Polythioethers bearing side groups for efficient degradation by E1cB reaction: reaction design for polymerization and main-chain scission

Ryo Kawatani; Keito Hagiwara; Anri Tanaka; Yasuhiro Kohsaka

doi:10.1039/d3ra03751g

Polythioethers bearing side groups for efficient degradation by E1cB reaction: reaction design for polymerization and main-chain scission

RSC Adv. 2023 Jul 10;13(30):20782-20786. doi: 10.1039/d3ra03751g. eCollection 2023 Jul 7.

Authors

Ryo Kawatani¹, Keito Hagiwara¹, Anri Tanaka¹, Yasuhiro Kohsaka^{1

2}

Affiliations

¹ Faculty of Textile Science and Technology, Shinshu University 3-15-1 Tokida Ueda Nagano 386-8567 Japan kohsaka@shinshu-u.ac.jp.
² Research Initiative for Supra-Materials (RISM), Interdisciplinary Cluster for Cutting Edge Research (ICCER), Shinshu University 4-17-1 Wakasato Nagano City Nagano 380-8553 Japan.

Abstract

We have previously reported the polycondensation by the tandem reactions of dithiols and α-(bromomethyl)acrylates, consisting of conjugate substitution (S_N2' reaction) and conjugate addition (Michael addition) reactions. The resulting polythioethers underwent a main-chain scission (MCS) by E1cB reaction, which is the reverse reaction of conjugate addition, although it was not quantitative due to the equilibrium. Herein, the modification of the structures of polythioethers led to irreversible MCS, whereby the β-positions of ester moieties were substituted with a phenyl group. This slight modification in the polymer structure influenced the monomer structures and polymerization mechanisms. The understanding of reaction mechanisms by model reactions was required to obtain high molecular weights of polythioethers. It was clarified that the consequent additions of 1,4-diazabicyclo[2.2.2]octane (DABCO), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and PBu₃ were effective to achieve high molecular weight. The resulting polythioethers decomposed by irreversible MCS via E1cB reaction with DBU.