# Tailor-Made Poly(vinylamine) via Purple LED-Activated RAFT Polymerization of N-vinylformamide

Izabela Kurowska, Alexis Dupre-Demorsy, Stéphane Balayssac, Marie

Hennetier, Audrey Ric, Valérie Bourdon, Tsuyoshi Ando, Hiroharu Ajiro,

Olivier Coutelier, Mathias Destarac

► To cite this version:

Izabela Kurowska, Alexis Dupre-Demorsy, Stéphane Balayssac, Marie Hennetier, Audrey Ric, et al. Tailor-Made Poly(vinylamine) via Purple LED-Activated RAFT Polymerization of N-vinylformamide. Macromolecular Rapid Communications, 2022, 44 (4), pp.2200729. 10.1002/marc.202200729. hal-03897653

HAL Id: hal-03897653

https://hal.science/hal-03897653v1

Submitted on 16 Apr 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

# Tailor-Made Poly(vinylamine) via Purple LED-Activated RAFT Polymerization of N-vinylformamide

Izabela Kurowska, Alexis Dupre-Demorsy, Stéphane Balayssac, Marie Hennetier, Audrey Ric, Valérie Bourdon, Tsuyoshi Ando, Hiroharu Ajiro, Olivier Coutelier, and Mathias Destarac*

Photo-iniferter reversible addition-fragmentation chain transfer (PI-RAFT) polymerization of N-vinylformamide (NVF) is demonstrated by using purple light. PNVFs with predetermined molar masses and narrow molar mass distributions are obtained. High RAFT chain-end fidelity is confirmed by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) and electrospray-ionization time-of-flight mass spectrometry (ESI-TOF-MS), and chain extension experiment. To demonstrate the potential of this approach, an original poly(N-vinylpyrrolidone)-b-poly(N-vinylformamide) (PVP-b-PNVF) diblock copolymer is synthesized and characterized by aqueous size-exclusion chromatography (SEC), asymmetric flow field-flow fractionation (A4F), and ¹H diffusion-ordered spectroscopy nuclear magnetic resonance (¹H DOSY NMR). Finally, selective hydrolysis of PNVF block to corresponding pH-responsive poly(N-vinylpyrrolidone)-b-poly(N-vinylformamide) (PVP-b-PVAm) is performed.

## 1. Introduction

Poly(vinylamine) (PVAm) is a pH-sensitive, water-soluble polymer with the highest content of primary amine groups.[1] Its attractive properties and non-toxicity have made it a valuable material for a broad range of applications such as surface modification,[1] biomedicine,[2] and water purification.[3]

Since it is impossible to isolate the monomer for the direct synthesis of PVAm due to imine-enamine tautomerization, many alternative approaches have been developed to introduce primary amine groups into a polymer. For example, PVAm can be obtained by Hofmann rearrangement of polyacrylamide,[4] or hydrazinolysis of poly(N-vinylphtalimide).[5] However, many years of research have shown that the most straightforward precursor for the production of poly(vinylamine)s is poly(N-vinylformamide) (PNVF), which readily hydrolyzes to PVAm under both acidic and alkaline conditions.[6]

Despite the continuous development of reversible-deactivation radical polymerization (RDRP), the synthesis of well-defined PNVF, and hence corresponding PVAm, remains a challenge.[7] To our knowledge,

one single work by Yamago and co-workers showed a controlled polymerization of NVF by organotellurium-mediated radical polymerization (TERP).[8] Interestingly, while reversible addition-fragmentation chain transfer (RAFT) polymerization allows the production of polymers with well-controlled macro-molecular characteristics from a broad library of monomers, both in organic and aqueous media, this technique has only been used

I. Kurowska, A. Dupre-Demorsy, S. Balayssac, O. Coutelier, M. Destarac
Laboratoire des IMRCP
UMR 5623
Université Paul Sabatier
CNRS, Toulouse 31062, France
E-mail: mathias.destarac@univ-tlse3.fr

I. Kurowska
Faculty of Chemistry
University of Bialystok
Ciolkowskiego 1k, Bialystok 15-245, Poland

I. Kurowska
Doctoral School of Exact and Natural Sciences
University of Bialystok
Ciolkowskiego 1k, Bialystok 15-245, Poland

A. Dupre-Demorsy, T. Ando, H. Ajiro
Division of Materials Science
Graduate School of Science and Technology
Nara Institute of Science and Technology
Ikoma, Nara 630-0192, Japan

