NANOPHASE SEPARATION AND CRYSTALLIZATION IN PEIM-12 4'-PHTHALOIMIDOBENZOYL-DODECAMETHYLENEOXYCARBONYL)

Nanophase separated 4'-phthaloimidobenzoyl-dodecamethyleneoxycarbonyl) (PEIM-12) is studied by solid-state C-13-NMR (nuclear magnetic resona nce), differential scanning calorimetry and X-ray and neutron diffract ion techniques. On cooling from the melt, PEIM-12 shows a layer struct ure that has been described in the literature either as a nanophase-se parated material or a monotropic, thermotropic liquid crystal. Further crystallization leads to two possible crystalline phases (I and II). The Mew measurements reveal a biphasic behavior below the thermal tran sition temperatures. The lamellar superstructure is shown by neutron a nd 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. Cry stal II possesses conformational order in the center of the flexible s pacer, while crystal I shows order at the ends. Sufficient conformatio nal disorder remains, however, in both crystals, to make them condis c rystals, short for conformationally disordered crystals. Calorimetry a grees with the measured entropies of disordering. The disagreement bet ween the earlier analyses is eliminated by assuming that PEIM-12 is a special borderline liquid crystal former. Small changes in the structu ral order (head-to-head or head-to-tail) can change the behavior from that of a monotropic, thermotropic liquid crystal to an amphiphilic, n anophase-separated liquid crystal. (C) 1997 by John Wiley & Sons, Ltd.