| Abstract: | Nanophase separated poly(4,4′-phthaloimidobenzoyl-dodecamethyleneoxycarbonyl) (PEIM-12) is studied by solid-state 13C-NMR (nuclear magnetic resonance), differential scanning calorimetry and X-ray and neutron diffraction techniques. On cooling from the melt, PEIM-12 shows a layer structure that has been described in the literature either as a nanophase-separated material or a monotropic, thermotropic liquid crystal. Further crystallization leads to two possible crystalline phases (I and II). The new measurements reveal a biphasic behavior below the thermal transition temperatures. The lamellar superstructure is shown by neutron and X-ray scattering to be largely independent of the crystals and may even exist above the melting point. The two crystal forms are shown by NMR to differ in conformational ordering in the flexible spacers. Crystal II possesses conformational order in the center of the flexible spacer, while crystal I shows order at the ends. Sufficient conformational disorder remains, however, in both crystals, to make them condis crystals, short for conformationally disordered crystals. Calorimetry agrees with the measured entropies of disordering. The disagreement between the earlier analyses is eliminated by assuming that PEIM-12 is a special borderline liquid crystal former. Small changes in the structural order (head-to-head or head-to-tail) can change the behavior from that of a monotropic, thermotropic liquid crystal to an amphiphilic, nanophase-separated liquid crystal. © 1997 John Wiley & Sons, Ltd. |
