The mechanism behind enhanced mechanochemical stability of intramolecular cross-linked polymers

Mechanochemistry, a process in which chemical transformations in polymers are induced by mechanical stress, is one of the main reasons behind loss of function in plastic materials. The vast majority of the mechanochemical transformations result in chain fragmentation and Mw reduction, degrading the materials’ mechanical properties.¹ Developing materials with prolonged lifetimes is of high interest not only for introducing products with improved performance, but also to reduce the amount of waste.
Recently, we have demonstrated a novel approach to inherently enhance the resistance of macromolecules to mechanical fragmentation. Inspired by the structure of the largest protein in the human body, titin which, due to the presence of sacrificial intramolecular hydrogen bonds (HB),² absorbs mechanical energy without undergoing fragmentation, we incorporated covalent intramolecular cross-links to synthetic polymers and demonstrate their improved resilience towards chain fragmentation.^{3, 4}
Here, we describe our studies comparing the intramolecular cross-links in synthetic covalent polymers to the inhibition of chain fragmentation by HB in titin. To achieve this, several polymeric systems were prepared and tested, changing different cross-link parameters such as length, strength and more. Our findings suggest that the folded polymers tend to focus mechanical stress on weak intramolecular cross-links, removing the absorbed energy from the chain center.

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