CORRELATING FORMULATION AND
PERFORMANCE IN ALL-ACRYLIC WATERBORNE
PRESSURE SENSITIVE ADHESIVE LATEXES

Julie Bratasanu, Victoria Aguilar, Leila Issoufou Alfari, Mathieu Leocmach, Benoit Mahler, Eric Drockenmuller, Elodie Bourgeat-Lami, Matteo Ciccotti, Costantino Creton, Damien Montarnal

► To cite this version:

Julie Bratasanu, Victoria Aguilar, Leila Issoufou Alfari, Mathieu Leocmach, Benoit Mahler, et al. CORRELATING FORMULATION AND PERFORMANCE IN ALL-ACRYLIC WATERBORNE PRESSURE SENSITIVE ADHESIVE LATEXES. Macromolecular Chemistry and Physics, 2025, 226 (8), pp.2400475. 10.1002/macp.202400475. hal-04995016

HAL Id: hal-04995016

https://hal.science/hal-04995016v1

Submitted on 18 Mar 2025

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<figure><img src="image_1.png" /></figure>
CORRELATING FORMULATION AND
PERFORMANCE IN ALL-ACRYLIC
WATERBORNE PRESSURE SENSITIVE
ADHESIVE LATEXES

Julie Bratasanu,¹ Victoria Aguilar,² Leila Issoufou Alfari,³ Mathieu Leocmach,³ Benoit Mahler,³
Eric Drockenmuller,⁴ Elodie Bourgeat-Lami,¹ Matteo Ciccotti,² Costantino Creton,² * Damien
Montarnal¹*

¹ Université Claude Bernard Lyon 1, CPE Lyon, CNRS, UMR 5128, Catalysis, Polymerization, Processes and Materials (CP2M), 43 Bd du 11 novembre 1918, F-69616 Villeurbanne, France.

² Laboratoire Sciences et Ingénierie de la Matière Molle, UMR7615 ESPCI Paris, PSL University, Sorbonne Université, CNRS, F-75005 Paris, France.

³ Université Claude Bernard Lyon 1, CNRS, UMR5306, Institut Lumière Matière (ILM), 43 Bd du 11 novembre 1918, F-69616 Villeurbanne, France.

⁴ Université Claude Bernard Lyon 1, CNRS, INSA-Lyon, UMR 5223, Ingénierie des Matériaux Polymères, 43 Bd du 11 novembre 1918, F-69616 Villeurbanne, France.

KEYWORDS. Pressure sensitive adhesives, adhesion energy, shear debonding time, rheology, miniemulsion polymerization, latexes, polyacrylates.

ABSTRACT.
This work investigates the correlation between the formulation of waterborne acrylic pressure-
sensitive adhesives (PSAs) and their resulting adhesive performance. A library of *n*-butyl
acrylate-based latexes was synthesized via miniemulsion polymerization. Controlled variations
in the composition of these polyacrylates - such as the inclusion of rigid comonomers, latent
crosslinkers and chain transfer agents - enabled precise control over key network structures in the
particles leading then to a range of physical parameters in the cast PSA films such as the glass
transition temperature, entanglement and crosslink density. The viscoelastic and mechanical
behaviors of the resulting networks were carefully characterized using a combination of
techniques, including linear rheology, dynamic mechanical analysis, and tensile testing. These
properties were then correlated with adhesive performance, as measured by probe tack and shear
holding time tests. This comprehensive approach allowed for the identification of the optimal
formulation balance that delivers the best compromises of adhesive performance, directly
correlating these outcomes with the macromolecular design.
Introduction

Pressure sensitive adhesives (PSAs) are a type of non-reactive viscoelastic polymers that stick to
surfaces when a light pressure is applied for a short period. Unlike other adhesive categories such
as hot-melt or structural adhesives, PSAs do not require chemical reactivity or heat activation to
bond with a substrate, making them easy and safe to use. They are widespread in many daily live
applications requiring low to medium shear holding times such as Post-it® notes, labels,
stickers¹⁻³ and bio-medical adhesives.⁴⁻⁶ Additionally, they are also employed in applications
requiring high shear holding times, where they efficiently replace mechanical fasteners in
electronic devices⁷,⁸ and in the interior components and panels of automotive manufacturing.⁹

