Effect of bulky 2,6-bis(spirocyclohexyl)-substituted piperidine rings in bis(hindered amino)trisulfide on thermal healability of polymethacrylate networks

Motohiro Aiba,Yuzo Ishigaki,Hideyuki Otsuka,Motoshi Yamanaka,Michinari Futamura,Akira Takahashi,Kazuaki Okamoto,Mitsuo Oda,Take-Aki Koizumi,Chihiro Ooka

doi:10.1039/d1ma00811k

Abstract

Bulky 2,6-bis(spirocyclohexyl)-substituted piperidine rings in bis(hindered amino)trisulfide affords low chain-transfer constant and thermal healability at moderate temperature.

Highlights

Bis(dialkylamino) disulfides were found to exhibit lower bond dissociation energy of S–S linkage (e.g., BDE of 26–31 kcal molÀ1) than dialkyldisulfides (60–70 kcal molÀ1), since the generated thiyl radicals are stabilized by the resonance from the lone pair of electrons on the nitrogen atoms.[8]
The dynamic cross-linking point containing BIBSCPS-S3 moiety can be efficiently incorporated into polymer networks with ethyl, n-butyl, or n-hexyl methacrylate monomers, which is in good accordance with the relatively low chain-transfer constants of the BIBSCPS-S3 moiety determined by the Mayo equation
After deprotection of the reaction mixture, BIBSCPS-S3-OH was separated from its tetrasulfide analogue due to the solubility difference in ethyl acetate and its molecular structure was confirmed by 1H NMR, 13C NMR, and Fourier transform-infrared (FT-IR) spectra and mass spectroscopy

Summary

Introduction

Bis(dialkylamino) disulfides were found to exhibit lower bond dissociation energy of S–S linkage (e.g., BDE of 26–31 kcal molÀ1) than dialkyldisulfides (60–70 kcal molÀ1), since the generated thiyl radicals are stabilized by the resonance from the lone pair of electrons on the nitrogen atoms.[8]. Polymers, the topological rearrangement from linear to cyclic polymers, and self-strengthening of cross-linked elastomers.[10,11,12,13,14,15,16] Afterward, we reported that the trisulfide analogue of BITEMPS-S2, bis(2,2,6,6-tetramethylpiperidin-1-yl)trisulfide (BITEMPS-S3), behaves as a DCB to produce air-stable thiyl and dithiyl radicals upon heating at mild temperature (as shown in Scheme 1b).[17] the poly(n-hexyl methacrylate) network containing BITEMPS-S3 units at cross-linking points afforded nearly quantitative damage healability only by simple hot pressing at 110 1C for 24 h, which were almost comparable to one containing BITEMPS-S2 units (100 1C for 24 h) These results indicate that bis(dialkylamino) disulfide and bis(dialkylamino) trisulfide should be recognized as one of the intrinsic DCBs, it is necessary to develop DCBs triggered at more moderate temperature. We report the dynamic covalent chemistry of bis(2,6bis[spirocyclohexyl]piperidin-1-yl)trisulfide (BIBSCPS-S3), where the bis(dialkylamino) trisulfide moiety is sterically hindered by two spirocyclohexyl groups in each piperidine ring, and describe its intrinsic self-healing property in the polymer networks

Results and discussion

Evaluation of polymethacrylate networks

Conclusions