Polystyrene Chains with Different Grafting Densities on the Surface of Graphene Oxide by "Grafting Through” Method

 Graphene oxide (GO) modified with a double bond-containing chemical was used in the preparation of polystyrene composites by combination of “grafting through” and reversible addition-fragmentation chain-transfer (RAFT) polymerization methods. The main objectives were (1) application of two reaction sites for in situ grafting of polystyrene chains from the GO surface, (2) increasing of grafting density in the polymerization process by grafting through two different sites and (3) evaluation of styrene RAFT polymerization in two different grafting densities and various GO contents.

After modification of GO with ethylenediamine (EDA) using nucleophilic ring opening reaction that is resulted in amine-functionalized GO (GOA), coupling reaction was conducted between the GOA and (3-methacryloxypropyl) dimethylchlorosilane (MCS) to obtain GOOHD layers with different modifier contents. Then, grafting through RAFT polymerization method was utilized for preparation of polystyrene composites.

X-ray photoelectron spectroscopy shows successful modification of the GO layers with EDA and MCS. Molecular bonding characterization was performed by Fourier transform infrared spectroscopy for the neat and modified GO. Variations in electron conjugation were studied by Raman spectroscopy. Molecular weight and polydispersity index of the free and anchored polystyrene chains were calculated from the size exclusion chromatography. By using thermogravimetric analysis, thermal properties and grafting ratios of the modifiers and polystyrene chains were studied. Grafting ratio of the modifiers was 12.9% and 7.5% for the modified GO layers with high and low grafting densities, respectively. Morphology of the GO layers was investigated through transmission and scanning electron microscopy. Oxidation changed the flat and smooth graphite to wrinkled layers, and grafting polystyrene chains resulted in turbid layers.