Their adhesive performance relies on the combination of viscous and elastic behavior, which
allows for an optimal balance between fast adhesion to substrates and long-term resistance to
mechanical stress. The viscous contribution of PSAs is essential for optimal interface contact.
Uniform and efficient contact between the adhesive and the substrate can be obtained even on
rough or heterogeneous surfaces.¹⁰. Moreover, the ability of PSAs to dissipate energy and
distribute stresses far from the crack tip during the debonding phase is crucial for ensuring
adhesion and also linked to their viscous characteristics. However, a purely viscous material
would lack the cohesion needed to withstand static mechanical stress over long times. Enhancing
elasticity of PSAs through crosslinking is thus essential for maintaining strong adhesion over
time.¹¹ Here also, a balance must be achieved, as over crosslinking increases the modulus, limits
the contact surface and diminishes drastically adhesive properties by preventing the
conformation to the natural roughness of the substrate. These different requisites are often
summarized by the empirical Dahlquist criterion,¹² proposing that the shear storage modulus G'
should not exceed 0.1 MPa between $10^{-2}$ to 10 Hz. Moreover, the damping factor tan (δ) should be in the range 0.2-0.5 to exhibit optimal dissipative properties.¹³

Over time, several PSAs chemistries and synthesis methods have been developed to provide industrially relevant PSAs, ranging from styrene-isoprene block copolymers hot melts¹⁴,¹⁵ and acrylic or rubber solvent based¹⁶⁻¹⁸ to acrylic waterborne PSAs.¹⁹⁻²¹. To improve sustainability, industries are increasingly adopting waterborne formulations, significantly reducing the use of volatile organic compounds (VOCs). In particular, polyacrylate-based latexes are widely used because they are cost-effective and offer a wide variety of monomer combinations, which allows for the development of a broad range of adhesive properties. The vast majority of acrylic waterborne PSAs consists of random copolymers, synthesized via free radical polymerization, mostly produced through batch or semi batch emulsion polymerization.²¹⁻²³. For specific formulations, such as highly hydrophobic or water sensitive monomers, miniemulsion polymerization may be employed,²⁴⁻²⁶, although industrial scale-up can be challenging. To achieve specific properties, the formulation of waterborne PSAs requires precise tuning of the monomer composition, density of chain entanglement, and crosslink density.²⁷,²⁸

First of all, PSAs ideally require glass transition temperatures ($T_g$) in the 50-70 °C range below the application temperature²⁹ and high molar masses between entanglements ($M_e$) corresponding to entanglement moduli $G_N$ below 100 kPa. To satisfy these conditions, n-butyl acrylate (BA with $T_g$ PBA = -54 °C³⁰ and $G_N$ PBA= 78 kPa³¹) is commonly employed as main component in the formulation of acrylic PSAs. Other monomers, such as 2-ethylhexyl acrylate (2EHA, with $T_g$ P2EHA = -70 °C³⁰ and $G_N$ PEHA= 60 kPa²⁷) can also frequently be used. Generally, these monomers makes up 70 - 90% of the formulation and are combined with less flexible monomers such as methyl methacrylate (MMA)³² or isobornyl acrylate (IBOA),³³ to finely adjust the final $T_g$. Small
amounts of acrylic or methacrylic acid are almost always added in acrylic PSAs to improve adhesion to polar surfaces, such as glass or metals, by promoting hydrogen bonding.<sup>34-36</sup> These dynamic interactions not only enhance the material's cohesion but also significantly delay chain relaxations.<sup>37</sup>