M. Hennetier, A. Ric
Université de Toulouse
Institut National Polytechnique de Toulouse – Ecole d'Ingénieur de Purpan
Département Sciences Agronomiques et Agroalimentaires
Toulouse Cedex 03, Toulouse 31076, France

V. Bourdon
Institut de Chimie de Toulouse
UAR 2599
Université Paul Sabatier
CNRS, Toulouse 31062, France

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/marc.202200729

© 2022 The Authors. Macromolecular Rapid Communications published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

DOI: 10.1002/marc.202200729
<figure><img src="image_3.png" /><figcaption>**Scheme 1.** General scheme of PI-RAFT polymerization of NVF under purple light irradiation.</figcaption></figure>

for the synthesis of few NVF-based copolymers. Pich and co-workers showed a series of statistical copolymers based on cyclic poly(N-vinylamides) with a maximum NVF content of 50%.[9] Also, Beckman et al. reported the synthesis of poly(ethylene glycol)-b-poly(N-vinylformamide) diblock copolymers.[10] Nevertheless, this work lacks in-depth studies describing the complex behavior of NVF throughout the copolymerization, especially since monomer conversion was low and dispersity relatively high.

Photo-iniferter RAFT (PI-RAFT) polymerization is a rapidly evolving tool for the controlled synthesis of polymers, where light directly activates the chain transfer agent (CTA).[11,12] Taking advantage of the fascinating properties of this method, such as mild reaction conditions, the ease of manipulation and the absence of an exogenous source of radicals, we found PI-RAFT an exciting route to polymerization of the challenging NVF monomer.

Herein, for the first time, we present the controlled polymerization of NVF by PI-RAFT using purple light-emitting diodes (LEDs). Furthermore, the synthesis of a well-defined PVP-b-PNVF diblock copolymer, followed by selective hydrolysis of the PNVF segment into the corresponding PVP-b-PVAm was demonstrated. PNVF was synthesized by PI-RAFT using purple light ($\lambda_{max}$ = 395–400 nm). As CTA, we chose S-cyanomethyl O-ethyl dithiocarbonate (CTA1), which our group recently described as an effective RAFT agent for the polymerization of non-cyclic N-methyl-N-vinylacetamide (NMVA), structurally very similar to NVF.[13] The polymerizations were carried out with CTA1 as the only source of radicals at ambient temperature with DMSO as a solvent (**Scheme 1**).

## 2. Results and Discussion

The PI-RAFT polymerization of NVF proceeded successfully using a homemade photoreactor, shown in detail in Figure S1 (Supporting Information). The polymerization obeyed first-order kinetics (Figure S2, Supporting Information) with rate depending on the light intensity, which was controlled by changing the number of LEDs in the photoreactor. As expected, the higher the intensity of the purple LEDs, the higher the radical concentration, and as a result, the faster the polymerization (**Figure 1a**). This trend was strongly attenuated for 4 mW cm⁻² (corresponding to 66 LEDs) after 4 h of polymerization, which may be attributed to a gradual loss of RAFT active terminal groups during polymerization. This effect was reflected in the evolution of macromolecular characteristics with higher number-average molar masses determined by SEC ($M_{n,SEC}$) than the theoretical values (Figure 1b; Table S1 (Supporting Information), entries 1–5) and a gradual increase of dispersities ($D$) with conversion ($D \approx 1.53$ at 87% conversion). The reduction of the light intensity resulted in a better control over the polymerization. $M_{n,SEC}$ were closer to the theoretical

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /><figcaption>**Figure 1.** The effect of purple light intensity on: a) NVF conversion with time, b) $M_n$ and dispersities versus conversion. $[CTA1]_0$ = 16.2 mmol L⁻¹, $[NVF]_0$ = 4.53 mol L⁻¹, 30% w/w in DMSO at ambient temperature.</figcaption></figure>

values, while the dispersities remained at a similar level ($D$ between 1.19 and 1.32) throughout the polymerization (Table S1 (Supporting Information), entries 6–17). However, there was no significant difference in $M_{n,SEC}$ and $D$ values for experiments carried out with 1.1 mW cm⁻² and 2.7 mW cm⁻² (corresponding to 12 and 30 LEDs). Therefore, we chose a reactor with 2.7 mW cm⁻² for the rest of the study as the best compromise between control of the polymerization and ease of manipulation.

