Dielectric relaxation in solutions of poly (ϵ-caprolactone)

Dielectric relaxation has been studied for poly (ϵ-caprolactone) in dioxane solution. As expected from the head-to-tail structure [-(CH2)5COO-]x, at a given temperature there are two distinct dielectric loss peaks. Radio-frequency bridge measurements reveal a low-frequency peak due to a component of the repeat unit dipole parallel to the direction of the chain backbone and amounting to about 0.8 Debye per ester group. The position of this peak on the frequency scale varies with molecular weight as predicted from the longest normal-mode relaxation time, τ1≅M[η]η0/RT The second relaxation, which is independent of chain length, is conveniently studied over a wide range of concentrations by the technique of time-domain reflectometry (TDR). This peak is associated with relaxation by local conformational rearrangement of a component of the dipole moment perpendicular to the chain direction, amounting to about 1.6 Debye per ester group. The extrapolated frequency of maximum loss at infinite dilution is about 3 GHz at 300K, with an apparent activation energy of about 30 kJ mol−1. The dependence of the local relaxation time on concentration can be fitted by a familiar free-volume equation of the type τ = A exp(B/vf), in which the free volume vf is a linear function of composition.