From a comparative study of the polarity of poly(neopentyl glycol hexafluoroglutarate) (PNFG) and its hydrogenated counterpart, poly(neopentyl glycol glutarate) (PNG), the influence of the presence of the fluorine atoms on the conformational characteristics of polyesters is investigated. At 30 degrees C, the experimental Values of the mean-square dipole moment per repeating unit of PNG and PNFG chains, [mu(2)/x are 5.25 and 9.16 D-2, respectively. A critical interpretation of the experimental results using the rotational isomeric state model suggests that the conformational energies associated with the gauche states about both the (CH2)-H-alpha-C*(O*) and (CH2)-H-beta-(CH2)-H-alpha bonds of the acid residue of PNG have, respectively, lower and higher energy than the alternative trans states. Similar conclusions are reached for the conformational energies associated with the skeletal bonds of the (CF2)-F-beta-(CF2)-F-alpha-C*(O*) segment of the acid residue of PNFG chains. This study leads us to conclude that differences in the orientations of the dipoles associated with the ester groups, rather than differences in the rotational populations about the skeletal bonds of the chains, may be responsible for the significant higher polarity of the fluorinated polyesters.