For further investigation of the behavior of NVF during PI-RAFT, a set of three different initial concentrations of CTA1 ($[CTA1]_0$ = 66.5, 16.2, and 6.45 mmol L⁻¹) was selected, which respectively corresponded to theoretical $M_n$ of 5000, 20 000, and
<figure><img src="image_6.png" /><figcaption>**Figure 2.** Evolution of M<sub>n</sub> and D during PI-RAFT polymerization for different targeted molar masses.</figcaption></figure>

50 000 g mol<sup>-1</sup>. The controlled character of the polymerization was confirmed in all cases. The M<sub>n,SEC</sub> of the obtained polymers increased linearly with monomer conversion and were in excellent agreement with theoretical values (Figure 2; Table S2, Supporting Information). Moreover, SEC chromatograms were monomodal and shifted to lower elution time with increasing monomer conversion (Figure S3, Supporting Information). A kinetic study also revealed the influence of CTA1 concentration on the polymerization rate that increased with an increase of [CTA1]<sub>0</sub> (Figure S4, Supporting Information), which is not surprising considering the CTA acts as a radical source in PI-RAFT. The conversion of NVF reached high values (≈90%) after 6 h of irradiation for 5 and 20 kg mol<sup>-1</sup>, and the polymers were characterized by low dispersity (D ≈1.2). For 50 kg mol<sup>-1</sup>, the monomer conversion value was lower (70%) after 6 h, while the dispersity slightly increased.

We also conducted xanthate-free and purple light-free experiments to establish their essential role in polymerization. In the case of the xanthate-free experiment, even after 16 h of irradiation under purple light, no polymerization occurred (Figure S5a, Supporting Information). Also, the reaction mixture containing xanthate and NVF in DMSO did not polymerize when exposed to daylight for 48 h (Figure S5b, Supporting Information). Moreover, an ON/OFF experiment was also conducted to highlight the spatiotemporal control of the photopolymerization (Figure S5c, Supporting Information).

In order to confirm the nature of end-groups, PNVF-CTA1 of low molar mass was synthesized and then analyzed by ¹H nuclear magnetic resonance (¹H NMR), size-exclusion chromatography (SEC), matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) and electrospray-ionization time-of-flight mass spectrometry (ESI-TOF-MS) after precipitation. M<sub>n,SEC</sub> = 2200 g mol<sup>-1</sup> and D = 1.08 were in good agreement with the expected M<sub>n,th</sub> = 1800 g mol<sup>-1</sup>. MALDI-TOF-MS spectrum (Figure 3) detected two populations. The major one with a general formula C<sub>2</sub>H<sub>2</sub>N-(C<sub>3</sub>H<sub>5</sub>NO)<sub>n-1</sub>-CH<sub>2</sub> = CH<sub>2</sub>-NHCHO corresponded to the sodium adduct of a PNVF terminated by a double bond from the decomposition of the xanthate terminal group under the MALDI-TOF-MS laser, which was commonly observed

for other poly(N-vinylamides).[13,14] In turn, the second minor population could not be identified and did not correspond to thiol nor hydrogen-terminated chains, which are possible to obtain by RAFT polymerization. Nevertheless, the presence of the xanthate group as chain-end was confirmed by ¹H NMR spectroscopy by the presence of characteristic signals at 4.5–4.7 ppm and 1.4 ppm ascribed to the methylene and methyl protons of the O-ethyl xanthate group (Figure S6, Supporting Information). The ESI-TOF-MS spectrum was complex and revealed five different populations. (Figure S7, Supporting Information). Three of them were related to a polymer terminated with a xanthate group (C<sub>2</sub>H<sub>2</sub>N-(C<sub>3</sub>H<sub>5</sub>NO)<sub>n</sub>-S(C = S)OCH<sub>2</sub>CH<sub>3</sub>) cationized with hydrogen or sodium. The two other minor populations corresponded to a polymer ended with a double bond from the xanthate decomposition.

The controlled character of the polymerization was further confirmed by a chain extension experiment from a well-defined PNVF-CTA1 (Table S3, Supporting Information). As shown in Figure S8a (Supporting Information), the SEC chromatograms of the chain extended PNVF shifted toward lower elution time with conversion and with the total disappearance of the initial PNVF-CTA1. M<sub>n,SEC</sub> were in excellent agreement with theoretical values, with consistently low dispersities (D < 1.25), Figure S8b (Supporting Information).

