Polyoxometalate-based Supramolecular Polymers And Their Self-assembly Behaviors In Solutions

Supramolecular polymer materials have attracted enormous attention in recent years due to their unique structures and functions. Much progress has been made on both design and synthesis of supramolecular polymers.Recent research focuses on organic molecules as building blocks, and there have been few reports on the inorganic materials which can be introduced into supramolecular polymers.From both the novelty of the concept and the function of potential applications, the research on this type of supramolecular polymers is very helpful for the design and synthesis of functional hybrid materials in future.Polyoxometalates (POMs) are a kind of molecular clusters built from the connection of {MOX}polyhedra, and M is a d-block element in its highest oxidation state. Its size is about0.5-5nm. POMs exhibit various topologies and interesting functional properties of optics, electromagnetism, catalysis and biochemistry. POMs are good building blocks for the fabrication of hybrid materials and molecular devices.Using the concept of supramolecular chemistry to combine the polymer and polyoxometalate cluster together is a new way for the development of supramolecular polymers. Such a new hybrid material not only has processability of the polymer material, but also catalytic and redox properties which belong to POMs. At the same time, the research on the self-assembly behavior of this kind hybrid materials in solvents of variable quality, which will provide experimental basis for the development of hierarchical ordered complex material through supramolecular self-assembly.In this paper,we combine POMs with cationic terminated polymers together based on the principle of electrostatic interaction, which results in the formation of inorganic-organic hybrid supra-molecular polymers.We further investigate the self-assembly behavior of this kind hybrid materials in solvents of variable quality.The thesis includes the following three parts:1.We introduces the concept of supramolecular self-assembly, research progress of supramolecular self-assembly, and the classification and functionality of the supramolecular polymer.2.We proposed a simple and efficient way to synthesize star-like supramolecular polymers. The electrostatic combination of a Keplerate cluster,[Mo132O372(CH3COO)30(H20)72]42-with cationic terminated poly(styrene) yields polyoxometalate-based supramolecular star polymers, which can further self-assemble into vesicular aggregates in the chloroform/methanol mixture solvents. We suspect that the driving force for the vesicular structures was a delicate balance between van der Waals attractive forces and repulsive entropic effects between adjacent star-like supramolecular polymers in the CHCI3-MeOH mixtures.3.We report the first experimental insight on the intra-/inter-spherical polymer brush (SPB) interactions in solvents of variable quality by TEM-imaging the POM-based model system where the spherical micelle (SVP-6) and vesicle (SVP-3)fabricated by the electrostatic self-assembly of [PW12O40]3-with (C8H8)48o(C8H10N)57(S480-b-V57) were used as spherical polymer brush models. The brush chains have a relatively extended conformation in the chloroform solution and chloroform mixture containing9.1%methanol. When the methanol content increases from17%to23%,the isolated and oligomeric SPBs and multi-SPB aggregates (MSAs) are discovered all together by TEM imaging. Further increase in the methanol content leads to the complete formation of MSAs. Both the outer coronas and cores show a remarkable shrinkage. The polymer chains between the cores are fully interpenetrated in the oligomers and MSAs. These features are assigned to the intra-/inter-SPB van der Waals attractions with the weakening solvent quality. Such implementation would benefit the development and understanding of programmable and hierarchical self-assembly of brush-like macromolecules into complex materials.