Through regulating the content and proportion of biphenyl carbonyl and unsymmetrical biphenyl segments in polyimide resin backbone

polyimide precursor solid resins with different carbonyl content were prepared. These precursor resins have good meltability

when heated to 320~330℃

PI resin completely melted

resulting in low melt viscosity resin

as the temperature increased further

the melt viscosity increases rapidly due to the crosslinking reaction. The precursor resins were heated and foamed

forming the thermosetting rigid closed-cell PI foams which have high closed-cell rate (

>

86%) and high thermal properties (

T

g

>

353℃

T

10

>

519℃) . The study found that the introduction of the biphenyl carbonyl segment into the PI resin main chain could obviously improve the PI foam toughness without sacrificing its mechanical strength and modulus.