570 Full Paper wileyonlinelibrary.com Macromolecular Chemistry and Physics © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/macp.201500349 Poly(methyl methacrylate)/Graphene Microparticles Having a Core/Shell Structure Prepared with Carboxylated Graphene as a Pickering Stabilizer Gansukh Erdenedelger, Trung Dung Dao,* Han Mo Jeong* Two kinds of carboxylated thermally reduced graphenes (carboxylated TRGs) with different lateral sizes are examined as a Pickering stabilizer in the suspension polymerization of methyl methacrylate. The size and the shape of the prepared composite particles are irregular due to agglomeration, more evidently when the larger carboxylated TRG is used. In addition, car- boxylated TRG is distributed not only on the surface but also inside the composite particles. It indicates that the carboxylated TRG alone is not a stable Pickering agent. However, a very small dosage of acrylic acid remedies all these issues because acrylic acid interacts with carboxylated TRG and synergizes the stabilizing effect. The compression molded composite of the core/shell poly(methyl methacrylate)/carboxylated TRG particles exhibits a very low percolation threshold of electrical conductivity of 0.03 vol%. It demonstrates that the carboxylated TRG shells of the composite particles effectively form a segregated conductive network throughout the composite. G. Erdenedelger, Dr. T. D. Dao, Prof. H. M. Jeong Department of Chemistry Energy Harvest-Storage Research Center University of Ulsan Ulsan 680-749, Republic of Korea E-mail: daotrungdung_vn@yahoo.com; hmjeong@mail.ulsan.ac.kr an extremely high surface area, and a high aspect ratio, and thus it can make a percolative network in polymer compos- ites at an extremely low loading—less than 1 wt%. [1–3] Bulk quantities of graphene can be produced through the rapid heating of graphite oxide (GO) because the GO sheets are reduced and exfoliated simultaneously upon rapid heating due to the thermal decomposition of oxygen-containing groups of GO and the pressure of gas products (mainly CO 2 ) that builds up instantaneously between the sheets. [4] This method is economical and eco-friendly because thermally reduced graphene (TRG) can be mass-produced without the use of any solvent or reducing agent. These TRG sheets are normally few-layer graphene with a specific surface area, ranging from 300 to 1500 m 2 g -1 , according to the Brunauer–Emmett–Teller (BET) measurements. [5–7] TRG has not only a high electrical conductivity but also an affinity with various solvents and polymers because some oxygen-containing functional 1. Introduction Polymer composites filled with electrically conductive nano- fillers have attracted tremendous attention in practical applications such as static-charge dissipation, electro- magnetic shielding, electronic devices, sensors, and actua- tors. Graphene, a single-atom thick 2D sheet of carbon atoms bonded into a honeycomb structure, is a fascinating nanocarbon for the preparation of electrically conductive polymer composites. It has a superior electrical conductivity, Macromol. Chem. Phys. 2016, 217, 570−580