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

The dynamic compliances J′(ω) and J″(ω) and the dielectric permittivities ɛ′(ω) and ɛ″(ω) are reported over a wide range of frequency ω and temperature for comb-branched and brush-shaped poly(n-butyl acrylate) prepared by atom transfer radical polymerization. The analysis here of the viscosity η 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 JS 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 ɛ″(ω) 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′(ω) and J″(ω) 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 δ-relaxation at frequencies lower than the principal α-relaxation, similar to behavior reported for certain polymers with mesogenic side chains.