Chain-stiffness and lyotropic liquid crystallinity of polysilylene bearing(S)-2-methylbutyl and n-decyl substituents

The intrinsic viscosity [eta], the radius of gyration <S-2> (1/2), and the isotropic-cholesteric phase boundary concentration c, (between the isotropi c and biphasic regions) for poly [(n-decyl-(S)-2-methylbutyl)-silylene] dis solved in isooctane were measured as functions of the weight-average molecu lar weight M-w. By analyzing the results of [eta] and <S-2 >1/2 in terms of the wormlike-chain model, the persistence length q was determined to be 70 nm. Using this q, the scaled particle theory for the hard wormlike-spheroc ylinder model successfully predicted c(I) at high M-w but underestimated it at low M-w. The underestimate may be ascribed to the flexibility effect in the vicinity of the polymer-chain ends on c(1), which is more appreciable than the same effect on [eta].