Vapor phase infiltration (VPI) has emerged as a scalable process for transforming polymer products into a variety of organic-inorganic hybrid materials with potential applications in a number of commercial industries. Recently, VPI has been used create hybrid aluminum oxide / Polymer of Intrinsic Microporosity 1 (AlOx / PIM-1) membranes with enhanced stability and chemical separation performance. While these hybrid membranes have demonstrated excellent performance in chemical separations, the fundamental characteristics of the VPI process that leads to their enhanced properties is largely unknown. Understanding these characteristics is critical to scaling up the VPI process for membrane production as well as for translating the VPI technique to additional metalorganic precursor / polymer membrane systems. For this purpose, this talk explores using in situ quartz crystal microbalance gravimetry (QCM) to parameterize and gain fundamental understanding of the infiltration of PIM-1 with trimethylaluminum (TMA) and co-reaction with water vapor. The in situ mass uptake measured via QCM during VPI indicates that at 90 oC ~70% of the TMA sorbed by PIM-1 remains after 17.5 hours of desorption. This result lends experimental evidence that a chemical association forms between TMA and PIM-1. Interestingly, while many VPI systems with chemical associations exhibit orders of magnitude hindered out-diffusion of excess precursor during the desorption step, the relative in-diffusion and out-diffusion coefficients of TMA into PIM-1 at 90 oC are similar in magnitude. The low hindering of the hybrid material is likely due to PIM-1’s large and interconnected free volume and may help explain why PIM-1 can be infiltrated relatively quickly and to a full extent as compared with other precursor / polymer systems. Overall, this work provides quantitative and qualitative perspectives into the infiltration process establishing diffusion coefficients, understanding chemical conditions, quantifying equilibrium sorption, and more that will aid in the scale-up and translation of VPI to other precursor / polymer systems for advanced chemical separations.

In situ quartz crystal microbalance gravimetry to explore the vapor phase infiltration of polymer of intrinsic microporosity 1 with trimethylaluminum and water vapor

ACS Fall 2021

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