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Terminal Functionalization with a Triptycene Motif that Dramatically Changes the Structural and Physical Properties of an Amorphous Polymer Fumitaka Ishiwari, Gen Okabe, Hibiki Ogiwara, Takashi Kajitani, Masatoshi Tokita, Masaki Takata, and Takanori Fukushima J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b09242 • Publication Date (Web): 03 Oct 2018 Downloaded from http://pubs.acs.org on October 3, 2018
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Journal of the American Chemical Society
Terminal Functionalization with a Triptycene Motif that Dramatically Changes the Structural and Physical Properties of an Amorphous Polymer Fumitaka Ishiwari,†,‡ Gen Okabe,†,‡ Hibiki Ogiwara,†,‡ Takashi Kajitani,†,‡ Masatoshi Tokita,§ Masaki Takata,‡,# and Takanori Fukushima*,† †
Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama 226-8503, Japan. ‡
RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan.
§
Department of Chemical Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan. #
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
ABSTRACT: A surprising terminal-group effect on the structural and physical properties of an amorphous polymer is reported. We recently demonstrated that triptycene derivatives with substituents at the 1,8,13-positions show specific self-assembly behavior, enabling the formation of a well-defined “2D + 1D” structure based on nested hexagonal packing of the triptycenes. Upon terminal functionalization with a 1,8-substituted triptycene (1,8-Trip, Scheme 1), a liquid polymer, polydimethylsiloxane (PDMS, Mn = 18~24 kDa), turned into a highly viscous solid that exhibits birefringence at 25 °C. Small-angle and wide-angle X-ray scattering measurements revealed that the resulting telechelic PDMS assembles into a 2D + 1D structure, where layers of PDMS domains, formed between 2D assemblies of the triptycene termini, stack into a 1D multilayer structure with a layer spacing of 18~20 nm. Due to this structuring, the complex viscosity of the telechelic PDMS was dramatically enhanced, providing a value four orders of magnitude greater than that of original PDMS. Remarkably, the structural and physical properties of PDMS were hardly changed upon terminal functionalization with another regioisomer of triptycene (1,4-Trip, Scheme 1), which differs only in the substitution pattern.
INTRODUCTION Construction of a periodically ordered structure with polymer assemblies has been an important subject not only in fundamental polymer science but also in the development of advanced soft materials that are used in nano-patterning1 and directional (ion-, charge-, and heat-) transporting,2 as well as optical3 and mechanical applications.4 The most promising approach to achieve this goal is to use block-co-polymers composed of incompatible main chains, which facilitate phase separation at the nanoscale.5 Recently, supramolecular block copolymers, where immiscible polymer segments are connected non-covalently, have shown to behave like conventional covalently bonded block copolymers.6,7 Side-chain functionalization to incorporate incompatible segments in a polymer chain is also useful.8 Meanwhile, in general, terminal functionalization is not considered to be effective for achieving the controlled assembly of polymers into a periodically ordered structure. Indeed, although numerous one-dimensional (1D) supramolecular polymers have been developed using specifically designed terminal groups capable of hydrogen bonding, metal coordination, and host/guest binding,9,10 the formation of periodically ordered structures with these polymers has scarcely been reported. To the best of our knowledge, examples are limited to relatively low molecular weight polyethylene (< 2.2 kDa),11a,b polypropylene oxide (< 2.2 kDa),11c–e poly(ethylene-co-butylene) (
