High density Polymethacrylimide ( PMI) foam was prepared by using methacrylic acid( MAA) and
acrylonitrile(AN) as the main monomers. The influence of the flowing agent dosage, foaming temperature and foaming
time on the density of PMI foam was discussed. The microstructure, mechanical performance and dielectric electrical
properties at 10 GHz of the high-density PMI foam were studied. The results indicate that high-density PMI foam
with the density of 150 to 450 kg/ m3 can be obtained by foaming 40 min at 170 to 180℃ with 1 to 5 phr flowing agent.
The bubble edges and bubble walls of the high-density PMI foam gradually thickened with the increase of the
foam density, following the decrease of the average cellular diameter. Meanwhile, the mechanical properties including
compression strength, tensile strength was improved gradually, which was closen to the theoretically calculated values,
and the dielectric constant and dielectric loss increased linearly at the same time.