Permanent or long-term crosslinking of PSAs is also crucial to improve their shear holding times, particularly as their service temperature is significantly higher than their T<sub>g</sub>. Up to a certain point, crosslinking also enables strain hardening and promotes the stretchability of fibrils at the later stages of probe tack or peel tests. The stretchability of these fibrils dramatically enhances the energy dissipation and the overall adhesion performance.<sup>38</sup> However, over-crosslinking drastically reduces the instantaneous adhesion.<sup>39</sup> Crosslinking can be achieved through multiple strategies by the incorporation of specific comonomers: i) bifunctional comonomers,<sup>40-42</sup> ii) functional monomers bearing latent heat-, moisture- or UV-curable reactive groups,<sup>43-45</sup> or functional monomers that can be involved in strong non-covalent interactions (hydrogen bonding, metal chelation<sup>46</sup>). While the monomer composition of the copolymers controls the T<sub>g</sub> and the average molecular weight between entanglements, the molar mass distribution - and the effective presence of entanglements in the final crosslinked networks - governs the viscoelastic and adhesive properties. High molar masses lead to a high density of entanglements in the networks, and while such features are reported to improve cohesive properties and enhance the shear holding times,<sup>47</sup> they also induce poor dissipation in the relevant frequency ranges, between 0.01 to 1 Hz, and reduce the tackiness.<sup>37</sup> In contrast, low molar masses lead to poorly - or non-entangled networks, potentially not even able to crosslink, with absence of strain hardening, and poor adhesive performance because of flow.<sup>48</sup> Control over the molar mass distribution is often achieved through the use of chain transfer agents (CTAs)
during the polymerization. CTAs regulate the length of the growing polymer chains by facilitating termination and re-initiation processes.<sup>32</sup> Thiol-based CTAs, such as dodecanethiol (DDT),<sup>49,50</sup> are prevalent for this purpose. Partially water-soluble CTAs such as 2-ethylhexyl thioglycolate can also be used.<sup>51</sup>

While the monomer composition and synthesis method control the structure of the polymer and of the emulsified particle, the prediction of adhesive properties from compositions alone is not currently possible. An intermediate characterization of the rheological properties of the film cast from the latex is usually carried out. The relationship between the elastic and dissipative components of the rheological properties of the PSAs and their adhesive performance has been presented with the help of various discriminating diagrams. Chang *et al.*<sup>52</sup> proposed to plot the shear storage modulus *G*′ as a function of the loss modulus *G*′′, allowing to classify PSAs into several categories ranging from high shear PSAs, low temperature PSAs to removable PSAs. Extension of Chang’s plot for data at high (0.1-100 Hz) and low (0.01 Hz)<sup>20</sup> frequencies has been extensively used to predict the tack/peel and shear performance, respectively.

Other studies have proposed a different phenomenological approach by identifying the distinct mechanisms during the various tests (e.g., cavitation, formation and extension of fibrils during probe tack and peeling) and correlate them to the corresponding viscoelastic prerequisites. For example, Deplace et al.<sup>32</sup> proposed an empirical criterion for highly dissipative crosslinked samples: tan(δ)/G' > 0.5 x 10<sup>-5</sup> Pa<sup>-1</sup>, which indicates that the PSAs exhibit fibrillation during initial stages of probe tack. At later stages of the test, when fibrils are highly extended, strain hardening is an essential requisite for a debonding without residues. This property, however, cannot be assessed through linear viscoelasticity and requires non-linear testing methods, such as tensile testing or elongational rheology.<sup>53</sup> A further analysis of the uniaxial extension stress-
strain curves in terms of reduced strain $\sigma_R = f(\frac{1}{\lambda})$ ($\sigma_R = f(\frac{1}{\lambda})$ - where $\sigma_R = \frac{\sigma_N}{\lambda - \frac{1}{\lambda^2}}$ and $\lambda$ are the reduced stress and the uniaxial extension, respectively) enabled to define two parameters characterizing the stiffness in large strain of the PSA. The minimum value of the reduced stress is defined as $C_{hard}$ and characterizes approximately the density of permanent crosslinks. The parameter $C_{soft}$ characterizes approximately the density of entanglements that are able to relax the stress (for complete description, see section 4.7 in the Supporting Information)

The ratio of $C_{soft}$ to $C_{hard}$ reflects the relative contribution of dissipation through temporary crosslinks or disentanglement compared to the elasticity provided by permanent crosslinks. High $C_{soft}/C_{hard}$ ratios are typically associated with high tackiness and extended fibrillation plateaus, while lower ratios suggest greater shear holding times but reduced tack performance.32,54

Systematic and comprehensive studies directly linking the synthesis and composition of waterborne PSAs to their adhesive performance are relatively scarce. They mostly concluded that there is an inherent trade-off between tackiness and shear strength in the design of PSAs.

