Catalyst-Free Photoinduced End-Group Removal of Thiocarbonylthio Functionality

Carmean, R. Nicholas; Figg, C. Adrian; Scheutz, Georg M.; Kubo, Tomohiro; Sumerlin, Brent S.

doi:10.1021/acsmacrolett.7b00038

Cited by 67 publications

(75 citation statements)

References 41 publications

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“…Neither a decrease in I polyrotaxane nor increase in I αCD remarkably occurred under either condition in the SEC (Figure B,C), suggesting that the dissociation was triggered by UV irradiation. This is consistent with the previous report that UV irradiation induces the photo‐cleavage of thiocarbonylthio groups to generate radical species . In order to further investigate whether the photo‐cleavage of CPADB stoppers trigger the dissociation of the αCD/PEG‐CPADB polyrotaxanes, polyrotaxane capped with adamantanes (Ad) was prepared as a control (αCD/PEG‐Ad polyrotaxane) (Figure S3, Supporting Information).…”

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confidence: 85%

Suspending Polyrotaxane Dissociation via Photo‐Reversible Capping of Terminals

Arisaka

Yui

2019

Macromol. Rapid Commun.

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dissociation have a predetermined outcome. For instance, existing approaches to polyrotaxane dissociation involve cleavage of terminal linkages, including ester, acetal, disulfide, and o-nitrobenzyl groups. The release of the cyclic molecules cannot be stopped once the terminal linkage has been cleaved. If the dissociation could be suspended at an arbitrary time, the amount of released cyclic molecules and mechanical properties of polyrotaxanecrosslinker-based resins or hydrogels could be modulated. In order to perform the on-off release of cyclic molecules via physical stimuli, we focused on reversible covalent bonds, which are generally robust yet reversibly broken and reformed in response to light, heat, or catalysts. [20] In particular, a dithiobenzoate derivative, which is commonly used as a chain transfer agent for reversible-deactivation radical polymerization, [21,22] is known for its reversible covalent bonding capability and is reversibly cleaved by irradiation with ultra-violet (UV) light. [23,24] Here, we hypothesized that photo-reversible capping at polyrotaxane terminals would allow for the on-off controlled release of cyclic molecules. To demonstrate this hypothesis, polyrotaxanes capped by dithiobenzoates as stoppers at both terminals of the axis polymers were designed (Figure 1). We expected the cleavage of the dithiobenzoates to be triggered by irradiation with UV light, leading to the release of the cyclic molecules. When the irradiation is stopped, the terminals would be immediately re-capped by the dithiobenzoates, suspending the release of the cyclic molecules.In the present study, we synthesized polyrotaxanes in which both terminals of polyethylene glycol (PEG, M n : 10 000) threaded into the cavities of multiple α-cyclodextrins (αCDs) are capped with 4-cyanopentanoic acid dithiobenzoate (CPADB) (Figure 2). The polyrotaxane was coded as "X/Y-Z polyrotaxane," where X, Y, and Z indicate threading cyclic molecule, axis polymer, and stopper, respectively. The successful synthesis of αCD/PEG-CPADB polyrotaxane was evaluated by 1 H-NMR measurements ( Figure S1, Supporting Information) and size exclusion chromatography (SEC) ( Figure S2, Supporting Information). The peaks associated with the aromatic ring of CPADB occurred at 7.51, 7.71, and 7.92 ppm in the 1 H-NMR spectrum of the αCD/ PEG-CPADB polyrotaxane in DMSO-d 6 ( Figure S1A, Supporting Information), indicating the presence of CPADB at the polyrotaxane terminals. Although this result indicates that the PEG terminals were modified with CPADB molecules, the formation of a mechanically interlocked structure remain to be confirmed. The CPADB molecules must cap both PEG terminals and be Polyrotaxanes

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confidence: 85%

Suspending Polyrotaxane Dissociation via Photo‐Reversible Capping of Terminals

Arisaka

Yui

2019

Macromol. Rapid Commun.

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“…To sterically access the ω chain-end for catalytic activation, a photoinduced end-group removal strategy 30 previously developed in our group was used as the key step in generating a hydrogen capped PMMA (PMMA-H) that contained a sterically unhindered ester on the ω terminus. Transesterification of PMMA-H resulted in the monosubstituted ω-functionalized product (PMMA-Bn) which was verified through MALDI-TOF-MS ( Fig.…”

Section: Resultsmentioning

confidence: 99%

Synthetic upcycling of polyacrylates through organocatalyzed post-polymerization modification

et al. 2017

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“…In the case of dithiolate esters, visible light is reported to be ineffective at initiating efficient polymerization whereas UV photolysis effects polymerization 7,15,16 . However, UV photolysis results in poor end group fidelity, due to unspecified side reactions that degrade the dithiolate ester 16,17 . The trithiocarbonate RAFT agents are effective photoiniferters under both UV and visible light photolysis, although the photochemical efficiency of these processes is suggested to be modest at best 13,[18][19][20][21][22][23] .…”

Section: Scheme 1 Initiation and Propagation In A Raft Polymerizatiomentioning

confidence: 99%

State Dependent Photochemical and Photophysical Behavior of Dithiolate Ester and Trithiocarbonate RAFT Polymerization Agents.

Falvey¹,

Thum²,

Wolf³

2020

Preprint

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The rise in popularity of photochemically initiated RAFT polymerization (photoRAFT) along with the broad spectrum of proposed, and possible, initiation mechanisms results in the need for careful characterization of the photophysical properties of some common RAFT agents. Direct irradiation of the RAFT agent as a means to generate radicals, also known as the photoiniferter mechanism, is one commonly proposed mechanism. The current study shows that the dithioesters and trithiocarbonates have lowest singlet, and triplet excited state energy levels that are close to, or lower then C-S bond dissociation energies. Excitation of these agents into their S<sub>1</sub> band results in negligible radical production, while excitation into S<sub>2</sub> or higher results in the decomposition of dithioesters and trithiocarbonates resulting in radical formation, but with low quantum yields. Likewise, there is significant literature precedence for an electron transfer initiation mechanism, PET-RAFT. It is shown that the dithioesters and trithiocarbonates all show peak reduction potentials at ca. -1.0 V (vs. SCE). However, transient absorption spectroscopy studies of the electron transfer from a mediator shows that theses reactions occur rapidly only when the mediator potential is more negative than -1.2 V (vs. SCE).

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Catalyst-Free Photoinduced End-Group Removal of Thiocarbonylthio Functionality

Cited by 67 publications

References 41 publications

Suspending Polyrotaxane Dissociation via Photo‐Reversible Capping of Terminals

Suspending Polyrotaxane Dissociation via Photo‐Reversible Capping of Terminals

Synthetic upcycling of polyacrylates through organocatalyzed post-polymerization modification

State Dependent Photochemical and Photophysical Behavior of Dithiolate Ester and Trithiocarbonate RAFT Polymerization Agents.

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