Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2020 Nov 10;53(21):9208-9219.
doi: 10.1021/acs.macromol.0c02245. Epub 2020 Oct 21.

Solvent Effects and Side Reactions in Organocatalyzed Atom Transfer Radical Polymerization for Enabling the Controlled Polymerization of Acrylates Catalyzed by Diaryl Dihydrophenazines

Affiliations

Solvent Effects and Side Reactions in Organocatalyzed Atom Transfer Radical Polymerization for Enabling the Controlled Polymerization of Acrylates Catalyzed by Diaryl Dihydrophenazines

Blaine McCarthy et al. Macromolecules. .

Abstract

Investigation of the effects of a solvent on the photophysical and redox properties of the photoredox catalyst (PC), N,N-di(2-naphthyl)-5,10-dihydrophenazine (PC 1), revealed the opportunity to use tetrahydrofuran (THF) to modulate the reactivity of PC 1 toward achieving a controlled organocatalyzed atom transfer radial polymerization (O-ATRP) of acrylates. Compared with dimethylacetamide (DMAc), in tetrahydrofuran (THF), PC 1 exhibits a higher quantum yield of intersystem crossing (ΦISC = 0.02 in DMAc, 0.30 in THF), a longer singlet excited-state lifetime (τ Singlet = 3.81 ns in DMAc, 21.5 ns in THF), and a longer triplet excited-state lifetime (τ Triplet = 4.3 μs in DMAc, 15.2 μs in THF). Destabilization of 1 •+, the proposed polymerization deactivator, in THF leads to an increase in the oxidation potential of this species by 120 mV (E 1/2 0 = 0.22 V vs SCE in DMAc, 0.34 V vs SCE in THF). The O-ATRP of n-butyl acrylate (n-BA) catalyzed by PC 1 proceeds in a more controlled fashion in THF than in DMAc, producing P(n-BA) with low dispersity, Đ (Đ < 1.2). Model reactions and spectroscopic experiments revealed that two initiator-derived alkyl radicals add to the core of PC 1 to form an alkyl-substituted photocatalyst (2) during the polymerization. PC 2 accesses a polar CT excited state that is ~40 meV higher in energy than PC 1 and forms a slightly more oxidizing radical cation (E 1/2 0 = 0.22 V for 1 •+ and 0.25 V for 2 •+ in DMAc). A new O-ATRP procedure was developed wherein PC 1 is converted to 2 in situ. The application of this method enabled the O-ATRP of a number of acrylates to proceed with moderate to good control (Đ = 1.15-1.45 and I* = 83-127%).

