The effect of polar groups on the dielectric loss of polyethylene

The dielectric loss tangent for polyethylene with low dielectric loss was approximated by tan δ = C f Σ( nμ 2 ), where n and μ are the number and dipole moment of polar groups, respectively, and C f is a parameter. The type and number of polar groups in the polyethylenes were mainly determined from infrared spectra obtained with a Fourier transform spectrometer. It was found that the contribution of hydroxyl and carbonyl groups to tan δ was significantly large, but the contribution of double bond groups was less significant. The tan δ was observed to decrease with a decrease of methyl group density although the overall contribution of methyl groups to tan δ was small. This suggests that tan δ is closely related to the secondary structure of polyethylenes, thus indicating the methyl groups seem to play an important role in the secondary structure.