Detection of the Difference in Local Chain Conformation Between Cyclic and Linear Oligomers in Solution: An X-Ray...

The particle scattering functions $P\left(k\right)$ as functions of the magnitude $k$ of the scattering vector for cyclic and linear oligo(dimethylsiloxane)s were measured in bromocyclohexane at 29.5 ${}^{\circ }C$ . A significant difference was observed in $P\left(k\right)$ between the cyclic and linear samples, both with the degree of polymerization $x$ equal to 5, in the range of $k\gtrsim$ 0.4 ${\AA }^{-1}$ , while $P\left(k\right)$ for the cyclic and linear samples of $x=5$ almost coincide with each other in the range of $k\lesssim$ 0.4 ${\AA }^{-1}$ . The behavior of $P\left(k\right)$ for the cyclic sample of $x=9$ is almost the same as that for the cyclic sample of $x=5$ for $k\gtrsim$ 0.4 ${\AA }^{-1}$ . These results indicate that the difference in the local chain conformation between cyclic and linear chains is detectable by examining the behavior of $P\left(k\right)$ even in the case of oligomers. However, the analysis of $P\left(k\right)$ using either a coarse-grained model or full-atom molecular structures in vacuum, both having been commonly employed in literatures, was not effective for the present experimental data. This result suggests that solute-solvent interference must be considered for analysis of $P\left(k\right)$ of such small cyclic chains.