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Article

Aqueous Radical Photopolymerization Catalyzed by Resorufin

by
Wenqiao Zhou
1 and
Chunming Liu
1,2,*
1
School of Polymer Science and Polymer Engineering, University of Akron, Akron, OH 44325, USA
2
Department of Chemistry, University of Akron, Akron, OH 44325, USA
*
Author to whom correspondence should be addressed.
Organics 2026, 7(1), 5; https://doi.org/10.3390/org7010005 (registering DOI)
Submission received: 15 October 2025 / Revised: 25 December 2025 / Accepted: 8 January 2026 / Published: 15 January 2026
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Abstract

Commercially available resorufin was shown to function as an organic photocatalyst for visible-light-induced aqueous radical polymerization under low-irradiance illumination. Polymers with narrow molecular weight distributions and high monomer conversions were successfully synthesized from acrylate and acrylamide monomers. The photopolymerization catalyzed by resorufin was consistent with a reductive quenching mechanism. Good temporal control of the reaction was achieved by toggling visible light irradiation.

1. Introduction

Photopolymerization has experienced rapid advancements over recent decades, generating increased interest in both industry and academia [1,2,3,4,5,6]. Compared with conventional thermal processes that typically require high temperatures, photopolymerization can reduce energy input and enable spatiotemporal control, aligning with key goals of green chemistry [6,7,8,9,10,11,12,13]. Light-activated polymerization can proceed through two general types: free-radical polymerization and ionic polymerization, with free-radical mechanisms dominating for vinyl monomers [2,14,15]. Owing to the broad monomer scope and rapid kinetics, radical photopolymerization is widely used in practical applications, including coatings, biomaterials, and 3D printing [4,5,6,7,16,17,18,19,20,21,22,23].
The photoinitiating system (PIS) plays a central role in radical photopolymerization [2,24]. Early photoinitiating systems predominantly employed Type I initiators, which undergo unimolecular bond cleavage to generate radicals directly with high initiation efficiency. Historically, many classic Type I initiators were optimized for UV irradiation (and, in some cases, for short-wavelength visible light) and are most commonly applied in organic media [2,24,25,26,27,28]. Type II initiators were later introduced, which extend the accessible spectral range and improve light-harvesting efficiency. These systems rely on bimolecular interactions between photosensitizers and electron/hydrogen donors, but often suffer from reduced quantum efficiency due to back electron transfer, solvent cage effects, the formation of non-initiating radical species, and other competitive processes [26,29,30,31,32,33,34,35,36]. By incorporating an additional redox additive, three-component systems (TCSs, also referred to as Type III initiators) were developed. These multi-component initiating systems enable dye regeneration and suppress recombination losses, thereby improving light utilization efficiency and enabling polymerization under low-intensity irradiation [20,21,35,37,38,39,40].
The use of photopolymerization processes requires an appropriate PIS, depending on the requirements of the intended application, which extends beyond initiation efficiency to additional criteria, including commercial availability, ease of preparation, compatibility with monomer solubility, and suitability for the wavelength and power of the light sources [1,2,41]. Water is an attractive solvent owing to its low toxicity, low cost, and wide availability. For biomedical and biomaterial-related applications, the PIS is often expected to be water-soluble, have low cytotoxicity, and minimize photodamage [1,41,42].
Visible light sources are broadly available, cost-effective, energy-efficient, and can proceed at ambient temperature with low energy input, which is attractive from a sustainability perspective [34,43,44]. Compared with UV, visible light has longer wavelengths and lower photon energy, reducing photodamage concerns thus improving operational safety [40,45]. However, many visible light PISs are still tailored to blue/violet light, which increases the risk of blue-light hazard (BLH) and can cause photochemical retinal injury [46]. Meanwhile, the green-light-responsive PISs remain comparatively underexplored with far fewer reports to date [26,32].
Phenoxazine-based dyes have attracted increasing attention as visible light photoinitiators, particularly in controlled and/or aqueous photopolymerization [26,27,30,31,36,47,48,49,50,51,52,53]. Resorufin is a water-soluble phenoxazine dye exhibiting strong absorption in the green region [54,55,56]. Resorufin has also been widely used as fluorescent probes and for live-cell viability/cytotoxicity, which thus has potential applications as reported in [54,57,58,59,60]. In addition, resorufin is commercially available, which lowers the practical barrier to adoption compared with many organic photoredox catalysts that require multistep synthesis and tuning [48]. Motivated by these considerations, this work investigated resorufin as a photocatalyst for radical photopolymerization under low-irradiance green light in aqueous media, which has potential in application scenarios that often require stringent, multi-criteria constraints, such as in situ polymerization, targeted drug delivery, and cell encapsulation [1,61].

