# High-hardness photocrosslinked coatings from a partially biobased and semi-aromatic unsaturated polyester

Klara Jastak, Elise Brument, Fabrice Burel, Nicolas Désilles, Laurence Lecamp

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Klara Jastak, Elise Brument, Fabrice Burel, Nicolas Désilles, Laurence Lecamp. High-hardness photocrosslinked coatings from a partially biobased and semi-aromatic unsaturated polyester. Reactive and Functional Polymers, 2025, 216, pp.106420. 10.1016/j reactfunctpolym.2025.106420. hal-05267571

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# High-hardness photocrosslinked coatings from a partially biobased and semi-aromatic unsaturated polyester☆

Klara Jastak, Elise Brument, Fabrice Burel, Nicolas Désilles*, Laurence Lecamp

INSA Rouen Normandie, Univ Rouen Normandie, Normandie Université, CNRS, PBS UMR 6270, F-76000 Rouen, France

## ARTICLE INFO

### Keywords:

Unsaturated polyesters

Biobased

Thiol-ene

Photocuring

Coatings

## ABSTRACT

This study presents the photochemical crosslinking of a partially biobased, semi-aromatic unsaturated polyester. Firstly, a polyester was synthesized from the condensation of diethyl 2,6-pyridinedicarboxylate, a biobased monomer derived from bacteria, and *cis*-2-butene-1,4-diol. Polyesters with molar masses up to 20,700 g/mol were obtained, with glass transition temperatures (T~g~) reaching 51 °C. Secondly, photocrosslinked coatings were prepared by addition of a photosensitive thiol derivative of coumarin: 7-mercapto-4-methyl coumarin (0,1 eq / unsaturation). The resulting system was irradiated with a polychromatic lamp for one hour at 30 °C, allowing a thiol-ene reaction and a concomitant [2 + 2] cycloaddition. The resulting coatings were apolar (23 %), hard (König hardness 222 ± 1 s), well crosslinked (swelling rate of 0.11 ± 0.05) and exhibited a T~g~ of 74 °C.

## 1. Introduction

With a global market worth $11.16 billion in 2024 [1], unsaturated polyester resins (UPs) are the second most widely used thermosetting resins in the world, and around 20 % of the world's production of UP resins is used to produce coatings for various substrates (wood, metal, etc.) and applications (automotive, construction, etc.). They are synthesized by polycondensation between a diacid (or one of its derivatives) and a diol, and industrially, petroleum-based monomers are used, most of them being harmful for the environment and human health. In addition, their crosslinking, which results in a thermoset material, is carried out in presence of a reactive diluent, often styrene, which has serious effects on humans and the environment [2].

Nowadays, environmental challenges are driving researchers to work not only on developing new structures from biosourced monomers, but also on obtaining thermoset materials using less energy-intensive and greener methods. Photocrosslinking is a particularly relevant process for the production of coatings and could be a very smart way, in the case of UPs, of achieving this goal of a more environmentally-friendly process, thanks to its numerous advantages: it requires little energy, reactions are often carried out at room temperature, and formulations are usually solvent-free, with no VOC emission [3]. Thus, this technique has already been successfully used for the production of UPs from itaconic acid [4–11] or fatty acids [12], sometimes using thiol-ene reactions [13–15].

Our research team is in this framework with the recent development of an original photocrosslinkable biobased semi-aromatic polyester [16]. This polyester was synthesized from pyridinedicarboxylic acid (PDA), a biobased monomer [17–19] increasingly used for the synthesis of polyesters [20–22] intended for food packaging film applications for example [23–25], and diethyloctadecen-9Z-dioate (de-AODD), a biosourced unsaturated aliphatic diester derived from vegetable oils. The polyester was then formulated with 7-mercapto-4-methyl coumarin, as photosensitive crosslinking agent, before exposure to UV light in order to photoinitiate both thiol-ene and cycloaddition routes. Unfortunately, despite the presence of an aromatic ring within the structure, the thermal and mechanical properties of the obtained coatings were not satisfactory (T~g~ = −34 °C and very low König hardness of 15 s), probably due to a low crosslink density combined with the flexibility of the long carbon chain of de-AODD. In comparison, unsaturated polyesters crosslinked 3 h with classical systems based on styrene led to thermosets with T~g~ ranging from 63 °C (10 % w/w styrene) to 110 °C (30 % w/w styrene) [26], and up to 197 °C (50 % w/w styrene) after a post-curing step [27]. Thus, obtaining photocrosslinkable, biobased and rigid UPs coatings is still a real challenge.

