A surprise from 1954: siloxane equilibration is a simple, robust, and obviouspolymer self-healingmechanism

Abstract Click to copy section link Section link copied! Tetramethylammonium silanolate-initiated ring-opening copolymerization of octamethylcyclotetrasiloxane (D 4 ) and bis(heptamethylcyclotetrasiloxanyl)ethane (bis-D 4 ) renders cross-linked network polymers that contain ethylene bridges and active silanolate end groups. These “living” reactive anionic species are not neutralized by ambient atmosphere exposure (are stable to water, oxygen, CO 2 ) and promote thermally activated equilibration among different network isomers and cyclic oligomers. The cross-link density of these living networks can be controlled by the ratio of D 4 :bis-D 4 , and the density of active chain ends is determined from the initiator:monomer ratio.

We report that samples prepared with particular ratios of initiator:D 4 :bis-D 4 can be cut with a sharp knife, even into two pieces, and can heal by siloxane equilibration to restore the original strength of the silicone sample. Fracture toughness measurements were carried out and revealed complete (mechanical) healing. Broken and healed samples generally failed in locations other than the initially cracked region. We call attention to publications and patents from the 1950s that suggest that this self-healing behavior was likely obvious 60 years ago.

ACS Publications Copyright © 2012 American Chemical Society Subjects what are subjects Article subjects are automatically applied from the ACS Subject Taxonomy and describe the scientific concepts and themes of the article. Deformation Nucleic acid structure Self healing materials Silicones Stress