Vapor-phase infiltration, a postpolymerization modification process, has demonstrated the ability to create organic–inorganic hybrid membranes with excellent stability in organic solvents while maintaining critical membrane properties of high permeability and selectivity. However, the chemical reaction pathways that occur during VPI and their implications on the hybrid membrane stability are poorly understood. This paper combines in situ quartz crystal microbalance gravimetry (QCM) and ex situ chemical characterization with first-principles simulations at the atomic scale to study each processing step in the infiltration of polymer of intrinsic microporosity 1 (PIM-1) with trimethylaluminum (TMA) and its co-reaction with water vapor. Building upon results from in situ QCM experiments and SEM/EDX, which find TMA remains within PIM-1 even under long desorption times, density functional theory (DFT) simulations identify that an energetically stable coordination forms between the metal–organic precursor and PIM-1's nitrile functional group during the precursor exposure step of VPI. In the subsequent water vapor exposure step, the system undergoes a series of exothermic reactions to form the final hybrid membrane. DFT simulations indicate that these reaction pathways result in aluminum oxyhydroxide species consistent with ex situ XPS and FTIR characterization. Both NMR and DFT simulations suggest that the final aluminum structure is primarily 6-fold coordinated and that the aluminum is at least dimerized, if not further “polymerized”. According to the simulations, coordination of the aluminum with at least one nitrile group from the PIM-1 appears to weaken significantly as the final inorganic structure emerges but remains present to enable the formation of the 6-fold coordination species. Water molecules are proposed to complete the coordination complex without further increasing the aluminum’s oxidation state. This study provides new insights into the infiltration process and the chemical structure of the final hybrid membrane including support for the possible mechanism of solvent stability.

Vapor-phase infiltration (VPI) infuses polymers with metalorganics to create organic−inorganic hybrid materials with properties distinct from the parent polymer. While many studies exist demonstrating the utility of VPI, few studies investigate the stability of the chemical structure and properties of the hybrid material under longterm use conditions. Herein, the durability to simulated washing of AlO x -poly(ethylene terephthalate) hybrid fabrics prepared via VPI with trimethylaluminum (TMA) and water vapor at temperatures 60, 80, 100, 120, and 140 °C under excess TMA infiltration conditions is investigated. The inorganic loading of the fabrics varies with VPI process temperature, with fabrics prepared below 100 °C containing ∼25 wt % inorganic and fabrics prepared above 100 °C having ∼17 wt % inorganic as measured by thermogravimetric analysis. Consistent with literature reports, AlO x -PET fabrics exhibit changes in color and photoluminescence that vary with the infiltration temperature. Fabrics infiltrated at lower temperatures (100 °C and below) with high inorganic loading lose a significant quantity of inorganic following washing. This loss is attributed to the formation of highly brittle, oxide-rich hybrid layers near the fibers' surfaces that delaminate and are removed during the washing process. Decreasing the inorganic loading of fabrics at these low infiltration temperatures (by controlling the relative precursor/fabric quantity) improves the wash durability of these hybrid fabrics. At higher infiltration temperatures, a negligible amount of inorganic is lost. In addition to these physical changes, differences in the photoluminescence and chemical structure, indicated by infrared spectroscopy, are observed for all fabrics and provide insights into their chemical structure and degradation pathways.

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In this work, the vapor-phase infiltration (VPI) of polyethylene terephthalate (PET) fabrics with trimethylaluminum (TMA) and coreaction with water vapor is explored as a function of limiting TMA reagent conditions versus excess TMA reagent conditions at two infiltration temperatures. TMA is found to sorb rapidly into PET fibers, with a significant pressure drop occurring within seconds of TMA exposure. When large quantities of polymer are placed within the chamber, minimal residual precursor remains at the end of the pressure drop. This rapid and complete sorption facilitates the control of inorganic loading by purposely delivering a limited quantity of the TMA reagent. The inorganic loading for this system scales linearly with a Precursor:C=O molar ratio of up to 0.35 at 140 °C and 0.5 at 80 °C. After this point, inorganic loading is constant irrespective of the amount of additional TMA reagent supplied. The SEM analysis of pyrolyzed hybrids indicates that this is likely due to the formation of an impermeable layer to subsequent infiltration as the core of the fibers remains uninfiltrated. The Precursor:C=O molar ratio in the subsaturation regime is found to tune the hybrid fabric morphology and material properties such as the optical properties of the fabric. Overall, this work demonstrates how a reagent-limited processing route can control the inorganic loading in VPI synthesized hybrid materials in a simpler manner than trying to control kinetics-driven methods.

Understanding chemical interactions between organic and metal-organic molecules has wide-ranging interest to the vapor deposition community for creating hybrid organic-inorganic materials via techniques such as molecular layer deposition and vapor phase infiltration (VPI). In the case of VPI, a vapor-phase metal-organic precursor is infused into the bulk of a polymer and becomes incorporated at the nanoscale through either chemical interaction with the polymer or the formation of a non-volatile species via the introduction of a co-reactant. VPI has applicability in a number of industrially relevant fields including the creation of novel organic-inorganic hybrid membranes which have shown enhanced stability in organic solvents, while retaining high permeance and selectivity. Motivated by this application, this work uses density functional theory (DFT) to explore chemical interactions occurring during the VPI of polymer of intrinsic microporosity (PIM-1, a polymeric membrane material) with trimethylaluminum (TMA) and its co-reaction with water. These computations revealed that the coordination between the polymer and metal-organic is a critical mechanism for the formation of the hybrid and its resultant solvent stability. To expand understanding of this critical characteristic and accelerate the design of organic-inorganic hybrid materials, a DFT dataset of computed binding energies was generated from suitable and representative atomic-level models of several common polymer functional groups and over 100 metal-organic precursors. From this dataset, a predictive machine learning model for the binding energy of metal-organic molecules to polymers has been developed. This predictive model, along with the chemical guidelines obtained from feature analysis, will aid the selection of potential candidates for novel organic-inorganic hybrid membranes as well as hybrid material creation as a whole.