Considering the advantages and limitations of our previous study, we decided to keep the use of PDA, this time in its diethyl form, and make it react with *cis*-2-butene-1,4-diol, instead of AODD to reduce the carbon chain length. Hence, a partially biosourced and semi-aromatic polyester

<footnote>* This article is part of a Special issue entitled: 'Photopolymer Science' published in Reactive and Functional Polymers.</footnote>

<footnote>* Corresponding author.
E-mail address: nicolas.desilles@insa-rouen.fr (N. Désilles).</footnote>
was synthesized and then crosslinked under UV in the presence of a photosensitive coumarin derivative.

## 2. Materials and methods

### 2.1. Materials

2,6-pyridine dicarboxylic acid (PDA26, ≥ 98 %), cis-2-butene-1,4-diol (BD, 97 %), 7-mercapto-4-methyl coumarin (MMC, ≥ 97 %), titanium (IV) isopropoxide (Ti(O-i-Pr)4, 97 %), ethanol (≥ 99 %), dichloromethane and sulfuric acid (99.9 %) were purchased from Sigma Aldrich. Deuterated chloroform (CDCl3) was supplied by Eurisotop. All reagents were used as received without further purification.

### 2.2. Synthesis

#### 2.2.1. Diethyl 2,6-pyridinedicarboxylate (de-PDA) synthesis

2,6-pyridinedicarboxylic acid (3 g, 0.18 mmol) was solubilized, under magnetic stirring, in 100 mL of ethanol in a round-bottomed flask fitted with a condenser. Sulfuric acid (200 µL) was then added and the system was heated under reflux for 24 h. The mixture was concentrated on a rotary evaporator, solubilized in dichloromethane, washed with water and a saturated NaHCO3 solution, and dried over MgSO4. The organic phase was then recovered, filtered and concentrated under reduced pressure (yield: 90 %).

¹H NMR (300 MHz, CDCl3, δ): 8.29 (d, 2H), 8.0 (t, 1H), 4.49 (q, 4H), 1.45 (t, 6H)

$$T_m = 44^{\circ}C, T_{5\%} = 172^{\circ}C$$

#### 2.2.2. Polymer synthesis

de-PDA (1 g, 4.48 mmol), cis-2-butene-1,4-diol (1.18 g, 13.4 mmol) and Ti(O-i-Pr)4 (0.08 M in toluene solution) (0.56 mL, 0.045 mmol) were introduced into a 150 mL three round-bottomed flask and heated from 90 °C to 180 °C with a 30 °C/h temperature ramp. Then, the reaction was placed under vacuum at 50 mbar for 1 h, then at 10⁻² mbar for 1 to 3.5 h. In the end, 0.75 g, 0.81 g and 0.91 g (after 1 h, 2 h and 3.5 h of vacuum at 10⁻² mbar, respectively) of a brown solid corresponding to the desired product was obtained. The reaction yield was calculated considering the amount of limiting reagent (de-PDA) and the elimination of ethanol.

### 2.3. Preparation of formulations and coatings

Formulations were prepared by using a thiol/polymer repeating unit ratio 0.1/1 (i.e. 0.09 % w/w MMC/polymer). To produce the coatings, each formulation was dissolved in dichloromethane at a 10 mg/mL concentration. Then, a 100 µL drop of this solution was deposited on a glass plate and, after solvent evaporation, irradiated at 3 cm from the polychromatic light of a Hg-Xe lamp (Hamamatsu LC8) equipped with a filter selecting the wavelengths between 300 and 450 nm. The incident light intensity, measured at 365 nm, was 240 mW/cm². The resulting films had a thickness between 10 and 20 µm.

### 2.4. Measurements

¹H NMR spectra were obtained by using a Bruker 300 MHz spectrometer at room temperature, by dissolving 10 mg of product in 0.5 mL of CDCl3. The chemical shifts were given in ppm and the non-deuterated residual solvent peak (δ = 7.26 ppm) was referred as the internal standard.

Perkin Elmer Spectrum 2000 FTIR, equipped with an ATR device (ATR MK II Golden Gate Specac), was used to acquire FTIR spectra, from 10 scans in a nominal resolution of 8 cm⁻¹ in the 600 cm⁻¹ to 4000 cm⁻¹ range.