To expand on this understanding, this paper presents a detailed study in which the compositional parameters and structural features of a series of 22 acrylic latexes are systematically varied. Their thermomechanical and viscoelastic properties are characterized by equilibrium swelling, DMA, rheology and tensile testing, while their adhesive performance is assessed through probe tack and shear holding time tests. Both tests were run using state-of-the art setups with the greatest care for reproducible results including controlled temperature, meticulous preparation of samples and testing conditions.

The correlations between the compositional parameters, the viscoelastic properties and the final adhesive performance demonstrate that specific formulations of networks combining a low
crosslink density with high density of entanglement can result in PSAs that exhibit both high tackiness and long shear debonding times.

# 1. Synthesis of acrylic PSA networks with tunable parameters

An extensive library of acrylic waterborne polymer latexes was synthesized, then film-cast and cured to obtain soft crosslinked networks. While not all formulations were specifically designed to optimize adhesive properties, they provided a basis for understanding the relationship between adhesive performance and key physical parameters of the networks such as the $T_g$, entanglement and crosslink densities and viscoelastic behavior. In this first part of the study, we show in particular that the main physical parameters of the networks can be varied almost independently from one another by adjusting the formulation using three distinct handles (Tables 1 and S1).

The first handle is the variation of the weight ratio (i.e. from 20:80 to 60:40) of the main comonomers (i.e. BA and IBOA), which account for ca. 98 wt% of the overall copolymers, to adjust the $T_g$ of the copolymer. The second handle is the incorporation of a mono-methoxy silane-functionalized latent crosslinker, (i.e. (3-acryloxypropyl) dimethyl methoxysilane (A1)), in amounts ranging from 0.2 to 1 wt% based on monomers (bom). The third handle is the introduction DDT as CTA at contents ranging from 0 to 1 wt% according to the total content of monomers. Besides, all formulations contained 1 wt% of acrylic acid (AA).

All monomers were mixed into a single organic phase, degassed and copolymerized using a conventional miniemulsion procedure. Hexadecane (4 wt% based on monomers) was used as to stabilize the monomer droplets against Ostwald ripening. The oil phase was then emulsified in degassed water containing sodium dodecyl sulfate (SDS, 10 mM). The resulting emulsion, with a
20 wt% oil content, was transferred to a reactor maintained at 70 °C. A water-soluble initiator, potassium persulfate (KPS), was injected at 1 wt% (based on monomer weight) to initiate the polymerization.

Overall, seven series of latexes totaling 22 samples were produced. The complete formulations are provided in Table S1 in the Supporting Information, with the key variations summarized in a 3D representation in Fig 1. Series A B, and C focus on the variation of the IBOA/BA ratio, while series D examines the variation of crosslink density through the variation of A1 content. Series E and F explore the impact of DDT concentration on the obtained *M*<sub>w</sub>, and Series G corresponds to formulations optimized for both probe tack energy and shear holding time.

<figure><img src="image_2.png" /><figcaption>**Figure 1.** 3D representation of the different series produced, based on their composition.</figcaption></figure>

