INTERPLAY BETWEEN THE MOLECULAR-STRUCTURE AND THE FORMATION OF THERMOTROPIC MESOMORPHIC PHASES IN TRANS MICROTACTIC POLY[OXY(HEXAMETHYLCYCLOTETRASILOXANE-2,6-DIYL)]S

trans-Microtaetic poly[oxy(hexamethylcyclotetrasiloxane-2,6-diyl)]s of different stereoregularity of the main chain (mu = trans/cis greater than or equal to 58/32) were studied using DSC and X-ray diffraction. Increasing mu led to an increase in crystallinity, a slight increase i n phase transition temperatures, and had almost no effect on the tempe rature-mediated evolution of the phase states of the polymer. The poly mers with mu greater than or equal to 68/32 were shown to be mesomorph ic compounds; structural characteristics of the two mesomorphic modifi cations were determined. By using molecular mechanics it was demonstra ted that the 2(1) conformation is the only one feasible for the molecu les of trans stereoregular polymer. Interplay between the hierarchy of energy states of the trans isomeric macromolecule and the thermotropi c hierarchy of the phases of the corresponding polymer was discussed. Resting on the energy criteria of the molecular mechanics and the data of X-ray diffraction, a scheme of two-level conformational disorderin g was suggested. It was demonstrated that the existence of mesomorphic state in polymers with mu greater than or equal to 68/32 is associate d with a certain conformational order retained in the trans sequences at temperatures above the melting temperature of the crystalline phase . The most probable models for the structure of mesomorphic modificati ons were selected by minimization of the potential energy of the syste ms. It was fond that an increase in the symmetry of planar unit eel in the basis plane during the polymesomorphic transition is due to the g rowth of the area per macromolecule in the 2(1) conformation in the or dered plane rather than to the conformational changes in the macromole cules.