Chemical heterogeneity in liquid-crystalline

OBERETAL. Chemical Heterogeneity in Liquid-Crystalline Polyesters 221... 

Aromatic liquid crystalline (LC) copolyesters of commercial importance are made by processes which produce compositionally heterogeneous chemical sequences along the polymer chain. Such chemical heterogeneity is responsible for a number of interesting properties of thermotropic LC polymers. These properties include a small amount of 3Current address General Electric Plastics, Mount Vernon, IN 47620... 

CDC are defined only by their size (most scientists agree on sizes below 1 pm others set 0.5 pm as the upper limit). CDC are very heterogeneous in all other aspects (e.g., thermodynamic stability, chemical composition, and the physical state, including solid, liquid, or liquid-crystalline dispersions) [ 1 ]. The most prominent examples are nanoparticles, nanoemulsions, nanocapsules, liposomes, nanosuspensions, (mixed) micelles, microemulsions, and cubosomes. Some CDC have reached the commercial market. Probably the best known example is the microemulsion preconcentrate of cyclosporine (Sandimmun-Neoral), which minimized the high variability of pharmacokinetics of the Sandimmun formulation. In addition, intravenous injectable CDC have been on the commercial market for many years. Examples include nanoemulsions of etomidate (Etomidat-Lipuro) and diazepam (Diazepam-Lipuro) [2-4], mixed micelles (Valium-MM, Konakion), and liposomes (AmBisome) [5]. 

The above results suggest that in general, the chemical behavior of probe molecules in highly ordered liquid crystalline phases such as this one may be governed by rather complex, heterogeneous solubilization effects. The manifestation of this in individual systems will depend primarily on solubility factors. The behavior of 8 in the smectic phase of CCH-2 is likely to be related to that in CCH-4, but a more exhaustive study of these systems has yet to be carried out. 

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