UV curing kinetics were acquired on a Vertex 70 spectrometer from

Bruker, equipped with a diamond ATR accessory (ATR MK II Golden Gate Specac), with a resolution of 8 cm⁻¹, from 4000 to 500 cm⁻¹ and a spectrum (averaged over 10 scans) every 5 s. A 100 µL drop of the previously mentioned formulation was placed on the ATR diamond cell. After complete evaporation of the solvent, the solid film obtained was irradiated with the polychromatic light coming from a Hg-Xe lamp (Hamamatsu LC8) equipped with a filter selecting the wavelengths between 300 and 450 nm. The conversion of the ethylenic double bond of MMC was determined by measuring the evolution over time of the area of the double band ranging from 1550 and 1630 cm⁻¹ and compared to the residual area of this band at the end of the reaction. The conversion was then calculated as following:

$$\text{Conversion (\%)} = \frac{(S_c)_0 - (S_c)_t}{(S_c)_0 - (S_c)_f} \times 100$$

with (Sc)0, (Sc)t and (Sc)f the areas of the band, respectively at initial time (t0), t (t1) and final time (tF).

UV-visible spectra were recorded on a Cary 50 spectrophotometer from Varian. A solution of prepolymer and MMC (thiol/polymer repeating unit ratio 0.1/1) at 10 mg/mL in dichloromethane was deposited on a quartz plate. After evaporation of the solvent, the obtained film was irradiated at 3 cm from the polychromatic light of a Hg-Xe lamp (Hamamatsu LC8) equipped with a filter selecting the wavelengths between 300 and 450 nm. The incident light intensity, measured at 365 nm, was 240 mW/cm². The absorbance of the thin film (10–20 µm) was measured from 200 to 600 nm.

MALDI TOF (Matrix Assisted Laser Desorption Ionization - Time of Flight) analyses were performed using a Bruker Daltonics AutoFlex III time-of-flight mass spectrometer, equipped with a laser emitting at a wavelength of 355 nm, and the FlexControl 3.3 and FlexAnalysis 3.3 software packages. Samples were prepared using the thin film method by depositing 1 µL of matrix containing 2,5-dihydroxybenzoic acid (DHB) (10 mg/mL), with NaCl salt and 1 µL of polymer solution (5 mg/mL in dichloromethane) onto the target. Spectra were acquired in positive ion reflector mode using an m/z mass range of 500 to 4000, a laser frequency of 100 Hz, a pulsed ion extraction delay of 10 ns and a laser attenuation of 50 %. Spectra were averaged over 3000 acquisitions. The acceleration voltage was 19 kV.

Size Exclusion Chromatography (SEC) PL-GPC50 system from Varian equipped with two columns (PLgel 5 µm MIXED-D columns, 300 × 7.5 mm), a pre-column (PLgel 5 µm Guard, 50 × 7.5 mm), and a differential refractive index detector (sensibility: 2.5 × 107 RIU per mV, wavelength 880 ± 30 nm) was used. The mobile phase was dichloromethane (HPLC grade) with a flow rate of 1 mL/min. Samples were injected with a concentration of 5 mg/mL. Average molar masses were determined by using PMMA calibration.

Thermogravimetric analysis (TGA) was performed by using a TG 309 Libra from Netzsch. Alumina crucibles were used with a 40 mL.min⁻¹ nitrogen flow, a temperature ranging from 30 to 800 °C, and a 10 °C. min⁻¹ heating rate. 5 % weight loss temperatures (T5%) were measured.

Thermal properties were investigated by Differential Scanning Calorimetry (DSC) using a DSC25 from TA Instruments. Hermetic aluminum pans were used with a 50 mL.min⁻¹ nitrogen flow, a temperature ranging from -50 to 125 °C, and a 10 °C.min⁻¹ heating rate. Melting temperatures (Tm) were measured at the extremum of the peaks and glass transition temperatures (Tg) were measured at the mid-point.

Film swelling was carried out by adding the glass support and the film into a 100 mL flask with 50 mL of dichloromethane. The swelling lasted 24 h, until a constant mass was obtained. Swelling rate was then calculated as follows:

$$\text{Swelling rate} = \frac{m_s - m_d}{m_d}$$

with mS the swollen mass and mD the dry mass.

