Ordering, Graphoepitaxial Orientation, and Conformation of a Polyfluorene Derivative of the “Hairy-Rod” Type on an Oriented Substrate of Polyimide

Abstract

Spin-coated films of an ethylhexyl derivative of polyfluorene can be converted on a pretreated polyimide substrate into highly oriented films by annealing in the liquid crystalline state. Together with improving orientation segregation of the wormlike molecules with respect to chain lengths and lamella formation proceeds. End groups are preferentially assembled in interlamellar regions. This morphological feature is thought to influence all measurements of intrinsic properties of polyfluorene films with similar histories. Electron diffraction patterns of the film are identical with X-ray fiber diagrams of fibers drawn from the melt and annealed in the liquid crystalline state. The experimental data show that the polymer molecules adopt a helical (5/q) conformation, packing in a trigonal unit cell. Molecular modeling based on ab initio MO calculations have been carried out to obtain independent estimates of chain geometry and conformation. These calculations are more in favor of a 5/2 rather than a 5/1 helix, with the argument of the observed packing of the individual PF chains and a plausibly low torsion angle of adjacent fluorene building blocks only for a 5/2 helix.

Double screw-sense inversions of helical chiral-achiral random copolymers of fluorene derivatives in phase separating solutions

“…The phase-separating solutions were verified to have no optical anisotropy, 17 which means that the induced CD does not arise from a liquid crystal phase. The polyfluorene chain is known to take 5/2 or 5/1 helical conformations favorably 14,16 so that the CD induction indicates uneven population of the right-and lefthanded helical conformations of the copolymer main-chain. The Kuhn dissymmetry factor g c De/e at 410 nm (the CD peak position) reaches the asymptotic value at approximately 60 min (cf.…”

“…From electron and X-ray diffraction, 14,15 as well as molecular modeling, 14,16 these polymers are known to take a helical conformation, but chirality introduced to the side chain of the polymers was not found to induce circular dichroism (CD) on their backbone chain in dilute solution. This finding probably results from weak intramolecular chiral interactions that cannot discriminate against the handedness of the backbone helical conformation.…”

Structure, photophysics, and the order-disorder transition to theβphase in poly(9,9-(di-n,n-octyl)fluorene)

“…A branched side chain polyfluorene derivative, poly(9,9-di(ethylhexyl)fluorene) or PF2/6, only exhibits optical properties relating to the α form. Diffraction studies by Lieser et al 31 are therefore somewhat surprising because this polymer clearly adopts a well-ordered structural phase with good evidence for 5 1 or 5 2 fluorene helices.…”

Structure and Dynamics of Nondilute Polyfluorene Solutions

“…In contrast to this semiflexible chain structure, PF was reported to adopt an extended helical conformation in the liquid crystalline undiluted state. 6 The intermediate scattering function and orientation relaxation function of nondilute solutions of PF in toluene, obtained from dynamic (isotropic and anisotropic) light scattering over a broad concentration range in the isotropic regime, are presented in sections IIIB1 and IIIB2. The chain length and concentration of the transport properties are outlined in sections IIIC and IIID, and the main results are summarized in the concluding section IV.…”