Characterization of biodegradable polyurethane nanoparticles and thermally induced self-assembly in water dispersion

Waterborne polyurethanes (PU) with different compositions of biodegradable oligodiols as the soft segment were synthesized as nanoparticles (NPs) in this study. Using dynamic light scattering (DLS), multiangle light scattering (MALS), transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS), we demonstrated that these NPs were compact spheres with different shape factors. The temperature-dependent swelling of the PU NPs in water was distinct. In particular, PU NPs with 80 mol % polycaprolactone (PCL) diol and 20 mol % poly(L-lactide) (PLLA) diol as the soft segment had significant swelling (∼450%) at 37 °C. This was accompanied by a sol-gel transition observed in about 2 min for the NP dispersion. The thermally induced swelling and self-assembly of these NPs were associated with the secondary force (mainly hydrogen bonding) and degree of crystallinity, which depended on the soft segment compositions. The thermo-responsiveness of the PU NPs with mixed biodegradable oligodiols may be employed to design smart biodegradable carriers for delivery of cells or drugs near body temperature.