Rigid Cyclic Polymer in Solution: Cycloamylose Tris(phenylcarbamate) in 1,4-Dioxane and 2‑Ethoxyethanol

Six cyclic amylose tris­(phenylcarbamate) (ATPC) samples have been prepared from enzymatically synthesized cyclic amylose ranging in the number of repeat units <i>N</i> from 24 to 290. Synchrotron-radiation small-angle X-ray scattering measurements were made for the samples in 1,4-dioxane (DIOX) and 2-ethoxyethanol (2EE) to determine the <i>z</i>-average radius of gyration ⟨<i>S</i>²⟩_<i>z</i> and the particle scattering function <i>P</i>(<i>q</i>). Molar mass dependencies of ⟨<i>S</i>²⟩_<i>z</i> in the two solvents were successfully explained by the current theories for the wormlike ring with the same parameters for linear ATPC in the corresponding solvent, that is, the helix pitch <i>h</i> (or contour length) per residue and the Kuhn segment length λ^–1 (stiffness parameter, twice the persistence length). The latter parameter λ^–1 is 22 and 16 nm in DIOX and 2EE, respectively. Except for the low-<i>q</i> region, <i>P</i>(<i>q</i>) was also explained by the rigid ring having the same contour length <i>Nh</i> as that for linear ATPC. Further, their local conformation estimated from circular dichroism spectra is essentially unaltered from that for linear ATPC at least when <i>N</i> ≥ 24