Macromolecular Phase-Separation and Self-Assembly Controlled by Heteroleptic Complexation

• Applicant: Mostafa Ahmadi, Ph.D.
• Subject Area: Preparatory and Physical Chemistry of Polymers
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 491930291

The multifaceted functions and mechanical properties of natural materials originate from the combination of a wide range of transient and permanent bonds in hierarchical structures. To replicate biomimetic functions like self-healing and stimuli-responsiveness, chemists try to employ various combinations of bonds in increasingly complex structures. Specifically, the versatile phase-separated morphology of amphiphilic block copolymers has been frequently combined with dynamicity of transient bonds to develop new functions. Transient supramolecular block copolymers (SBCs) benefit from the dynamic bond between blocks, which on the one side avoids macro-phase separation, and on the other side allows the exchange of blocks, therefore, enabling a dynamic morphology capable of self-healing and even rearrangement in response to external stimuli. Transient SBCs are developed based on hetero-complementary hydrogen bond and host–guest interactions, demonstrating a wealth of morphologies, ranging from micelle to fibers, lamellae, and vesicles, with a wide range of applications. Specifically, the orthogonal assembly of binary associations results in ordered structures promoting the conductivity, useful in electronic devices, and the stimuli-responsiveness allows the on-demand structure decomposition, beneficial in many biomedical applications like drug-delivery. This wealth of microstructure and application has been rarely explored based on metal–ligand complexes. This is because of the limited exploitation of self-sorting mechanisms in polymers for directing complexation towards the hetero-complementary bonding. This is very unfortunate considering the unique specificities of metal–ligand complexes, like the ease and wide range of tunability and properties such as catalysis, emission, and sensing. Therefore, the employment of heteroleptic metal–ligand complexes can promote the application of transient SBCs in new fields that are not accessible by hydrogen bonds or host–guest interactions. We have recently expanded the library of heteroleptic complexes used in polymer science, which allows forming novel networks without primary loop defects. This material platform establishes the framework for transient bonding of inconsistent polymer segments, enabling the construction of self-assembled micelles and fibers, and arrested phase-separation in conetworks, controlled by complex selectivity. To account for that, we will visualize the structures by a combination of microscopy, scattering, and rheology, and quantify their dynamic character by fluorescence-based techniques like FRET. The consequent understanding of the interplay between supra- and macromolecular traits of self-assembly will bring us closer to the development of macromolecular machines with well-defined rearrangements in response to external stimuli.

• DFG Programme: Research Grants
• International Connection: Spain
• Cooperation Partner: Professor Albert Poater, Ph.D.
• Co-Investigator: Professor Sebastian Seiffert, Ph.D.