Dielectric properties of the polymerization of an aromatic polyimide

Abstract Dielectric measurements made over a wide range of frequency are shown to provide a sensitive means for observing the chemistry of the polymerization process of an aromatic polyimide continuously as the monomer mixture undergoes major changes in viscosity leading to a fully cured, insoluble, crosslinked thermoset. Dynamic dielectric measurements of the polymerization of the high temperature polyimide prepared from a mixture of BTDE, MDA, NE and designated LaRC-160 have been made at a series of frequencies from 5 to 5 × 10 6 Hz. The capacitance ( C ), dissipation ( D ), and the conductivity ( G ) together with time and temperature were recorded. The complex permittivity (e∗) has been determined throughout the cure cycle. Using their frequency dependence, e′ and e″ have been separated into their ionic and dipolar components. The time and temperature dependence of the dielectric data are correlated with the previously reported imidization cure chemistry of the LaRC-160 system (ref. 1). The high temperature crosslinking reaction has also been observed dielectrically and compared with published viscosity and reaction data. Changes in the time-temperature properties of this polyimide system as a function of resin age over a period of six months have also been studied. In addition, the effect of the resin's composition on the time-temperature cure properties of the polymer has been examined using dynamic dielectric measurements.