MORPHOLOGICAL DEVELOPMENT IN ALKYL-SUBSTITUTED SEMIFLEXIBLE POLYMERS

Nonsymmetrically substituted semiflexible polymers were synthesized by reacting (hydroxypropyl)cellulose (HPC) with hexyl, octyl, dodecyl, a nd octadecyl isocyanates. X-ray diffraction studies indicate that the polymer chains are assembled in regular, layered arrays. Polymers with six and eight carbons in the side chains (C6HPC and C8HPC) showed sph erulitic structures typical of common crystalline polymers when examin ed by a polarized optical microscope (POM), whereas liquid crystalline (LC) textures were observed for C12HPC and C18HPC. When the polymers were slowly cooled from the melt, crystalline (C) textures could be ob tained for C12HPC and C18HPC at preselected temperatures slightly high er than the corresponding (isotropic --> LC) transition temperatures d etermined by DSC cooling scans. Upon further cooling, liquid crystalli ne structures appeared at temperatures 5-6 degrees C lower. The unusua l POM observations are in contrast to conventional thermal transitions reported for liquid crystalline polymers, where the isotropic --> LC transition takes place at a temperature higher than that of the LC --> C transition, but are consistent with Keller's studies on another liq uid crystalline polymer.