Mesomorphic phases of poly(DI‐n‐alkylsiloxane)s

Abstract

AbstractThe phase behavior of poly(dialkylsiloxane)s which are symmetrically substituted with ethyl, n‐propyl, and n‐butyl side groups has been investigated by solid state NMR and differential scanning calorimetry. All polymers exhibit disordering transitions before isotropization. The observation of conformational and motional changes is correlated to the different thermal transitions. Diffusive rotation of the chain segments around the molecule long axis is indicated by 29Si‐NMR below the isotropization transition. The remarkably fluid character is explained in part by the coexistence of anisotropic and isotropic motional states of the ‐OSiEt2‐ segments. Molecular motion below the upper disordering transition is restricted but still fast with respect to the 29Si‐NMR time scale. Long range reorganization processes have to be considered to explain the difference between α2‐PDES and β2‐PDES. The stepwise disordering at the onset of different motional processes, which results in the formation of a columnar liquid crystalline phase of these highly flexible chain molecules, is discussed with respect to the amphiphilic constitution of the molecules having an inorganic backbone substituted by organic side groups.