Influence of Polymethylmethacrylate microstructure on its conductive properties at high temperature

Abstract

The influence of a set of tacticity-governed microstructures on the conductive properties of poly(methyl methacrylate) has been studied at high temperatures. Those structures are specially the mmmr and the mmmmrx (x = m or r), which occur when an isotactic sequence breaks-off, and also the rrrm-based termini of syndiotactic sequences. The electrical properties have been studied at the electrical modulus level, assuming a dispersive conductivity to explain conduction processes and Havriliak-Negami equation to evaluate dipolar contribution. A good agreement between experimental data and the model is observed, and some considerations about the conductive processes can be concluded. Conductivity is thermally activated at the temperature range considered, and ac regime can be associated with a correlated ion hopping of carrier process, which does not reacha strongly correlated regime, what we associate with a high relaxation time of carriers at high temperatures that do allow carriers to follow processes associated to a.c. regime.Interestingly, conductivity is shown to be dependent on the mmmrm-based stereosequences longer than one heptad. These stereosequences have been shown to exhibit enhanced free volume and rotational motion, what may explain the conductivity-mmmrm structure correlations as found on this work.