The surface energy of the film was determined by using a Digidrop
Goniometer from GB. Static contact angles were measured by using three liquids (water, diiodomethane and glycerol), and three measurements were averaged to obtain contact angles and their standard deviations. The dispersive γds and polar γps components of the surface energy (γs = γps + γds) were calculated by using Owens-Wendt relation, and the surface polarity (P) was calculated using the equation:

$$P (\%) = \frac{\gamma^{ps}}{\gamma^{s}} \times 100$$

A König pendulum from TQC was used to measure the film hardness. After calibration with a glass plate (König hardness 245 ± 10 s), three measurements were averaged.

## 3. Results and discussion

### 3.1. Synthesis and characterization of unsaturated polyesters

The structure of PDA being close to that of FDCA, the conditions of Gruter et al. [28] for the synthesis of PEF were first used, namely the use of titanium isopropoxide as a catalyst and a triple excess of diol. After optimization of several parameters such as initial (limited to 90 °C due to easy evaporation of BD: T5% = 121 °C) and final temperatures, duration of each step, and applied pressures (to achieve maximum reaction progress and the formation of long polymer chains), the transesterification reaction between de-PDA and BD gave a polymer with a yield ranging from 76 % to 93 % (Scheme 1, Table 1).

The structural investigation is now presented for the polyester of Entry 1 in Table 1. First, FTIR analysis (Fig. 1) showed the shift of the stretching band of the ester carbonyl function (C=O) from 1741 to 1716 cm⁻¹, compared to the initial de-PDA. It is noteworthy that the stretching band of cis BD unsaturations (CH=CH) usually observed between 1630 and 1660 cm⁻¹ was hard to detect on FTIR spectra.

Then, SEC analysis in dichloromethane indicated a number average molar mass M~n~ = 3250 g/mol (PMMA equivalent) and a dispersity D equal to 3.8 (Fig. SI.1).

The MALDI-TOF spectrum of the polyester (Fig. 2) revealed the presence of several cationized species ([M + Na]⁺) at m/z 768, 987, 1206, 1425, 1644, 1863, 2082 and 2301 with a m/z difference of 219 between each consecutive ions. This value exactly corresponded to the molar mass M~0~ of the repeating unit of the expected polyester. Furthermore, as shown in Table 2, different chain-ends may be assumed. According to the m/z values in Fig. 2, these ions corresponded to the theoretical masses calculated for polymers having alcohol groups at both ends of the chain (in bold).

Finally, ¹H NMR analysis, in terms of chemical shifts, integrations and multiplicity, confirmed the chemical structure of the obtained polyester (Fig. 3). Furthermore, low intensity signals at 5.84 ppm (proton g) as well as at 4.32 and 5.01 ppm (protons *e* and *f*), slightly shielded compared to those within the repeating unit, confirmed the presence of β-unsaturated alcohol chain-ends, totally in agreement with MALDI-TOF results. The number average molar mass of the polyester was then calculated from the values of the integrations of the terminal *e* protons (I~e~) and of *c* protons (I~c~) in the repeating units, and was found close to 7500 g/mol, i.e. 33 repeating units:

$$n = \frac{I_c}{I_e}$$

<figure><img src="image_3.png" /><figcaption>**Scheme 1.** Unsaturated polyester synthesis route.</figcaption></figure>

<table><caption>**Table 1**

Physicochemical properties of the synthesized unsaturated polyesters.</caption><thead><tr><th>Entry</th><th>Time (h) under 10<sup>-2</sup> mbar vacuum</th><th>M&#773;<sub>n</sub> SEC (g. mol<sup>-1</sup>)</th><th>D</th><th>M&#773;<sub>n</sub> NMR (g. mol<sup>-1</sup>)</th><th>Yield (%)</th><th>T<sub>5%</sub> (°C)</th><th>T<sub>g</sub> (°C)</th></tr></thead><tbody><tr><td>1</td><td>1</td><td>3250</td><td>3.8</td><td>7500</td><td>76</td><td>252</td><td>48</td></tr><tr><td>2</td><td>2</td><td>6500</td><td>4.4</td><td>20,700</td><td>82</td><td>256</td><td>51</td></tr><tr><td>3</td><td>3.5</td><td>insoluble</td><td>insoluble</td><td>insoluble</td><td>93</td><td>258</td><td>58</td></tr></tbody></table>

<figure><img src="image_4.png" /><figcaption>**Fig. 1.** FTIR spectra of reagents and obtained polymer (Entry 1).</figcaption></figure>

