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Diffusion in Aqueous Solutions of Poly(ethylene glycol) at Low Concentrations

We have observed the scaling behavior of the diffusion coefficient of poly(ethylene glycol) (PEG) ranging from dimer to n-mer of 14 000 ethylene glycol units in D 2 O and in a (1:1) mixture of D 2 O and diethylene glycol, solvents of both low and moderate viscosities. The accepted scaling relationship for diffusion of polymers at infinite dilution is D 0 = KM -a , where a ranges from 0.5 for a Θ solvent to 0.6 for a good solvent, as originally proposed by Flory. Measuring D 0 as the extrapolated value of D versus concentration in a PGSE-NMR experiment, we find a surprisingly good fit to this scaling relationship over the entire molecular weight range for both solvent systems. The values of a obtained in D 2 O at 25°C, D 2 O at 5°C, and a D 2 O/diethylene glycol mixture at 25°C were 0.597± 0.020, 0.534±0.021, and 0.542 ± 0.058, respectively. The extension of the scaling behavior down to the dimer species is believed to be due to the high local segmental friction coefficient of the ethylene oxide unit