Increased Chemical Stability of Vapor-Phase Infiltrated AlO_x–Poly(methyl methacrylate) Hybrid Materials

Vapor-phase infiltration (VPI) transforms polymers into unique organic–inorganic hybrid materials with properties that differ from the parent polymer. Here, hybrid materials created by the infiltration of poly(methyl methacrylate) (PMMA) with trimethylaluminum (TMA) exhibit enhanced chemical stability when immersed in various solvents including toluene, cyclohexanone, and tetrahydrofuran that normally dissolve the parent PMMA. While all AlOx–PMMA hybrid materials show enhanced stability compared to the parent PMMA polymer, the VPI process temperature affects the hybrid material’s structure (inorganic loading fraction and chemical bonding to the organic component), resulting in differences in chemical stability. At lower VPI process temperatures, inorganics become primarily physically entrapped or entangled with the polymer chains, leading to chemical stability that is dependent on solvent chemistry, including observed leaching of the inorganic component in aqueous solvents. In contrast, at higher VPI process temperatures, despite less inorganic loading, the inorganic is primarily chemically bound to the organic polymer, leading to hybrid structures that are completely insoluble in all explored solvents. Further, chemical stability does not require complete infiltration of the polymer. For the most stable hybrid chemistries, it is possible to infiltrate to a depth of only about 0.5 μm to make a bulk acrylic object (e.g., Plexiglas) resistant to chemical dissolution. However, process scale-up for treatment of bulk objects requires sufficient drying of the bulk acrylic prior to VPI treatment to prevent chemical vapor deposition (CVD) like growth of metal oxide on the surface due to reactions between the vapor-phase metalorganic precursor and desorbing water at the acrylic surface.