2. Experimental Section

2.1. Materials

The structures of the chemicals used in this work are shown in Figure 1. N,N-Dimethylacrylamide (DMA, 99%, Sigma-Aldrich, St. Louis, MO, USA), acrylamide (AM, 99%, Sigma-Aldrich.), and poly (ethylene glycol) methyl ether acrylate (PEGA-480, Sigma-Aldrich) were used after passing through an alumina column (aluminum oxide, Al2O3, for chromatography, Acros Organics, Bridgewater, NJ, USA) to remove the inhibitors. Isopropylacrylamide (NIPAM, 97%, Sigma-Aldrich) was purified after recrystallization. N,N,N′,N″,N″-Pentamethyl-diethylenetriamine (PMDETA, 99%, Tokyo Chemical Industry Co., Ltd., Tokyo, Japan) and 2-hydroxyethyl 2-bromoisobutyrate (HEBiB, 95%, Sigma-Aldrich) were used after distillation. Chloroform-D (CDCl3, 99.8%, Cambridge Isotopes Laboratories, Inc., Tewksbury, MA, USA), deuterium oxide (D2O, 99.9%, Cambridge Isotopes Laboratories, Inc.), lithium bromide (LiBr, 99%, Sigma-Aldrich), N,N-dimethylformamide (DMF, HPLC grade, 99.9%, Sigma-Aldrich), and resorufin (Marker Gene Technologies, Inc., Eugene, OR, USA) were used as received. Milli-Q water (0.04 μS/cm) was obtained from the MilliporeSigma™ Direct-Q™ 3 water purification system (Fisher Scientific™, Pittsburgh, PA, USA).

2.2. Characterizations

Nuclear magnetic resonance spectra (NMR). 1H NMR spectra were recorded in deuterium oxide (D2O) or deuterated chloroform (CDCl3) at room temperature at 500 MHz using an Agilent NMRS (500 MHz) spectrometer (Agilent Technologies Inc., Santa Clara, CA, USA). 1H NMR of the on-off experiment were recorded in deuterium oxide (D2O) at room temperature at 300 MHz using an Agilent Mercury (300 MHz) spectrometer (Agilent Technologies Inc.). All chemical shifts were recorded in parts per million (ppm) relative to the reference peak solvent at δ = 4.79 ppm for D2O and δ = 7.26 ppm for CDCl3.
Size-exclusion chromatography (SEC). The relative number average molar masses (Mn) and the molar mass distributions (Đ) were obtained from a Tosoh EcoSEC HLC-8320GPC system with TSKgel GMHHR-M columns and a refractive index detector (RI) inside (Tosoh, Tokyo, Japan). HPLC-grade DMF with 0.1 M LiBr was used as an eluent at a flow rate of 1.0 mL min−1 at 30 °C. The system was calibrated using polystyrene standards with a narrow molecular weight distribution. Data was analyzed using EcoSEC GPC System Workstation software.
Fluorometer. The fluorescence spectra of the solutions were measured using an AgilentCary Eclipse fluorescence spectrometer (Agilent Technologies Inc.) with a disposable plastic cuvette (Semimicro style, PMMA, 10 mm light path, 1.5 mL capacity) at room temperature. The excitation wavelength was fixed at 530 nm. The excitation and emission slit widths were set at 1.5 nm for resorufin solution and reaction mixtures. The excitation and emission slit widths were set at 5 nm.

