The Diffusion of Short Polymer Chains in Dilute Solution

Abstract

AbstractThe variation of diffusion coefficient with chain length predicted by the Kirkwood‐Riseman theory is discussed using various models for polymethylene chains. The relative magnitudes of the free‐draining and impermeable contributions to the molecular friction coefficient are evaluated, and, for the range of chain lengths studied, less than 40 chain atoms, the details of the chain model are shown to be less important than the value of the friction coefficient per segment (ζ). — Diffusion data on short polymethylene chains in various solvents are analysed according to the Kirkwood‐Riseman theory and variations of ζ with both chain length and solvent are necessary for their interpretation. The significance of these variations with respect to segmental motion and solvent structure is discussed. — Diffusion data on poly(ethylene oxide) (PEO) in water and in quinoline and on poly(hexamethylene oxide) in quinoline are also considered. These systems do not show Kirkwood‐Riseman behaviour in that impermeability remains at short chain lengths. The behaviour observed is analysed and found to be consistent with solvent molecules diffusing with the solute molecules, through hydrogen bonds at the terminal hydroxyl groups, and, for the system PEO/ water, through additional hydrogen bonds at the ether oxygen atoms along the chain.