where ∞ corresponds to the film thickness at an infinite purging time and  indicates the characteristic time of the deswelling process. The ∞ values as a function of tTMA are reported in Figure and 3b for PLA and PMMA, respectively. As highlighted in a very recent paper , the ratio ∞/MAX indicates the fraction of TMA molecules that are stably incorporated into the polymer matrix through a chemical reaction. Interestingly, the ratio ∞/MAX is fairly constant (figure ) for both polymers, with average values corresponding to 0.94 ± 0.01 for PLA and 0.36 ± 0.05 for PMMA. These results indicate that almost all the TMA molecules are adsorbed and chemically trapped into the PLA matrix. Conversely, PMMA exhibits a low TMA incorporation efficiency because of reduced sorption and weaker reactivity with TMA compared to PLA, even if the process is performed at a temperature that is identified to correspond to the thermodynamic equilibrium for the reaction of TMA molecules with the reactive sites of the PMMA matrix. Further confirmation of this interpretation of the SE data is provided by measuring the thickness of the residual Al2O3 film that is left over the Si substrate upon removal of the polymer template by to be around one order of magnitude higher than those obtained using PMMA as a template, confirming that the amount of TMA stably incorporated in the PLA films is significantly larger than in the PMMA films, in good agreement with operando SE results. The dominant change in the IR spectra after forming the adduct is a redshift of the C=O stretch mode that is 77.45 cm -1 for PLA and 66.55 cm -1 for PMMA. The value of the redshift value for PMMA agrees well with the previous calculated value of 65 cm -1 . and the similar, but larger, magnitude for PLA is consistent with similarities in the TMA-polymer interaction mode and differences in adduct geometry and binding strength. The methyl transfer reaction is exothermic for PLA with a reaction energy of -1.44 eV relative to the adduct formation, while the reaction was endothermic for PMMA with a reaction energy of 0.16 eV relative to the adduct. This agrees with previous conclusions that the methyl transfer is not a viable reaction when TMA interacts at PMMA and the TMA:C=O adduct is a more preferred interaction mode with PMMA.