Dynamic supramolecular poly(isobutylene)s for self-healing materials

Abstract

Mono- and bifunctional supramolecular poly(isobutylene)s (PIBs) bearing hydrogen-bonding motifs (barbituric acid or a Hamilton wedge) are prepared by a combination of living carbocationic polymerization (LCCP) and azide–alkyne “click” reactions to investigate their dynamics and self-healing behaviour. Barbituric acid (7) or Hamilton wedge (8) functionalized polymers (3a–c, 4a–d, 5a–c, 6a) with molecular weights of ∼3000 up to 30 000 g mol⁻¹ exhibit complete end group transformation as proven by NMR and MALDI methods. Temperature-dependent rheology in the melt reveals thermoreversible formation of supramolecular clusters. Stoichiometric mixing of the polymers by solution blending affects the extent of clustering by specifically interacting barbituric acid/Hamilton wedge moieties. Frequency-dependent measurements on bifunctional barbituric acid functionalized PIBs reveal a strong rubbery plateau and terminal flow, caused by the formation of dynamically bridged clusters. In addition, fluorescence recovery after photobleaching (FRAP) measurements on the same supramolecular polymers reveal a multitude of different chain dynamics. Small discs of these polymers show self-healing at room temperature after being cut and brought into contact at the fractured surface.