Polystyrene-grafted graphene nanoplatelets with various graft densities by atom transfer radical polymerization from the edge carboxyl groups

An initiator and hydroxyl containing modifier, 4-hydroxybutyl 2-bromopropionate (CBr), was synthesized through the coupling reaction of 1,4-butanediol and alpha-bromoisobutyryl bromide. Subsequently, graphene oxide (GO) was functionalized with CBr from the edge carboxyl groups by an esterification reaction to yield initiator-anchored graphene nanoplatelets (GCBr). Then, GCBr was used in different amounts as the precursor for atom transfer radical polymerization of styrene for evaluation of the effects of graphene loading and graft density on the kinetics and properties of the products. Successful edge-functionalization of GO with CBr and polystyrene was also proved by FTIR. A carbon to bromine ratio of 21.92 from the results of XPS shows that about 1 molecule of CBr was attached to every 3.65 aromatic rings of GCBrH. GPC results show that molecular weight and PDI values of the attached chains are higher, and molecular weight and conversion values increase with increasing grafting density. The amount of modifier and polystyrene attachment to the graphene edge was evaluated by TGA. The relaxation behavior of chains in the presence of graphene layers and also the effect of graft content on the chain confinement were studied using DSC. The ordered and disordered crystal structures of carbon were evaluated using Raman spectroscopy. The same XRD angle for the high and low graft densities at 7.5 degrees shows that expansion of the graphene interlayer is independent of the population of attached chains on the graphene edge. Finally, an opaque and wrinkled morphology of graphene nanoplatelets was observed by scanning and transmission electron microscopy.