Mechanochemically triggered bond formation in solid-state polymers

Abstract

Polybutadiene was functionalized with dibromo-, dichloro-, and bromochloro-carbene to give gem-dihalocyclopropanated (gDHC) polymers, in which the gDHCs act as mechanically activated functional groups or mechanophores. The polymers were extruded to determine the mechanophore activity in the solid state. The extent of gDHC ring opening depends on both the polymer composition and the macroscopic shear stress, ranging from 6.0% to over 30% after an hour of extrusion. In addition, the 2,3-dibromoalkene formed from mechanical activation of the gem-dibromocyclopropane was found to undergo subsequent nucleophilic substitution by chloride in the solid state. The number of solid-state substitution reactions far exceeds the number of main-chain bonds broken, a finding with implications for the future use of mechanophores in self-strengthening or self-healing polymers.