PubMed Disclaimer

Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1.
Figure 1.
(A) Mechanism of organocatalyzed atom transfer radical polymerization (O-ATRP) using alkyl halide initiators (left) and structures of organic photocatalysts (PCs) used by our group (right). (B) Figure adapted from ref . Previous work demonstrated that N,N-dinaphthyl dihydrophenazines such as PC 1 (far left) access charge transfer (CT) excited states. Electrostatic potential (ESP) mapped electron density of PC 1 in the ground state (1PC[S0]) and triplet excited state (3PC*[T1,CT]) enables visualization of the shift of electron density (“red” indicates electron-rich regions, while “blue” indicates electron-poor regions) from the phenazine core in the ground state to one N-naphthyl substituent in the CT excited state (middle). Numbers indicate the computed partial charge (δ, in units of e) using the ESP CHELPG formalism. The polar CT excited state of PC 1 is destabilized in less polar solvents leading to a blue shift in the wavelength of emission of PC 1*. This solvatochromic phenomenon is displayed in the photograph (right), wherein a UV-light is being used to irradiate solutions of PC 1 in solvents of increasing polarity (from left to right: 1-hexene, benzene, dioxane, tetrahydrofuran (THF), pyridine, and N,N-dimethylformamide (DMF).
Figure 2.
Figure 2.
Effects of a solvent on the photophysical and redox properties of PC 1. (A) Jablonski diagram representing the energetic states of PC 1 (black lines) and the photophysical processes PC 1 engages in (arrows). For results using toluene, see the Supporting Information. (B) Plot of the excited-state reduction potential (E0*) and oxidation potential (E1/20) of PC 1 in DMAc and THF. E0* was calculated using the equation E0* = E1/2ES1, where E1/20 was measured using cyclic voltammetry, and ES1 was determined by fitting a vibronic progression to the emission profile of PC 1 (see the Supporting Information for more details). E0* and E1/20 are expected to affect catalytic performance in the activation and deactivation steps of the polymerization, respectively.
Figure 3.
Figure 3.
Plots of growth of the polymer Mn as a function of monomer conversion (left graphs, black squares) with Mn,theo values represented by the gray dashed line for the O-ATRP of n-BA mediated by PC 1 in DMAc (A) and THF (B). Dispersity values for each P(n-BA) sample are shown (blue squares, secondary y-axis). Plots of the normalized differential refractive index (dRI) signal as a function of retention time for GPC traces of each aliquot from the polymerizations (C). See the Supporting Information for more details.
Figure 4.
Figure 4.
(A) Crude 1H NMR spectra of aliquots removed from the reaction of PC 1 with 2 equiv of DBMM in THF (left). NMR samples were prepared by concentrating each aliquot, dissolving the crude material in C6D6, and adding the sacrificial electron donor, triethylamine (TEA), to the solution. Circles represent peaks corresponding to the phenazine core protons as indicated on the structures of PC 1 and 2 (right). (B) Normalized UV-visible absorption spectra of aliquots from the O-ATRP of n-BA before irradiation (black dashed line, 0 min; absorption profile of PC 1), after irradiation (blue traces), synthesized and isolated 2 (purple trace), and electrochemically generated 2•+ (green trace; residual 2 is present). Magnification of the spectral region near the maximum wavelength of absorption (λabs) for PC 1 (right). (C) 1H NMR spectra of aliquots from the O-ATRP of n-BA before (turquoise trace) and after (orange trace) the addition of TEA (left). For comparison, the 1H NMR spectra of isolated PC 1 (black trace) and 2 (purple trace) are shown. Electron paramagnetic resonance (EPR) spectra (right) of an aliquot from the O-ATRP of n-BA (turquoise trace) and 2•+ (purple trace). For the latter spectrum, 2•+ was generated via reaction of PC 1 with 2.0 equiv of DBMM. See the Supporting Information for more details.
Figure 5.
Figure 5.
(A) Plot of growth of polymer Mn as a function of monomer conversion (left graph, black squares) with theoretical values (gray dashed line) for the O-ATRP of n-BA mediated by PC 2 (2 was introduced to the reaction in a discrete fashion after synthesis and isolation). Dispersity values for each P(n-BA) sample are shown (purple squares, secondary y-axis). Plot of the normalized differential refractive index (dRI) signal as a function of retention time for the GPC traces of each aliquot from the polymerization (right graph). (B) Schematic for the procedure developed to generate PC 2 in situ starting from PC 1. (C) Plots analogous to those shown in (A) for the O-ATRP of n-BA catalyzed by 2 using the procedure for in situ generation of 2 as described in (B).

