SYNTHESIS AND MECHANICAL ANALYSIS OF TRANSIENT- COVALENT DOUBLE NETWORKS

Nature uses a combination of dynamic hydrogen bonds and static covalent bonds in e.g. the muscle sarcomer to achieve toughness in otherwise elastic materials. The dynamic bonds can open when a force is applied, thereby providing a stress-relieve mechanism to prevent rupturing of the covalent links. Upon release of external force the hydrogen bond network can heal to restore the former properties. To mimic these astonishing effects we envisioned a similar combination in elastomeric compounds by creating a dual network of hydrogen bonded and covalently linked polyisoprene. We synthesized a number of dual networks by first modifying polyisoprene with hydrogen bond forming urazole groups to form supramolecular networks with a cross-linking density between 0 and 15 mol%. In a second step covalent crosslinks were added by hydrosilylation with a bissilane linker. Linear rheological analysis of the transient network showed a dissipation mechanism extrapolated to be on the order of 0.01 - 0.10 s at ambient temperature. In combination with neutron scattering, which provides unrivalled and first insights on the chain level, the self-healing properties of these novel semi-transient networks are studied on the molecular level in static and dynamic deformation through a selective labelling of chains. Understanding of the self-healing mechanism in these mixed covalent and transient systems will allow the development of new polymeric materials with advanced functionality.