Glass transitions in the stable crystalline states of dibenzofuran and fluorene

✍ Scribed by Hiroaki Fujita; Hiroki Fujimori; Masaharu Oguni

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 521 KB
• Volume: 27
• Category: Article
• ISSN: 0021-9614
• DOI: 10.1006/jcht.1995.0098

✦ Synopsis

Heat capacities of dibenzofuran and fluorene were measured with an adiabatic calorimeter in the temperature ranges 245Q(T/K)Q375 and 200Q(T/K)Q419, respectively. Glass transitions were discovered at Tg=316 K for both the compounds in the stable crystalline state due to freezing-in of the reorientational motion of the pseudo-planar molecule. In dibenzofuran, the molar-heat-capacity jump at Tg was estimated to be (6.820.2) J•K -1 •mol -1 and the molar activation energy for the reorientation to be (9825) kJ•mol -1 . In fluorene, the molar-heat-capacity jump at Tg was estimated to be (7.020.3) J•K -1 •mol -1 , and the enthalpy relaxation as a function of time showed a remarkable non-exponentiality. The latter was interpreted potentially to be related to non-planarity of the molecule. 71995 Academic Press Ltd.