New method to analyze dielectric relaxation processes: a study on polymethacrylate series

The relaxation properties of polymethacrylates of the n ‐alkyl series with n  = l, 2 and 4 (poly(methyl methacrylate) ( PMMA ), poly(ethyl methacrylate) ( PEMA ) and poly( n ‐butyl methacrylate) ( PnBMA )) have been measured and analyzed in order to relate their properties to the size of the lateral side chains. The n ‐alkyl series has been regarded as a model system and was used in this work to test a graphical data analysis method. Essentially, four relaxation processes were detected in the three polymers: the γ, β, α and αβ relaxations, in increasing order of temperature. It was found that the γ relaxation has a low activation energy, of around 36.3–38.5  kJ  mol −1 , independent of the side chain, exhibiting low entropy of activation values when referring to the Eyring description of the activation parameters. The β relaxation was found to be similar in PMMA and PEMA , showing an activation energy of 88.8  kJ  mol −1 , increasing to 112.8  kJ  mol −1 in PnBMA . The activation entropy was also found to be low for this relaxation, although greater than that for the γ relaxation. In contrast, the α relaxation is quite different in these polymers. We observed a gradual shift in the glass transition temperature towards lower temperatures as the side chain increases in length. The manner in which the α transition makes its way into the dielectric spectra is more abrupt in PMMA than in PnBMA , denoting a higher fragility in the former polymer. Finally, there is a significant difference in the coalescence scenarios of the α and β relaxations for temperatures higher than the glass transition temperature, where they give rise to the so‐called αβ relaxation. © 2013 Society of Chemical Industry