2.3. Photopolymerization

General procedure for photopolymerization. The structures of the chemicals used in this work are shown in Figure 1. HEBiB, PMDETA, and resorufin (photocatalyst) were mixed in water with a certain molar ratio, and the concentration of the monomer was kept at 1 M. Before exposure to visible light, the mixture was degassed by at least three freeze–pump–thaw cycles to remove O2 and then backfilled with N2. The reaction mixture was illuminated constantly by the green LED during the reaction (Figure S1). After a predetermined time, the reaction was terminated by introducing air into the vial. The reaction solution was dialyzed in water using a dialysis membrane (Spectra/Por®, 3500 Dalton, 54 mm flat width, Cole-Parmer, Vernon Hills, IL, USA) to remove the small molecules, and the purified product was dried under vacuum to remove the solvent. The conversion of monomer was determined by the 1H NMR spectrum of the final reaction mixture, with trioxane as the internal standard. The molecular weight and molecular weight distribution were determined by size-exclusion chromatography (SEC).
Temporal control experiment. The temporal control (on-off) experiment was performed in the NMR tube in situ. The setup is shown in Figure S2. A total of 1 mL of D2O solution from the reaction mixture was placed in an NMR tube with a J. Youngs valve (Bel-Art™ SP Scienceware™ Wilmad™ Low Pressure Vacuum Tube, Fisher Scientific™, Waltham, MA, USA). Before exposure to visible light, the mixture was degassed by at least three freeze–pump–thaw cycles to remove O2 and then backfilled with N2. Trioxane was added to the reaction mixture as the internal standard before the reaction. The conversion of monomers was monitored using NMR spectra of the reaction mixture.
Irradiation Sources. The illumination was provided by a green (530 nm) LED light (M530L3-C1, Thorlabs, Inc., Newton, NJ, USA). The light intensity was measured to be 7.0 mW/cm2 using the optical power and energy meter (PM100D, Thorlabs, Inc.).

3. Results and Discussions

3.1. Photocatalytic Activity of Resorufin

The photophysical properties of resorufin, such as the absorption and fluorescence properties, are known to be sensitive to the environment [56,62]. Figure S3 shows the fluorescence properties of resorufin are pH sensitive in aqueous environments. To check the photocatalytic activity of resorufin in the reaction mixtures, we checked the fluorescence spectra before running the polymerizations. As shown in Figure 2, under 530 nm excitation, the resorufin showed a fluorescence peak around 590 nm. And the fluorescence peaks were obvious in all the reaction mixtures with different monomers, when the monomer, HEBiB (initiator), PMDETA, and resorufin were mixed with 200:1:0.1:0.01 molar ratio (the monomer concentration was kept at 1 M).

