In-Situ Nanocomposite Synthesis: Arylcarbonylation and Grafting of Primary Diamond Nanoparticles with a Poly(ether−ketone) in Polyphosphoric Acid

In a model reaction to demonstrate the presence and reactivity of sp 2 C−H, the primary particles (∼5 nm) of detonation nanodiamond (DND) were arylcarbonylated with 2,4,6-trimethylphenoxybenzoic acid in polyphosphoric acid (PPA) via a Friedel−Crafts reaction. The possibility of grafting primary DND particle was supported by the results from FTIR, scanning electron microscopy (SEM), and elemental analysis. From the latter result, we estimated the degree of functionalization to be ∼2.3 atom %. The arylcarbonylated DND achieved better and stable dispersion than pristine DND in common organic solvents. PPA-treated DND from the control experiment retained most of the pristine DND’s properties, except that its thermo-oxidative stability is noticeably improved as indicated by the result from thermogravimetric analysis (TGA in air). Subsequently, 3-phenoxybenzoic acid (PBA) was polymerized in PPA with the pristine DND (1.0−30 wt %) in situ to generate meta -poly(ether−ketone)-grafted DND composites, m PEK- g -DND. It was found that the m PEK- g -DND nanocomposites were not only soluble in methanesulfonic acid (MSA), but also dispersed well in solvents such as N -methyl-2-pyrrolidinone (NMP) and tetrahydrofuran (THF). Their intrinsic viscosity values ranged from 0.67 to 1.42 dL/g in MSA at 30 °C. Interestingly, a polyelectrolyte effect was observed for the nanocomposites with DND content >10 wt %. As compared to the neat m PEK polymer, the glass transition temperatures of these nanocomposites were increased by as much as 19 °C, while their short-term thermal and thermo-oxidative stabilities, as defined by the temperatures at which 5 wt % loss ( T d5% ) occurred during TGA scans, were increased by 34−88 °C in air and 59−108 °C in nitrogen. The wide-angle X-ray diffraction results showed that the intensity of the characteristic diamond d -spacing (111) at 2.05 Å grew proportionately with the DND content in the samples. Morphological studies (SEM and TEM) provided further evidence to support the feasibility of polymer grafting and formation of in-situ nanocomposites.