Preparation and Application of Macromolecular Silane Coupling Agent for Polyimide-Based Composites

This study presents targeted contributions to the development of macromolecular silane coupling agents (MSCAs) and high-performance fiber-reinforced polyimide (PI) composites. Three novel MSCAs were synthesized via chemical imidation and transamidation reactions, using hexafluoroisopropylidene diphthalic anhydride and 2,3,3',4'-diphenyl ether tetracarboxylic acid as dianhydride monomers, 4,4'-diaminodiphenyl ether and 1,3-bis(4'-aminophenoxy)benzene as diamine monomers, and aminopropyltriethoxysilane (KH550) as the capping agent. Structural characterization by FTIR, ¹H NMR, and XPS confirmed the successful synthesis of the target products, with silicon contents of 3.29%, 3.37%, and 3.66%, respectively. The MSCAs exhibited excellent thermal stability, with 10% weight loss temperatures ranging from 462 °C to 543.3 °C, and good solubility in most polar organic solvents, addressing the poor processability of conventional macromolecular coupling agents. Compared with small-molecule KH550, the MSCAs significantly enhanced interfacial properties: the average tensile and flexural strengths of the composites increased by 11.0% and 9.8%, respectively, compared to 3.9% and 4.0% for KH550. SEM analysis demonstrated that MSCAs improved resin adhesion to fibers and fiber-resin compatibility. Additionally, the T5, T10, and glass transition temperatures of the composites were further optimized due to polymer chain diffusion and entanglement. This work provides a feasible strategy for interfacial design in high-performance polyimide composites.