Dual-functional molecular engineering of silicon-alkyne polyimides: A novel strategy for balancing processability and thermal stability in high-performance composites

Abstract

To address the poor processability of conventional aromatic polyimides while preserving their exceptional thermal properties, a novel diamine monomer, bis(m-aminophenylethynyl)dimethylsilane (SiMDA), was synthesized through a two-step reaction. Subsequently, SiMDA was copolymerized with 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 4-phenylethynylphthalic anhydride to yield a phenylethynyl-terminated polyimide (SiPI). The synergistic incorporation of silylmethyl (-Si(CH₃)₂-) and alkyne (-C≡C-) moieties markedly enhanced the solubility of SiPI in low-boiling-point solvents (e.g., acetone, THF) and substantially lowered its melt viscosity (0.14 Pa·s at 184°C). Notably, despite its improved processability, SiPI maintained outstanding thermal stability, exhibiting a 5% weight loss temperature (T_d5) of 511°C under nitrogen and a char yield of 63% at 800°C. To evaluate the efficacy of this dual-functional design, two reference polyimides were synthesized for comparative analysis: one derived from 4,4′-diaminodiphenyl ether (ODA) and the other from 2,2′-bis(trifluoromethyl)diaminobiphenyl (TFMB). These comparisons underscore the distinctive advantages of SiMDA in achieving an optimal balance between processability and thermal stability. Furthermore, quartz fiber-reinforced SiPI composites demonstrated superior high-temperature mechanical performance, retaining 78.63% of their bending strength (285.00 MPa) and 67.89% of their interlayer shear strength (23.02 MPa) at 300°C. This study not only proposes a molecular engineering strategy to reconcile the trade-off between processability and thermal stability in polyimides but also expands their potential for high-temperature applications in aerospace, microelectronics, and other advanced fields.