Use of polyimide- graft -bisphenol a diglyceryl acrylate as a reactive noncovalent dispersant of single-walled carbon nanotubes for reinforcement of cyanate ester/epoxy composite

Dispersion of single-walled carbon nanotubes (SWNTs) into individuals or small bundles and strong nanotube/matrix interfacial strength remain as challenges in exploiting the excellent mechanical properties of SWNTs in structural composites. Noncovalent functionalization of SWNTs is an attractive option for compatibilization of nanotubes with the matrix as it does not destroy the nanotube graphene structure. We have designed and successfully synthesized a new reactive comb-like polymer, polyimide-graft-bisphenol A diglyceryl acrylate (PI-BDA), which is shown to be highly effective in dispersing SWNTs into individual nanotubes or small bundles, as evidenced by transmission electron microscopy (TEM) and UV-vis-NIR absorption spectra. SWNTs dispersed with PI-BDA were added to a thermosetting resin blend of cyanate ester and epoxy (CE-EP) (70/30, w/w) and composite fibers with SWNT loading ranging from 0 to 1.5 wt % were successfully fabricated. The strong π-π interaction between SWNTs and PI-BDA backbone was evidenced by Raman spectra, and the covalent reaction between PI-BDA side-chain and matrix was confirmed by FT-IR and ¹H NMR. Our designed dispersant interacts noncovalently with nanotubes but reacts with the thermosetting matrix. With addition of PI-BDA dispersant, only 1 wt % SWNTs optimally increases the tensile modulus, strength, and toughness by 80% (to 4.70 ± 0.24 GPa), 70% (to 142.3 ± 6.9 MPa), and 58% (4.1 ± 0.4 MJ m^-3) compared to the neat resin blend (with E = 2.61 ± 0.14 GPa, σ = 83.7 ± 3.3 MPa, and T = 2.6 ± 0.2 MJ m^-3). Improvement in thermal properties was also observed.