**Table 1.** Monomer composition in the various PSA latexes and main properties of the polymers (*M*<sub>w</sub>) and of the cured networks (gel fraction and *T*<sub>g</sub>).
<table><thead><tr><th>Series</th><th>Latex</th><th>BA<br>wt%</th><th>IBoA<br>wt%</th><th>AA<br>wt%</th><th>A1<br>wt%</th><th>DDT<br>wt% **</th><th>M<sub>w</sub><br>kg mol<sup>-1</sup></th><th>X<sub>gel</sub><br>%</th><th>T<sub>g</sub><br>°C</th></tr></thead><tbody><tr><td>A</td><td>ISO20_X1_DDT0</td><td>78</td><td>20</td><td>1</td><td>1</td><td>0.0</td><td>*</td><td>98</td><td>-26</td></tr><tr><td>A</td><td>ISO40_X1_DDT0</td><td>58</td><td>40</td><td>1</td><td>1</td><td>0.0</td><td>*</td><td>97</td><td>-8</td></tr><tr><td>A</td><td>ISO50_X1_DDT0</td><td>48</td><td>50</td><td>1</td><td>1</td><td>0.0</td><td>*</td><td>97</td><td>6</td></tr><tr><td>A</td><td>ISO60_X1_DDT0</td><td>38</td><td>60</td><td>1</td><td>1</td><td>0.0</td><td>*</td><td>98</td><td>19</td></tr><tr><td>B</td><td>ISO20_X1_DDT0.4</td><td>78</td><td>20</td><td>1</td><td>1</td><td>0.42</td><td>176</td><td>72</td><td>-30</td></tr><tr><td>B</td><td>ISO40_X1_DDT0.4</td><td>58</td><td>40</td><td>1</td><td>1</td><td>0.42</td><td>104</td><td>76</td><td>-8</td></tr><tr><td>B</td><td>ISO50_X1_DDT0.4</td><td>68</td><td>50</td><td>1</td><td>1</td><td>0.42</td><td>115</td><td>71</td><td>8</td></tr><tr><td>B</td><td>ISO60_X1_DDT0.4</td><td>78</td><td>60</td><td>1</td><td>1</td><td>0.42</td><td>111</td><td>65</td><td>20</td></tr><tr><td>C</td><td>ISO20_X0.5_DDT0.4</td><td>77.5</td><td>20</td><td>1</td><td>0.5</td><td>0.42</td><td>132</td><td>28</td><td>-29</td></tr><tr><td>C</td><td>ISO40_X0.5_DDT0.4</td><td>57.5</td><td>40</td><td>1</td><td>0.5</td><td>0.42</td><td>95</td><td>43</td><td>-7</td></tr><tr><td>D</td><td>ISO20_X0.2_DDT0.4</td><td>78.8</td><td>20</td><td>1</td><td>0.2</td><td>0.42</td><td>108</td><td>0.8</td><td>-28</td></tr><tr><td>D</td><td>ISO20_X0.5_DDT0.4</td><td>78.5</td><td>20</td><td>1</td><td>0.5</td><td>0.42</td><td>132</td><td>28</td><td>-29</td></tr><tr><td>D</td><td>ISO20_X0.7_DDT0.4</td><td>78.3</td><td>20</td><td>1</td><td>0.7</td><td>0.42</td><td>49</td><td>67</td><td>-28</td></tr><tr><td>D</td><td>ISO20_X1_DDT0.4</td><td>78</td><td>20</td><td>1</td><td>1</td><td>0.42</td><td>176</td><td>72</td><td>-30</td></tr><tr><td>E</td><td>ISO20_X1_DDT0.2</td><td>78</td><td>20</td><td>1</td><td>1</td><td>0.16</td><td>545</td><td>88</td><td>-34</td></tr><tr><td>E</td><td>ISO20_X1_DDT0.4</td><td>78</td><td>20</td><td>1</td><td>1</td><td>0.42</td><td>176</td><td>72</td><td>-30</td></tr><tr><td>E</td><td>ISO20_X1_DDT0.7</td><td>78</td><td>20</td><td>1</td><td>1</td><td>0.75</td><td>81</td><td>48</td><td>-33</td></tr><tr><td>E</td><td>ISO20_X1_DDT1.0</td><td>78</td><td>20</td><td>1</td><td>1</td><td>1.0</td><td>54</td><td>1</td><td>-31</td></tr><tr><td>F</td><td>ISO20_X0.5_DDT0.2</td><td>78.5</td><td>20</td><td>1</td><td>0.5</td><td>0.16</td><td>205</td><td>82</td><td>-27</td></tr><tr><td>F</td><td>ISO20_X0.5_DDT0.4</td><td>78.5</td><td>20</td><td>1</td><td>0.5</td><td>0.42</td><td>132</td><td>28</td><td>-29</td></tr><tr><td>F</td><td>ISO20_X0.5_DDT0.7</td><td>78.5</td><td>20</td><td>1</td><td>0.5</td><td>0.75</td><td>97</td><td>0.3</td><td>-31</td></tr><tr><td>F</td><td>ISO20_X0.5_DDT1.0</td><td>78.5</td><td>20</td><td>1</td><td>0.5</td><td>1.0</td><td>49</td><td>0</td><td>-33</td></tr><tr><td>G</td><td>ISO20_X0.2_DDT0.1</td><td>78.8</td><td>20</td><td>1</td><td>0.2</td><td>0.08</td><td>475</td><td>78</td><td>-26</td></tr><tr><td>G</td><td>ISO20_X0.2_DDT0.2</td><td>78.8</td><td>20</td><td>1</td><td>0.2</td><td>0.16</td><td>345</td><td>55</td><td>-29</td></tr></tbody></table>
<table><tr><td>G</td><td>ISO40_X0.2_DDT0.1</td><td>58.8</td><td>40</td><td>1</td><td>0.2</td><td>0.08</td><td>525</td><td>71</td><td>-6</td></tr><tr><td>G</td><td>ISO40_X0.2_DDT0.2</td><td>58.8</td><td>40</td><td>1</td><td>0.2</td><td>0.16</td><td>330</td><td>64</td><td>-7</td></tr></table>

