| “Structures dictates properties”is the principle that we pursue in the study of supramolecular self-assembly.Many materials with intriguing properties often have more complex and ordered structures.Effective structural analysis is a prerequisite to further improve material properties in the future.It has been well recognized that living organisms are coordinated and interacted with each other by hierarchical ordered structures,resulting in unique functions.In scientific research,only through understanding the basic structures of materials can we effectively solve many problems in material properties and other aspects.Nowadays,due to the rapid development of science and technology,more and more instruments based on structural analysis have been developed.Synchrotron radiation technology,transmission electron microscope technology,atomic force microscope technology,and scanning electron microscope technology are all excellent equipment for analyzing the structures of materials.Through in-depth research with these advanced instruments,people have a deeper understanding of the assembly structures,and lay a solid foundation for the next generation of materials with excellent properties.Molecular nanoparticles are a class of basic building blocks with precise chemical structures and diverse surface modifications.Through precise control of its symmetry,anisotropic and directional interactions can be introduced,leading to controllable hierarchical structures.In this work,we report a modular approach to construct a library of star-like macromolecules with precisely defined chemical structure based on POSS nanoparticles.The composition and symmetry can be precisely regulated.In addition,the self-assembly behaviors of bulk and solution were systematically studied in detail with small-angle X-ray scattering(SAXS)and transmission electron microscopy(TEM).It mainly includes four parts,as follows:(1)Through the combination of the thiol-ene click and Steglich esterification reaction,two types of star-like building blocks with different symmetry were successfully synthesized.The first was symmetrical building blocks with POSS core,which introduced a different number(8-16-32)of alkynyl groups on its surface through a hyperbranching method.Therefore,a symmetrical functional building blocks with high chemical reactivity at the end was formed.The other was to break the three-dimensional symmetrical structure of POSS and prepare a type of asymmetric star-like building blocks with precise regional heterogeneity.These chemical structures of building blocks and its intermediates were characterized by nuclear magnetic resonance technology(NMR),gel permeation chromatography(SEC)and matrix-assisted laser desorption ionization time of flight mass spectrometer(MALDI-To F-MS).It provides a good foundation for the further construction of a variety of giant molecules with different symmetry.(2)Based on the above-mentioned star-like building blocks with different symmetry,two different star-like macromolecules were designed and prepared successfully.One was the symmetric star-like block copolymers that linear block copolymers m PEGm-b-PSn-N3 with different molecular weights were respectively reacted with symmetric star-like building blocks by the efficient Cu AAC click reaction.Therefore,six kinds of symmetrical star-like block copolymers with different numbers of arms(8,16,32)were prepared.The SEC results showed that the symmetric star-like building blocks would not affect the reactivity as the number of alkynyl groups increased.The other was asymmetric patchy clusters which combined monofunctional POSS(CPOSS,BPOSS,DPOSS and FPOSS)with different interactions into six asymmetric star-like building blocks((yne)(8-n)(POSS)(OH)n(n=1,2,3),regio-isomers exist when n=2 and 3).Molecular library based on 18 different patchy clusters with precisely defined composition,symmetry,and surface properties were formed.The successful preparation of these multifunctional star-like macromolecules with different symmetry indicates that the building blocks of POSS core are robust and have high reactivity for the synthesis of macromolecules with different structures.(3)The self-assembly behaviors of asymmetric patchy clusters were studied by SAXS,TEM,DSC,and other characterization methods.Diverse nanostructures including unconventional complex spherical phases(F-K?phase and DQC phase)could also be found in these asymmetric patchy clusters.Through the separate study of each group of samples with different chemical structures,we further elucidated the molecular composition,symmetry,and temperature had significant effects on the self-assembly.For the CPOSS/DPOSS patchy clusters,the phase structure changed in the direction of reducing interface curvature(a transition sequence from disorder(Dis)to hexagonally packed cylinders(HEX)and then to double gyroids(DG))with the number of adjacent DPOSS increased(7C1D,o2-6C2D,o3-5C3D).When samples had the same chemical composition but with different regio-configuration(o2,m2,p2-6C2D/o3-5B3D,om-5B3D),they tended to adopt similar molecular packing with a local self-sorting process to alleviate excess unfavorable interfacial contact.Therefore,the stability of the self-assembled structures also became poor regularly(o2-6C2D>m2-6C2D>p2-6C2D,and o3-5C3D>om-5C3D),which caused by different molecular symmetry.After replacing CPOSS with crystalline BPOSS,its melting temperature decreased as the number of BPOSS decreases.At the same time,with the symmetry of the molecular structure changes,the melting temperature also decreased regularly(o2-6B2D>m2-6B2D>p2-6B2D,and o3-5B3D>om-5B3D).Under the certain temperature conditions,the hexagonally packed cylinders(HEX)structure with the same molecular packing parameter was formed,and the stability of the phase structure was the same as that of CPOSS/DPOSS samples.The self-assembly of CPOSS/FPOSS and BPOSS/FPOSS samples all showed a lamellar phase(LAM)structure,which was caused by the excessive volume fraction of FPOSS with rod-like crystals.(4)With the Steglich esterification of cyclooctyne(DBCO)and asymmetric star-like building blocks,a series of asymmetric star-like polymers with specific functional groups at the ends was prepared.The molecular structures and self-assembly behaviors were characterized by appropriate chemical tests.A method for the preparation of unimolecular micelle with controllable functional groups was developed,and a kind of elementary reaction based on Tpy was found,which provides the possibility for the preparation of multivalent unimolecular micelle and their multifunctional structures. |
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