As each repeating unit bearing an unsaturation is likely to become a grafting site for 7-mercapto-4-methyl coumarin (MMC) and thus a crosslinking site, attempts to increase the molar mass of the polyester were then made by increasing the time of the vacuum synthesis step, at 10⁻² mbar, to 2 h and 3.5 h (Table 1 - Entry 2 and 3, respectively). The molar mass was found to increase well, reaching 20,700 g/mol (or 93 repeating units) for 2 h (see ¹H NMR spectrum in Fig. SI.2). With 3.5 h of vacuum, the polymer became insoluble in boiling CH₂Cl₂ (T₉ = 40 °C), possibly indicating that side reactions afforded crosslinking for long reaction times. However, the polymer was fully soluble in boiling N,N-dimethylformamide (T₉ = 153 °C), precluding any crosslinking and demonstrating that very long chains were obtained.

Concerning the thermal properties, the polymers had a 5 % degradation temperature around 255 °C whatever their molar mass, and were amorphous with a glass transition T₉ which increased from 48 °C up to 58 °C with the chain length (Fig. SI.3). Compared to our previous study [16], the use of BD instead of AODD therefore allowed a significant increase in the T₉ of the polymer (from -58 °C to +58 °C).

In order to have a polymer with a significant number of potential crosslinking sites while remaining soluble, the unsaturated polyester corresponding to Entry 2 in Table 1 was chosen for the subsequent photocrosslinking step.
<figure><img src="image_5.png" /><figcaption>Fig. 2. MALDI-TOF of the obtained polymer (Entry 1).</figcaption></figure>

<table><caption>**Table 2**
Theoretical m/z values of expected [M + Na]$^+$ ions for polyester having different chain-ends.</caption><thead><tr><th rowspan="2">Repeating units<br>n</th><th colspan="2">Ester-alcohol ending</th><th colspan="2">Alcohol-alcohol ending</th><th colspan="2">Ester-ester ending</th></tr><tr><th>M</th><th>[M + Na]$^+$</th><th>M</th><th>[M + Na]$^+$</th><th>M</th><th>[M + Na]$^+$</th></tr></thead><tbody><tr><td>1</td><td>265.0950</td><td>288.0848</td><td>307.1056</td><td>330.0954</td><td>442.1376</td><td>465.1274</td></tr><tr><td>2</td><td>484.1482</td><td>507.1380</td><td>526.1588</td><td>549.1486</td><td>661.1908</td><td>684.1806</td></tr><tr><td>3</td><td>703.2013</td><td>726.1911</td><td>745.2119</td><td><strong>768.2017</strong></td><td>880.2439</td><td>903.2337</td></tr><tr><td>4</td><td>922.2545</td><td>945.2443</td><td>962.651</td><td><strong>987.2549</strong></td><td>1099.2971</td><td>1122.2869</td></tr><tr><td>5</td><td>1141.3077</td><td>1164.2975</td><td>1183.3182</td><td><strong>1206.3080</strong></td><td>1318.3503</td><td>1341.3401</td></tr><tr><td>6</td><td>1360.3608</td><td>1383.3506</td><td>1402.3714</td><td><strong>1425.3612</strong></td><td>1537.4034</td><td>1560.3932</td></tr><tr><td>7</td><td>1579.4140</td><td>1602.4038</td><td>1621.4246</td><td><strong>1644.4144</strong></td><td>1756.4566</td><td>1779.4464</td></tr><tr><td>8</td><td>1798.4671</td><td>1821.4569</td><td>1840.4777</td><td><strong>1863.4675</strong></td><td>1975.5097</td><td>1998.4995</td></tr></tbody></table>

<figure><img src="image_6.png" /><figcaption>Fig. 3. 300 MHz ¹H NMR spectrum of the obtained polymer in CDCl₃ (Entry 1).</figcaption></figure>
## 3.2. Study of the photochemical step and characterization of the obtained coatings

Combining thiol-ene reaction with cycloaddition by the use of 7-mercapto-4-methyl coumarin has already shown its efficiency in our previous work [16] and proceeds according to Scheme 2.