3.2. Photopolymerization of DMA Catalyzed by Resorufin

First, the photocatalytic activity of resorufin in the polymerization of DMA was evaluated (Figure 3A). The polymerization reactions were conducted for 6 h under constant green light illumination, and the results are summarized in Table 1. In entry 1, DMA (monomer), HEBiB (initiator), PMDETA, and resorufin were mixed with 200:1:0.1:0.01 molar ratio. The NMR spectra of reaction mixture before and after the reaction are shown in Figure 3B. After the reaction, the peaks of the vinyl hydrogens of the DMA monomer (d, 5.84 ppm) clearly decreased with reference to the peak of the internal reference, trioxane (s, 5.28 ppm). And the formation of PDMA polymers was confirmed by the appearance of peaks of the hydrogens on the polymer backbone around 1–3 ppm (Figure S4). The conversion of monomers was ~78%, which was calculated based on the peak area of the vinyl hydrogens of the DMA monomer (d, 5.84 ppm) relative to the peak area of trioxane (s, 5.28 ppm). The number-average molecular weight M n , SEC and the polydispersity Đ were ~91 k and ~1.32, determined by SEC after dialysis (Figure 3C). The initiation efficiency of HEBiB ( I * ) was ~17%, based on the ratio between the measured number-average molecular weight M n , SEC and the theoretical number-average molecular weight M n , th .
In the control experiments without either green light illumination (entry 2) or resorufin (entry 3), no polymer was obtained. These results indicate that the photoexcited resorufin was the key component for polymer growth, because resorufin was the only species in the system that can absorb green light. Since ~17% of initiators were activated under a 1:0.01 initiator to resorufin molar ratio, this means 1 resorufin molecule activated 17 initiators on average. Thus, resorufin should have functioned as the photocatalyst instead of the photoinitiator.
To elucidate the quenching mechanism, we also performed control experiments in the absence of the HEBiB initiator (entry 4) or PMDETA (entry 5). In entry 4, no polymer was obtained without the HEBiB initiator, indicating that polymer growth should follow a radical mechanism initiated by radicals generated from HEBiB. In entry 5, no polymer was obtained in the absence of PMDETA, suggesting that photoexcited resorufin (Res*) cannot efficiently generate active radical species directly from HEBiB without PMDETA. Instead, PMDETA is required to produce the active radicals. In photocatalysis, radicals can be generated via either oxidative or reductive quenching of the photoexcited photocatalyst (PC*) [42,63,64,65,66,67]. Since PMDETA acts as a reducing agent and is essential for radical generation, the resorufin-catalyzed photopolymerization most likely proceeds through a reductive quenching mechanism.
To further support the quenching mechanism, the fluorescence of resorufin was measured at different PMDETA concentrations (Figure S5). The emission intensity decreases systematically with increasing PMDETA concentration under 530 nm excitation, while the emission maximum remains essentially unchanged. The corresponding Stern–Volmer plot is approximately linear over the examined range, indicating efficient quenching of Res* by PMDETA. These results are consistent with the proposed reductive quenching pathway.
In addition, the polymerization catalyzed by resorufin was found to be oxygen sensitive (entry 6). Oxygen is known to inhibit free-radical polymerization by reducing both effective radical generation and chain propagation. Oxygen can scavenge carbon-centered radicals to form less-propagating peroxyl radicals. In dye-mediated systems, oxygen can also quench the excited state, further reducing productive radical generation.
Based on the results in Table 1, we can conclude that the photopolymerization catalyzed by resorufin should follow the reductive quenching mechanism (Figure 4): the photoexcited resorufin (Res*) is first reduced by PMDETA to the anion radical (Res•−), which then reacts with HEBiB initiator to generate the propagating radical for polymer growth.

3.3. Effect of PMDETA on Photopolymerization of DMA Catalyzed by Resorufin

In addition, we studied the effect of PMDETA concentration on the photocatalytic polymerization of DMA catalyzed by resorufin. Based on the proposed mechanism (Figure 4), higher PMDETA concentration should increase the concentrations of the resorufin anion radical (Res•−). As shown in Table 2, compared to entry 1, the M n , SEC was double in entry 7 with the same reaction time, while the concentration of PMDETA was increased by 10 times compared to entry 1. However, the conversion of monomers was nearly unchanged, the polydispersity Đ was increased, and the initiation efficiency I * was decreased. These indicate that the high concentration of PDMETA makes the radical polymerization less controlled. The doubling of Mn and increase in Đ compared to entry 1 were probably due to the bi-molecular terminations or irreversible chain transfers, and the drop of I * indicated that a large portion of the resorufin anion radical (Res•−) did not react with the initiators. In entries 8 and 9, where the PMDETA concentration was even higher, the Mn and monomer conversion further dropped significantly compared to entry 7, and the Đ and I * were similar to entry 7. These results suggest that higher PMDETA concentration will make polymerization less controlled.

