Effect of Various Functional Groups Between the Aromatic Rings of Dianhydrides on the Thermal, Mechanical and Dielectric Properties of Polyimide/Hollow Silica Fiber Composites Using 2,2‐bis[4‐(4‐aminophenoxy)phenyl] Propane Diamine

ABSTRACT In this work, the effect of various functional groups between the aromatic rings of dianhydrides on the properties of polyimide (PI)/hollow silica (HS) fiber composites is investigated. For this study, four PI/HS fiber composites are synthesized using 2,2‐bis[4‐(4‐aminophenoxy)phenyl] propane (BAPP) diamine and four different chemical structure of dianhydrides, such as 3,3',4,4'‐biphenyltetracarboxylic dianhydride (BPDA), 4,4’‐(oxydiphthalic anhydride) (OPDA), 3,3',4,4'‐benzophenonetetracarboxylic dianhydride (BTDA) and 4,4’‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) as well as HS fiber prepared using the electrospinning and high temperature calcination technique. The experimental results of four PIs indicate that the incorporation of a flexible and unbulky ether group between the aromatic rings of dianhydride monomer into the PI matrix can decrease the thermal stability, tensile strength, and T g with increasing chain flexibility. The storage modulus of PI/HS fiber composites can be increased about 50%–60% as compared to pure PI matrix. By adding more HS fiber and hexafluoroisopropylidene groups into PI backbone can lower their high‐frequency dielectric constant due to the increasing amount of low dielectric constant air inside HS fiber and fluorine‐containing groups. The dielectric constants are about 2.82 and 2.59 at 22 and 40 GHz for the 5 wt.% 6FDA‐BAPP/HS fiber composites. These phenomena are possibly accredited to the steric hindrance effect caused by the presence of HS fiber and fluorine‐containing groups, which can interrupt the regular chain packing of PI with increasing their free volumes and decreasing dielectric properties.