Compression-induced transformation of aldehydes into polyethers: A first-principles molecular dynamics study

First-principles molecular dynamics simulations are used to investigate the behavior of bulk acetaldehyde (MeCHO) under conditions of increasing pressure. The results demonstrate that increasing pressure causes the aldehydes to polymerize, yielding polyethers through a process involving the rapid formation of $CO$ bonds between multiple neighboring MeCHO molecules. Attempts to induce polyether formation at different densities through the application of geometric constraints show that polymerization occurs only once a critical density of $∼1.7g/cm3$ has been reached. The results of simulations performed at several different temperatures are also consistent with a process that is induced by reaching a critical density. The origins of this effect are rationalized in terms of the structural requirements for the formation of $CO$ bonds between multiple MeCHO molecules in rapid succession. Specifically, the collective formation of $CO$ bonds requires the typical distance between the $sp2$ carbon atoms and oxygen atoms in neighboring MeCHO molecules to reach a value of approximately 2.5 Å. Radial distribution functions calculated at different densities show that this structural requirement is reached when the density is near the observed threshold. The observed reaction may be useful in the context of lubrication, with polyethers being effective lubricants and the extreme conditions experienced in sliding contacts providing the ability to reach the high densities needed to induce the reaction. In this context, the calculations indicate that polyether formation is associated with significant energy dissipation, while energy dissipation is minimal once the polyethers are formed. Furthermore, the polyethers are stable with respect to multiple compression/decompression cycles and pressures of at least 60 GPa.