Preparation and Properties of Rigid Polyimides from Dianhydrides Having Various Number of Phenylene Units and <i>p</i>-Phenylenediamine

Rigid aromatic polyimides PI-PP-m (m = 0, 1, 2, 3, 4) were synthesized from p-phenylenediamine and dianhydride DA-m having various numbers (m) of phenylene units, 3,3'4,4'-biphenyltetracarboxylic dianhydride (DA-0), 3,3''4,4''-p-terphenyltetracarboxylic dianhydride (DA-1), 3,3'''4,4'''-p-quarterphenyltetracarboxylic dianhydride (DA-2), 3,3''''4,4''''-p-quinquephenyltetracarboxylic dianhydride (DA-3), and 3,3'''''4,4'''''-p-sexiphenyltetracarboxylic dianhydride (DA-4), by a conventional two-step procedure that included ring-opening polymerization and subsequent thermal cyclic dehydration. The PI-PP-m (m = 0, 1, 2, 3) films were characterized by wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetry (TG), dynamic mechanical analysis (DMA), and stress-strain curves. The properties were compared on the basis of the number (m) of phenylene units. The glass transition temperatures (Tg) were observed at 270-280 ℃ as tan δ peak temperatures of DMA, and the values did not depend on m. The decrement of storage modulus at the Tg was smaller with increasing m. The thermal properties of PI-PP-0 were compared with those previously reported for Upilex-S type polyimides prepared from p-phenylenediamine and DA-0.