Optical anisotropies of polyoxyethylene oligomers

The mean-squared optical anisotropies 〈γ2〉 of four oligomers of polyoxyethylene glycol dimethyl ether have been determined from measurements of depolarized Rayleigh scattering by carbon tetrachloride solutions at 25°C. They have been interpreted using the valence optical scheme and rotational isomeric state theory. The energies of the gauche states relative to trans were taken to be 900 cal mol–1 and –250 cal mol–1 for rotations about C—O and C—C bonds respectively. Gauche states of opposite signs for C—O—C bond pairs were excluded; those for C—C—O bond pairs were assigned an energy of 800 cal mol–1. Bond optical anisotropies were assigned the values ΔαCC= 0.95 A3, ΔαCH= 0.21 A3, and ΔαCO= 0.58 A3. Calculations of 〈γ2〉 carried out with these parameters successfully reproduce the observed values of 〈γ2〉. The foregoing rotational state energies are in close agreement with those deduced previously from the characteristic ratio 〈r2〉0/nl2 for the polymer, from the dipole moments 〈µ2〉 of oligomers and polymer, and from the temperature coefficients of these quantities.