Distinguishing channel-type crystal structure from dispersed structure in β-cyclodextrin based polyrotaxanes via FTIR spectroscopy

Combining with XRD analysis, Fourier transform infrared (FTIR) spectroscopy is employed to discern the self-assembled structures of β-cyclodextrins (β-CDs) threaded onto the polymer backbone in the polyrotaxanes (PRs) by means of the relative changes of absorption intensity of the characteristic peaks of β-CDs at 1153 and 1025 cm^-1. For quantitative analysis, six parameters are proposed to describe the relative absorption intensity variations of these peaks associated with a channel-type crystal structure or a dispersed structure of β-CDs entrapped. Among them, absorbance ratio (AR), relative absorbance difference (RAD) and transmittance difference (TD) values are suitable. When the AR, RAD and TD data get below 1.04, 4.8 and 1.27, respectively, the PRs obtained would possess a dispersed structure. If these values go beyond 1.32, 34.5 and 9.47, respectively, they would hold a channel-type crystal structure. This finding provides a useful judgment to distinguish the self-assembled structures of β-CDs residing along the polymer backbone in the PRs.