Synthesis And Properties Of Benzoxazine/Phthalonitrile Blends

In this paper, a series of fluorene-based bisphthalonitrile monomers with different flexible side chain length were successfully synthesized via the nucleophilic displacement of the nitro-substituent from 4-nitrophthalonitrile. The structure of products was confirmed by Fourier transform infrared (FT-IR) and 1H nuclear magnetic resonance (NMR). A series of phthalonitrile blending resins were prepared from 4-aminophenoxyphthalonitrile (4-APN) and BPFPN by directly powder-mixing and copolymerization. The curing reaction behaviors of APN/BPFPN blends were investigated. The monofunctional benzoxazine monomer based on phenol and aniline (P-a) was blended with the fluorene-based bisphthalonitrile monomers with different flexible side chain length (BFPN), amino-containing fluorene-based bisphthalonitrile monomers (AFPN), autocatalytic phthalonitrile monomers (APN) and bisphenol A-based bisphthalonitrile monomer, in order to improve property of monofunctional benzoxazine and phthalonitrile resin. The curing behaviour of the blends was studied by differential scanning calorimetry (DSC), the thermomechanical properties and thermal stability of the cured blends were studied by dynamic mechanical thermal analysis(DMA) and thermo gravimetric analysis (TGA).The results indicated that the introduction of 4-APN accelerated the curing rate of BPFPN, and the existence of 4-APN decreased the curing temperature of APN/BPFPN systems. The curing behaviors of the APN/BPFPN blends appeared to be related to the APN content. The thermal properties and processability of the polymer are improved and the resins achieved char yield above 60% at 800 ?.The glass transition temperature (Tg) and char yield at 800 ? (Yc) of the cured blends based on P-a and phthalonitrile increased with the addition of phthalonitrile, which leading to the enhancement of Tg and thermal stabilities. Among them, the Tg of copolymer of P-a/4-APN-7:3 is 89 ? higher than that of poly(P-a). And the values of 5% and 10% weight loss temperatures and the char yield at 800 ? are increased by 101 ?, 91 ?, and 30.1%,respectively. By the materials containing 30% phthalonitrile, in P-a/BFPN blended system, Tg and YC ranged from 196 ? to 232 ? and from 56.4% to 66.9%, respectively; in P-a/AFPN blended system, Tg and Yc ranged from 208 ? to 229 ? and from 61.4% to 68.1%,respectively, which were better than monofunctional benzoxazine. Although Tg and Yc decreased with the flexible side chain length increased in P-a/AFPN and P-a/BFPN blended system, its cured polymer displays the high Tg and the improved thermal stability without sacrificing any thermal properties than monofunctional benzoxazine resin. In P-a/BAPh blended system,T5, T10 and Yc increased with the addition of P-a, in which BAPh is the main part. The T5, T10 and Yc were 447 ?; 506 ?, 72.9%, respectively when the blends with a 1:1 weight ratio of P-a and BAPh, and Tg was 365 ?.