Phenylphosphine oxide containing polyimide matrix resins for atomic oxygen-resistant fiber-reinforced composites

Abstract

Phenylethynyl-endcapped imide oligomers with different calculated molecular weights (calcd number average molecular weight ( $\overline{M_{\mathrm{n}}}$ )) and phosphorous (P) contents (P loading) were synthesized by the reaction of diethyl ester of 4,4′-oxydiphthalic acid, monoethyl ester of 4-phenylethynyl phthalic acid, and the P-containing diamines including [2,5-bis(4-aminophenoxy)phenyl] diphenylphosphine oxide and di(3-aminophenyl)methylphosphine oxide via in situ polymerization of monomeric reactant method. The amide–ester solutions were impregnated with carbon fiber (C_f) and quartz fiber (Q_f) cloth to give high quality prepregs that were then thermally cured to yield the C_f-reinforced polyimide (PI) composite (C_f/PI) and Q_f-reinforced PI composite (Q_f/PI), respectively. The C_f/PI composites showed high mechanical properties with a flexural strength of 1554 ± 93 MPa, a flexural modulus of 112 ± 3 GPa and an interlayer shear strength of 90 ± 5 MPa, respectively. The atomic oxygen (AO) resistances of the neat resins and composites were evaluated on a ground-based simulation facility. Experimental results indicated that the P structures offer PIs with 55–75% lower weight losses and a self-healing property. The fiber-reinforced composites showed further lower erosion rates than neat resins. In addition, the effects of calcd $\overline{M_{\mathrm{n}}}$ and P loadings on the melt processabilities of the B-staged imide oligomers and the AO resistance of the cured PIs were systematically investigated.