Structural phase transformation in tetrakis(4,4'-(2,2-diphenyl-vinyl)-1, 1'-biphenyl)methane

摘要

An irreversible structural phase transformation is observed in tetrakis(4,4'-(2,2-diphenyl-viny])-1,1'-biphenyl)methane, C(DPVBi)_4, upon increasing the temperature. The PI phase of the as-synthesized material is crystalline with tiny (typically 10-20nm) crystallites. The PI phase has hexagonal symmetry (space group P6) with the following lattice parameters a = 2.068 nm and c = 2.194 nm. When PI is annealed above its melting point (T_m = 260℃), the structure transforms irreversibly into a different hexagonal phase, PII, (space group P6/m) with lattice parameters a = 2.102 nm, c = 3.370nm. The PII phase melts at around T_m = 278℃. When heated above 278℃, C(DPVBi)_4 becomes amorphous with random molecular packing. The amorphous phase has a glass transition temperature, T_g, around 138℃. The PI phase transforms directly into the amorphous phase if the sample is continuously heated above the melting point (T_m = 278℃) of PII.