Viscoelastic and dielectric studies on comb- and brush-shaped poly(n-butyl acrylate)

The dynamic compliances J'(omega) and J"(omega) and the dielectric permittivities epsilon'(omega) and epsilon"(omega) are reported over a wide range of frequency omega and temperature for comb-branched and brush-shaped poly(n-butyl acrylate) prepared by atom transfer radical polymerization. The analysis here of the viscosity eta for the comb- and brush-shaped polymers indicates the need to account for an increase of the persistence length with increasing density of the side chains. Enhanced values of J(s) are attributed to a dilution effect arising from the side chains on the values that would otherwise arise from the backbone chain. The dielectric loss epsilon"(omega) demonstrates a deviation from frequency-temperature superposition at a certain range of frequency, with the deviation increasing with increasing density of the side chains. The deviation occurs for a frequency range for which J'(omega) and J"(omega) are approaching their terminal response, but no corresponding deviation from frequency-temperature superposition is noted for these functions. The dielectric behavior in this region is attributed to a delta-relaxation at frequencies lower than the principal a-relaxation, similar to behavior reported for certain polymers with mesogenic side chains. (c) 2008 Elsevier Ltd. All rights reserved.