Synthesis and Characterization of Rigid-Rod Star-block Copolymers of a Varying Number of Arms

The synthesis and initial characterization of rigid-rod star-block copolymers exhibiting thermotropic mesophases are described. The copolymers consisted of flexible poly(dimethylsiloxane) cores having two to six arms, at the ends of which 4-[(methoxybenzoyl)oxy]benzoic acid mesogens were attached through amide linkages. The siloxane arm lengths were kept constant at approximately 2500 Ma. These block copolymers were of very well-defined structures with narrow molecular weight distributions. They were characterized by thermal and optical techniques. Clear evidence of phase separation between the flexible segments and the rigid blocks was obtained by the invariance of the low-temperature glass transition phenomena observed corresponding to the glass transition of the siloxane homopolymer. All the polymers of this series showed nematic liquid-crystalline texture in optical microscopy. © 1992, American Chemical Society. All rights reserved.