Solution SAXS measurements over a wide temperature range to determine the unperturbed chain dimensions of polystyrene and a cyclic amylose derivative

Abstract

The mean-square radii of gyration <S2> of two polystyrene (PS) samples with weight-average molar masses Mw of 2.18 × 104 and 3.88 × 104 in toluene and 2-butanone and of a cyclic amylose tris(phenylcarbamate) (cATPC) with a Mw of 4.73 × 104 in tetrahydrofuran were determined by synchrotron radiation small-angle X-ray scattering measurements over a wide range of temperatures from −77 °C to 70 °C. Both PS and cATPC are sufficiently soluble to enable SAXS measurements even at −77 °C in the solvents used. The <S2> of cATPC does not depend on temperature over the range investigated here. This result may be reasonable for such rigid ring polymers. In contrast, the radii of PS depend on temperature to a significant degree, whereas the second virial coefficient is mostly temperature independent. The resulting characteristic ratio C∞ for PS in toluene decreases monotonically with increasing temperature, as predicted both by the rotational isomeric state (RIS) and by (helical) wormlike chain models. However, C∞ in 2-butanone exhibits a minimum ∼10 °C and increases with increasing temperature, suggesting that the RIS energy parameters should be affected by the intermolecular interactions between the polymer and solvent. Mean-square radii of gyration <S2> for two polystyrene samples in toluene and 2-butanone and a cyclic amylose tris(phenylcarbamate) (cATPC) sample in tetrahydrofuran were determined by SAXS between −77 and 70 °C. Whereas <S2> of cATPC does not depend on temperature over the range investigated, those for polystyrene depend to a significant degree. The characteristic ratio for polystyrene in toluene monotonically decreases with increasing temperature. However, that in 2-butanone has a minimum ∼10 °C, suggesting that the RIS energy parameters are affected by the intermolecular interactions between the polymer and solvent.