The main aim of this work is to study the respective contribution of the hard and soft blocks of a metal-ligand containing block copolymer to the self-healing behavior. To this aim, different block copolymers containing terpyridine were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. These block copolymers consisted of polystyrene as the hard block, n-butyl acrylate (BA) as soft block and terpyridine units as the ligand moiety placed at different locations in the soft block. These block copolymers were complexed with manganese(II) chloride to introduce transient crosslinks and, thus, self-healing behavior. Homopolymers with the hard and soft block only were also synthesized and tested. A quasi-irreversible crosslinking, i.e. by using nickel(II) nitrate, was performed in order to study the dynamics of the permanently (strongly) crosslinked network. Rheological master curves were generated enabling the determination of the terminal flow in these networks and the reversibility of the supramolecular interactions. Additionally, the macroscopic scratch healing behavior and the molecular mobility of the polymer chains in these supramolecular networks were investigated. A kinetic study of the scratch healing was performed to determine the similarities in temperature dependence for rheological relaxations and macroscopic scratch healing. In our previous work, we have explored the effect of strength of the reversible metal-ligand interaction and the effect of changing the ratio of hard to soft block. This work goes further in separating the individual contributions of the hard and soft blocks as well as the reversible interactions and to reveal their relative importance in the complex phenomenon of scratch healing.

The macroscopic interfacial healing behaviour in a series of urea-urethane networks as function of the hydrogen bonds and disulphides content is presented. The polymers were prepared with different crosslinking densities but with the same amount of dynamic covalent bonds (disulphide linkages). Tensile and fracture measurements were adopted to evaluate the degree of recovery of the mechanical properties after damage. Healing kinetics and healing efficiencies were quantitatively determined as a function of network composition, healing temperature and contact time. Finally, the recovery of mechanical properties was correlated with the viscoelastic response of the networks through rheological measurements and time-temperature superposition principle (TTS). The application of the TTS approach on both fracture healing and DMTA and subsequent mathematical descriptive model led to a better understanding of the influence of polymer architecture and that of the amount of reversible groups on the healing process.

This work presents a detailed study into the rheological properties and fracture healing behaviour of two poly(urea-urethane) polymers containing (i) hydrogen bonds and (ii) hydrogen bonds and disulphide linkages. The experimental procedure here presented using the temperature and time superposition allowed for the identification of the contribution of each reversible bond type to the network behaviour (rheology) and healing (fracture). During the experimental data analysis it was found that the same shift factors required to construct the rheological master curves from separate isothermal small-amplitude oscillatory shear (SAOS) measurements at different temperatures could also be applied to obtain a master curve for the fracture healing data as a function of healing time and temperature. This work shows therefore the apparent direct relationship between rheological response and macroscopic fracture healing.

In the present work we show the effect of the crosslinking degree on the mechanical and healing behaviour of a healable thermoset dual-network polymer. A hyphenated rheological test (i.e. simultaneous rheology and FTIR) was used to follow the effect of the curing process on the mechanical behaviour in relation to the underlying chemical reactions. The effect of curing on the bulk properties and the polymer interfacial healing was studied using gap closure kinetics and a fracture mechanical test. The increased crosslinking density at longer curing times led to a more temperature-stable polymer network with significantly higher mechanical properties (elastic modulus and strength at break). It was found that the damage closure kinetics decrease with the curing degree but the ultimate interfacial healing efficiency does not. The results here reported highlight the effect of the crosslinking density on the kinetics of damage closure with a low impact on the maximum interfacial healing efficiency as long as the amount of reversible bonds remains constant.