Synthesis and Characterization of Soluble and Thermally Stable Poly(ether-imide-urea)s Hojjat Toiserkani Department of Chemistry, College of Sciences and College of Oil Engineering, Hormozgan University, Bandar Abbas 3995, Iran Received November 27, 2013; E-mail: Toiserkani@yahoo.com Two series of new modified poly(ether-imide-urea)s, P O a-P O c and P S a-P S c,with benzoxazole or benzothiazole pendent groups were successfully synthesized by diphenyl azidophosphate (DPAP)-activated one-pot polyaddition reaction of two bis(imide-dicarboxylic acid)s, 2-[3,5-bis(4-trimellitimidophenoxy)phenyl]benzoxazole(1 O ) or 2-[3,5- bis(4-trimellitimidophenoxy)phenyl]benzothiazole(1 S )with various kinds of aromaticdiamines a-c. In thisdirect method, the polymers were prepared by polyaddition reactions of the insitu-formed diisocyanate with the aromatic diamines. For comparative purposes, reference poly(ether-imide-urea)s, P R a-P R c, were also prepared by reacting a bis(imide-dicarboxylic acid) lacking pendent groups, namely, 3,5-bis(4-trimellitimidophenoxy)benzene (2)with the same diamines under similar conditions. Characterization of polymers was accomplished by inherent viscosity measurements, FTIR, 1 H NMR spectroscopy and thermogravimetry. The polymers were obtained in quantitative yields with inherent viscosities between 0.19 and 0.37 dL g ¹1 . The solubilities of modified poly(ether-imide-urea)s in common organic solvents as well as their thermal stability were enhanced compared to these of the corresponding unmodified poly(ether- imide-urea)s. The glass-transition temperature, 10% weight loss temperature, and char yields at 800 °C were, respectively, 7-28, 14-38 °C, and 3-7% higher than those of the reference polymers innitrogen atmosphere. Polyimides present both great scientific and commercial interest, because of their combination of outstanding key prop- erties, including thermal and thermooxidative stability, high mechanical strength, high modulus, good adhesion to common substrates, excellent electrical properties, and superior chemical resistance. 1-3 However, despite the excellent combined prop- erties, theirwidespread applications have been limited in some fields, because aromatic polyimides are normally insoluble in common organic solvents and have extremelyhigh glass- transition temperatures (T g ’ s) or melting temperatures, which preclude melt processing. Consequently, the search for new polyimides with better processability, and the same thermal stability should result in new materials for many applications. The incorporation of ether groups or other flexibilizing linkages into the main chain generally leads to lower glass-transition temperature as well as a significant improvement in solubility without greatly sacrificing other advantageous polymer prop- erties. 4-7 On the other hand, the introduction of bulky groups into the polymer chain 8-13 or the attachment of bulky lateral groups 14-21 can impart a significant increase in T g by restricting the segmental mobility, while providing an enhanced solubility due to decreasing packing and crystallinity. Combining these two structural modifications minimized the trade-off between the processability and useful and positive properties of aro- matic polyimides. In our previous studies, two benzoxazole- or benzothia- zole-containing dicarboxylic acids bearing two preformed imide rings, 2-[3,5-bis(4-trimellitimidophenoxy)phenyl]benzoxazole (1 O ) and 2-[3,5-bis(4-trimellitimidophenoxy)phenyl]benzothia- zole(1 S ) were synthesized and used for the preparation of corresponding alternating poly(ether-imide-amide)s, 22 poly- (ether-imide-ester)s 23 and poly(ether-imide-urethane)s. 24 As part of our continuing efforts to develop soluble poly- imides with good thermal stability, the current work dealswith the synthesis and characterization of two series of new modi- fied poly(ether-imide-urea)s, P O a-P O c and P S a-P S c, bearing benzoxazole or benzothiazole pendent groups derived from two bis(imide-dicarboxylic acid)s, 1 O and 1 S with various kinds of aromaticdiamines a-c in dry dimethyl sulfoxide (DMSO) in the presence of diphenyl azidophosphate (DPAP) via “one-pot” procedure. The effect of pendent groups on solubility and thermal properties of the resulting modified polymers is inves- tigated by comparison with polymers missing pendent group, reference P R a-P R c, obtained from 1,3-bis(4-aminophenoxy)- benzene (3) and the same diamines. Since the designed poly- (ether-imide-urea)s are composed offlexible ether linkages, and pendent groups, they should be expected to exhibit an enhanced solubility, and excellent thermal properties in com- parison with reference polymers. Experimental Materials. All chemicals were purchased either from Merck or Fluka Chemical Co. Diphenyl azidophosphate (DPAP) was purchased from Merck and used as received. Dimethyl sulfox- ide (DMSO, Merck), and triethylamine (TEA, Merck) were purified by distillation under reduced pressure over calcium hydride and stored over 4-¡ molecular sieves. 1,3-Phenylene- diamine (a, Merck) was purified by sublimation before use. © 2014 The Chemical Society of Japan Published on the web January 17, 2014; doi:10.1246/bcsj.20130330 Bull. Chem. Soc. Jpn. Vol. 87, No. 5, 631-638 (2014) 631