Development of Model Polymer Networks Containing Sacrificial Bonds Allowing the Release of Hidden Length

Details

Supervisors

Fustin, Charles-André

Faculty

Faculté des sciences

Degree label

Master [120] en sciences chimiques, à finalité approfondie

Abstract

Many biological materials, such as nacre, bones, silk or byssus from mollusks possess a remarkable combination of high resistance, toughness and even sometimes elasticity. Studies have revealed that these outstanding properties often imply the presence of sacrificial bonds and hidden lengths in the organic components. Sacrificial bonds are (weak) chemical bonds that break before stronger bonds when a deformation is applied on the material, while hidden lengths are the difference in length between folded and non-folded domains in polymer chains, or supplementary length released when sacrificial bonds (inter-chains or intra-chains) break. The concept of sacrificial bonds has already been studied in artificial materials such as elastomers, hydrogels or composites, for instance. However, few examples are found on the rupture of sacrificial bonds allowing the release of hidden length having a controlled size in artificial polymers, and even less in polymer networks. The scarcity of examples shows that such systems are still intricate to implement. Indeed, the requirements in terms of composition and topological structure to obtain optimal properties are still unclear. Even for materials that showed improved properties, the details of the principles, from a molecular point of view, leading to such behavior are not well understood either. This is why, in this project, we will develop model polymer network via a systematic approach that will enable the independent variation of key parameters such as the size of the hidden length and the presence of sacrificial bonds and hidden lengths. The development of such networks will enable, in future projects, to study the influence of such key parameters on the mechanical properties of materials. First, two macrocycles containing a sacrificial bond and a hidden length were synthesized, the two macrocycles having a different size of the hidden length. 4-arm PEG (polyethylene glycol) stars were functionalized with moieties that can react with the amino groups of the macrocycles via a Michael addition. Model polymer networks were formed by reacting the PEG stars with different linkers, either using the two macrocycles (each having a different size of the hidden length) as linkers, or a linker that contains a sacrificial bond but no hidden length or even a linker that contains neither the sacrificial bond nor the hidden length. Finally, the efficiency and the reproducibility of the synthesis of these networks was studied by rheology, to assess if they could be used in further studies as model polymer networks.