References

    1. Matyjaszewski K; Tsarevsky NV Macromolecular Engineering by Atom Transfer Radical Polymerization. J. Am. Chem. Soc 2014, 136, 6513–6533. - PubMed
    2. Braunecker WA; Matyjaszewski K Controlled/Living Radical Polymerization: Features, Developments, and Perspectives. Prog. Polym. Sci 2007, 32, 93–146.
    3. Kamigaito M; Ando T; Sawamoto M Metal-Catalyzed Living Radical Polymerization. Chem. Rev 2001, 101, 3689–3746. - PubMed
    1. Pan X; Fantin M; Yuan F; Matyjaszewski K Externally controlled atom transfer radical polymerization. Chem. Soc. Rev 2018, 47, 5457–5490. - PubMed
    2. Liebfarth FA; Mattson KM; Fors BP; Collins HA; Hawker CJ External Regulation of Controlled Polymerizations. Angew. Chem., Int. Ed 2013, 52, 199–210. - PubMed
    1. Parkatzidis K; Wang HS; Truong NP; Anastasaki A Recent Developments and Future Challenges in Controlled Radical Polymerization: A 2020 Update. Chem 2020, 6, 1575–1588.
    2. Corrigan N; Boyer C 100th Anniversary of Macromolecular Science Viewpoint: Photochemical Reaction Orthogonality in Modern Macromolecular Science. ACS Macro Lett. 2019, 8, 812–818. - PubMed
    3. Corrigan N; Yeow J; Judzewitsch P; Xu J; Boyer C Seeing the Light: Advancing Materials Chemistry through Photo-polymerization. Angew. Chem., Int. Ed 2019, 58, 5170–5189. - PubMed
    4. Chen M; Zhong M; Johnson JA Light-controlled living radical polymerization: mechanisms, methods, and applications. Chem. Rev 2016, 116, 10167–10211. - PubMed
    5. Corrigan N; Shanmugam S; Xu J; Boyer C Photocatalysis in Organic Polymer Synthesis. Chem. Soc. Rev 2016, 45, 6165–6212. - PubMed
    1. Miyake GM; Theriot JC Perylene as an Organic Photocatalyst for the Radical Polymerization of Functionalized Vinyl Monomers through Oxidative Quenching with Alkyl Bromides and Visible Light. Macromolecules 2014, 47, 8255–8261.
    2. Treat NJ; Sprafke H; Kramer JW; Clark PG; Barton BE; de Alaniz JR; Fors BP; Hawker CJ Metal-free atom transfer radical polymerization. J. Am. Chem. Soc 2014, 136, 16096–16101. - PubMed
    3. Discekici EH; Anastasaki A; Read de Alaniz J; Hawker CJ Evolution and Future Directions of Metal-Free Atom Transfer Radical Polymerization. Macromolecules 2018, 51, 7421–7434.
    1. Theriot JC; Lim CH; Yang H; Ryan MD; Musgrave CB; Miyake GM Organocatalyzed atom transfer radical polymerization driven by visible light. Science 2016, 352, 1082–1086. - PubMed
    2. Pearson RM; Lim CH; McCarthy BG; Musgrave CB; Miyake GM Organocatalyzed Atom Transfer Radical Polymerization Using N-Aryl Phenoxazines as Photoredox Catalysts. J. Am. Chem. Soc 2016, 138, 11399–11407. - PMC - PubMed
    3. Pan XC; Lamson M; Yan JJ; Matyjaszewski K Photo-Induced Metal-Free Atom Transfer Radical Polymerization of Acrylonitrile. ACS Macro Lett. 2015, 4, 192–196. - PubMed
    4. Dadashi-Silab S; Pan XC; Matyjaszewski K Phenyl benzo[b]phenothiazine as a visible light photoredox catalyst for metal-free atom transfer radical polymerization. Chem. - Eur. J 2017, 23, 5972–5977. - PubMed
    5. Ryan MD; Theriot JC; Lim CH; Yang HS; Lockwood AG; Garrison NG; Lincoln SR; Musgrave CB; Miyake GM Solvent effects on the intramolecular charge transfer character of N,N-diaryl dihydrophenazine catalysts for organocatalyzed atom transfer radical polymerization. J. Polym. Sci., Part A: Polym. Chem 2017, 55, 3017–3027. - PMC - PubMed
    6. Singh VK; Yu C; Badgujar S; Kim Y; Kwon Y; Kim D; Lee J; Akhter T; Thangavel G; Park LS; Lee J; Nandajan PC; Wannemacher R; Milian-Medina B; Luer L; Kim KS; Gierschner J; Kwon MS Highly efficient organic photocatalysts discovered via a computer-aided-design strategy for visible-light-driven atom transfer radical polymerization. Nat. Catal 2018, 1, 794–804.
    7. McCarthy BG; Pearson RM; Lim CH; Sartor SM; Damrauer NH; Miyake GM Structure-Property Relationships for Tailoring Phenoxazines as Reducing Photoredox Catalysts. J. Am. Chem. Soc 2018, 140, 5088–5101. - PMC - PubMed
    8. Cole JP; Federico CR; Lim CH; Miyake GM Photoinduced Organocatalyzed Atom Transfer Radical Polymerization Using Low ppm Catalyst Loading. Macromolecules 2019, 52, 747–754. - PMC - PubMed
    9. Buss BL; Lim CH; Miyake GM Dimethyl-dihydroacridines as Photocatalysts in the Organocatalyzed Atom Transfer Radical Polymerization of Acrylate Monomers. Angew. Chem., Int. Ed 2020, 59, 3209. - PMC - PubMed
    10. Kutahya C; Allushi A; Isci R; Kreutzer J; Ozturk T; Yilmaz G; Yagci Y Photoinduced Metal-Free Atom Transfer Radical Polymerization Using Highly Conjugated Thienothiophene Derivatives. Macromolecules 2017, 50, 6903–6910.
    11. Sartor SM; Lattke YM; McCarthy BG; Miyake GM; Damrauer NH Effects of Naphthyl Connectivity on the Photo-physics of Compact Organic Charge-Transfer Photoredox Catalysts. J. Phys. Chem. A 2019, 123, 4727–4736. - PMC - PubMed
    12. Koyama D; Dale HJA; Orr-Ewing AJ Ultrafast Observation of a Photoredox Reaction Mechanism: Photoinitiation in Organocatalyzed Atom-Transfer Radical Polymerization. J. Am. Chem. Soc 2018, 140, 1285–1293. - PubMed
    13. Jockusch S; Yagci Y The active role of excited states of phenothiazines in photoinduced metal free atom transfer radical polymerization: singlet or triplet excited states? Polym. Chem 2016, 7, 6039–6043.
    14. Sartor SM; McCarthy BG; Pearson RM; Miyake GM; Damrauer NH Exploiting Charge-Transfer States for Maximizing Intersystem Crossing Yields in Organic Photoredox Catalysts. J. Am. Chem. Soc 2018, 140, 4778–4781. - PMC - PubMed

LinkOut - more resources