Enhancement of the crosslink density, glass transition temperature, and strength of epoxy resin by using functionalized graphene oxide co-curing agentsElectronic supplementary information (ESI) available: Results of FT-IR spectra, TD-TGA curves, XPS spectra, DSC curves, DMA analysis, and UTM analysis of EP nanocomposites. See DOI: 10.1039/c5py01483b

We synthesized diamine-functionalized graphene oxide, DDS-GO and HMDA-GO, by introducing 4,4′-diaminodiphenyl sulfone (DDS) or hexamethylenediamine (HMDA) into the carboxylic acid groups on graphene oxide (GO) via amide bonds. The introduction of diamines was confirmed by analytical methods such as FT-IR, TG-DTA, XPS, AFM, and optical microscopy. Then, we applied DDS-GO and HMDA-GO as co-curing agents for epoxy (EP) nanocomposites that were prepared by mixing bisphenol-A type EP and DDS curing agent ( ca . 21 wt%). Interestingly, when 1.0 wt% of DDS-GO was added to the EP/DDS mixture, the crosslink density (CD) increased from 0.028 to 0.069 mol cm −3 . Due to the higher CD, both the glass transition temperature and tensile strength of the EP/DDS/DDS-GO nanocomposite effectively improved from 160.7 °C to 183.4 °C and from 87.4 MPa to 110.3 MPa, respectively. Epoxy nanocomposites are fabricated by using diamine-functionalized GO and exhibit high T g , tensile strength, and crosslink density.