Polyoxazoline-modified graphene oxides with improved water and epoxy resin dispersibility and stability towards composite applications

Graphene oxide (GO) is modified with poly(2-ethyl-2-oxazoline) (PEOZ) and poly[(2-ethyl-2-oxazoline-co-(ethylenimine)] (PEOZ-PEI) to enhance its dispersibility in water and epoxy resin. PEOZ with a terminal primary amine and POZ-PEI with multiple backbone secondary amines are synthesized with scalable methods and characterized by nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), and gel permeation chromatography (GPC). GO modifications are performed at room temperature and 90 degrees C with/without N,N '-dicyclohexylcarbodiimide (DCC) and modified-GOs are analyzed by FTIR, thermogravimetric analysis (TGA), and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX). It is observed that the polymer incorporation varies based on the reaction condition, polymer type, and functional group type and position. The dispersion quality and stability of modified GOs are studied in water by particle size analyzer and visually and in epoxy resin by rheometer. PEOZ-modified GOs show better dispersibility and stability than PEOZ-PEI-modified GOs in both media since PEOZ is monofunctional, preventing the agglomerate formation and improving polymer exposure to the dispersion media by its longer length and higher water-solubility, whereas PEOZ-PEI has lower water solubility, multiple amines for interactions leading to agglomeration and limited polymer exposure to the dispersion media. The tailorable polymer grafting and the increased dispersibility of modified GOs in both media are promising indicators of their possible applications in composites.