Photo-crosslinkable polyurethanes reinforced with coumarin modified silica nanoparticles for photo-responsive coatings

Coumarin and poly-epsilon-(caprolactone) diol (PCL)-based polyurethanes (PUs), were reinforced with modified silica nanoparticles (mSiNPs), in which a novel coumarin molecule was synthetized. The behavior as photo-responsive coatings of these materials was studied. The silica nanoparticles (SiNPs) modification was analyzed by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and UV spectroscopy. The yield of photo-crosslinking in nanocomposites loaded with mSiNPs was studied by UV vis spectroscopy, which showed higher conversion degree than nanocomposites with unmodified SiNPs and non-reinforced PUs. The dispersion of mSiNPs on segregated microdomains was observed by transmission electron microscopy (TEM). The presence of coumarin grafted on the SiNPs surface (mSiNPs) leads to an improvement on the thermal stability of PU matrix. Meanwhile, they were able to maintain the mechanical performance before and after the irradiation process mainly due to the improved nanofiller-matrix interaction. Contact angle measurements were also assayed to study the hydrophobicity changes on the surface of modified nanocomposites. The observed phase segregation was associated with the mechanical and thermal properties of the materials and the photo-crosslinking of coumarin moieties bring to the final material high responsiveness to be employed as photo-switchable coatings.