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Norbornenyl-based RAFT agents for the preparation of functional polymers via thiol-ene chemistry

Milan M. Stamenović (UGent) , Pieter Espeel (UGent) , Wim Van Camp (UGent) and Filip Du Prez (UGent)
(2011) MACROMOLECULES. 44(14). p.5619-5630
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Organization
Abstract
A synthetic platform for the preparation of various norbornenyl (Nb) containing reversible addition fragmentation chain transfer (RAFT) agents has been developed. The design of the chain transfer agents (CTAs) is based on the desymmetrization of alpha,alpha'-dibromo-p-xylene by monosubstitution with an alkoxide anion and subsequent replacement of the residual bromine atom in the benzylic bromide to create several series of RAFT CTA including trithiocarbonate, xanthate and dithiobenzoate CTAs, allowing for the possibility to introduce other functional groups besides Nb, such as an allyl group. While a norbomene functionality was chosen as most reactive functional group toward thiols in radical-mediated thiol-ene chemistry, an ally] group was introduced for the sake of direct comparison of the double bond reactivity in the thiol-ene reaction. Control of the radical polymerization of acrylates, styrene and vinyl acetate has been achieved by using this novel family of CTAs. The results indicate that the Nb group remained intact at low monomer conversions (e.g., below 50% for styrene and vinyl acetate, below 30% for acrylates) and at optimal reaction temperatures (e.g., 70 degrees C for styrene and vinyl acetate, 62 and 65 degrees C for 1-ethoxyethyl acrylate and methyl acrylate, respectively), while the monomer-to-CTA ratio was kept high. Polymers with high end-group fidelity were modified with a series of thiol-containing compounds, leading to alpha-semitelechelics with different chain-end structures. While allyl-containing polymers exhibited a significantly lower reactivity, modification of the Nb-containing semitelechelics was rapid and fully accomplished under the same reaction conditions. However, for the given conditions, dodecanethiol and benzyl mercaptan showed a lower reactivity toward Nb-containing polymers, as evidenced by the obtained modification efficiency of 70% and 45%, respectively.
Keywords
RING-OPENING METATHESIS, TRANSFER RADICAL POLYMERIZATION, CLICK-CHEMISTRY, BLOCK-COPOLYMERS, MOLECULAR BRUSHES, POLY(ACRYLIC ACID), VINYL-ACETATE, MODULAR SYNTHESIS, ROMP, FRAGMENTATION-CHAIN-TRANSFER

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Chicago
Stamenović, Milan M., Pieter Espeel, Wim Van Camp, and Filip Du Prez. 2011. “Norbornenyl-based RAFT Agents for the Preparation of Functional Polymers via Thiol-ene Chemistry.” Macromolecules 44 (14): 5619–5630.
APA
Stamenović, M. M., Espeel, P., Van Camp, W., & Du Prez, F. (2011). Norbornenyl-based RAFT agents for the preparation of functional polymers via thiol-ene chemistry. MACROMOLECULES, 44(14), 5619–5630.
Vancouver
1.
Stamenović MM, Espeel P, Van Camp W, Du Prez F. Norbornenyl-based RAFT agents for the preparation of functional polymers via thiol-ene chemistry. MACROMOLECULES. 2011;44(14):5619–30.
MLA
Stamenović, Milan M., Pieter Espeel, Wim Van Camp, et al. “Norbornenyl-based RAFT Agents for the Preparation of Functional Polymers via Thiol-ene Chemistry.” MACROMOLECULES 44.14 (2011): 5619–5630. Print.
@article{1909274,
  abstract     = {A synthetic platform for the preparation of various norbornenyl (Nb) containing reversible addition fragmentation chain transfer (RAFT) agents has been developed. The design of the chain transfer agents (CTAs) is based on the desymmetrization of alpha,alpha'-dibromo-p-xylene by monosubstitution with an alkoxide anion and subsequent replacement of the residual bromine atom in the benzylic bromide to create several series of RAFT CTA including trithiocarbonate, xanthate and dithiobenzoate CTAs, allowing for the possibility to introduce other functional groups besides Nb, such as an allyl group. While a norbomene functionality was chosen as most reactive functional group toward thiols in radical-mediated thiol-ene chemistry, an ally] group was introduced for the sake of direct comparison of the double bond reactivity in the thiol-ene reaction. Control of the radical polymerization of acrylates, styrene and vinyl acetate has been achieved by using this novel family of CTAs. The results indicate that the Nb group remained intact at low monomer conversions (e.g., below 50\% for styrene and vinyl acetate, below 30\% for acrylates) and at optimal reaction temperatures (e.g., 70 degrees C for styrene and vinyl acetate, 62 and 65 degrees C for 1-ethoxyethyl acrylate and methyl acrylate, respectively), while the monomer-to-CTA ratio was kept high. Polymers with high end-group fidelity were modified with a series of thiol-containing compounds, leading to alpha-semitelechelics with different chain-end structures. While allyl-containing polymers exhibited a significantly lower reactivity, modification of the Nb-containing semitelechelics was rapid and fully accomplished under the same reaction conditions. However, for the given conditions, dodecanethiol and benzyl mercaptan showed a lower reactivity toward Nb-containing polymers, as evidenced by the obtained modification efficiency of 70\% and 45\%, respectively.},
  author       = {Stamenovi\'{c}, Milan M. and Espeel, Pieter and Van Camp, Wim and Du Prez, Filip},
  issn         = {0024-9297},
  journal      = {MACROMOLECULES},
  keyword      = {RING-OPENING METATHESIS,TRANSFER RADICAL POLYMERIZATION,CLICK-CHEMISTRY,BLOCK-COPOLYMERS,MOLECULAR BRUSHES,POLY(ACRYLIC ACID),VINYL-ACETATE,MODULAR SYNTHESIS,ROMP,FRAGMENTATION-CHAIN-TRANSFER},
  language     = {eng},
  number       = {14},
  pages        = {5619--5630},
  title        = {Norbornenyl-based RAFT agents for the preparation of functional polymers via thiol-ene chemistry},
  url          = {http://dx.doi.org/10.1021/ma200799b},
  volume       = {44},
  year         = {2011},
}

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