Novel aromatic polyamides with 1,3-benzoazole groups in the main chain. 1.Polymers derived from 2-(4-carboxyphenyl) benzoxazole-5-and 6-carboxylic acids. Synthesis and characterization

Two series of aromatic poly(amide-benzoxazole)s have been obtained from 5-c hlorocarbonyl-2-(4-chlorocarbonylphenyl)benzoxole(NBOC) and 6-chlorocarbony l-2-(4-chlorocarbonylphenyl)benzoxazole (OBOC). NBOC and OBOC were synthesi zed by a three-step process with high yields, and they were reacted with ar omatic diamines by using the in situ silylation method which yielded polyme rs of high inherent viscosities. The solubility of these polymers was simil ar to that of aromatic polyamides, being soluble in aprotic polar solvents. All polymers could be processed to tough, creasable amorphous films with g ood mechanical properties, the values of tensile strength ranging from 92 t o 113 MPa with moduli above 2 GPa. The glass transition temperatures were a bove 300 degreesC, whilst the onset of thermal degradation ranged from 455 to 515 degreesC. A theoretical study was also done, by means of computation al chemistry methods, to relate the orientation of the benzoxazole ring in both series with monomer reactivity and polymer properties. (C) 2001 Elsevi er Science Ltd. All rights reserved.