the mesophases of PEIM-9 (poly(4,4′-phthaloimidobenzoylnonamethylene-oxycarbonyl))

“…Line broadening due to (1) can be eliminated partially, and line broadening due to (3) can be eliminated completely by sufficiently fast spinning about the magic angle. Line broadening due to (2) shows no dependence on spinning speed. The homogeneous line-broadenings (4) and (5) have a very weak dependence on H 0 , but are susceptible to an increase in the decoupling field strength H 2 .…”

“…Because of this, the line width is susceptible to further averaging by a coherent process (higher proton decoupling field or faster spinning speed). It is easy to see that the line-broadening due to mechanisms (1), (2) and (3) is linearly dependent on the external field strength (H 0 ), but is independent of the proton decoupling field (H 2 ). Line broadening due to (1) can be eliminated partially, and line broadening due to (3) can be eliminated completely by sufficiently fast spinning about the magic angle.…”