Revealing the Chemical Interactions between PMMA and TMA for Insights into Sequential Infiltration Synthesis

Sequential infiltration synthesis (SIS) is emerging as an important method for generating novel hybrid inorganic–polymer materials and is predicted to have numerous applications in technologies such as robust thin film materials for lithography, and preparation of materials with specific optical properties. Characterization of the mechanisms of SIS remains a challenge due to the nature of the materials formed in SIS and the dynamic nature of the processes occurring. To assist our understanding, we describe here a solution-based model for assessing the interactions occurring in the SIS chamber. The widely utilized pairing of poly(methyl methacrylate) (PMMA) and trimethyl aluminum (TMA) was chosen for this fundamental study. PMMA and TMA are both soluble in toluene, and importantly this is an inert solvent for TMA. Liquid cell FTIR reveals the formation of complexes of TMA and the ester of PMMA, with a linear relationship between the proportion of complexes formed and the mole ratio of TMA and available ester moieties. Furthermore, liquid cell FTIR, 1H NMR, and 13C NMR spectra show that dimeric TMA is observed when TMA is in excess. Although evidence of significant electron delocalization suggests an increase in the ester activation, it did not lead to reaction products even when TMA was in excess. In order to develop a better understanding of the participation of H2O in the SIS reactions, we developed several strategies for introducing water at various concentrations into the polymer matrix. The resultant nanocomposite materials were characterized by FTIR, DSC, and TGA, further highlighting the chemical changes observed in solution and demonstrating equivalence with interactions occurring in solid polymeric matrices in the conventional SIS process.