Chen S H, Su A C, Su C H, Chen S A
Department of Materials Science and Engineering, National Dong Hwa University, Hualien 974, Taiwan.
J Phys Chem B. 2006 Mar 9;110(9):4007-13. doi: 10.1021/jp0555145.
Here we report the phase behavior of poly(9,9-di-n-hexyl-2,7-fluorene) (PFH), which previously received little attention as compared to its homologues poly(9,9-di-n-octyl-2,7-fluorene) (PFO) and poly(9,9-di-(2'-ethylhexyl)-2,7-fluorene) (PFEH). By means of differential scanning calorimetry, X-ray diffraction, and electron microscopy, we show that there exist four different phases in PFH. The as-cast film is mainly composed of a mesomorphic beta phase with layer spacing of ca. 1.4 nm. This beta phase is inherently metastable and, upon heating above 175 degrees C, transforms into a crystalline (alpha) form that melts into a nematic (N) liquid above 250 degrees C. Upon stepwise cooling, the nematic melt crystallizes into the alpha phase first, followed by solid-solid transformation into another crystalline (alpha') form. Unit cell structure of the alpha form is monoclinic whereas that of the alpha' form is triclinic, but departures from strict orthogonality are slight (by ca. 6 degrees). These observations not only support our previous assignment of two crystalline forms (both orthorhombic in structure) in PFO but also provide insights to the crystalline nature of the polyfluorene series.
在此，我们报告了聚（9,9-二正己基-2,7-芴）（PFH）的相行为，与它的同系物聚（9,9-二正辛基-2,7-芴）（PFO）和聚（9,9-二（2'-乙基己基）-2,7-芴）（PFEH）相比，PFH此前很少受到关注。通过差示扫描量热法、X射线衍射和电子显微镜，我们表明PFH中存在四种不同的相。铸膜主要由层间距约为1.4 nm的介晶β相组成。这种β相本质上是亚稳的，在加热到175℃以上时，转变为结晶（α）形式，在250℃以上熔化为向列（N）相液体。逐步冷却时，向列熔体首先结晶为α相，随后发生固-固转变为另一种结晶（α'）形式。α形式的晶胞结构为单斜晶系，而α'形式的晶胞结构为三斜晶系，但与严格正交性的偏差很小（约6度）。这些观察结果不仅支持了我们之前对PFO中两种结晶形式（结构均为正交晶系）的归属，也为聚芴系列的结晶性质提供了见解。
