Revealing the\nChemical Interactions between PMMA and\nTMA for Insights into Sequential Infiltration Synthesis

Sequential\ninfiltration synthesis (SIS) is emerging as\nan important\nmethod for generating novel hybrid inorganic–polymer materials\nand is predicted to have numerous applications in technologies such\nas robust thin film materials for lithography, and preparation of\nmaterials with specific optical properties. Characterization of the\nmechanisms of SIS remains a challenge due to the nature of the materials\nformed in SIS and the dynamic nature of the processes occurring. To\nassist our understanding, we describe here a solution-based model\nfor assessing the interactions occurring in the SIS chamber. The widely\nutilized pairing of poly(methyl methacrylate) (PMMA) and trimethyl\naluminum (TMA) was chosen for this fundamental study. PMMA and TMA\nare both soluble in toluene, and importantly this is an inert solvent\nfor TMA. Liquid cell FTIR reveals the formation of complexes of TMA\nand the ester of PMMA, with a linear relationship between the proportion\nof complexes formed and the mole ratio of TMA and available ester\nmoieties. Furthermore, liquid cell FTIR, <sup>1</sup>H NMR, and <sup>13</sup>C NMR spectra show that dimeric TMA is observed when TMA\nis in excess. Although evidence of significant electron delocalization\nsuggests an increase in the ester activation, it did not lead to reaction\nproducts even when TMA was in excess. In order to develop a better\nunderstanding of the participation of H<sub>2</sub>O in the SIS reactions,\nwe developed several strategies for introducing water at various concentrations\ninto the polymer matrix. The resultant nanocomposite materials were\ncharacterized by FTIR, DSC, and TGA, further highlighting the chemical\nchanges observed in solution and demonstrating equivalence with interactions\noccurring in solid polymeric matrices in the conventional SIS process.