Synthesis Of Polystyrene Ps Polyhedral Oligomeric Silsesquioxane Poss Based Giant Molecules With Sequence Controlled Poss Heads
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Synthesis of Polystyrene (PS)-polyhedral Oligomeric Silsesquioxane (POSS)-based Giant Molecules with Sequence-controlled POSS Heads
The design and the synthesis of sequence-controlled linear giant molecules by controlling the sequences and functionalities precisely are great challenges in the field of macromolecular chemistry. In this article, we designed a method to synthesize sequence-controlled linear giant molecules by using two different kinds of polyhedral oligomeric silsesquioxanes (POSSes) based building blocks. Five POSSes heads were attached successively and alternately as a linear chain with a polystyrene tail as a purification tag via azide-alkyne cycloaddition (SPAAC) "click" reactions, oxime ligations, and thiol-ene "click" coupling (TECC). In order to precisely test controlled sequences and functionalities of the POSSes heads, we used many different characterizations, 1HNMR spectra, 13CNMR spectra, FT-IR spectra, UV-vis spectra, and GPC traces, to characterize every precursor of the giant molecules. 1HNMR and 13CNMR also showed the change of the vinyl groups on VPOSSes after TECC reactions. This study pioneers the synthesis for giant molecules with accurately controlled sequences, functionalities, compositions, and topologies. Furthermore, these features defined giant molecules can also be used to test several specific supermolecular self-assembling behaviors.
Synthesis and Self-assembly of Star-shape Giant Molecules Based on Hydrophilic Polyhedral Oligomeric Silsesquioxane (POSS)
The chemical and physical properties of materials are determined not only by composition but also hierarchical structures. Hierarchical structures are formed by "bottom up" method, self-assembly of nano-scale building blocks into supramolecular assemblies via secondary interactions.1 In recent years, a series of functionalized POSS were utilized as "nanoatoms" to synthesize well-defined giant molecules. As a kind of giant molecules, giant surfactants are focused in my work. To investigate the fundamental principles of self-assembly, the giant surfactants with precise molecular structures have been synthesized by clicking "nanoatoms" to flexible polymer tails with controlled molecular weight. Because the self-assemblies of giant surfactants are sensitive to topological structures, a series of "giant surfactant" with multi-heads or multi-tails have been synthesized.2 In my work, the APOSS based star-shape giant molecules with or without polystyrene (PS) tails were precisely synthesized via "living" radical polymerization and "click chemistry". The chemical structure of the product was confirmed by 1H NMR spectrum, 13C NMR spectrum, GPC spectra, FT-IR spectra and MALDI-TOF mass spectra. After the self-assembly of samples in solution, the structures formed were investigated by transmission electron microscopy (TEM), static light scattering (SLS) and dynamic light scattering (DLS).
Design, Synthesis and Self-assembly of Polyhedral Oligomeric Silsesquioxane (POSS) Based Hybrid Materials
The giant molecules systems exhibit very interesting behaviors in the supramolecular assemblies over the past several years compared to other macromolecular systems. As an old Chinese saying goes "good tools are prerequisites for a successful execution of a job". This dissertation focuses on the synthetic possibilities based on the previous work and try to explore some progress in the first part. The second part of the dissertation encapsulates the self-assembly behaviors of the synthesized giant molecular systems. A pre-functionalization method was developed to achieve giant molecular families with more abundant functionalities. Fluorinated polyhedral oligomeric silsesquioxane (FPOSS), long alkyl chain functionalized POSS (C8POSS), and protected carboxylic acid group functionalized POSS (tAPOSS) were designed and prepared. These kinds of molecules are viewed as molecular nanoparticles (MNPs). The reactivities of the modules was proved by combining them with polymer systems like polystyrene via "click" chemistry. These precisely defined functionalized POSS-containing hybrids could serve as model molecules to investigate the self-assembly behaviors of giant molecules.The solution self-assembly of a giant surfactant consisting of a polystyrene-block-poly (ethylene oxide) (PS-b-PEO) diblock copolymer tail tethered onto a fluorinated polyhedral oligomeric silsesquioxane (FPOSS) cage in 1,4-dioxane/water was investigated. Abundant unconventional micellar structures including toroids, two-dimensional hexagonally patterned colloidal nanosheets, and laterally structured vesicles were observed.2 This study not only exhibits various unique morphologies, but also promotes the fundamental understanding on the pathways of the transformations between different morphologies in the solution self-assembly behavior of giant surfactants.In the MNPs and polymer hybrid systems, the MNPs were with precise molecular weights and chemical compositions. But the polymers used still have a molecular weight distribution which originates from the nature of the polymerization methods applied. To eliminate the polydispersity effect from the system, it is crucial to have molecular systems with precise molecular weights and chemical structures from the physical point of view. Upon this anticipation, we have designed a series of dendrons which are compositionally identical, but their linkers are in different chemical connection geometries. These sets of macromolecules are composed of hydroxyl group functionalized POSS (DPOSS) and isobutyl functionalized POSS (BPOSS). The final dendron structure consists of three parts, one DPOSS at the apex, four BPOSSs at the periphery and the flexible linkers. Note that this series of dendrons is topological isomers. Self-assembled structures of four dendron topological isomers were studied using SAXS and TEM. The results help us to understand the role of linkers in a amphiphiles system and give us some guidance on how to design a molecular system in the future.