3.4. Temporal Control of Aqueous Radical Photopolymerization Catalyzed by Resorufin

We performed the in situ on-off experiment using DMA monomer (Figure 5). The molar ratio of the reactants was the same as entry 1 ([M]:[I]:[PMDETA]:[R] = 200:1:0.1:0.01). The green light illumination of the reaction mixture was switched on for 1 h and then off for 1 h alternately, and the on/off switching cycle was repeated three times. The composition of the reaction mixture was determined hourly by 1H NMR (Figure S6). The conversion of monomer was calculated based on the peak area of the vinyl hydrogens of DMA monomer (d, 5.84 ppm) relative to the peak area of trioxane (s, 5.28 ppm) on the NMR spectrum of the reaction mixture (Figure S7) [68].
As shown in Figure 5A, the conversion of monomers shows a corresponding response to the absence and presence of light. The monomer conversion increased persistently in the presence of light, while it was almost unchanged or increased very slowly during the dark period. The repeated response demonstrates reproducible temporal control over multiple cycles, supporting the precision of light-regulated initiation. Such robust light responsiveness provides a basis for future spatiotemporal control under mild, aqueous conditions.
Figure 5B shows the semi-log kinetic plot of monomer conversion vs. cumulative time for the on-off experiment. ln M 0 / M t increased linearly with cumulative illumination time, indicating well-behaved kinetic behavior and reliable light-gated progression, which was not influenced by intermittent light illumination. Monomer conversion increased, supporting that light is required to turn on the polymerization under these conditions. Consistently, polymer growth took place predominantly during the illuminated periods, which further proved that light is the essential factor to switch the polymerization on and off. This temporal control behavior is consistent with the proposed mechanism, in which the photoexcitation of resorufin was essential for generating the active species. Without light illumination, the resorufin could not be photoexcited, and the productions of the resorufin anion radicals and the active species to initiate polymerization were also stopped. Importantly, polymerization resumes promptly upon re-irradiation, and the conversion continues to increase mainly during the illuminated intervals, indicating that radical generation is effectively gated by light.

3.5. Photopolymerization of Other Water-Soluble Monomers

In the end, we demonstrated the activity of resorufin in catalyzing the polymerizations of other water-soluble monomers (Table 3). The formation of polymers was proven by NMR spectra (Figures S8–S10), where the peaks between 1 and 2 ppm correspond to the hydrogens on the polymer backbones. The conversions of PEGA-480 (entry 10), NIPAM (entry 11), and AM (entry 12) were above 40% after 6 h of reaction, and the polydispersity of the polymer products was as narrow, as in the case of DMA (entry 1). These results suggest that resorufin was active in catalyzing the polymerizations of acrylamide and acrylate monomers in water.
We also noticed that the initiation efficiencies I * show differences for different types of monomers. The initiation efficiencies were ~10–20% for the acrylamides (DMA, NIPAM) and ~50% for the acrylate (PEGA-480). The results were reasonable, because the reactivity or stability of the active end should be determined by the monomer structure after the addition of the first monomer to the initiator in the first step. This indicates that the resorufin anion radical was more reactive towards acrylates than acrylamides. Another noticeable feature was that the SEC spectra of all the polymers showed two peaks (Figure 3C and Figure 6). Since the polymers were purified by dialysis before SEC measurements, it is unlikely to be from residual monomers or small molecules. So far, we have not figured out the reasons for the feature. One of the potential explanations is that resorufin has been reported to be reduced to dihydroresorufin by a two-electron process [69]. If this reaction becomes competitive, it could alter the distribution of active redox states and introduce heterogeneity in activation/deactivation, which may contribute to more than one chain population.

4. Conclusions

In conclusion, resorufin was demonstrated as an organic photocatalyst for visible-light-induced aqueous radical photopolymerization under low-irradiance green light at ambient temperature. Polymers with narrow molecular weight distributions using acrylate and acrylamide monomers were successfully synthesized. The results are consistent with a reductive quenching pathway and show efficient temporal response through repeated light on–off switching. Future work will expand the study to additional initiators and electron donors, with formulation optimization and deeper mechanistic/kinetic studies across more monomers. If feasible, evaluation in biologically relevant environments will also be considered.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/org7010005/s1, Figure S1. Photograph of the experimental setup for radical photopolymerization; Figure S2. Photograph of the experimental setup for the on-off experiment; Figure S3. Effect of pH on the fluorescence of resorufin ([Resorufin] = 0.02 mg/mL); Figure S4. (A) 1H NMR spectrum of purified PDMA. (B) 1H NMR spectrum of the reaction solution before and after radical photopolymerization; Figure S5. Quenching of resorufin fluorescence by PMDETA. (A) Fluorescence spectra of resorufin under 530 nm excitation in different concentrations of PMDETA. The concentration of resorufin was 4.5 × 10−6 M. (B) Plot of resorufin fluorescence intensity (I0/I) vs. PMDETA concentration based on the spectra in A; Figure S6. 1H NMR spectrum of the on-off experiment of DMA; Figure S7. 1H NMR spectrum of the on-off experiment of DMA with integrated peak areas; Figure S8. (A) 1H NMR spectrum of purified PNIPAM. (B) 1H NMR spectrum of the reaction solution before and after radical photopolymerization; Figure S9. (A) 1H NMR spectrum of purified P(PEGA-480). (B) 1H NMR spectrum of the reaction solution before and after radical photopolymerization; Figure S10. (A) 1H NMR spectrum of purified PAM. (B) 1H NMR spectrum of the reaction solution before and after radical photopolymerization.

