Castor oil-based hyperbranched polyurethanes as advanced surface coating materials

21st Century is treated as the century for highly branched macromolecules, because of their unique structural architecture and outstanding performance characteristics, in the field of polymer science. In the present study, castor oil-based two hyperbranched polyurethanes (HBPUs) were synthesized via A2 + B3 approach using castor oil or monoglyceride of the castor oil as the hydroxyl containing B3 reactant and toluene diisocyanate (TDI) as an A2 reactant along with 1,4-butane diol (BD) as the chain extender and poly(ɛ-caprolactone) diol (PCL) as a macroglycol. The adopted ‘high dilution and slow addition’ technique offers hyperbranched polymers with high yield and good solubility in most of the polar aprotic solvents. Fourier transforms infra-red spectroscopy (FTIR) and nuclear magnetic resonance (NMR) analyses confirmed the chemical structure of synthesized polymers, while wide angle X-ray diffraction (WXRD) and scanning electron microscope (SEM) resulted the insight of their physical structures. The degree of branching was calculated from 1H NMR and found to be 0.57 for castor oil based hyperbranched polyurethane (CHBPU), while it was 0.8 for monoglyceride based hyperbranched polyurethane (MHBPU). The studies showed that MHBPU and CHBPU exhibited tensile strength 11 MPa and 7 MPa, elongation at break 695% and 791%, scratch hardness 5 kg and 4.5 kg, gloss 84 and 72, respectively. Thermal properties like thermo stability, melting point, enthalpy, degree of crystallinity and glass transition temperature (Tg); and chemical resistance in different chemical media were found to be almost equivalent for both the polyurethanes. The measurements of dielectric constant and lost factor indicated that both the HBPUs behave as dielectric materials. Thus the synthesized HBPUs have the potential to be used as advanced surface coating materials.

► Castor oil modified two hyperbranched polyurethanes (HBPUs) have been developed.
► HBPUs exhibited excellent performance as surface coating materials.
► Monoglyceride based HBPU exhibited higher tensile strength than direct oil based one.
► Thermal stability for both the polymers are above 250 °C.
► Both the HBPUs have acceptable dielectric properties.