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

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