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Phase structure, morphology and phase boundary diagram in an aromatic polyimide (BPDA–PFMB)/ m ‐cresol system
Author(s) -
Park JaeYoung,
Kim Doyun,
Harris Frank W.,
Cheng Stephen Z. D.
Publication year - 1995
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/pi.1995.210370309
Subject(s) - materials science , differential scanning calorimetry , liquid crystal , phase (matter) , polarized light microscopy , bpda , polyimide , phase diagram , birefringence , phase transition , crystallography , polymerization , glass transition , polymer , polymer chemistry , chemistry , organic chemistry , composite material , optics , thermodynamics , physics , optoelectronics , layer (electronics)
Abstract An organo‐soluble aromatic polyimide has been synthesized from 3,3′, 4,4′‐bis(phenyltetracarboxylic) dianhydride (BPDA) and 2,2′‐bis (trifluoromethyl)‐4,4′‐diaminobiphenyl (PFMB) via a one‐step polymerization in m ‐cresol. The phase boundary diagram for this system has been established by differential scanning calorimetry, polarized light microscopy (PLM) and wide angle X‐ray diffraction (WAXD) experiments. A crystallosolvate form I has been found over the entire concentration region at low temperatures. When the temperature is increased, an isotropic phase has been observed below concentrations of about 40%. In the relatively high concentration region between 45 and 95%, a transition from the crystallosolvate from I to a crystallosolvate form II has been observed. Form II exhibits a different WAXD pattern. In a narrow concentration region between the isotropic and the crystallosolvate form II (40–45%), a biphase behavior has been found. The birefringence of this region may be an indication of a liquid crystalline phase. The BPDA–PFMB polymer crystal has been found in the very high concentration region (>95%) for temperatures >250°C. The morphologies of these phases have been investigated via PLM and transmission electron microscopy. Above the gel/sol transition temperature, the form I shows negative birefringent spherulites consisting of thin lamellae. The form II exhibits a tendency of positive birefringent spherulites. Possible mechanisms of the formation of the metastable phase morphology and their associations with the mechanical gel/sol transition are also discussed.