Chain-Stiffness and Lyotropic Liquid Crystallinity of Polysilylene Bearing (S)-2-Methylbutyl and n-Decyl Substituents

The intrinsic viscosity [η], the radius of gyration 〈S²〉^1/2, and the isotropic−cholesteric phase boundary concentration c_I (between the isotropic and biphasic regions) for poly[(n-decyl-(S)-2-methylbutyl)silylene] dissolved in isooctane were measured as functions of the weight-average molecular weight M_w. By analyzing the results of [η] and 〈S²〉^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-spherocylinder 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_I, which is more appreciable than the same effect on [η].