Understanding the effects of carboxylated groups of functionalized graphene oxide on the curing behavior and intermolecular interactions of benzoxazine nanocomposites

Novel benzoxazine (BOZ)/carboxylated graphene oxide (GO-COOH) composites were prepared via in situ intercalative polymerization. The curing behaviour, morphology and intermolecular interactions of GO-COOH based nanocomposites were investigated and compared with those of a graphene oxide (GO) blend system to clarify the influence of carboxylic groups. Compared to GO, GO-COOH with a large amount of carboxylic groups, relatively higher thermal stability, and exfoliated sheet morphology might be more easily dispersed and reacted in the BOZ matrix. The GO-COOH nanoplatelet based composites possessed a different polymerization path from that of the GO based system, implying that carboxylic groups not only provided catalytic effects but also participated in the grafting polymerization reactions between carboxyl groups of GO-COOH and phenolic hydroxyl groups of BOZ. A significant improvement of both the glass transition temperature (Tg) and crosslinking network density of the GO-COOH blend system further confirmed that covalent bonding occurred between filler and polymer chains, indicating that the GO-COOH nanoplatelets had a stronger influence on the thermal property improvement of the nanocomposites than that of the GO blend system. Surprisingly, a very low amount (1 wt%) of GO-COOH can affect the thermal properties of the composite remarkably, leading to a more than 30 °C increase of Tg in comparison with pure benzoxazine.