Temperature-dependent reaction between trimethylaluminum and poly(methyl methacrylate) during sequential vapor infiltration: experimental and ab initio analysis

Abstract

Vapor-phase, metal-containing organic compounds can diffuse into polymers and modify the material composition and structure. In this work, using a sequential vapor infiltration process based on atomic layer deposition chemistry, we combine in situ Fourier transform infrared transmission and quartz crystal microbalance experiments with ab initio quantum chemical modeling analysis to evaluate and identify likely reaction mechanisms when poly(methyl methacrylate) (PMMA) thin films are exposed to trimethylaluminum (TMA) vapor. We find that TMA readily diffuses into the PMMA, where it physisorbs to ester carbonyl units (C]O) to form a metastable C]O/Al(CH 3 ) 3 adduct structure that desorbs at moderate temperatures (<100 C). The Lewis-acidic TMA withdraws charge from the C]O, shifting its stretching frequency from 1732 cm À1 in untreated PMMA to 1670 cm À1 after TMA exposure. At higher temperatures IR results show a new feature near 1568 cm À1 that is stable, even upon exposure to water vapor, indicating covalent bond formation. Based on known TMA-polymer reaction mechanisms and ab initio model results, we propose that at T > 100 C, TMA reacts with PMMA to form covalent resonant C]O/Al-O-C bonding units, and does not form -O-C-O-Al(CH 3 ) as previously hypothesized. This mechanistic insight will help elucidate other polymer/Lewis-acid vapor reactions and could enable new applications for sequential vapor infiltration processes.

Effect of the Density of Reactive Sites in P(S‐r‐MMA) Film during Al2O3 Growth by Sequential Infiltration Synthesis

“…These data indicate that, in the presence of MMA units in the polymer matrix, the amount of Al 2 O 3 grown during the SIS process is directly proportional to the concentration of MMA units in the RCP chains. This picture is perfectly consistent with previous experimental results showing that CO functional groups in the MMA units act as seeds for the growth of Al 2 O 3 during the SIS process …”

Vapor phase infiltration of zinc oxide into thin films of cis-polyisoprene rubber

“…In VPI literature, this mode has been attributed to metalorganic precursors binding to carbonyl groups, both for DEZ 32 and trimethylaluminum. 8,33,34 This suggests that DEZ entrapment is at least partially explained by binding and reaction with these carbonyl groups, which are not inherent to the pure polyisoprene structure but are rather easily created via pre-heating oxidation. This proposed mechanism is furthermore supported by the analysis of high-resolution XPS spectra of oxygen and carbon ( Fig.…”

Trimethylaluminum Diffusion in PMMA Thin Films during Sequential Infiltration Synthesis: In Situ Dynamic Spectroscopic Ellipsometric Investigation

“…The most studied SIS process has been the infiltration of trimethylaluminum (TMA) in combination with H2O for the synthesis of Al2O3 into polymeric films, and in situ quartz crystal microbalance (QCM) measurements and in situ Fourier Transform Infrared (FTIR) Spectroscopy 12,[16][17][18][19][20] have been the mostly used in situ techniques for investigating the infiltration mechanism. Both characterization techniques demonstrated the dependence of effective infiltration on the presence of intermolecular interactions between the metalorganic precursor and some functional groups in the polymer, and the influence of process parameters as temperature, precursor exposure, purge duration, and pulse sequence.…”