*These samples were partially crosslinked after the polymerization. ** Based on the total amount of monomer.

Complete characterization of the latexes immediately after synthesis is provided in the Supporting Information in Table S1. Monomer conversions were consistently above 85%, and all latexes displayed an average hydrodynamic diameter ($Z_{av}$) ranging from 88 to 101 nm, with a low polydispersity index (PdI between 0.014 and 0.056). These measurements were confirmed by cryo-TEM imaging, which revealed spherical particles with a relatively narrow particle size distribution (Fig. S3, $D_w/D_n = 1.033$).

The molar mass and molar mass dispersity ($D$) were determined using Size Exclusion Chromatography (SEC). In the absence of DDT, the samples could not be analyzed by SEC due to partial crosslinking resulting from intermolecular transfer reactions resulting in chain coupling.⁵⁰ All latexes exhibited broad chain dispersities, with $D$ values ranging from 2.5 to 4.0. The weight average molar masses ($M_w$) generally decreased from 500 to 50 kg mol⁻¹ as the amount of DDT increased from 0.1 to 1 wt% (Fig. S4 - S6 in Supporting Information). More detailed analyses indicate that samples with the highest fraction of crosslinkers (1 wt%) also showed higher molar masses. This might be related to a small extent of condensation of silanes during polymerization, after drying or before analysis.

## Film formation and curing

Further analyses of uncured polymers were conducted after casting and complete drying of the latex- up to one week at 25 °C under atmospheric pressure for the thicker films. The curing reaction, which involves condensation of silanes, was monitored at 100 °C by rheology,
specifically through repeated stress relaxation experiments. While time-monitoring using
dynamic rheology is typically employed to determine gel time at the *G'/G'''* crossover for a given
frequency (e.g., 1 Hz), this method was not suitable for samples with high density of
entanglements that already demonstrated before curing *G' > G'''* at 1 Hz. Repeated stress
relaxations tests every 20 min allowed us to probe very low frequency regimes. The curing
process was then characterized by an increase of relaxation times and a higher value of the
plateau modulus at 1000 s, indicating the formation of a permanently crosslinked network (Fig
S7 in the Supporting Information). We found that almost complete curing could be achieved
within 100 min at 100 °C. To ensure full curing for all formulations, all films were thus cured at
100 °C for 16 hours.

Post-curing dynamic rheology was carried out at various temperatures, ranging from 0 to 100 °C. In all cases, the data could be collapsed into single master curves, indicating complete curing and good thermal stability of the polyacrylates within this temperature range.

