Self-Ordering within Thin Films of Poly(olefin sulfone)s

Abstract

A study has been performed of the manner in which two structural features of poly(olefin sulfone)s, helical backbones and calamitic side chains, 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 (respectively, polymers II and IV). The polymers all have ordered phases according to X-ray powder diffraction studies on samples cooled from the melt, a layer spacing of about 45 Å being detected in the films as in the bulk. Those polymers with mainly eicosene sulfone residues had crystalline phases with large domains, the layers deriving from the helical backbones alone, the smectic A phases of the parent poly(eicosene sulfone) being either suppressed or reduced in extent by the presence of the aromatic moieties, which were almost randomly orientated. Those with one or two cyanobiphenyls per residue were liquid crystalline. In the latter the layer spacing derives from both backbone and side chains and is reduced when the residues bear a second mesogen as a consequence of a constraining effect from the stiff backbone, as a novel model predicts. The spacers give rise to a glass transition and segregate the planes in which the stiff backbones are assembled from the regions in which the aromatic groups aggregate on account of the strong pi-pi interactions. Amorphous and optically isotropic spun cast films of these polymers became ordered on cooling from the melt or just on annealing, with the order, as determined by studies on the optical properties, being homeotropic for the aromatics and being planar for the backbones in a monodomain. For this arrangement we introduce the term homeo-planar smectic. Order parameters as high as 0.63 were measured for polymer I, from a clear film. The cyanobiphenyl chromophores formed H aggregates, with blue shifts in absorption and red shifts in fluoresence, and a little surprisingly these resulted in a circular dichroism, detectable when the films were inspected at an angle of 45 degrees to the normal.

Photoinduced optical anisotropy in new poly(amide imide)s with azobenzene units

“…No differences between the position of absorption maximum in film and in solution are observed (3b-d, 4f-h) in the case of all polymers except for polymer 3a(4e). The p-p * transition of the azobenzene in the film is 18 nm hypsochromically shifted with respect to the solution which indicates the formation of H aggregates [22]. …”

Alignment of Photo‐Crosslinkable Copolymer Liquid Crystals Induced by Linearly Polarized Ultraviolet Light Irradiation and Annealing: Effect of Heating Rate

“…It was reported that the mesogenic groups aligned homeotropically by heating for the polymer LC films with azobenzene side groups [24] and cyanobiphenyl side groups. [28] The length of the spacer between the polymer backbone and the mesogenic groups, and the type of the polymer main chain influence the homeotropic alignment by annealing. [24,28] In the case of the P2 film, the formation of the polydomain structure of the mesogenic groups, and the interaction between the mesogenic groups and the glass substrate during the annealing will be highly changed when the heating rate is changed, resulting in the different re-orientational behavior.…”

“…[28] The length of the spacer between the polymer backbone and the mesogenic groups, and the type of the polymer main chain influence the homeotropic alignment by annealing. [24,28] In the case of the P2 film, the formation of the polydomain structure of the mesogenic groups, and the interaction between the mesogenic groups and the glass substrate during the annealing will be highly changed when the heating rate is changed, resulting in the different re-orientational behavior. Further study on the alignment behavior using CPLCs with a 6CiB group and an nCB group with spacers of different lengths is still underway.…”

Photoinduction and Control of the Supramolecular Chirality in Liquid Crystalline Azomaterials

“…The CD spectra of the irradiated polymers exhibit an exciton couplet corresponding to the p À p à absortion band of the azobenzene and centered between 330 and 340 nm, that is blue-shifted in comparison to the p À p à absorption band of the UV-vis spectra corresponding to isolated azobenzene groups [20,21]. These exciton couplets are due to the splitting of an H-band as a consequence of a chiral interaction between adjacent chromophores [27][28][29]. The Cotton effect at 390 nm can be due to the superposition of the band of the exciton couplet centered around 330-340 nm, the induced Cotton effects of the isolated azobenzene units and J-aggregates [30].…”