Preparation of Low-dielectric Permittivity Polyimide Resins with High Surface Activity from Chemically Bonded Hyperbranched Polysiloxane

Thermosetting resin matrix is the key component of advanced wave-transparent composites, where low dielectric constant, excellent processability, high thermal stability, as well as good bonding ability are required for resins. Herein, we prepared a series of phenylethynyl terminated polyimide (PI) resins by grafting amine-functionalized hyperbranched polysiloxane (HBPSi) to PI chains during the in situ polymerization. The effects of HBPSi on the processability of oligomers, molecular packing, thermal stability, dielectric property and bonding ability to reinforce Kevlar fibers of the cured PI/HBPSi composite resins have been examined in detail. The dielectric constants of the cured composite resins were greatly reduced from 3.29 to 2.19 without compromising its processability and thermal stability. Meanwhile, the 10 wt% HBPSi-containing PI resin demonstrated better bonding ability to reinforce fibers with the interfacial shear strength (IFSS) of 37.64 MPa, compared with that of neat PI-6 matrix (27.34 MPa), and better adhesion to metal with the lap shear strength of 10.48 MPa, 50% higher than that of neat resin PI-6 (6.98 MPa). These resultant PI/HBPSi composite resins exhibit excellent comprehensive properties, indicating their great potential as low-dielectric constant resin matrix in radar radome.