Highly branched polyurethane: Synthesis, characterization and effects of branching on dispersion of carbon nanotubes

A novel approach to physical absorption of multi-walled carbon nanotubes (MWCNTs) into highly branched polymer chains for making advanced polymeric nanocomposites is presented. In this effort, a series of s-triazine based hyperbranched polyurethanes (HBPs) were synthesized by an A2 + Bn (n = 3, 6, 9) approach in two-step reaction sequences, based on a multi-hydroxy triazine core, poly(ε-caprolactone)diol, and diphenyl methane diisocyanate. The structural and thermal properties of the HBPs were investigated by FT-IR spectroscopy, 1H NMR spectroscopy, TGA, and DSC measurements. Contribution of the synthesized highly branched polyurethanes to dispersion of MWCNTs by physical adsorption was evaluated by SEM and TEM measurements. MWCNTs were soluble in N,N′-dimethylformamide with extended branches of HBP in the solution as analyzed by UV–vis spectroscopy. With an increase of branch density, the ability of solubilization of HBP for MWCNTs increased due to the cage-like superstructure of HBP, however, was not further enhanced for highly branched polymers due to decreased pocket size. The crystallinity of HBP significantly decreased with an increase of branching, whereas it increased with an increase of MWCNTs content.