Influence of the end groups on dynamics of propylene glycol oligomers studied by wideband dielectric spectroscopy

The relaxational dynamics of poly(propyleneglycol) (PPG) and poly(propyleneglycol)-diglycidylether (PPGDE) compounds, the latter with different average number of repeating units, was studied by broadband dielectric spectroscopy (10 mHz to 10 GHz) from above to below the glass transition temperature in the range 115-350 K. The dielectric response of all systems showed a high temperature single relaxation while below a crossover temperature T-B it split in a main (alpha-) and a secondary (beta-) relaxation. The effect on the main and secondary relaxation of different groups terminating the polymer chain was analyzed: in particular, a decrease of the secondary relaxation time was observed for PPGDE with respect to PPG with the same molecular weight. Moreover the change of the Vogel temperature T-0 paralleled what previously found for similar systems. The relationship between main and secondary relaxation and the microscopic nature of this latter were analyzed in the framework of the coupling model. (C) 2002 Elsevier Science B.V. All rights reserved.