SELF-ORDERING WITHIN THIN-FILMS OF POLY(OLEFIN SULFONE)S

A study has been performed of the manner in which two structural featu res of poly(olefin sulfone)s, helical backbones and calamitic side cha ins, create order in films. For this purpose copolymers were prepared with one (polymer I) or two (polymer III) cyanobiphenyls per residue, and terpolymers were prepared with both such residues diluted to below the 5% level within an otherwise poly(eicosene sulfone) chain (respec tively, polymers II and TV). The polymers all have ordered phases acco rding to X-ray powder diffraction studies on samples cooled from the m elt, a layer spacing of about 45 Angstrom being detected in the films as in the bulk. Those polymers with mainly eicosene sulfone residues h ad crystalline phases with large domains, the layers deriving from the helical backbones alone, the smectic A phases of the parent poly(eico sene sulfone) being either suppressed or reduced in extent by the pres ence of the aromatic moieties, which were almost randomly orientated. Those with one or tyro cyanobiphenyls per residue were liquid crystall ine. In the latter the layer spacing derives from both backbone and si de chains and is reduced when the residues bear a second mesogen as a consequence of a constraining effect from the stiff backbone, as a nov el model predicts. The spacers give rise to a glass transition and seg regate the planes in which the stiff backbones are assembled from the regions in which the aromatic groups aggregate on account of the stron g pi-pi interactions. Amorphous and optically isotropic spun cast fil ms of these polymers became ordered on cooling from the melt or just o n annealing, with the order, as determined by studies on the optical p roperties, being homeotropic for the aromatics and being planar for th e backbones in a monodomain. For this arrangement we introduce the ter m homeo-planar smectic. Order parameters as high as 0.63 were measured for polymer I, from a clear film. The cyanobiphenyl chromophores form ed H aggregates, with blue shifts in absorption and red shifts in fluo resence, and a little surprisingly these resulted in a circular dichro ism, detectable when the films were inspected at an angle of 45 degree s to the normal.