SYNTHESIS AND PROPERTIES OF POLYAZOMETHINES HAVING FLEXIBLE (N-ALKYLOXY)METHYL SIDE-CHAINS

By solution condensation of 2,5-bis((n-alkyloxy)methyl)terephthalaldehydes with p-phenylenediamine a series of para-linked aromatic polyazomethines having (n-alkyloxy)methyl (CH2OCnH2n+1, n = 4, 6, 8, 12) side chains were prepared and their structures and properties were investigated. The presence of the side chains played a role in improving the solubility of the polymers of not too high molecular weight, but the polyazomethines of very high molecular weight could not be made soluble even in trifluoroacetic acid. Thermal stability decreased with increasing side-chain length. The polyazomethines showed basically three thermal transitions: disordering of the side-chain crystal (T(s)), solid-mesophase transition (T(m)), and mesophase-isotropic transition (T(i)). T(s) could be observed in the polymers of n greater-than-or-equal-to 6 and T(i) only in that of n = 12. As usual T(m) decreased drastically with increasing side-chain length. UV-vis spectroscopic studies made in sulfuric acid showed that the main-chain azomethine bond has a quite low stability against acid-catalyzed hydrolysis, but the side-chain ether bond has a different hydrolytic stability, depending on the side chains. In the solid state the as-polymerized samples crystallized into a layered structure, and the layer spacing determined by X-ray diffraction increased linearly with increasing side-chain length, suggesting that the side chains are interdigitated.