Effects of Cure on the Ionic Conductivity and Relaxation Strength of a Reversible Polymer Network Studied by Dielectric Spectroscopy.

This study employs broadband dielectric spectroscopy (BDS) to investigate the cure kinetics and chemical equilibria of a Diels-Alder (DA) reversible network. Focusing on segmental dynamics, the α-relaxation and ionic conductivity are studied during heating and subsequent cooling right after isothermal precuring at 55 °C. During first heating, the glass transition temperature (
T
_g
) shows a systematic, stepwise upshift from -35 °C to 46 °C, manifesting both increasing conversion and the shift of the ratio between endo- to exo-cycloadducts. Upon cooling, all experiments yield
T
_g
values around 40 °C indicating partial depolymerization, which is confirmed by kinetic model simulations. Ionic conductivity analysis, employing the Debye-Stokes-Einstein relation, confirms charge transport assisted by segmental motions with partial decoupling of the α-relaxation time from ionic conductivity (fractional DSE behavior) between
T
_g
and
T
_g
×1.2. Surprisingly, the degree of coupling, given by the FDSE exponent
S
, drops until reaching the gel point (~30 min.) with no further changes upon extended cure. In contrast, a continuous increase in dc-conductivity with curing time is observed, attributed to enhanced intrinsic conductivity via improved H-bonding. Investigation of the α-relaxation strength and shape reveals subtle trends, reflecting changes in the dipole-dipole correlation and equilibrium shifts between cycloadducts. This work offers insights into the glass transition dynamics in reversible polymeric networks and might provide a basis for similar studies in systems undergoing chemical or physical transformations.