Mechanochemical C-C bond stability as a function of substitution: a computational and experimental study

In polymer mechanochemistry, homolytic C-C bond scission is surprisingly ubiquitous, even in the presence of bonds that are more chemically or mechanically susceptible. Despite that, C-C bond scission is often viewed as a side reaction, although it can be harnessed for C-C bond activation and plastic recycling. Selective C-C bond scission reactions have been demonstrated mainly in strained or unusually long bonds in cyclic or very sterically crowded molecules. In this study, we employ the constrained geometries simulate external force (CoGEF) method to systematically explore how common substituents influence the mechanical stability of unstrained C-C bonds through electronic and steric effects. By identifying structural motifs that affect the calculated bond scission force, we provide insight into the mechanochemical stability, or potential mechanochemical recyclability of different polymer chemistries. Moreover, we introduce a new protocol to experimentally evaluate mechanochemical selectivity in mechanophores which do not provide clear spectroscopic signals, using poly(phthalaldehyde) mechanochemical depolymerization as a probe.