Preparation and Performance of Low Viscosity Poly(silicon-alkyne imide) Resins and Their Composites

Silicon-containing arylacetylene (PSA) resin holds great promise for applications in the aerospace industry, attributed to its outstanding heat resistance. However, lacking of toughness after curing limits its applications. Polyimide resin combines high heat resistance and high mechanical properties, which can be used to modify PSA resin. The idea of copolymerizing polyimide and PSA is proposed to prepare a novel resin with better comprehensive properties. Ethynyl-terminated polyimide (PI) was synthesized from 4,4'-oxydiphthalic anhydride (ODPA), bis(4-aminophenoxy)benzene (1,3,4-APB), and 3-aminophenylacetylene (APA). The structure of PI was characterized by infrared spectroscopy and nuclear magnetic resonance hydrogen spectroscopy. Poly(silicon-alkyne imide) (PSI) resin was synthesized through the copolymerization of PI with PSA resin. The rheological properties of the PSI resin were examined using a rotational rheometer. The temperature range of PSI-10 (w(PI)=10%) resin melting viscosity less than 1 Pa·s was 98～187 ℃, and the viscosity less than 1 Pa·s can be maintained for more than 6 h at 110 ℃, which could meet the requirements of resin transfer molding (RTM) process. The curing characteristics of the PSI resin were investigated using differential scanning calorimetry, which allowed for the determination of its curing process. Thermogravimetric analysis was employed to assess the thermal stability of PSI resin, revealing that the 5% mass loss thermal decomposition temperature (T_d5) and the residual carbon rate at 800 ℃ (Y_r800) for the PSI-10 resin were 602 ℃ and 89.8%, respectively. The flexural strength of the PSI resin, as determined by a universal testing machine, was 34.0 MPa, a 64% increase compared to that of the pure PSA resin. Quartz fiber-reinforced PSI-10 composite demonstrated superior mechanical properties with a flexural strength of 340 MPa and an interlaminar shear strength (ILSS) of 23.0 MPa. This enhancement in mechanical performance is attributed to the addition of PI, which not only enhances the resin's toughness but also strengthens the interfacial adhesion between the resin and the reinforcing material.