The Tgs of the different polymers were measured in the fully cured state and ranged from - 33 to 19 °C. Overall, the Tgs were primarily influenced by the IBOA:BA ratio and followed the trends predicted by the Fox mixing model,⁵⁵ thus confirming the statistical copolymerization of IBOA and BA. A more detailed analysis (Fig. S8) revealed that samples with the highest amounts of DDT (0.75 and 1 wt%) exhibited slightly lower Tgs. This drop in Tg is attributed to the lower molar mass of these samples.

The formation of a high gel fraction ($X_{gel}$) after curing is promoted by both a high molar mass of the precursors and a high content of silane latent crosslinker. Correspondingly, we found gel fractions ranging from 0 to 98% amongst the different samples. These gel fractions correlate
positively with the content of A1 (the crosslinker) and negatively with DDT (CTA) (Fig. 2),
while they show no significant dependence on the IBOA content.

<figure><img src="image_3.png" /><figcaption>**Figure 2.** 2D-contour plot of the gel fraction as a function of the DDT CTA and A1 crosslinker weight fractions A1 for the 22 samples. The black squares correspond to the measured data points, while the contour curves are linearly interpolated to illustrate the relationship between these two variables and the resulting gel fraction.</figcaption></figure>

$M_w$ of the polymer precursors, the $T_g$, and the gel fraction of the networks are key parameters for describing the structure of these materials. While these three parameters do not capture the full complexity of the networks, we expect, as a first approximation, that they serve as relatively good predictors of the dissipative and elastic components of the viscoelastic properties. The $M_w$ rather correlates with the entanglement density and the intermediate relaxation times; $T_g$ is related to the monomer friction at short relaxation times; and the gel fraction ($X_{gel}$) characterizes the presence of networks defects ($X_{gel} < 1$ quantifies the presence of a soluble fraction but also indicates that non-elastically active dangling chains are present in the network).

## 2. Evaluation of dependence on $T_g$ (IBOA parameter) with Series A, B and C.
Dynamic rheology was carried out for all series from -10 to 80 °C. The data were shifted to a reference temperature: T<sub>ref</sub> of 20 °C using conventional time-temperature superposition principles to build mastercurves. Additionally, these rheological data were complemented by dynamic mechanical analysis (DMA) at 1 Hz, covering the temperature range from -50 to 100 °C.

The DMA results for Series A (Fig. 3a-b) show, as expected, that the α-transition shifts to higher temperatures with increasing amounts of IBOA, while other observables, such as the shape and peak values of tan(δ) or the presence of a rubbery plateau above T<sub>g</sub>, remain unchanged.
<figure><img src="image_4.png" /><figcaption>**Figure 3.** Series A (tuning IBOA content, 1 wt% A1 and 0 wt% DDT): DMA analyses: a) *E'* and *E''* and b) tan (δ). Mastercurves (T<sub>ref</sub> = 20 °C) of c) storage and loss moduli and d) tan (δ).</figcaption></figure>

The mastercurves from dynamic rheology, on the other hand, offer better precision in the rubbery
regime, and the presence of distinct relaxations is more easily identified in the frequency-
dependence than in the temperature-dependence. The mastercurves of Series A (0% DDT) (Fig.
3c-d) reveal a single T<sub>α</sub> event (although it appears slightly bimodal) leading to a *G'* plateau
corresponding to well crosslinked networks. The absence of disentanglement relaxations at low
frequencies may be related to the extremely high molar mass of the polymer segments. Series A,
exhibiting either a lack of relaxation or very high moduli in the relevant frequency ranges (e.g., about 0.01-10 rad s⁻¹), did not show sufficient tackiness for proper measurement and was therefore not investigated further.

<figure><img src="image_5.png" /><figcaption>**Figure 4.** Mastercurves ($T_{\text{ref}} = 20$ °C) for Series B (tuning $T_g$, 1 wt% A1 and 0.4 wt% DDT) (a, b) and Series C (tuning IBOA content, 0.5 wt% A1 and 0.4 wt% DDT) (c, d).</figcaption></figure>

Series B and C, while both showing the same leftward shift in transitions with increasing amounts of IBOA, show distinct transitions at low frequencies. These transitions correspond to the network strands and the relaxation of network defects, such as dangling chains and extractables (approximately 30 wt%) (Fig. 4). The value of tan(δ) observed during this
disentanglement transition appears to be correlated with the crosslink density. In Series B, where the modulus relaxes by only about one decade from the entangled regime (around 100 kPa) to the final crosslink plateau at low frequencies, tan(δ) values are lower compared to Series C. Series C, containing a lower amount of crosslinker and a much higher fraction of extractables (60-70%), displays a broader relaxation range, spanning nearly two decades in modulus.

