Morphology of melt-crystallized β′ phase crystals of monodisperse poly(9,9-dioctylfluorene)

- A novel β′ phase crystal of monodisperse PFO was prepared by melt crystallization.
- The β′ phase crystal has lamellar structure.
- The unit cell parameters and space group of β′ phase were given.
- The β′ phase crystals are more thermal stable than the β phase crystals.

A novel β′ phase crystal with lamellar structure of monodisperse poly(9,9-dioctylfluorene) (PFO) has been prepared by means of melt crystallization, demonstrating similar optical properties with β phase crystals. A preliminary determination of unit cell dimensions and molecular packing (orthorhombic, a = 1.30 nm, b = 2.22 nm, c = 3.36 nm, 4 chains, with space group Pmc21 and density 1.06 g/cm3) was made by combined analysis of the selected-area electron diffraction (SAED) and X-ray diffraction (XRD) patterns. In the lamellar crystals, the molecular backbone chains are parallel to the lamellar plane with the alkyl side chains interdigitation in the thickness of lamella.