Synthesis of UV-curable organic–inorganic hybrid urethane acrylates and properties of cured films

Abstract

An organic–inorganic hybrid urethane acrylate hydrolytic condensate (HUA-HC) was prepared through sol–gel method with an acid catalyst of low concentration from a hybrid urethane acrylate prepolymer (HUA), which is a disfunctional silane containing hydrolysable ethoxysilane groups (Si–OEt). The synthesis was monitored by Fourier-transformed infrared spectroscopy, 1H nuclear magnetic resonance (NMR), 13C NMR and 29Si NMR. The photopolymerization kinetics studied by photo differential scanning calorimetry showed that HUA-HC had a faster apparent photopolymerizaton rate and a higher conversion of double bonds than HUA under 72 °C due to the vicinity of double bonds in HUA-HC. However, HUA-HC showed a slower apparent photopolymerizaton rate and a lower conversion of double bonds than HUA at higher temperatures above 72 °C, which indirectly indicates that more extensive condensation between ethoxysilane (Si–OEt) and silanol (Si–OH) groups in HUA-HC than that in HUA. Both 100-μm-thick films of HUA-HC and HUA cured by ultraviolet (UV) light showed high pencil hardness (> 4 H) and excellent abrasion resistance (< 40 mg after 600 cycles). 2-mm-thick specimen of HUA-HC and HUA cured by UV light showed high tensile strength (> 30 MPa). The cured HUA-HC film showed better performance than the cured HUA film in the investigated aspects due to more inorganic Si–O–Si linkages in HUA-HC, which is also the reason that HUA-HC film had higher decomposition temperatures and more residue than HUA in thermal gravity analysis.