Stratingh seminar - R.P. Sijbesma: Mechanofunctional polymers: Luminescent probes & catalytic triggers

Mechanically induced reactivity of polymeric materials has been known as a destructive force for a long time - it is the basis of molecular weight reducing techniques such as mastication and ultrasonic polymer degradation. How-ever, recent developments are making it clear that mechanical forces on polymers may also be employed in a non-destructive way. Fully utilizing that feature of mechanochemistry requires a sophisticated approach with molecular level control over functionality engineered into the material.

Recently, we have shown that the incorporation of chemiluminescent diox-etane units in a polymer results in the emission of light when the strained four-membered ring opens under mechanical force. This process probes mecha-nochemical chain scission with unprecedented spatial and temporal resolu-tion, and has the capability to provide exceptionally detailed insight in the ori-gins and mechanisms of failure in polymeric materials. An indication of the level of insight that may be garnered from the use of mechanoluminescent probes comes from a collaborative study of multiple networks, where the lumi-nescent probes uniquely identified the nature of the toughening mechanism to be an increase in dissipative volume ahead of the crack.In the presentation, I will highlight uses of dioxetane probes to tackle fundamental questions in materials science, where understanding of failure mechanisms is often lacking due to the limited possibility to probe events at the molecular scale. Examples will include irreversible softening in elastomers (Mullins effect), chain scission upon solvent swelling of glassy polymers, and the development of catalytic mechanoluminescent probes.