Efficient exfoliation of graphite in chloroform with a pyrene-containing hyperbranched polyethylene as stabilizer to render pyrene-functionalized high-quality graphene

The use of stabilizers in liquid-phase exfoliation of graphite can effectively promote graphite exfoliation in common solvents, and concurrently render functionalized graphene by adsorbing them on the exfoliated graphene surface. Thus, the exploration of novel stabilizers is especially important for graphene liquid-phase production and related applications. Herein, we report the successful application of a pyrene-functionalized hyperbranched polyethylene (HBPE@Py) as the stabilizer for graphite exfoliation in chloroform. The polymer has a global hyperbranched polyethylene backbone and multiple covalently bonded pyrene moieties as branch ends. It can be synthesized via ethylene copolymerization using a Pd-diimine catalyst under mild conditions, 0.1 MPa/25 degrees C. Due to the cooperative effect of the CH-pi and pi-pi interactions between the HBPE@Py and graphene surface, some of the polymer is irreversibly adsorbed on the latter, thus effectively preventing their re-stacking and concurrently rendering pyrene-functionalized graphene. This allows us to obtain stable dispersions of few-layer graphene with relatively high concentrations (0.10-0.50 mg mL(-1)) and exfoliation efficiencies (1.6-13.0%). The resultant graphene is confirmed to be high-quality and shown to be highly stable when dispersed in chloroform, even the free polymer has been thoroughly removed. From the dispersion, a flexible, conductive graphene film and polymer-based graphene nanocomposites have been successfully prepared. (C) 2018 Elsevier Ltd. All rights reserved.