Optical anisotropies of polyoxyethylene oligomers

Abstract

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 Δα_CC= 0.95 ų, Δα_CH= 0.21 ų, and Δα_CO= 0.58 ų. 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.