PHASE MORPHOLOGIES IN BLOCK-COPOLYMERS OF POLYSTYRENE AND COLUMNAR LIQUID-CRYSTALLINE POLYDIETHYLSILOXANE

Well-defined diblock copolymers of polystyrene (PS) and polydiethylsil oxane (PDES) were synthesized by sequential anionic polymerization. By means of differential scanning calorimetry (DSC), the PDES blocks wer e shown to exist in the columnar mesophase at ambient temperatures. PS -b-PDES block copolymers with a PS content >21 wt.-% build lamellar st ructures, below this percentage PS cylinders were found that are arran ged in sheets, forming a (somewhat irregular) overall lamellar structu re. Both the low PS content at which the transition from lamellar to c ylindrical structures takes place, as well as the peculiar organizatio n of the PS cylinders in the latter were ascribed to the mesomorphic n ature of the PDES block in combination with the fact that the glass tr ansition temperature of PS (T-g approximate to 100 degrees C) is much higher than the isotropization temperature of the PDES block (T-i (ca. 50 degrees C).