Cationic reversible addition–fragmentation chain transfer (RAFT) polymerizations have permitted the controlled polymerization of vinyl ethers and select styrenics with predictable molar masses and easily modified thiocarbonylthio chain ends. However, most cationic RAFT systems require inert reaction conditions with highly purified reagents and low temperatures. Our groups recently developed a living cationic polymerization that does not require these rigorous conditions by utilizing a strong organic acid (pentacarbomethoxycyclopentadiene (PCCP)) and a hydrogen bond donor. By combining our PCCP acid promoted polymerization with a chain transfer agent, we have designed a tolerant cationic RAFT system that can be performed neat, open to the air, and at room temperature. Additionally, this system allows us to utilize catalytic amounts of the PCCP acid to furnish polymers with chain end functionality that can be easily isolated and further manipulated to make functional materials.
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Substituent effects in iniferter photopolymerization: can bond homolysis be enhanced by electronics?
Photoinduced-RAFT polymerization is a technique of increasing interest due to the combination of control over polymerization that RAFT processes afford with the mild reaction conditions and spatial and temporal control of photochemical processes. Iniferter RAFT polymerization is an interesting subclass of photoinduced-RAFT that eliminates the need for an added photocatalyst, as the RAFT agent is directly excited by the photon source. Iniferter RAFT is a photochemical process leading to carbon–sulfur bond homolysis. In this work we find a surprising effect of substituents on the dithiobenzoate moiety of the chain transfer agent (CTA). Donating groups dramatically accelerate the iniferter process, while withdrawing groups retard the reaction substantially. This is interpreted though electrochemistry, since homolysis of the carbon–sulfur bond is associated with a formal oxidation of the thiocarbonylthio groups and reduction of the carbon to a radical. Through this study, the unique efficiency of 2-cyano-2-propyl 4-methoxydithiobenzoate (CPMODB) as an iniferter was uncovered, as this polymerization was found to progress at a drastically enhanced rate, even when compared to similar tris[2-phenylpyridinato-C 2 , N ]iridium( iii ) photocatalyzed polymerizations using an unsubstituted dithiobenzoate RAFT agent.
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- Award ID(s):
- 1749730
- NSF-PAR ID:
- 10218008
- Date Published:
- Journal Name:
- Polymer Chemistry
- Volume:
- 11
- Issue:
- 38
- ISSN:
- 1759-9954
- Page Range / eLocation ID:
- 6129 to 6133
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Photoinduced electron/energy transfer (PET)-reversible addition–fragmentation chain transfer polymerization (RAFT) and conventional photoinitiated RAFT were used to synthesize polymer networks. In this study, two different metal catalysts, namely, tris[2-phenylpyridinato-C2,N]iridium(III) (Ir(ppy)3) and zinc tetraphenylporphyrin (ZnTPP), were selected to generate two different catalytic pathways, one with Ir(ppy)3 proceeding through an energy-transfer pathway and one with ZnTPP proceeding through an electron-transfer pathway. These PET-RAFT systems were contrasted against a conventional photoinitated RAFT process. Mechanically robust materials were generated. Using bulk swelling ratios and degradable cross-linkers, the homogeneity of the networks was evaluated. Especially at high primary chain length and cross-link density, the PET-RAFT systems generated more uniform networks than those made by conventional RAFT, with the electron transfer-based ZnTPP giving superior results to those of Ir(ppy)3. The ability to deactivate radicals either by RAFT exchange or reversible coupling in PET RAFT was proposed as the mechanism that gave better control in PET-RAFT systems.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D0PY01086C
