Dipole Moment of Poly(ethylene oxide) in Solution and Its Dependence on Molecular Weight and Temperature

Abstract

The dipole moment of poly(ethylene oxide) (PEO) and its dependence on molecular weight and temperature have been investigated by measuring the dielectric constant and the density of dilute PEO-benzene solutions in the temperature range from 25 to 55°C. The dipole moments of the polymers (μmolecule2)1/2, increased linearly with respect to the square root of the degree of polymerization n, which confirms the theoretical prediction that the long-range excluded volume interactions have little effect on the dipole moment of polymers such as PEO. The estimated value for diethyl ether μDE is 1.20D, according to the relationship between (μmolecule2)1/2 and n1/2 for PEO oligomers,10,17 which leads to a C-O bond moment, mC-O, of 1.07 D. The averaged dipole moment per constitutional repeating unit (μ2)1/2 for PEO polymers is 1.040 ± 0.002 [D] at 25°C. The following dipole moment ratio and the temperature coefficient were obtained for PEO in benzene: (μ2)/m2 = 0.472 ± 0.002 (at 25°C) and d ln(μ2)/dT = (2.11 ± 0.28) × 10−3 K−1 (25–45°C). The experimental results are compared with the conformational characteristics of PEO investigated by the rotational isomeric state (RIS) analyses by Abe et al. and Sasanuma et al.