Liquid crystalline polymers. 8 - Thermal behavior and molecular simulationof some oligomers containing a propylenic spacer

The present paper studies the influence of chain chemical structure over th e ordering capacity and liquid crystalline behaviour of some polyethers. Th e polymers were synthesized using the phase transfer catalysis technique, s tarting from 1,3-dibromopropane and various bisphenols, as follows: 4,4'-di hydroxyazobenzene, 4,4'-dihydroxydiphenyl, bisphenol A and 4,4'-tiodiphenol . The polyethers were characterised by H-1-NMR, DSC and optical microscopy techniques. Probably, due to the dehydrobromuration reactions, that have as a result chain-ends desactivation, oligomeric products have been obtained. Only the oligomers containing azobenzene and biphenyl units presented liqu id crystalline properties, modification of the ratio between these two bisp henols generating either an enantiotropic or a monotropic behaviour. The th ermal properties of the synthezised products were compared with those of si milar polyethers containing an oxetanic spacer, the polymers having compara ble chain flexibilities. Molecular simulations were performed, to evaluate chain flexibility and for a better understanding of the influence of chains conformation upon the ordering capacity.