Confinement effect of graphene nanoplatelets on atom transfer radical polymerization of styrene: grafting through hydroxyl groups

Dual characteristics polystyrene chains were synthesized by grafting through atom transfer radical polymerization in the presence of surface-modified graphene nanoplatelets. After oxidation of graphene, it was functionalized by different amounts of 3-(trimethoxysilyl) propyl methacrylate (MPS) through the surface hydroxyl groups. Polymerization of styrene in the presence of modified graphene and initiator, ethyl alpha-bromoisobutyrate, was accomplished at 110 C. Then, the effects of various graft densities and different graphene loadings on the heterogeneous graft and free polystyrene chains' characteristics and also their kinetics of polymerization were studied by gas-and gel-permeation chromatographies. Linear increase of ln(M-0/M) with time for all the samples shows that polymerization proceeds in a living manner. By increasing graphene content, M-n increases, and polydispersity index (PDI) decreases for free chains. However, a reverse behavior was observed for attached chains. Increasing graft density resulted in higher M-n and lower PDI values for free chains. Similar to the effect of graphene content, a reverse behavior was observed for the attached chains. Efficiency of grafting reactions along with the graft contents was studied by X-ray photoelectron spectroscopy (XPS), elemental analysis, and thermogravimetry analysis. The grafting ratio of MPS modifier was calculated to be 9.7 % via the data of Si contents in the XPS survey scan data. Finally, the morphology of the functionalized graphene was studied by transmission electron microscopy.