Effects and mechanism of graft modification on the dielectric performance of polymer-matrix composites

With the development of electronics industry, polymeric dielectric materials with high energy storage density have become increasingly important for the miniaturization of electronic components. In this research work, enhanced permittivity was obtained by graft modification of the epoxy resin matrix. Polyethylene glycol (PEG) and chrome acetylacetonate (Cr Acac) were employed as graft modification reagents. Methyl tetrahydrophthalic anhydride (MeTHPA) was used as curing agent for epoxy resin, which also acted as a precursor for the graft modification reagents. The permittivity of the graft-modified epoxy resin was improved by 30%. With the modified epoxy resin as matrix and nano-sized barium titanate (BaTiO3, BT) as fillers, the dielectric composite film showed a high permittivity of 37.75 and a low tangent loss of 0.022 at the frequency of 1 kHz. In contrast, the composite film without modification showed a much lower permittivity of 24.83. FTIR and UV spectra analysis indicates that graft modification with PEG has induced a number of ester groups, which possess strong dipole polarity. The graft modification with Cr Acac created a new conjugate system with a strong polar center and high inducible polarizability. The two effects led to improved permittivity of the derived epoxy resin and composites. Beside that, it is also likely that a synergistic effect existed between the two modification reagents, which further enhanced the polarity of the cured epoxy resin. (C) 2013 Elsevier Ltd. All rights reserved.