Covalent reversible chemistries give rise to polymers with reasonable mechanical properties yet require external stimuli to heal. Oppositely, supramolecular systems can heal autonomously, but their properties are still far away from most of those set by application requirements. Both downsides need to be addressed before intrinsic healing polymers can emerge out of academic literature and be found in daily life products. The aims of the research described in this thesis are: i) to develop intrinsic self-healing polymers with mechanical properties that significantly exceed those currently reported in the academic literature but can nevertheless repair cracks at room temperature; ii) to contribute to a better understanding of the importance of the polymer chain architecture on the physical processes during the repair of mechanical damage... ... Read more

We present a systematic study of the role of the aromatic dianhydride structure on the self-healing behavior of dimer diamine-based polyimides. By means of solid-state NMR and rheology, we studied the molecular and microscale dynamics of four polyimides comprising the same aliphatic branched diamine yet with variable dianhydride rigidities and correlated these to their macroscopic healing kinetics measured by tensile testing. Following the two-step kinetics of the healing process, we were able to differentiate and quantify the extent of mechanical strength recovery in each of the healing stages separately. Moreover, the detailed rheology and solid-state NMR allowed us to shed light on the role of the aromatic interactions and branches on the mechanical properties and mechanical integrity during macroscopic healing. The study reveals the relevance and interplay of primary and secondary interactions in the development of non-cross-linked strong and healing polymers able to maintain mechanical integrity during healing. ... Read more

In this work we report the effect of the hard block dianhydride structure on the overall properties of partially bio-based semi-aromatic polyimides. For the study, four polyimides were synthesized using aliphatic fatty dimer diamine (DD1) as the soft block and four different commercially available aromatic dianhydrides as the hard block: 4,4'-(4,4'-isopropylidenediphenoxy) bis-(phthalic anhydride) (BPADA), 4,4'-oxydiphthalic anhydride (ODPA), 4,4′-(Hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). The polymers synthesized were fully organo-soluble thermoplastic branched polyimides with glass transition temperatures close to room temperature. The detailed analysis took into account several aspects of the dianhydrides structure (planarity, rigidity, bridging group between the phtalimides, electronic properties) and related them to the results obtained by differential scanning calorimetry, rheology, fluorescence and broadband dielectric spectroscopy. Moreover, the effect of physical parameters (crystallization and electronic interactions) on the relaxation behavior are discussed. Despite the presence of the bulky branched soft block given by the dimer diamine, all polyimides showed intermolecular charge transfer complexes, whose impact depends on the electronic properties of the dianhydride hard block. Furthermore, the results showed that polyimides containing flexible and bulky hard blocks turned out fully amorphous while the more rigid dianhydride (BPDA) led to a nanophase separated morphology with low degree of crystallinity resulting in constrained segmental relaxation with high effect on its mechanical response with the annealing time. This work represents the first detailed report on the development and characterization of polyimides based on a bio-based fatty dimer diamine. The results highlight the potential of polymer property design by controlled engineering of the aromatic dianhydride blocks. ... Read more

On page 5 of 6 (Experimental Section, subsection Laser Speckle Imaging), the sentence “The LSI method is based on the multiple scattering of light, essentially the imaging equivalent of Ddffusive Wwve Ssectroscopy.[27]” was typeset incorrectly during production of the article, and is hereby corrected to (changes indicated in bold): “The LSI method is based on the multiple scattering of light, essentially the imaging equivalent of diffusive wave spectroscopy.[27]” Furthermore, the sentence “At frequencies below ∼0.1 Hz and above ≈100 Hz, localized repair dynamics vanish.” was typeset incorrectly during production of the article, and is hereby corrected to (changes indicated in bold): “At frequencies below ≈0.1 Hz and above ≈100 Hz, localized repair dynamics vanish.”. ... Read more

Self-healing polymers can significantly extend the service life of materials and structures by autonomously repairing damage. Intrinsic healing holds great promise as a design strategy to mitigate the risks of damage by delaying or preventing catastrophic failure. However, experimentally resolving the microscopic mechanisms of intrinsic repair has proven highly challenging. This work demonstrates how optical micromechanical mapping enables the quantitative imaging of these molecular-scale dynamics with high spatiotemporal resolution. This approach allows disentangling delocalized viscoplastic relaxation and localized cohesion-restoring rebonding processes that occur simultaneously upon damage to a self-healing polymer. Moreover, frequency- and temperature-dependent imaging provides a way to pinpoint the repair modes in the relaxation spectrum of the quiescent material. These results give rise to a complete picture of autonomous repair that will guide the rational design of improved self-healing materials. ... Read more

Traditional polyetherimides (PEIs) are commonly synthesized from an aromatic diamine and an aromatic dianhydride (e.g., 3,4′-oxidianiline (ODA) and 4,4′-oxidiphtalic anhydride (ODPA)) leading to the imide linkage and outstanding chemical, thermal and mechanical properties yet lacking any self-healing functionality. In this work, we have replaced the traditional aromatic diamine by a branched aliphatic fatty dimer diamine (DD1). This led to a whole family of self-healing polymers not containing reversible chemical bonds, capable of healing at (near) room temperature yet maintaining very high elastomeric-like mechanical properties (up to 6 MPa stress and 570% strain at break). In this work, we present the effect of the DD1/ODPA ratio on the general performance and healing behavior of a room temperature healing polyetherimide. A dedicated
analysis suggests that healing proceeds in three steps: (i) an initial adhesive step leading to the formation of a relatively weak interface; (ii) a second step at long healing times leading to the formation of an interphase with different properties than the bulk material and (iii) disappearance of the damaged zone leading to full healing. We argue that the fast interfacial adhesive step is due to van der Waals interactions of long dangling alkyl chains followed by an interphase ormation due to polymer chain interdiffusion. An increase in DD1/ODPA ratio leads to an increase in the healing kinetics and displacement shift of the first
healing step toward lower temperatures. An excess of DD1 leads to the cross-linking of the polymer thereby restricting the necessary mobility for the interphase formation and limiting the self-healing behavior. The results here presented offer a new route for the development of room temperature self-healing thermoplastic elastomers with improved mechanical properties using
fatty dimer diamines. ... Read more