Aqueous solution properties of oligo- and poly(ethylene oxide) by static light scattering and intrinsic viscosity

Abstract

Conformational properties of ethylene glycol, oligo-, and poly(ethylene oxide) ranging in weight-average molecular weight ( M w) from 62 to 1.1 × 10 7 have been studied by static light scattering and viscometry in salt-free and 0.45 M K 2SO 4 water and in benzene. Above M w = 6 × 10 3, intrinsic viscosity ([η]) and z-average square radius of gyration (〈 S 2〉 2) of PEO in a salt-free solution at 25°C, [η] = 4.33 × 10 −4 M w 0.67 9 dl g −1 and 〈 S 2〉 z = 4.08 × 10 −18 M w 1.1 6 cm 2, respectively. The second virial coefficient is positive in water at 25°C but one order of magnitude smaller than reported by Devanand et al. ( Macromolecules, 1991, 24, 5943). A θ-temperature for PEO in 0.45 M K 2SO 4 aqueous solution is determined to be 34.5°C and above M w = 4 × 10 2, [η] and 〈 S 2〉 z follow the power laws for an unperturbed polymer chain. The characteristic ratio ( C ∞) of PEO is 5.2 ± 0.1. 9.3Åwas determined for the persistence length and 8.7Å −1 for the molar mass per unit contour length of a PEO chain, based on the helical wormlike touched-bead model. The PEO chain in water behaves as a flexible polymer with a relatively large hydrodynamic diameter (9Å) because of the hydration of the PEO chain.