Concentration-induced conformational change in linear polymer threaded into cyclic molecules

The concentration-induced conformational change in hydroxypropylated polyrotaxane (H-PR) composed of poly(ethylene glycol) (PEG) and hydroxypropylated (x-cyclodextrins (CDs) was investigated at various concentrations from the overlap concentration c* to the semidilute regime by using the small-angle neutron scattering technique. We employed the generalized Zimm plot with the wormlike chain model to analyze the scattering functions of H-PR since they deviated from the Ornstein-Zernike equation particularly in the high-Q range. It was found that the persistence length of H-PR decreased with increasing polymer concentration c(p), while those of PEG remained unchanged in the same molar concentration regime. This unusual concentration dependence of polymer conformation for H-PR may indicate that CDs in H-PR could slide freely and rapidly over the whole range of PEG chains in the neighborhood of c*, but their mobility was suppressed as cp increased due to some molecular interaction among CDs.