Arguments in support of a critical length in polymethyl(α-n-alkyl)acrylate by TSDC investigations

Abstract After performing the synthesis of polymethyl(α- n -propyl)acrylate (C3), polymethyl(α- n -penthyl)acrylate (C5) and polymethyl(α- n -octyl)acrylate (C8) in the polymethyl(α- n -alkyl)acrylate family, we have analyzed the role of the length of the alkyl group on the molecular relaxations which occur in such amorphous material. The molecular relaxations were studied from elementary and complex spectra obtained by thermally stimulated depolarization current measurements. The analysis of the α and β modes allows the determination of the apparent activation entropy of relaxation ΔS and of the apparent activation enthalpy ΔH max at the maximum of the mode which is the dielectric manifestation of the glass transition. For the α mode, the main result shows minima in the variations of both ΔS and ΔH max with the length of the alkyl group. These minima occur for C3 samples. In the opposite, ΔS remains practically nil for the secondary β relaxation.