TOPIC：Precision Polymerizations with Designer Molecules toward Sequence-Controlled Polymers and Ring-Based Polymers
SPEAKER：Prof. Makoto Ouchi, Department of Polymer Chemistry, Kyoto University, Japan
TIME：October 25 (Tuesday)10:00  AM

LOCATION：Room 528, Chemistry Building A (化学楼5楼演讲厅)
INVITER：Prof. Xinyuan Zhu (朱新远教授)

Abstract:  Biopolymers such as DNA and proteins are expressing their functions based on sequence and position of functional groups in the pendant groups as well as shape (topology) of the main chain. On the other hand, for synthetic polymers, control of the chain length and terminal groups is now possible using living polymerizations, but that of topology and sequence is still extremely difficult. Our efforts have been directed to control of side-chain sequence and main-chain topology for vinyl polymers via creative design of molecules (i.e., initiators and monomers) in polymerizations leading to construction of new type of “well-defined polymers”.

Variety of vinyl (co)polymers have been synthesized from vinyl monomers via chain growth polymerization, but the sequence control is still difficult and no functions specific to sequence can be created. As far as we see the similarity with natural polymers consisting of same type of repeating unit, sequence-controlled vinyl polymers would open the door to advanced functions. We have realized special control of addition and polymerization process with designer initiators and monomers by manipulating unique bonds, such as formation, activation, cleavage, and regeneration, to approach the challenging subject, i.e., sequence control for vinyl polymers. For example, the divinyl “template” monomer can be easily constructed via efficient bond formations to achieve alternating sequence for carboxylic acid and hydroxyl side group. In the molecule, two type of cleavable and renewable bonds are incorporated between initiator (radical generator) and monomer (methacrylate) to realize iterative radical addition via cyclization. The pendant group of monomer is too bulky to give consecutive sequence, and thus the monomer is suitable to control of single unit addition. The bulky side chain can be cleaved and modified after the addition control, which allows iterative radical addition to synthesize sequence-controlled poly(methacrylates).

We have also achieved ring-expansion living cationic polymerization of vinyl ethers with designer cyclic initiator in which hemiacetal ester bond is embedded. In conjunction with SnBr4 as a Lewis acid catalyst, side reactions, such as β-hydrogen elimination and counteranion exchange with halogen of Lewis acid (i.e., Br– in SnBr4) can be almost suppressed. The ring-expansion propagation was fairly controlled leading to selective construction of the ring topology, though accompanied by ʺring fusionʺ. The ʺring fusionʺ occurred between two ring chains, so the higher concentration of the chain was, the bigger ring of higher molecular weight was obtained. However, as the fusion event is dynamic via reversible activation of the hemiacetal ester in the presence of SnBr4, ʺring fissionʺ from fused ring to single ring can be promoted via post-dillution of the solution, e.g. simply by adding solvent after almost quantitative monomer conversion, unless SnBr4 was deactivated. Also, various pendant groups can be incorporated in vinyl ether monomer to prepare unique ring-based polymer. Thus, the ring-expansion cationic polymerization can be potentially a powerful tool to construct ring polymer architectures similar to that for general linear polymers via living polymerizations.

References
(1) Ida, S.; Terashima, T.; Ouchi, M.; Sawamoto, M. J. Am. Chem. Soc. 2009, 131, 10808-10809.
(2) Ida,S.; Ouchi, M.; Sawamoto, M. J. Am. Chem. Soc. 2010, 132, 14748-14750.
(3) Hibi, Y.; Tokuoka, S.; Terashima, T.; Ouchi, M.; Sawamoto, M. Polym. Chem. 2011, 1, 341-347.
(4) Hibi, Y.; Ouchi, M.; Sawamoto, M. Angew. Chem. Int. Ed. 2011, 50(32), 7434-7437.
(5) Hibi, Y.; Ouchi, M.; Sawamoto, M., Nat. Commun., 2016, 7:11064 doi: 10.1038/ncomms11064.
(6) Oh, D.; Ouchi, M.; Nakanishi, T.; Ono, H.; Sawamoto, M., ACS Macro Letters 2016, 5, 745–749.
(7) Kammiyada, H.; Konishi, A.; Ouchi, M.; Sawamoto, M. ACS Macro Letters 2013, 2, 531–534. (8) Kammiyada, H.; Ouchi, M.; Sawamoto, M. Macromol Symp., 2015, 350, 105-116.

Short Biography:
Makoto Ouchi is an associate professor at Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University since 2004. He received his Ph.D. degree at Kyoto University in 2001 researching “stereospecific and regiospecific cationic polymerizations with designed Lewis acid catalysts” under supervision of Professor Mitsuo Sawamoto. He then  joined Toyota Central R&D Labs to develop poly(lactic acid)-based automobile resin. In 2004, he moved to Kyoto University to start his academic carrier as an Associate Professor. He spent one year and 5 month as a vising researcher in Prof. David A Tirrell’s group at California Institute of Technology to study protein engineering with non-canonical amino acids (2007-2009). After he returned to Japan, he was promoted to an associate professor in 2010. Since 2013, he is a researcher of PRESTO (molecular technology and new function), Japan Science and Technology Agency (JST). His current interests include development of precision polymerizations, especially sequence-controlled polymerization and ring-expansion polymerization as well as development of very active polymerization catalysts. Awards: Young Scientist Prize of the Annual Kobe Polymer Research Symposium (2011); Polymer Journal Zeon Award        (2012) from the Society of Polymer Science, Japan        (SPSJ).