Author Contributions

Conceptualization, W.Z. and C.L.; Methodology, W.Z. and C.L.; Validation, W.Z. and C.L.; Formal analysis, W.Z.; Writing—original draft, W.Z.; Writing—review & editing, W.Z. and C.L.; Supervision, C.L.; Project administration, C.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The original contributions presented in this study are included in the article/Supplementary Materials. Further inquiries can be directed at the corresponding author.

Acknowledgments

We thank the funding support provided by the University of Akron.

Conflicts of Interest

The authors declare no conflicts of interest.

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Organics 07 00005 g001
Figure 1. Abbreviations and chemical structures of (a) the electron donor, (b) the resorufin, (c) the initiator, and (d–g) the monomers used in this study.
Figure 1. Abbreviations and chemical structures of (a) the electron donor, (b) the resorufin, (c) the initiator, and (d–g) the monomers used in this study.
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Figure 2. The fluorescence spectra of resorufin in the reaction mixtures. Conditions: HEBiB (1 equiv), monomer (200 equiv), resorufin (0.01 equiv), and electric donor PMDETA (0.1 equiv). [M] = 1 M.
Figure 2. The fluorescence spectra of resorufin in the reaction mixtures. Conditions: HEBiB (1 equiv), monomer (200 equiv), resorufin (0.01 equiv), and electric donor PMDETA (0.1 equiv). [M] = 1 M.
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Figure 3. (A) Reaction scheme of radical photopolymerization of DMA catalyzed by resorufin. (B) 1H NMR spectra of the reaction mixture before polymerization (top) and after polymerization for 6 h (bottom). Trioxane was added as the internal standard. (C) SEC of the PDMA product.
Figure 3. (A) Reaction scheme of radical photopolymerization of DMA catalyzed by resorufin. (B) 1H NMR spectra of the reaction mixture before polymerization (top) and after polymerization for 6 h (bottom). Trioxane was added as the internal standard. (C) SEC of the PDMA product.
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Figure 4. The proposed mechanism of radical photopolymerization catalyzed by resorufin. Res: ground-state resorufin; Res*: photoexcited resorufin; Res•−: resorufin anion radical; PMDETA•+: PMDETA cation radical; M: monomer.
Figure 4. The proposed mechanism of radical photopolymerization catalyzed by resorufin. Res: ground-state resorufin; Res*: photoexcited resorufin; Res•−: resorufin anion radical; PMDETA•+: PMDETA cation radical; M: monomer.
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Figure 5. The in situ on-off experiment of the aqueous radical photopolymerization of DMA catalyzed by resorufin (red squares and red dots are experimental data). (A) The plot of monomer conversion by switching light on (white regions) and light off (gray regions). (B) Semi-log kinetic plot of monomer conversion vs. time for the on-off experiment. [DMA]:[HEBiB]:[PMDETA]:[Resorufin] = 200:1:0.1:0.01 and [DMA]0 = 1 M in D2O.
Figure 5. The in situ on-off experiment of the aqueous radical photopolymerization of DMA catalyzed by resorufin (red squares and red dots are experimental data). (A) The plot of monomer conversion by switching light on (white regions) and light off (gray regions). (B) Semi-log kinetic plot of monomer conversion vs. time for the on-off experiment. [DMA]:[HEBiB]:[PMDETA]:[Resorufin] = 200:1:0.1:0.01 and [DMA]0 = 1 M in D2O.
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Figure 6. SEC spectra of PDMA, PNIPAM, and P(PEGA-480).
Figure 6. SEC spectra of PDMA, PNIPAM, and P(PEGA-480).
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Table 1. The effect of reaction conditions on the aqueous radical photopolymerization of DMA catalyzed by resorufin.
