SELF-HEALING BY MECHANOCHEMICAL ACTIVATION OF A
POLYMERIZATION CATALYST
R.T.M. Jakobs1 and R.P. Sijbesma1
1
Eindhoven University of Technology, Den Dolech, Eindhoven, the Netherlands – e-mail: r.p.sijbesma@tue.nl
Keywords: self-healing, mechanocatalysis, thermoplastic polymer
ABSTRACT
We have developed a mechanoresponsive catalyst — a catalyst which can be switched between dormant and active states by mechanical deformation. For this purpose, we have synthesized derivatives of the well-known Grubbs metathesis catalysts that are latent due to the presence of two N-heterocyclic carbene ligands. In solution, these catalysts may be switched on by mechanochemical activation with ultrasound. When provided with polymeric ligands and embedded in an semi-crystalline matrix of high molecular weight tetrahydrofuran, the catalyst can be activated by mechanical deformation of a sample, which results in dissociation of one of the ligands. The activated Ruthenium alkylidene species catalyses the ring closing metathesis of a diene. More importantly, this catalyst initiates the polymerization and crosslinking reaction of cyclic dienes such as norbornene derivatives embedded in the polymeric matrix. The system constitutes a novel principle in self-healing materials, since it allows a material to respond to stress by catalyzing a (crosslinking) polymerization reaction – in this way reinforcing the material right at the time and place it is needed when it threatens to fail.
