Molecular dynamics in hyperbranched polyimides cross-linked with ethylene glycol diglycidyl ether

Chain dynamics in hyperbranched polyimides based on 2,4,6-triaminopyrimidine and 4,4′-oxydiphthalic anhydride (molar ratio 1:1) cross-linked with ethylene glycol diglycidyl ether was investigated by means of broadband dielectric relaxation spectroscopy and thermally stimulated depolarization currents techniques. The secondary γ relaxation increases in magnitude and slows down with increasing degree of cross-linking, whereas the α relaxation, associated with the glass transition, becomes faster. These effects were explained in terms of increase of free volume and of constraints to the motion imposed by cross-links.