Dielectric Polarization and the Stages of a Macromolecule's Growth

Abstract

To investigate the change in the orientation polarization, particularly during the growth of a macromolecule by addition reactions in a liquid, dielectric relaxation spectra of diglycidyl ether of bisphenol A have been studied in real time. It is found that in the plot of the dielectric permittivity, ∈', measured at a fixed frequency against the polymerization time, the first step of the (inverted) sigmoid-shape part of the spectrum resembling a relaxational decrease is a dc conduction effect. After this effect vanishes, the equilibrium permittivity, ∈ s , of the liquid increases with time as covalently bonded molecular clusters form at random sites in the bulk liquid, and the dipole orientational correlation increases as a result of hydrogen bonding between the newly formed OH groups. Thereafter, the macromolecule's continuous growth in the liquid decreases the net dipole moment of the covalently bonded network, which decrease ∈ s . Thus, after the conductance effect has become negligible, a plot of ∈ s against the polymerization time shows a maximum. Both the dc conductivity, σ 0 , and the distribution parameter for dielectric relaxation decrease with time, and σ 0 follows a scaling equation for gelation. The irreversible increase in relaxation time during a macromolecule's growth is explained in terms of a decrease in the configurational entropy, and a relation between the two is provided.