Impact of a Mechanical Bond on the Activation of a Mechanophore

In Abstract

Polymers made stronger with mechanical bonds

Self-healing and shock-absorbing properties are highly desirable to produce durable materials. Self-healing has been achieved by connecting polymer chains with molecules that cleave under tension and then reform (e.g. Diels-Alder adduct). A shock-absorbing material can be obtained when these chains are instead connected with a rotaxane architecture where a cyclic molecule attached at the end of one chain can slide along the axle of another chain like a rope in a pulley. Materials incorporating one of these features are already used, but they lack the strength of materials they are aiming to replace. However, combining the two strategies could improve the mechanical strength of these materials.

Researchers at the University of Manchester have combined the self-healing properties of a Diels-Alder adduct with the mobility of a mechanical bond to improve the mechanical resistance of polymers. The introduction of a rotaxane unit in a polymer chain slows down the mechanical dissociation of an adjacent Diels-Alder adduct. Computational models revealed that the constriction of the axle by the stretched macrocycle results in the accumulation of tensile and torsional stress in the mechanical bond (see picture). The presence of this competing high-stress region effectively diminishes the tension building around the Diels-Alder adduct and delays its dissociation. This research opens the possibility of manipulating the mechanical properties of a polymer by incorporating mechanical bonds at strategic positions within the backbone. This should ultimately enable the fabrication of strong self-repairing materials that are needed in highly-demanding environments from aerospace applications to prosthetic implants.

Read the full article here - DOI 10.1021/jacs.8b08590