Phenylethynyl-terminated oligoimides based on bis(p-aminophenoxy)dimethyl silane: Effect of siloxane structure on processability and thermal stability

A series of phenylethynyl-terminated oligoimides based on 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA), 2,2′-bis(trifluoromethyl)benzidine (TFDB), and bis( p-aminophenoxy)dimethyl silane (APDS) with different siloxane content and various calculated molecular weights were synthesized. The effect of siloxane structure on the processability of oligoimides and the thermal stability of cured polyimides (PIs) was investigated. The results indicated that the oligoimides have lower melt viscosity and broader processing window with the incorporation of flexible siloxane segment. The thermal stability of the cured PIs can be significantly enhanced by high-temperature postcuring due to the oxidative cross-linking of siloxane. The polyimide PI-s1-15 exhibited good balance between processability and thermal stability with the minimum melt viscosity of 0.4 Pa·s at 325°C and glass transition temperature as high as 470°C after postcuring at 450°C. The carbon fiber-reinforced composite T800/PI-s1-15 displayed excellent high-temperature performance, which gave the flexural strength and interlaminar shear strength of 703 and 33 MPa, respectively, when tested at the temperature as high as 450°C.