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Title
Japanese: 
English:Overcoming the entropy of polymer chains by making a plane with terminal groups: a thermoplastic PDMS with a long-range 1D structural order 
Author
Japanese: CHEN Yugen, 石割 文崇, 福井 智也, 梶谷 孝, 劉 浩男, Xiaobin Liang, Ken Nakajima, Masatoshi Tokitad, 福島 孝典.  
English: Yugen Chen, Fumitaka Ishiwari, Tomoya Fukui, Takashi Kajitani, Haonan Liu, Xiaobin Liang, Ken Nakajima, Masatoshi Tokitad, Takanori Fukushima.  
Language English 
Journal/Book name
Japanese: 
English:Chemical Science 
Volume, Number, Page Vol. 14    Issue 4    Page 2431–2440
Published date Jan. 2023 
Publisher
Japanese: 
English: 
Conference name
Japanese: 
English: 
Conference site
Japanese: 
English: 
Official URL https://pubs.rsc.org/en/content/articlelanding/2023/SC/D2SC05491D
 
DOI https://doi.org/10.1039/D2SC05491D
Abstract Due to its unique physical and chemical properties, polydimethylsiloxane (PDMS) is widely used in many applications, in which covalent cross-linking is commonly used to cure the fluidic polymer. The formation of a non-covalent network achieved through the incorporation of terminal groups that exhibit strong intermolecular interactions has also been reported to improve the mechanical properties of PDMS. Through the design of a terminal group capable of two-dimensional (2D) assembly, rather than the generally used multiple hydrogen bonding motifs, we have recently demonstrated an approach for inducing long-range structural ordering of PDMS, resulting in a dramatic change in the polymer from a fluid to a viscous solid. Here we present an even more surprising terminal-group effect: simply replacing a hydrogen with a methoxy group leads to extraordinary enhancement of the mechanical properties, giving rise to a thermoplastic PDMS material without covalent cross-linking. This finding would update the general notion that less polar and smaller terminal groups barely affect polymer properties. Based on a detailed study of the thermal, structural, morphological and rheological properties of the terminal-functionalized PDMS, we revealed that 2D assembly of the terminal groups results in networks of PDMS chains, which are arranged as domains with long-range one-dimensional (1D) periodic order, thereby increasing the storage modulus of the PDMS to exceed its loss modulus. Upon heating, the 1D periodic order is lost at around 120 °C, while the 2D assembly is maintained up to ∼160 °C. The 2D and 1D structures are recovered in sequence upon cooling. Due to the thermally reversible, stepwise structural disruption/formation as well as the lack of covalent cross-linking, the terminal-functionalized PDMS shows thermoplastic behavior and self-healing properties. The terminal group presented herein, which can form a ‘plane’, might also drive other polymers to assemble into a periodically ordered network structure, thereby allowing for significant modulation of their mechanical properties.

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