Surface-initiated ATRP of styrene from epoxy groups of graphene nanolayers: twofold polystyrene chains and various graft densities

Abstract

An initiator and amine group containing modifier, N-(2-aminoethyl)-2-bromo-2-methylpropanamide (OBr), was synthesized through the coupling reaction of ethylenediamine and alpha-bromoisobutyryl bromide. Subsequently, graphene oxide (GO) was functionalized with OBr in different densities by ring opening of epoxy groups. Then, the initiator-anchored graphene (GOBr) was used in different amounts as the precursor for grafting from atom transfer radical polymerization of styrene. Grafting of OBr on GO was approved by X-ray photoelectron spectroscopy, elemental analysis, and Fourier transform infrared spectroscopy. The crystal structure of carbon and also the stacking order of the nanolayers were studied by Raman spectroscopy. The expansion of the graphene interlayer by oxidation and modification processes was confirmed by X-ray diffraction. Conversion values were obtained from gas chromatography results. Free and attached polystyrene (PS) chains were thoroughly characterized by molecular weight and PDI values using size exclusion chromatography. The molecular weight and PDI values of free chains are lower than the attached chains. Thermogravimetric analysis was also used to investigate the degradation temperatures, char contents, grafting weight ratios, and grafting molar ratios for modifier and PS chains. The graphene nanolayer confinement effect on the relaxation of PS chains was evaluated by differential scanning calorimetry. T_g values increased by increasing graphene content and grafting density. Scanning electron and transmission electron microscopies show that graphene nanolayers are flat, GO nanolayers are wrinkled, and PS-attached nanolayers are opaque because of polymer grafting.