Network formation and thermo-mechanical properties of photo-curing hybrid coatings

by Nebioglu, Ahmet.

UV-moisture dual curable inorganic/organic hybrid coatings based on unsaturated polyester binders and silicate-clusters were successfully prepared. In situ formed nano to micro size inorganic clusters increased the abrasion resistance, adhesion, tensile strength and fracture toughness of the films. Free radical UV-crosslinking process was used to form the organic phase. An isocyanate functional alkoxysilane coupling agent was used to connect organic and inorganic phases. The effects of the silicate groups on the free radical photo-curing reaction kinetics were investigated utilizing a time-resolved Fourier transform infrared (FT-IR) spectroscopy and a differential scanning calorimeter equipped with a photocalorimetric accessory (photo-DSC). Inorganic network formation during the UV-initiated free radical crosslinking reactions was suggested to describe the complex gel-point behavior. It was proposed that inorganic silicate groups retard the organic crosslinking reactions. In order to depict the interaction of the silicate clusters and organic network formation, it was necessary to characterize the organic network structure. Therefore, a series of methods including dynamic mechanical thermal analysis and dynamic light scattering were utilized to understand the nature of the organic crosslinking reactions. The effect of the placement, i.e. whether internal or terminal, of the unsaturation on the polyester chains and concentration of the reactive monomer on the network structure formation was iii investigated. It was found that intramolecular cyclization reactions were detrimental in the network structure, and hence final film properties. Inclusion of the silicate groups inhibit the intramolecular cyclization reactions, and therefore affect the organic network structure formation. The UV-cured inorganic/organic hybrid films showed more homogeneous film morphology compared to the organic counterparts. In hybrid films a core-shell like inorganic/organic particle morphology was observed. The UV-crosslinked organic part forms the inside core, whereas the inorganic silicate part forms the surrounding shell. Network formation mechanism and film properties were extensively changed with the formation of these colloidal particles. iv