PREPARATION AND PROPERTIES OF THERMO-STABLE AROMATIC COPOLYIMIDE FIBERS

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Copolyimide fibers were prepared by thermal imidization method, starting from 4, 4'-diaminodiphenyl ether, pyromellitic dianhydride (PMDA), and 3, 3', 4, 4'-benzophenonetetracarboxylic dianhydride (BTDA), and their tensile and thermal properties were evaluated. In general, long term thermal stability (290°C) of the copolyimide fibers increased with increasing content of BTDA, because the copolymers containing more BTDA unit had lower crystallinity and lacked the physical deterioration by heat aging. In the case of the same polymer composition, thermal durability of the fiber drawn at lower temperature was better than that drawn at higher temperature because of the same reason. Dimensional stability at a high temperature (450°C) was good for the fibers containing PMDA ≥ 60mole%. A typical example was as follows: the fiber of PMDA/BTDA (mole ratio 60/40) hot-drawn 1.5 times at 350°C had tenacity (T) of 4.0g/d, elongation (E) of 16% and initial modulus of 62g/d, and percents retained of T and E after 112h at 290°C in air were 91 and 92%, respectively, and its shrinkage at 450°C was only 6%.