Since the synthesized polyester (Entry 2 of Table 1) had an average number of 93 unsaturations per chain, we limited ourselves to incorporate in the formulation for coatings only 0.1 equivalent of MMC relative to the repeating unit, which corresponds on average to around 8 to 9 crosslinking sites per polyester chain if all MMC molecules are grafted. The photoinitiated reaction was then monitored by real-time FTIR spectroscopy at 30 and 70 °C, i.e. approximately 20 degrees below and above the polyester glass transition temperature respectively, to assess the influence of the molecular mobility of the chains. As the characteristic absorption bands of the polyester ethylenic double bonds around 1630–1660 cm⁻¹ and of the MMC thiol function at 2500 cm⁻¹ were not intense enough to be observed (Fig. 4), the monitoring of thiolene photografting was not possible by FTIR spectroscopy. In contrast, a decrease in the absorption band at 1604 cm⁻¹, corresponding to the ethylenic double bond of MMC, was observed, confirming MMC dimerization under UV light (Fig. 4). This photodimerization was also confirmed by UV-visible spectroscopy (Fig. SI.4). Indeed, the following of the MMC characteristic absorption band at 336 nm showed a disappearance of the pyrone unit consecutive to the [2 + 2] cycloaddition.

Furthermore, Fig. 5 shows that the consumption of MMC's double bonds was slightly faster at 70 °C compared to 30 °C, and the conversion exceeded 90 % after 1 h of irradiation whatever the reaction temperature. 30 °C was therefore chosen for crosslinking, in an effort to save energy.

The photocrosslinked coating obtained after an irradiation during 1 h at 30 °C was then characterized. First, DSC analysis (Fig. SI.5) revealed that the obtained film was amorphous and its glass transition temperature increased at 74 °C, suggesting the crosslinking of the polymer. This crosslinking was also evidenced by the low swelling rate (0.11 ± 0.05) of the film. Moreover, the photocrosslinked film was apolar (polarity of 26.7 %), had a high König hardness of 222 ± 1 s., and a T₅% of 245 °C, slightly lower than the polyester's one, certainly due to the lower thermal stability of MMC (T₅% = 208 °C). We can therefore emphasize that the replacement of the long unsaturated chain by a shorter one has considerably improved the mechanical properties, in terms of glass transition temperature and hardness, of this PDA-based unsaturated polyester.

## 4. Conclusion

An original semi aromatic and partially biobased unsaturated polyester was synthesized by transesterification between a diester of dicarboxylic acid (de-PDA) and an unsaturated diol with a short carbon chain (cis-2-butene-1,4-diol). After optimization of the synthesis conditions, a polyester with a high average molar mass of 20,700 g/mol

<figure><img src="image_7.png" /><figcaption>Fig. 4. Evolution of FTIR spectra of the polyester +0.1 equivalent MMC under UV radiation at 30 °C.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Fig. 5. Conversion curves of MMC's double bonds versus irradiation time at 30 °C and 70 °C for the polyester (Entry 2) + 0.1 equivalent MMC.</figcaption></figure>

(corresponding to 93 ethylenic unsaturations per chain) and a T<sub>g</sub> of 51 °C was obtained. This one was then used to produce coatings under UV irradiation at 30 °C in the presence of 7-mercapto-4-methyl coumarin (MMC). This photosensitive molecule enabled the polyester to be crosslinked by a concomitant process consisting of its grafting onto the polyester by a thiol-ene reaction and its dimerization. The coating exhibited a T<sub>g</sub> of 74 °C and König hardness of 222 ± 1 s, demonstrating the possibility to use styrene free alternatives to obtain rigid polyester thermosets.

### CRediT authorship contribution statement

**Klara Jastak:** Writing – original draft, Validation, Investigation, Formal analysis, Data curation. **Elise Brument:** Investigation, Formal analysis, Data curation. **Fabrice Burel:** Writing – review & editing, Validation, Conceptualization. **Nicolas Désilles:** Writing – review & editing, Validation, Supervision, Resources, Project administration,

<figure><img src="image_9.png" /><figcaption>**Scheme 2.** Concomitant reactions between unsaturated polyester and MMC during UV irradiation.</figcaption></figure>
**Methodology, Funding acquisition, Conceptualization.** Laurence Lecamp: Writing - review & editing, Validation, Supervision, Resources, Project administration, Methodology, Funding acquisition, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors gratefully acknowledge the “Région Normandie” (project PhotobioUP) for the financial support. They also thank Dr. Corinne Loutelier-Bourhis for her expertise on the MALDI-TOF analyses.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.reactfunctpolym.2025.106420.

Data availability

The raw/processed data required to reproduce these findings cannot be shared at this time due to technical or time limitations. But they are available on demand.

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