To demonstrate the versatility of our approach, a block copolymer containing a PNVF segment was synthesized. We selected the well-known, biocompatible poly(N-vinylpyrrolidone) (PVP) as the first block. Recently, Gibson and coworkers described PI-RAFT under blue LED light as a tool for PVP synthesis.[15] However, the monomer conversion reached a maximum of 44% after 24 h of irradiation, while M<sub>n,SEC</sub> values were higher than expected. These results encouraged us to test a purple light to drive NVP polymerization. The polymerization was carried out in bulk with 2-((ethoxycarbonothioyl)thio)propanoate (CTA2), which was previously reported as a good chain transfer agent in controlled RAFT polymerization of PVP.[14,16] Surprisingly, the polymerization rate was extremely fast, with 94% conversion after 30 min of irradiation under purple light (Table S4 and Figure S9, Supporting Information). Dispersities remained low (D < 1.2) all along the polymerization, whereas M<sub>n,SEC</sub> displayed a linear relationship with conversion and were nearly identical to theoretical expectations.

Then, we synthesized PVP-CTA1 (M<sub>n,SEC</sub> = 5100 g mol<sup>-1</sup>, D = 1.11), which was subsequently used as a macro-CTA in the polymerization of NVF targeting a M<sub>n,th</sub> = 30 000 g mol<sup>-1</sup> at complete conversion (Table S5, Supporting Information). Here again, a controlled character of the polymerization could be observed, and the evolution of M<sub>n,SEC</sub> determined in aqueous conditions followed a linear pattern while keeping dispersities at a low level (D < 1.2) (Figure 4a). SEC chromatograms were monomodal throughout the copolymerization (Figure S10, Supporting Information). Nevertheless, SEC analysis could not demonstrate the efficient re-initiation of the macro-CTA as no common eluents could be found for SEC analysis of the PVP first block, only eluted in DMF, and the PVP-b-PNVF diblock insoluble in DMF and analyzed in water because of its great proportion of PNVF.

To overcome this limitation and clarify the formation of the block copolymer, we decided to use asymmetric flow field-flow fractionation (AF4) and diffusion-ordered spectroscopy nuclear
<figure><img src="image_7.png" /><figcaption>Figure 3. MALDI-TOF MS spectrum of PNVF-CTA1.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>**Figure 4.** Characterization of PVP-*b*-PNVF copolymer by different techniques: a) Evolution of *M*<sub>n</sub> and *D* versus conversion determined by aqueous SEC. b) A4F fractograms, and c) ¹H DOSY NMR spectra (500 MHz, DMSO, 298 K).</figcaption></figure>

magnetic resonance (DOSY-NMR) to analyze PVP-CTA1 and the
final precipitated copolymer. AF4 analysis showed a clear shift
between the fractogram of PVP-CTA1 and the one of the final
copolymer, with no residual trace of the first block, highlighting
the efficient diblock synthesis (Figure 4b). M<sub>n</sub> determined for the
PVP block by AF4 was slightly higher (M<sub>n,AF4</sub> = 6000 g mol<sup>-1</sup>, D

= 1.12) than the value measured by SEC but still in close agree-
ment. For the diblock copolymer, M<sub>n,AF4</sub> = 22 600 g mol<sup>-1</sup> was
almost identical to the theoretical value (M<sub>n,th</sub> = 22 500 g mol<sup>-1</sup>)
with D = 1.26. As shown in Figure 4c, the ¹H DOSY NMR
spectrum revealed two different diffusion coefficients for the ini-
tial PVP-CTA1 and the final diblock copolymer. As expected, the
<figure><img src="image_9.png" /><figcaption>**Figure 5.** Comparison of ¹H NMR spectra of PVP-CTA2, PVP-*b*-PNVF, and PVP-*b*-PVAm (300.13 MHz, D₂O, 298 K).</figcaption></figure>

macro-CTA with a lower hydrodynamic radius possessed a higher diffusion coefficient value ($D = 49 \ \mu m^2 s^{-1}$) compared to the diblock copolymer with $D = 6 \ \mu m^2 s^{-1}$.

Finally, selective hydrolysis of the PNVF block under basic conditions was performed.[6,8] The quantitative conversion of PNVF to PVAm was confirmed by ¹H NMR spectroscopy with the total disappearance of a broad signal corresponding to the formyl group (k and l), previously visible in the range of 7.7–8.1 ppm and shift of signals corresponding to methylene (i) and methyne (j) from 1.5 to 1.1 ppm and from 3.8 to 2.8 ppm, respectively. Figure 5.

