Role of main chain rigidity and side-chain substitution on the supramolecular organization of rigid-flexible polymers

The synthesis, characterization and supramolecular organization of rigid-flexible aromatic-aliphatic polyethers are reported. The polymers contain substituted quinquephenyl moieties along their main chains separated by flexible aliphatic units of various lengths. The oligophenylene segments bear different types of dodecyloxy tailed side groups, either attached on the periphery of side dendritic wedges (G1) or as direct side-chains (G0). Their structural characterization was performed by means of differential scanning calorimetry, polarizing optical microscopy and X-ray scattering from oriented fibers. These techniques revealed the presence of supramolecular organization in different levels and in the absence of solvent, reflecting a delicate balance of interactions produced by the rigid-flexible backbone segments and the size of dendritic side-chains. It was concluded that the polymers with only two dodecyloxy side-chains (zeroth generation, G0) possess smectic order. On the other hand, substitution of the quinquephenyl backbone with the dodecyloxy decorated dendrons (first generation, G1) disrupts the lateral order giving rise to a nematic state. These results are compared with the corresponding rigid-flexible polyethers having terphenyl rigid segments.