Following Homolytic Mechanochemical Kinetics with a Pyrenyl Nitrone Spin Trap

Abstract

The mechanochemical stability of a polymer is a fundamental parameter when choosing the ideal material for many different uses where mechanical loading may induce molecular weight reduction. The use of mechanophores has significantly improved the detection of mechanochemical reaction, but their incorporation to different polymers can be synthetically challenging. Alternatively, we return to the old strategy of using spin traps to quantify the radicals produced as a consequence of mechanochemical homolytic bond scission events. Several new spin traps have been developed in recent decades, and pyrenyl nitrones have been shown to effectively bind radicals, providing a spectroscopic methodology to follow radical concentration. Here we demonstrate the use of these probes as excellent tools to follow mechanochemical chain scission.

Intramolecular Cross‐Linking: Addressing Mechanochemistry with a Bioinspired Approach

“…Ther ate of homolytic mechanochemical events was also measured, using ap yrenyl nitrone spin trap recently demonstrated by us to provide reliable data in ultrasonication experiments (see the Supporting Information). [34] Thekinetics of radical formation was followed online by circulating the sonicated polymer solution through af low-cell in aU V/Vis spectrophotometer.A gain, the experiments were repeated 3 times for each polymer.S urprisingly,a ll SCPNs studied showed higher rates of radical production under ultrasonication, that is,m ore mechanochemical scission events occur compared to the linear polymer with the same DP (Figure 5, green).…”

“…[34] Thekinetics of radical formation was followed online by circulating the sonicated polymer solution through af low-cell in aU V/Vis spectrophotometer.A gain, the experiments were repeated 3 times for each polymer.S urprisingly,a ll SCPNs studied showed higher rates of radical production under ultrasonication, that is,m ore mechanochemical scission events occur compared to the linear polymer with the same DP ( Figure 5, green). [34] Thekinetics of radical formation was followed online by circulating the sonicated polymer solution through af low-cell in aU V/Vis spectrophotometer.A gain, the experiments were repeated 3 times for each polymer.S urprisingly,a ll SCPNs studied showed higher rates of radical production under ultrasonication, that is,m ore mechanochemical scission events occur compared to the linear polymer with the same DP ( Figure 5, green).…”

The effect of intramolecular cross links on the mechanochemical fragmentation of polymers in solution

“…23 On the one hand, the presence of these additional chemical bonds accelerates the rate of mechanochemical events, which were measured using a spin trap. 24 On the other hand, the polymer chain fragmentation is inhibited, leading to a pronounced stability of the physical properties. Two effects lead to this change in fragmentation rate: the reduction in the hydrodynamic radius reduces the efficiency of energy transduction to the polymer chains, and, the polymer architecture allows for mechanochemical scission of covalent bonds without chain fragmentation.…”

Effect of intramolecular crosslinker properties on the mechanochemical fragmentation of covalently folded polymers

“…On the other hand, the use of CLs having weaker bonds has a strong negative effect, as the raise in fragmentation rate is quite dramatic. In addition, similarly to SS bonds, which have been previously used as mechanophores, CSO 2 present similar mechanochemical rate, indicating these bonds can also be used as mechanophores.…”

“…The SCPNs containing CLs with sulfide, disulfide and sulfone bonds, all weaker than the carbon‐based backbone, undergo faster mechanochemical degradation, even if all of them present the same hydrodynamic volumes. Meanwhile, the SCPN folded by CLs containing cantered CO bonds is actually more mechanically stable, even though a CC bond scission is expected (and seen in the COGEF).…”