Crosslinked reduced graphene oxide/polymer composites via in situ synthesis by semicontinuous emulsion polymerization

This work presents the in situ synthesis of crosslinked polymer/graphene nanocomposites by seeded semicontinuous emulsion polymerization. The OH functionalities on the rGO platelets and in the polymer chains (introduced by the functional monomer hydroxylethyl methacrylate) were used as reactive sites, linked by the presence of NCO terminated polyurethane prepolymer (PU). The reaction was performed in semicontinous mode, using rGO and PU dispersed in water as a seed, whereas the monomers preemulsion was fed slowly. The hybrid latexes were kinetically stable enough to produce composite films by water evaporation, in which rGO platelets were uniformly dispersed and incorporated in a permanent way in the polymer matrix. The composites have a highly crosslinked structure, the degree of which depends on the loading of rGO and PU e.g., NCO/OH ratio. The electrical conductivity of the composites depends highly on the degree of crosslinking and the morphology, thus aligned platelets parallel to the top film surface are the most prospective morphology for the electrical conductivity. Determination of viscoelastic properties has shown that the composites are stiffer and contain smaller amounts of the mobile neat polymer phase with increasing content of rGO, which agrees well with an increase in their crosslinking.