Monomer self assembly and organo-gelation as a route to fabricate cyanate ester resins and their nanocomposites with carbon nanotubes

Abstract

A novel method is described for the preparation of porous cyanate ester networks by using the self-assembly and organo-gelation of the monomers and subsequent curing of the xerogels. Dicyanate esters (CE) were synthesized by the reaction of dihydroxy aromatic compounds (OH) with cyanogen bromide (CNBr) in the presence of triethylamine. Structures of the cyanate esters were confirmed by FT-IR, NMR and elemental analyses. Organo gels were prepared from the cyanate ester monomers with a polar aprotic solvent. Introducing single wall carbon nanotubes (CNT) in the monomer solution prior to gelation led to nano-composite gels. The morphology of the gels was studied by optical and scanning electron microscopies. The polymerization of the gels and the gel/single walled CNT composites was studied by differential scanning calorimetry. Polymerization temperature of the cyanate esters decreased with increasing weight percentage (1–5%) of CNT loading. The curing time of the cyanate esters also decreased with an increase in CNT loading. The xerogels were polymerized at 120°C for 3h, 170°C for 1h and post cured at 210°C for 1h. The morphology of the gels of the monomers, as well as those of cured cyanate esters and CNT–cyanate ester nanocomposites were investigated by scanning electron microscope. The morphology of the polycyanurate network consisted of porous fibrous network. The thermal properties of the cyanate ester and CNT–cyanate ester nanocomposites were studied by thermogravimetric analysis. Although the synthesis of cyanate ester resin is a mature area, we present gelation as a way of fabricating porous resins.