STRUCTURE AND PHASE-BEHAVIOR OF POLYAZOMETHINES HAVING FLEXIBLE (N-ALKYLOXY)METHYL SIDE-CHAINS

Structure and phase behaviour of a series of thermotropic polyazomethi nes having (n-alkyloxy)methyl side chains (-CH2O-n-CmH2m+1, m = 4, 6, 8, 12) have been studied by wide-angle X-ray scattering, differential scanning calorimetry (d.s.c.) and polarizing optical microscopy. In d. s.c. thermograms the samples showed basically three transitions. The f irst transitions were ascribed to solid-solid transitions resulting fr om a large increase in disorder of the side chains. The second ones we re assigned to crystal-mesophase transitions arising from melting of t he side chain crystals. The third ones were attributed to mesophase-is otropic melt transitions. All the samples showed layered structures in the mesophase as well as in the crystalline phase, in which the side chains were fully interdigitated. In the crystalline phase the repeat units of rigid main chain were found not to align parallel with those of neighbouring main chains, but slipped by 49 degrees. In the mesopha se the side chain crystals were molten and the layer spacings increase d proportionally with increasing side chain length. The structural reg ularity in the slipped repeat unit disappeared in the polymers bearing long side chains, whereas it was retained in those having short side chains. A unidirectional shearing made the layer plane align parallel on the surface. Copyright (C) 1996 Elsevier Science Ltd.