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Dielectric relaxation in poly(propylene glycol) oligomers of increasing chain length
, 3. modul, 2001, id:177
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Abstract
English abstract
The dielectric spectra of PPG of 9 different molecular weights have been measured. The dielectric spectra showed both a, b and a` relaxation peaks. In addition a small b` peak was discovered. The spectra were well described by a viscoelastic model, developed on grounds of the generalized BEL model. The temperature dependence of the a relaxation peak intensity were well described by the Debye model. The a relaxation time were well desribed by the shoving model. The b relaxation were successfully modeled by a two level potential well model. The a` peak appeared for molecular weights above a certain molecular weight (Mw*) attributed to the polymer limit. For weights below Mw* the behavior were small molecule-like, with the a relaxation involving the relaxation of the entire molecule. For higher molecular weights the a' peak was attributed to the longest normal mode, described by the Rouse model. No entanglement behavior was seen for the molecular weights studied, ranging from 58 g/mol to 4000 g/mol.

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