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Significant Progress Has Been Achieved by BIT in the Precisely Controlled Self-assembly of Supramolecular-Polymer System

release date :2019-10-24 07:56:00  |   [ close window ]ViewCount:

  Beijing Institute of Technology :Recently, Luo Yunjun-Li Xiaoyu research group of BIT’s School of Material Science & Engineering proposed a new strategy for the precisely controlled self-assembly of supramolecular-polymer system. Relevant achievements have been issued on a top journal, Journal of the American Chemical Society, with the title of Supramolecular hexagonal platelet assemblies with uniform and precisely-controlled dimensions. Chen Zhenfeng, a master enrolled in 2017, is the first author of this article, and Professor Luo Yunjun and Li Xiaoyu are co-authors of the paper.

  Regular geometry is widely present in the nature and artificial system, and the application of bottom-up methods to prepare regular geometry is one of the most important research topics in the chemical science and chemistry. In recent years, researchers have tried to synthesize two-dimensional nanostructures using various materials such as inorganic materials (such as graphene, metal chalcogenides, etc.) and soft substances (such as proteins, small organic molecules, supramolecular compounds, and crystalline polymers). Among these, the use of crystal-driven self-assembly of crystalline block polymers is an efficient and important method to synthesize two-dimensional platelet structures. However, this method is limited to several specific crystalline polymers, and the shape of the two-dimensional platelet is limited by the crystal structure of the crystalline block of the polymer. On the other hand, many host and guest systems have been fully studied. Host molecules have pores of various sizes and can include various guest molecules, including polymers.

  In consideration of this, Luo Yunjun-Li Xiaoyu research group of BIT proposed a new way to jointly assemble and prepare two-dimensional platelet structure assembly by host molecules of Tris(phenylene-1,2-dioxy)-Tricyclophosphazene (TPP) and guest molecules of block polymer. In this, shape of the platelet assembly is determined by the crystal structure of the host molecule. Therefore, this way significantly enriches choices of block polymers.

  The author designs three block ploymers that can be assembled together with host molecules in the solution to form a platelet assembly with a regular hexagonal shape. During the assembly process, and when the TPP molecule forms hexagonal pores, it can act on the polyethylene glycol block or polybutadiene block of the block polymer, which are to be packed in the formed channels, to form inclusion complex. While other blocks limit the growth direction of TPP, so that the assembly forms a two-dimensional platelet structure, and also provides colloidal stability to the assembly.

  A kind of hexagonal platelet structure block assembled by polymer and TPP is selected, and the author applies the “seed crystal growth method” to obtain small flat spherical platelet structure by ultrasonic crushing. With the core, new block ploymers and TPP are added for growth, and finally a hexagonal platelet structure with uniform sizes.

  Further, the author explores the growth law of the hexagonal layer structure. By calculating the hexagonal internal angle, side length and thickness of the platelet structure, the corresponding volume is calculated. It is found the increased volume of the platelet structure and the ratio of the mass of the newly added block polymer to the TPP/seed crystal platelet show strict linear relationship.

  Furthermore, based on the core of the hexagonal platelet structure, there is continuous growth of assembly consisting of two other block polymers and TPP, finally the a "triblock" hexagonal platelet assembly is formed. In addition, the author turned out the assembled platelet structure consisting of block polymers and TPP from the hexagonal prism crystal formed by polyethylene glycol homopolymer and TPP. These results prove the effectiveness, versatility and operability of this approach.

  This method combines crystallization-driven self-assembly with the function of the host-guest of the block polymer-supramolecular, provides a new precisely controlled synthesis strategy for geometric platelet assembly. This method can be expanded to other similar host and guest systems, providing a new thinking to design and prepare regular geometric assembly. Therefore, it can provide more possibilities for functionalization and application of block polymer assemblies.

Editor:News Center of BIT

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