A dual crosslinked self-healing system: Supramolecular and covalent network formation of four-arm star polymers

Restoration of large volume damage together with mechanical stability of self-healing polymers requires fast and efficient reversible crosslinking processes together with the presence of a static network. We investigate four-arm star polymers as a dual self-healing material, equipped with hydrogen bonding moieties and azide endgroups applicable for crosslinking based on "click" cycloaddition reaction (CuAAC). The concepts takes advantage of additional supramolecular network formation due to supra-molecular cluster formation. To this effect four-arm star poly(isobutylene)s were prepared via living carbocationic polymerization (LCCP) in combination with simple endgroup transformation steps and microwave-assisted click-chemistry to introduce thymine moieties as supramolecular tie points. Four-arm star thymine-telechelic PIB was obtained as a tough rubbery material as proven via meltrheology and SAXS measurements with clusters of approximate to 10 hydrogen bonding moieties resulting in a self-healing response at room temperature. To enable the design of a doubly crosslinked self-healing system, four-arm star PIBs bearing an average of 1.7 azide groups and 2.3 thymine endgroups/polymer were crosslinked with a three-arm star alkyne-telechelic PIB. A weakly crosslinked covalent network reinforced by supramolecular hydrogen bonding interactions was obtained in which "click"-crosslinking reduces the number of clustered hydrogen bonds from z10 to z8. Macroscopic self-healing studies of the double covalent and supramolecular network structure revealed fast and multiple self-healing at 20 degrees C within 24 h. The now designable four-arm star polymers enabled the design of a highly efficient self-healing system based on double network formation due to "click"-crosslinking and supramolecular cluster formation. (C) 2015 Elsevier Ltd. All rights reserved.