Crowned polyacetylene.: 4.: Solid state NMR studies on molecular motions and cis-trans isomerization of poly(4′-ethynylbenzo-15-crown-5)

Chain conformations and molecular motions of poly(4'-ethynylbenzo-15-crown-5) (PEB15C5) and its annealed sample (AN-PEB15C5) in the solid state were investigated by H-1 NMR and CP-MAS C-13 NMR measurements. The chain conformation was determined to be cis-transoidal for PEB15C5 and 70 degrees-deflected trans-transoidal for AN-PEB15C5. The exothermic peak at 180 degrees C observed in the DSC thermogram was due to the cis-trans isomerization. Motional modes of each chain were observed in the three temperature regions of gamma, beta and alpha with an increase of temperature, which are attributed to the sterically hindered oscillation of the side chains and the vibrational and free rotations of the main chain with the oscillating side chain. The free rotation of the trans chain in the alpha-region occured in a lower temperature region by 15 degrees C, comparing with that of cis chain.