Stiff Self-Healing Coating Based on UV-Curable Polyurethane with a “Hard Core, Flexible Arm” Structure

Two series of ultraviolet (UV)-cured
self-healing polyurethane
(PU) oligomers were synthesized through a prepolymer process from
isophorone diisocyanate (IPDI) or 1,6-hexamethylene diisocyanate (HDI),
polycarbonate diol (PCDL) of varying molecular weight (500, 1000,
and 2000 Da), and chemically modified cyclotriphosphazene as hard
cores were introduced. The synthesized oligomers contained rigid aromatic
rings as “hard cores” and long fatty chains as “flexible
arms”. Nuclear magnetic resonance spectrometer (H NMR) and
Fourier transform infrared spectroscopy were used to characterize
the structures of the oligomers. In addition, the UV-cured self-healing
PU coatings were prepared by designing some coating formulations with
the PU oligomers. The self-healing properties and mechanical properties
of the UV-cured coatings were investigated. The results revealed that
the coatings had self-healing properties based on hydrogen bonds.
As the molecular weight of PCDL decreased, the coatings exhibited
increased hardness, tensile strength, and glass transition temperature.
Furthermore, the coatings exhibited excellent thermostability. The
results proved the application prospects of the self-healing coatings
with high repair efficiency and excellent mechanical properties.