Table 1. The effect of reaction conditions on the aqueous radical photopolymerization of DMA catalyzed by resorufin.
Entry[M]:[I]:[PMDETA]:[Res]Conv. (%) b M n , th (kg/mol) M n , SEC (kg/mol) aĐ a I * (%)
1200:1:0.1:0.0178.315.591.01.3217.0
2 c200:1:0.1:0.01-----
3200:1:0.1:02.2----
4200:0:0.1:0.011.9----
5200:1:0:0.010.5----
6 d200:1:0.1:0.010.5----
M: monomer ( M = 1   M ); I: initiator; Res: resorufin; M n , SEC : the number-average molecular weight determined by SEC; Đ: polydispersity; Conv.: the monomer conversion percentage; M n , th : the theoretical number average molecular weight, M n , th = M / I × M monomer × C o n v . ; and I * : the initiation efficiency, I * = M n , th / M n , SEC × 100 % . a: Determined by size exclusion chromatography (SEC) in DMF, using polystyrene as a calibration standard. b: Determined by 1H NMR in D2O. c: Reaction run in the dark. d: Reaction run without freeze–pump–thaw. The reaction time for every entry was 6 h.
Table 2. The effect of PMDETA on the aqueous radical photopolymerization of DMA catalyzed by resorufin.
Table 2. The effect of PMDETA on the aqueous radical photopolymerization of DMA catalyzed by resorufin.
Entry[M]:[I]:[PMDETA]:[Res]Conv. (%) b M n , th (kg/mol) M n , SEC (kg/mol) aĐ a I * (%)
1200:1:0.1:0.0178.315.591.01.3217.0
7200:1:1:0.0177.115.3195.81.607.8
8200:1:3: 0.0123.34.662.41.697.4
9200:1:5: 0.0118.73.750.61.517.3
M: monomer ( M = 1   M ); I: initiator; Res: resorufin. The reaction time for every entry was 6 h. M n , SEC : the number-average molecular weight; Đ: polydispersity; Conv.: the monomer conversion percentage; M n , th : the theoretical number average molecular weight, M n , th = M / I × M monomer × C o n v . ; and I * : the initiation efficiency, I * = M n , th / M n , SEC × 100 % . a: Determined by size exclusion chromatography (SEC) in DMF, using polystyrene as a calibration standard. b: Determined by 1H NMR in D2O.
Table 3. The radical photopolymerization of different monomers in aqueous solution catalyzed by resorufin.
Table 3. The radical photopolymerization of different monomers in aqueous solution catalyzed by resorufin.
EntryMonomerConv. (%) b M n , th (kg/mol) M n , SEC (kg/mol) aĐ a I * (%)
1DMA78.3015.591.01.3217.0
10PEGA-48046.7944.997.21.3646.2
11 cNIPAM40.359.2148.51.196.2
12 dAM41.675.9---
Reaction conditions: [Monomer]:[Initiator]:[PMDETA]:[Resorufin] = 200:1:0.1:0.01. The reaction time for every entry was 6 h. M n , SEC : the number-average molecular weight; Đ: polydispersity; Conv.: the monomer conversion percentage; M n , th : the theoretical number average molecular weight, M n , th = M / I × M monomer × C o n v . ; and I * : the initiation efficiency, I * = M n , th / M n , SEC × 100 % . a: Determined by size exclusion chromatography (SEC) in DMF, using polystyrene as a calibration standard. b: Determined by 1H NMR in D2O. c: The reaction was run at 5 °C to prevent the coil-to-globule transition. d: The SEC result was unavailable due to the low solubility of PAM in DMF.
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Zhou, W.; Liu, C. Aqueous Radical Photopolymerization Catalyzed by Resorufin. Organics 2026, 7, 5. https://doi.org/10.3390/org7010005

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Zhou W, Liu C. Aqueous Radical Photopolymerization Catalyzed by Resorufin. Organics. 2026; 7(1):5. https://doi.org/10.3390/org7010005

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Zhou, Wenqiao, and Chunming Liu. 2026. "Aqueous Radical Photopolymerization Catalyzed by Resorufin" Organics 7, no. 1: 5. https://doi.org/10.3390/org7010005

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Zhou, W., & Liu, C. (2026). Aqueous Radical Photopolymerization Catalyzed by Resorufin. Organics, 7(1), 5. https://doi.org/10.3390/org7010005

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