Alumina Priming-Mediated Enhanced Binding of Diethylzinc with Carbonyl Groups in Poly(Methyl Methacrylate) during Vapor-Phase Infiltration

Vapor-phase infiltration (VPI) of inorganic materials in polymers is increasingly becoming popular for synthesizing various functional hybrid materials. While AlO_x infiltration using trimethylaluminum (TMA) has been extensively studied, the mechanism of diethylzinc (DEZ)-based ZnO_x infiltration, especially one that is initiated by AlO_x priming, has not received much attention because highly reactive hydroxyl groups generated by AlO_x-priming are expected to dominate the initial binding of DEZ, thus enabling the overall ZnO_x VPI. Here, we interrogate the ZnO_x infiltration mechanism in AlO_x-primed poly(methyl methacrylate) (PMMA) in comparison to the control AlO_x-only infiltration by utilizing a suite of complementary characterizations, including quartz crystal microbalance mass gain measurement, transmission electron microscopy, infrared reflection–absorption spectroscopy (IRRAS), and synchrotron X-ray absorption spectroscopy (XAS). The multivalent TMA precursor and associated hyperbranched AlO_x network can quickly saturate the AlO_x infiltration by clogging the polymer-free volume near the top. On the contrary, the ZnO_x infiltration using divalent DEZ precursor, once activated via AlO_x-priming, can lead to accelerated ZnO_x infiltration. With the help of IRRAS, XAS, and density functional theory (DFT) simulations, we uncover that the AlO_x-priming enhances the reactivity of neighboring carbonyl groups toward DEZ and opens up simultaneous reaction pathways, leading to accelerated high-fidelity infiltration of ZnO_x.