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BIT Made Important Progress in Supramolecular Polymerization of Block Copolymers

release date :2019-07-14 11:47:00  |   [ close window ]ViewCount:

      News Source: School of Materials Science and Engineering
             Translator: News Agency of BIT Han Yu
     

  Recently, Luo Yunjun and Li Xiaoyu from BIT proposed a new self-assembly strategy for block copolymer supramolecular polymerization. The related results are titled "One-pot universal initiation-growth methods from a liquid crystalline block copolymer" and published in the famous journal Nature Communications. Jin Bixin, a doctoral student at School of Materials Science and Engineering, is the first author of the paper, and Professor Luo Yunjun and Professor Li Xiaoyu are corresponding authors of the paper.

  The seeking of a highly efficient and universal method to tailor the assembly of synthetic systems at the nanoscale, simultaneously providing facile and precise control over the hierarchical morphologies and dimensions, has always been one of the ultimate goals of contemporary materials science and chemistry. The development of the supramolecular polymerization provides an interesting idea for the design and preparation of artificial structures with complex and versatile structures. Among them, the synthesis and preparation of many nanostructures are achieved by the initiation-growth methods (also called "seed growth"). However, in most cases, due to the dynamic nature of supramolecular interactions, these non-covalently based supramolecular polymer nanostructures have low stability, making it difficult to precisely control their size and subsequent functionalization. 

  Therefore, Luo Yunjun and Li Yuyu from the School of Materials Science and Engineering reported a one-pot strategy to precisely synthesize hierarchical nanostructures through an in-situ initiation-growth process from a liquid crystalline block copolymer based on the precise controllable self-assembly of liquid crystal block copolymers (Angew. Chem. Int. Ed. 2016, 55, 11392–11396). 

  By adding a small molecule (an "initiator" in supramolecular polymerization), it interacts with the shell-forming block of a liquid crystalline block copolymer ("monomer" in supramolecular polymerization) to reduce its solubility, thereby inducing the liquid crystalline block to aggregate. In the following growth step, these aggregates subsequently serve as seeds for the growth of the free monomeric polymer chains (unimers), driven by the LC ordering effect. Eventually, the fast recruitment of unimers leads to cylindrical micelles with uniform lengths. This in situ initiated assembly approach, able to precisely tune the dimensions of resultant assemblies by carefully adjusting the initiator content and polymer concentration, presents a straightforward yet highly efficient and universal one-pot synthesis method to produce uniform hierarchical nanostructures, and the length of the uniform cylindrical micelles
 (The "degree of polymerization" of the supramolecular polymer) can be precisely adjusted between 300 nm and about 5 microns. And the lengths of the growing micelles were narrowly distributed (PDI < 1.03).

  The authors further explored the process of dissociation and re-assembly of these supramolecular polymers under heating conditions, proving that the degree of polymerization is completely determined by the assembly conditions. Thus different micelle lengths are interconvertible by simply manipulating the initiator to polymer ratio and polymer concentration. To further show the universality of this assembly method, they examined several other small molecules as initiators, including D-tartaric acid (DTA) and D-lactic acid (DLA) for hydrogen bonds, 1,2,3,4,5-pentafluoro-6-iodobenzene (PFIB) and 1,4-diiodotetrafluorobenzene (DIFB) for halogen bonds, dimethylsulfate (DMS) and benzyl chloride (BC) for quaternization, and copper acetate (Cu2+) and Karstedt’s catalyst (Pt(0)) for coordination. Through a simple heating-cooling procedures, all initiators can be prepared into uniform length columnar micelles by one-pot method. The choice of initiators can substantially influence the micelle length. More interesting is, in this work, the authors also discover that by adding a small amount of initiators, which exhibits supramolecular interactions with the copolymer, the subsequent growth driven by the LC ordering effect of the copolymer can yield linear, branched, segmented, hairy plate-like, or star-like nanostructures in a one-pot manner.  

  From a general point of view, this facile yet efficient initiated assembly approach presents a simple methodology for self-assembly, simultaneously with high-level of control over the assembled nanostructures. This method can be extended to other similar block copolymers or supramolecular systems, not only will it become a new development direction in the field of polymer and supramolecular self-assembly, it is also expected to be used in the field of biomacromolecules to provide new ideas for the study of protein and polysaccharide aggregates.

 

Full text link: https://www.nature.com/articles/s41467-019-10341-7

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