ABSTRACT:A new rigid tetracarboxylic dianhydride, 3,3"'", 4,4"'"-p-sexiphenyltetracarboxylic dianhydride, was synthesized in seven steps starting from diethyl 4-bromophthalate. New aromatic polyimides containing a p-sexiphenyl unit were synthesized from this tetracarboxylic dianhydride and various aromatic diamines by the conventional twostep procedure of ring-opening polyaddition in a polar amide-type solvent and subsequent thermal cyclic dehydration. These polyimides had inherent viscosities of 1.20-1.69 dL g-1 , and were insoluble in organic solvents. The polyimides were characterized by differential scanning calorimetry (DSC), thermogravimetry (TG), wide-angle X-Ray diffraction measurements, and dynamic mechanical analysis (DMA). Typical polyimides were noncrystalline and showed excellent thermal stability, and had glass transition temperatures (Tg) at about 250'C. Decrease in the modulus at the glass transition temperature was less than corresponding polyimides having no p-sexiphenyl unit due to the presence of the rigid p-sexiphenyl unit.

ABSTRACT:A new rigid tetracarboxylic dianhydride, 3,3 ,4,4 -p-quinquephenyltetracarboxylic dianhydride, was synthesized in seven steps starting from diethyl 4-bromophthalate. New aromatic polyimides containing a pquinquephenyl unit were synthesized from this tetracarboxylic dianhydride and various aromatic diamines by the conventional two-step procedure of ring-opening polyaddition in a polar amide-type solvent and subsequent thermal cyclic dehydration. These polyimides had inherent viscosities of 0.20-1.20 dL g −1 , and were insoluble in organic solvents. The polyimides were characterized by differential scanning calorimetry (DSC), thermogravimetry (TG), wide-angle X-Ray diffraction measurements, and dynamic mechanical analysis (DMA). Typical polyimides had glass transition temperatures (T g ) at about 250 • C, and crystallized above T g s. The effects of p-quinquephenyl structure were reflected in the high storage modulus above the glass transition temperature. KEY WORDS 3,3 ,4,4 -p-Quinquephenyltetracarboxylic Dianhydride / Aromatic Polyimides / Glass Transition Temperature / Dynamic Storage Modulus / Aromatic polyimides are characterized by high glass transition temperature (T g ) along with high decomposition temperature and good mechanical properties, 1, 2 and are used in various fields including aerospace and electronics industries. The properties of the polyimides originate from unique aromatic heteroaromatic rings. Because of the rigidity of the ring, polyimides do not dissolve into organic solvents and melt without degradation. However, polyimides having rather rigid chemical structure between aromatic polyimide units exhibit high modulus and strength, 3, 4 and may be used to introduce highly rigid structure into polyimides and examine the properties of the polymers.Recently, we reported aromatic polyimides PI-Ar-m containing p-quarterphenyl (m = 2) 5 and p-sexiphenyl (m = 4) 6 unit, which were very rigid, and compared the properties of these polyimides with those of polyimides from 3,3 ,4,4 -p-terphenyltetracarboxylic dianhydride (m = 1) and 3,3 4,4 -biphenyltetracarboxylic dianhydride (m = 0), which have been previously prepared. 7 T g s were independent on the number of phenylene units (m) of the dianhydrides, while moduli were higher and decrement of moduli at the glass transition decreased with increasing m.We conducted the synthesis of a new rigid tetracarboxylic dianhydride, 3,3 ,4,4 -p-quinquephenyltetracarboxylic dianhydride, and aromatic polyimides (m = 3) were derived from it. This article is the first to report the synthesis and characterization of novel aromatic polyimides from tetracarboxylic dianhydride and aromatic diamines. The properties of polyimide, especially thermal behavior, are discussed. EXPERIMENTAL Materials4,4 -Diaminodiphenyl ether (VIa), 3,4 -diaminodiphenyl ether (VIb) 4,4 -diaminodiphenyl methane (VIc), m-phenylenediamine (VId), and p-phenylenediamine (VIe) were obtained commercially and purified by distillation under reduced pressure. 4,4 -bis(4-aminophenoxy)biphenyl (V...

(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 o C as tan δ peak temperatures of DMA, and the values did not depend on m. The decrement of storage modulus at the T g 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.