Liquid Crystalline Properties of Polyguanidines

Modified polyguanidines were prepared, and their liquid crystalline properties were studied using optical polarizing microscopy and X-ray diffraction. Parameters examined include chirality, the uniformity of the lengths of side chains, and attached side-chain mesogens. If the side chains on the repeat units are identical, then polymer has a more ordered structure in both solution and the solid state. Uniform lengths of the side chains are also important. Poly( N, N ‘-di- n -hexylguanidine), poly- I, exhibited a lyotropic smectic texture in contrast to a nematic texture of poly( N -( rac )- 2 -phenylethyl)- N ‘-methylguanidine) (poly-( rac -II )). Optically pure poly( N -(( R )- 2 -phenylethyl)- N ‘-methylguanidine) (poly-( R- II )) formed a cholesteric texture, whereas the corresponding racemic polyguanidine, poly-( rac- I I ), formed a nematic texture. Additionally, poly-( R -II ) displayed a mesophase at a lower critical concentration than either poly- I or poly-( rac- II ), implying that poly-( R- II ) is stiffer than these two other derivatives. Poly( N -6-((4 ‘ -methoxyphenylazo)phenyl-4-oxy)hexyl- N ‘- n -hexylguanidine) (poly- IV ), one of combined liquid crystalline structures (liquid crystalline backbone plus liquid crystalline side chains), displayed a lyotropic nematic texture presumably due to the strong dipolar−dipolar interaction between the main chain and side chains that folds the appendages parallel to the molecular axis. Poly( N -12-((4 ‘ -methoxybiphenyl-4-oxy)dodecyl- N ‘- n -dodecylguanidine) (poly- V ) and poly( N, N ‘-di- n -dodecylguanidine) (poly- VI ) exhibited thermotropic liquid crystalline behavior.