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

Abstract

Two series of aromatic poly(amide-benzoxazole)s have been obtained from 5-chlorocarbonyl-2-(4-chlorocarbonylphenyl)benzoxazole (NBOC) and 6-chlorocarbonyl-2-(4-chlorocarbonylphenyl)benzoxazole (OBOC). NBOC and OBOC were synthesized by a three-step process with high yields, and they were reacted with aromatic diamines by using the in situ silylation method which yielded polymers of high inherent viscosities. The solubility of these polymers was similar to that of aromatic polyamides, being soluble in aprotic polar solvents. All polymers could be processed to tough, creasable amorphous films with good mechanical properties, the values of tensile strength ranging from 92 to 113 MPa with moduli above 2 GPa. The glass transition temperatures were above 300°C, whilst the onset of thermal degradation ranged from 455 to 515°C. A theoretical study was also done, by means of computational chemistry methods, to relate the orientation of the benzoxazole ring in both series with monomer reactivity and polymer properties.