Supercritical carbon dioxide-soluble polyhedral oligomeric silsesquioxane (POSS) nanocages and polymer surface modification

Abstract

In this work, a functionalized polyhedral oligomeric silsesquioxane (POSS) has been investigated for its solubility in supercritical carbon dioxide for the first time in literature. POSS nanocages, which can be functionalized with a wide variety of organic substituents, are most commonly studied as nanofillers in polymer nanocomposites and coatings. Solubility of trifluoropropyl POSS in supercritical carbon dioxide has been determined by cloud-point measurements performed in a high-pressure view cell. At temperature and pressure ranges of 308–323K and 8.3–14.8MPa, these fluorinated organic–inorganic hybrid nanocage structures exhibit solubility up to 4.4% by weight, which is promising for green material processing applications using the environmentally benign solvent. Solubility of CO2-philic POSS decreases with increasing temperature, while the solubility isotherms at two different temperatures converge. Choosing the processing conditions from the performed solubility studies, trifluoropropyl POSS–supercritical carbon dioxide system has been applied in high-pressure surface modification of a high-molecular weight, rigid poly(methyl methacrylate) (PMMA). Scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analysis of the processed PMMA sheet show that the functionalized nanoparticles were deposited on the PMMA surface, forming a uniform coating of POSS aggregates. This work proves that functionalized POSS with CO2-philic groups can be solubilized in supercritical CO2, which might allow them to be applied in a plethora of materials modification processes using supercritical carbon dioxide.