Effect of side-chain asymmetry on the intermolecular structure and order-disorder transition in alkyl-substituted polyfluorenes

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We study relations among the side-chain asymmetry, structure, and order-disorder transition (ODT) in hairy-rod-type poly(9,9-dihexylfluorene) (PF6) with two identical side chains and atactic poly(9-octyl-9-methyl-fluorene) (PF1-8) with two different side chains per repeat. PF6 and PF1-8 organize into alternating side-chain and backbone layers that transform into an isotropic phase at TODT(PF6) and TbiODT(PF1-8). We interpret polymers in terms of monodisperse and bidisperse brushes and predict scenarios TODT<TbiODT and TODT∼TbiODT for high and low grafting densities (the side-chain length above or below the average grafting distance). Calorimetry and x-ray scattering indicate the condition TODT(PF6)∼TbiODT(PF1-8) following the low grafting prediction. PF6 side chains coming from the alternating backbone layers appear as two separate layers with thickness H(PF6), whereas PF1-8 side chains appear as an indistinguishable bilayer with a half thickness Hbilayer(PF1-8)/2≈H(PF6). The low grafting density region is structurally possible but not certain for PF6 and confirmed for PF1-8.


  • M. Knaapila
  • R. Stepanyan
  • M. Torkkeli
  • D. Haase
  • N. Fröhlich
  • A. Helfer
  • M. Forster
  • U. Scherf
External organisations
  • Technical University of Denmark
  • University of Helsinki
  • University of Wuppertal
  • DSM Research
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Atom and Molecular Physics and Optics
Original languageEnglish
Article number042504
JournalPhysical Review E - Statistical, Nonlinear, and Soft Matter Physics
Issue number4
StatePublished - 2016 Apr 28
Publication categoryResearch