Extended-chain lamellar crystals of monodisperse polyfluorenes

Polymer single crystals of monodisperse poly (9,9-dioctylfluorene)s (PFOs) with actual molecular weights of 6220, 12,437 and 24,874 Da corresponding to the numbers of fluorene repeating units of 16, 32 and 64, respectively, were grown from chloroform/ethanol solutions. In the single crystals, polymer chains adopt lamellar packing motif. The crystal structure determined by electron diffraction is identical for all three PFOs, and the single crystal has an orthorhombic unit cell with lattice parameters of a = 2.16 nm, b = 1.28 nm, and c = 336 nm. In these lamellar crystals, PFO backbones are arranged perpendicular to the lamellar surface and alkyl side chains are along the crystal-growth direction. The lamellar thickness is identical to the extended chain length of the corresponding polymer as demonstrated by atomic force microscopy (AFM) measurements. It is noteworthy to point out that F64 still maintain extended-chain packing habit even when the chain length is as long as 53 nm. Therefore, our results demonstrated that chains remain extended in this system. (C) 2013 Elsevier Ltd. All rights reserved.