**3. Conclusion**

In summary, we achieved the controlled polymerization of NVF by PI-RAFT using purple LED light for the first time. Polymers with a defined molecular weight and a narrow molecular weight distribution were obtained. High end-group fidelity was confirmed by MALDI-TOF-MS, ESI-TOF-MS, and a chain extension experiment. To demonstrate the efficiency of our approach, we synthesized an original PVP-*b*-PNVF diblock copolymer, which

was characterized by aqueous SEC, A4F, and ¹H DOSY NMR. Finally, selective hydrolysis of the PNVF block of the copolymer into the corresponding PVAm segment was performed. We strongly believe that our findings will pave the way for an easier access to well-defined PNVFs and PVAmS, thus creating opportunities for applications of PVAm-based complex macromolecular architectures in well-known and potentially new fields.

**Supporting Information**

Supporting Information is available from the Wiley Online Library or from the author.

**Acknowledgements**

I.K. thanks the French Ministry of Foreign and European Affairs for the Eiffel scholarship. This work was financially supported by Grant-in-Aid for Scientific Research on Innovative Areas, JSPS (JP22H04547).

**Conflict of Interest**

The authors declare no conflict of interest.
**Data Availability Statement**

The data that support the findings of this study are available from the corresponding author upon reasonable request.

**Keywords**

PI-RAFT, poly(N-vinylformamide), poly(vinylamine), xanthate

Received: September 5, 2022

Revised: November 15, 2022

Published online: December 13, 2022

[1] R. Pelton, *Langmuir* **2014**, *30*, 15373.

[2] Y.e Tian, Y. Zhao, C. Yin, S. Tan, X. Wang, C. Yang, T.-D Zhang, X. Zhang, F. Ye, J. Xu, X. Wu, L. Ding, J. Zhang, J. Pei, X.-T. Wang, R. X. Zhang, J. Xu, W. Wang, C. D. M. Filipe, T. Hoare, D.-C. Yin, A. Qian, X. Deng, *J. Controlled Release* **2022**, *345*, 20.

[3] Y. Huang, D. Wu, X. Wang, W. Huang, D. Lawless, X. Feng, *Sep. Purif. Technol.* **2016**, *158*, 124.

[4] A. E. Achari, X. Coqueret, A. Lablache-Combier, C. Loucheux, *Makromol. Chem.* **1993**, *194*, 1879.

[5] C. Nadal, S. Gineste, O. Coutelier, A. Tourrette, J.-D. Marty, M. Destarac, *Colloids Surf. Physicochem. Eng. Asp.* **2022**, *641*, 128502.

[6] L. Gu, S. Zhu, A. N. Hrymak, *J. Appl. Polym. Sci.* **2002**, *86*, 3412.

[7] K. Nakabayashi, H. Mori, *Eur. Polym. J.* **2013**, *49*, 2808.

[8] W. Fan, S. Yamago, *Angew. Chem., Int. Ed.* **2019**, *58*, 7113.

[9] H. Peng, W. Xu, A. Pich, *Polym. Chem.* **2016**, *7*, 5011.

[10] L. Shi, T. M. Chapman, E. J. Beckman, *Macromolecules* **2003**, *36*, 2563.

[11] M. Hartlieb, *Macromol. Rapid Commun.* **2022**, *43*, 2100514.

[12] N. Corrigan, J. Yeow, P. Judzewitsch, J. Xu, C. Boyer, *Angew. Chem., Int. Ed.* **2019**, *58*, 5170.

[13] A. Dupre-Demorsy, O. Coutelier, M. Destarac, C. Nadal, V. Bourdon, T. Ando, H. Ajiro, *Macromolecules* **2022**, *55*, 1127.

[14] A. Guinaudeau, S. Mazières, D. J. Wilson, M. Destarac, *Polym. Chem.* **2011**, *3*, 81.

[15] C. Stubbs, T. R. Congdon, M. I. Gibson, *Eur. Polym. J.* **2019**, *110*, 330.

[16] X. Zhao, O. Coutelier, H. H. Nguyen, C. Delmas, M. Destarac, J.-D. Marty, *Polym. Chem.* **2015**, *6*, 5233.