Hyperbranched Poly(amidoamine)‐Grafted Graphene Oxide as a Multifunctional Curing Agent for Epoxy‐Terminated Polyurethane Composites

Graphene oxide (GO) modified with hyperbranched poly(amidoamine) (PAMAM) structure (GOD) was used as a multifunctional curing agent in the preparation of thermally stable composites from epoxy‐terminated polyurethanes. The multifunctional GOD sample was prepared through a divergent approach by using (3‐Aminopropyl)triethoxysilane (APTES)‐functionalized GO as the core for grafting PAMAM dendrimer by sequential addition of methyl acrylate and ethylenediamine (EDA). Epoxy‐terminated polyurethanes with two different chain extenders of 1,4‐butanediol (BD) and pyromellitic dianhydride (PMDA) were prepared from the reaction of poly(ethylene glycol), hexamethylene diisocyanate, and chain extenders, and subsequent end group transformation of the isocyanate to epoxy functionalities. Fourier transform infrared spectroscopy and thermogravimetric analysis (TGA) proved successful preparation of GOD. TGA indicated improvement in char content and thermal stabilities of the composites with increasing GOD content and using the PMDA chain extender in comparison with the BD. Weight percentages of APTES, methyl acrylate, and EDA in the modified graphene samples were 15.8, 2.2, and 2.2 wt %, respectively, in each of the successive modification process of GO. Structural study of the graphitic and hybrid samples was accomplished with X‐ray diffraction and electron microscopies. A broad peak at about 21° in the patterns of hybrid composites originates from the amorphous structure of polyurethane.