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

Abstract

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 AlO x −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.

Vapor phase infiltration of zinc oxide into thin films of cis-polyisoprene rubber

“…These values are within the same order of magnitude as effective diffusivity values reported for infiltration of trimethylaluminum into poly(methyl methacrylate) 28 and can give valuable information about infiltration depth when upscaling the process to thicker films or macroscopic objects. 8,28 Diffusivity values in the order of 10 À6 cm 2 s À1 have been reported for the diffusion of gas molecules such as O 2 , N 2 , or CO 2 in (vulcanized) natural rubber, i.e. 8 orders of magnitude higher than the current findings; however, it was shown that the diffusivity rapidly decreases with increasing gas molecule size for natural rubber and other polymers.…”

“…In VPI literature, this mode has been attributed to metalorganic precursors binding to carbonyl groups, both for DEZ 32 and trimethylaluminum. 8,33,34 This suggests that DEZ entrapment is at least partially explained by binding and reaction with these carbonyl groups, which are not inherent to the pure polyisoprene structure but are rather easily created via pre-heating oxidation. This proposed mechanism is furthermore supported by the analysis of high-resolution XPS spectra of oxygen and carbon ( Fig.…”

“…The ability to increase chemical stability of polymers in solvents by VPI has been reported for different systems. 8,15 In a recent study by McGuinness et al, 8 the stability of AlO x -poly(methyl methacrylate) hybrid films was tested in various solvents. The authors found that the infiltration temperature controlled the physicochemical structure of the final hybrid material and its resultant chemical dissolution performance.…”

“…Unlike many other methods currently used, VPI incorporates the inorganic species homogeneously at the atomic level, and the species may be chemically bound or unbound to the polymer host. 8 VPI is capable of distributing the inorganic material uniformly inside polymers and the amount of loading can be tuned by infiltration hold times, pressures, and cycle numbers. 9,10 While VPI originated from the atomic layer deposition (ALD) community and shares similar precursor chemistries, the process mechanisms are substantially different.…”

Conformal Coating of Freestanding Particles by Vapor‐Phase Infiltration

“…A long intermediate purge was required to remove any trapped/adsorbed water molecules from the PS surface to minimize the surface deposition of an alumina thin-film that could occur from subsequent infiltration cycles. [30,31] We note that this procedure could also be performed directly on a PS-coated monolithic silicon substrate, but for disc particles larger than ≈1 μm, limited lateral infiltration distance results in an uneven coating on the bottom surface (see Supporting Information for discussion).…”