Influence of chemical structure of polyimide prepolymer on rheo-mechanicalproperties of polyimide foam composites

A study is reported of the effect of varying chemical composition of foam p olyimide prepolymers (H-complex) on the structure and properties of foam po lyimide resins and their composites with aromatic polyimide fiber felt. The melt theological behavior of the II-complex was found to be strongly depen dent on its chemical composition and structure reorganization in the melt w hich is akin to mesophasic structural transition states in liquid crystal p olymers. Changing the diamine part of the H-complex from 4,4-methylene dian iline to 1,3-diaminobenzene led to decreased steady shear viscosity at temp eratures and shear rates ranging between 95 degrees and 105 degreesC and 0. 01 and 1 s(-1), respectively. Additionally, changing the dialkyl moiety fro m dimethyl to diethyl in 3,3',4,4'-bemzophenonetetracarboxylic dialkyl este r (precursor to the H-complex) increased gelation time of the H-complex, en hancing processibility of the foam polyimide composites. The results Indica te that novel, lightweight foam polyimide composites with enhanced thermome chanical properties for beneficial uses can be prepared through chemical mo dification of the H-complex prior to its thermal imidization in the presenc e of the aromatic polyimide fiber felt.