Star-like polyurethane hybrids with functional cubic silsesquioxanes: preparation, morphology, and thermomechanical properties

Star-like polyurethane (PU) hybrid films containing octafunctional cubic silsesquioxanes are prepared by polyaddition reaction between octakis(dimethylsilyloxy) silsesquioxane isopropenyldimethylbenzyl isocyanate (OS-PDBI) and octakis(dimethylsilyloxy) hydroxypropyl silsesquioxane (HPS); and between OS-PDBI and hexane diol (HD). The effect of incorporation of nanostructured cubic silsesquioxanes (CSSQ) on the macroscopic properties of PU film and their thermomechanical properties are investigated. The obtained hybrid films are relatively transparent. Their morphologies and properties are studied by using Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), atomic force microscopy (AFM), thermogravimetry (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and contact angle measurements. The formation of urethane linkage disrupts the three-dimensional ordered structure of CSSQ in the hybrid film. AFM images show clearly that no phase separation in the macroscopic level for both PU hybrid films. TGA and DMA analyzes indicate that the incorporation of octafunctional silsesquioxane in PU hybrid film provides enhanced thermal stability and increased crosslink density. Moreover, the existence of cage structure also improves oxidation resistance and mechanical strength. The incomplete reaction between OSPDBI and HPS due to the steric hindrance of highly branched rigid CSSQ could result in a slight decrease in initial decomposition temperature. Furthermore, hardness and out-of-plane compressive modulus are also investigated by nanoindentation.