POLYIMIDES DERIVED FROM NONAROMATIC MONOMERS - SYNTHESIS, CHARACTERIZATION AND POTENTIAL APPLICATIONS

A number of mixed aromatic/cycloaliphatic as well as fully nonaromatic polyimides have been prepared. Whereas all the poly(amic acids) deriv ed from nonaromatic diamines involved salt-formation during the initia l stages of the polymerization, the majority of these eventually forme d homogeneous, highly viscous polymer solutions. Only in a few select cases involving all nonaromatic monomers traditional solution polymeri zation was unsuccessful. The polyimide derived from hexafluoroisopropy lidene diphthalic anhydride (6FDA) and trans-1,4-diaminocyclohexane (D ACH) yielded films with tough mechanical properties, a glass transitio n temperature of similar to 360 degrees C, good solvent resistance, an d a low dielectric constant of 2.6. Thermal stability of this polyimid e as determined by thermal gravimetric analysis in both air and nitrog en was quite good, exhibiting a weight loss of only 0.07 wt%/h at 350 degrees C under isothermal conditions in nitrogen. However, mechanical properties as a function of thermal aging in both air and nitrogen in dicated a maximum use temperature of only 350 degrees C under inert co nditions and less than 300 degrees C in the presence of oxygen.