A hyperbranched polyethylene-b-poly(methyl methacrylate) block copolymer (HBPE-b-PMMA) was synthesized herein via a tandem polymerization process

in which chain walking ethylene coordination polymerization was first carried out with a functionalized Pd-diimine catalyst to give a telechelic HBPE covalently tethered with a 2-bromoisobutyryl end group (HBPE-Br)

then atom radical transfer radical polymerization (ATRP) of MMA was initiated using the HBPE-Br as a macromolecular initiator

rendering the HBPE-b-PMMA copolymer.The ability of the as-synthesized copolymer to noncovalently exfoliate natural graphite (NG) leading to stable graphene solutions in toluene was further examined.The presence of PMMA blocks in the copolymer is well confirmed by the results from proton nuclear magnetic resonance (1H-NMR) and gel permeation chromatography (GPC) analysis.As indicated by UV-Vis spectroscopy test

the resulting copolymer can effectively exfoliate NG in toluene under the assistance of ultrasonication to render stable solutions of graphene with high concentrations up to 0.071 mg/mL.The results from high-resolution transmittance electron microscopy (HRTEM)

atomic force microscopy (AFM) and Raman spectroscopy commonly show that the resulting graphene nanosheets are free of structural defects

with a thickness of 2~4 layers.These high-quality

stable graphene solutions in toluene are potentially useful for the preparation and applications of polymer-based graphene nanocomposites.