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Abstract
The design of high-performance nanocomposites with improved mechanical, thermal or optical properties compared to starting polymers has generated special interest due to their use in a wide range of targeted applications. In the present work, polymer nanocomposites composed of polyurethane elastomers based on polycaprolactone or polycaprolactone/poly(ethylene glycol) soft segments and titanium dioxide (TiO2) nanoparticles as an inorganic filler were prepared and characterized. Initially, the surface of TiO2 nanoparticles was modified with (3-iodopropyl) trimethoxysilane as a coupling agent, and thereafter, the tertiary amine groups from polyurethane hard segments were quaternized with the silane-modified TiO2 nanoparticles in order to ensure covalent binding of the nanoparticles on the polymeric chains. In the preparation of polymer nanocomposites, two quaternization degrees were taken into account (1/1 and 1/0.5 molar ratios), and the resulting nanocomposite coatings were characterized by various methods (Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, contact angle, thermogravimetric analysis, dynamic mechanical thermal analysis). The mechanical parameters of the samples evaluated by tensile testing confirm the elastomeric character of the polyurethanes and of the corresponding composites, indicating the obtaining of highly flexible materials. The absorbance/transmittance measurements of PU/TiO2 thin films in the wavelength range of 200–700 nm show that these partially block UV-A radiation and all UV-B radiation from sunlight and could possibly be used as UV-protective elastomeric coatings.
Highlights
Thermoplastic polyurethanes (TPUs) are an important category of polymeric materials synthesized by step-growth polymerization of polyols as soft segments and aromatic/aliphatic diisocyanates along with chain extenders as hard segments [1]
The flexibility of the physical properties of polyurethanes is usually assigned to their complex morphology with alternating hard and soft segments as elements of the polymeric backbone, which leads to a microphase-separated specific organization triggered by the thermodynamic incompatibility between the constituent soft and hard domains [9,10,11]
In view of all these facts, this study reports the synthesis of new polyurethane elastomers with a variable soft-segment composition, along with the preparation of TiO2/polyurethane nanocomposites, by the quaternization of tertiary amine groups from polyurethane with silane-modified TiO2 nanoparticles
Summary
Thermoplastic polyurethanes (TPUs) are an important category of polymeric materials synthesized by step-growth polymerization of polyols as soft segments and aromatic/aliphatic diisocyanates along with chain extenders as hard segments [1]. By adjusting the nature or the volume fraction of the components that constitute the soft and hard segments or by modifying the polymerization pathway, thermoplastic polyurethanes with a unique and wide portfolio of mechanical properties, flexibility and/or biocompatibility can be obtained, leading to a variety of polymers with versatile structures [5,6,7,8]. The amount of ionic groups in polyurethane backbone is low (less than 15 mol%) [15,16], their presence in the polymeric material determines the formation of additional ionic networks through strong interaction via Coulombic forces or hydrogen bonds, with an effect on the physical and rheological behaviour of the resulting ionomers [16,17]. The increased interest shown in these polymers is generated by the fact that besides the standard properties of polyurethanes, the presence of ionic sequences determines modifications in the phase structure of polyurethanes, with an impact on their physical and rheological characteristics and implicitly on their application potential [18,22]
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