<figure><img src="image_6.png" /><figcaption>**Figure 5.** Stress-strain tensile and Mooney-reduced curves for samples from series B (a, c) and C (b, d).</figcaption></figure>

The impact of varying the $T_g$ was particularly evident in tensile tests (Fig. 5). For series B, increasing the IBOA content led to a more pronounced strain hardening, as indicated by a
dramatic increase in $C_{hard}$ from 20 to 650 kPa. However, strain softening should be interpreted with caution when measured near $T_g$, as this behavior can be highly strain rate-dependent. During a conventional tensile test run at a constant crosshead speed, the strain rate of the sample decreases over time, which can influence the softening behavior. In practice, we observed that the ratio $C_{soft}/C_{hard}$ decreased with higher IBOA contents, suggesting a reduction in tackiness as the amount of IBOA increased.

To confirm these observations, adhesive properties were assessed through probe tack testing at 25 °C (Figure, Table 2).

<figure><img src="image_7.png" /><figcaption>b)</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>c)</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>d)</figcaption></figure>

<figure><img src="image_10.png" /></figure>
**Figure 6.** Probe tack tests (25 °C, 100 µm thick films, probe speed 10 µm min⁻¹) conducted for a) series B and b) series C. c) Resulting adhesion energies and d) shear debonding time (50 °C, 100 µm thick films, 13.6 N shear force) of series B and C.

For series B, the combination of high gel fractions (about 70%) and high IBOA content significantly affected tackiness. Specifically, the sample ISO50_X1_DDT0.4 exhibited overly elastic behavior, which hindered energy dissipation and fibril formation, ultimately leading to interfacial debonding. This outcome could effectively be predicted by its low tan(δ)/G' values. However, lowering the T_g allowed for the development of a clear fibrillation plateau and efficient stress relaxation, resulting in overall PSA-like behavior.

Series C, with reduced crosslink densities (gel fractions around 30-40 %), showed considerably improved tackiness. Although ISO20_X0.5_DDT0.4 exhibited overall good PSA characteristics, including a fibrillation plateau and highly dissipative properties, its behavior was somewhat too liquid-like, with a plateau stress below 0.2 MPa and fibril extensibility under 500 %. In contrast, ISO40_X0.5_DDT0.4 demonstrated exceptional probe tack performance, featuring a higher fibrillation plateau, pronounced fibril strain hardening, and a maximum strain nearing 2000 %, while achieving adhesive debonding without leaving fibril residues on the stainless-steel probe.

Shear debonding tests of series B and C were measured at 50 °C in order to obtain debonding times that can be compared for all samples. They showed exact opposite performance to the probe tack tests (Fig. 6d and Table 2). The overly rigid sample ISO50_X1_DDT0.4, which demonstrated very poor adhesion, achieved the highest debonding time of 2600 s. Conversely, ISO40_X0.5_DDT0.4, with exceptional adhesion, exhibited a very low debonding time of less than 1 minute.
In summary, controlling the $T_g$ via the IBOA fraction in the samples, enables significant tuning of the dissipative properties of the networks by shifting the $T_α$ transition to relevant frequency ranges (0.01 – 10 rad s⁻¹). However, it is impossible to decouple these changes from concurrent variations in rigidity. As a result, tackiness and shear strength show opposite behaviors, making it challenging to find an ideal balance between the two properties. It is important to note that achieving a balance of properties is not always necessary for all adhesives. For example, hot melts swollen with high $T_g$ tackifier resins or solvent-based adhesives can be applied at high temperatures or under plasticized conditions, where they display excellent tackiness. Upon cooling or solvent evaporation, excellent shear strength can then be achieved.

Water-based PSAs are typically designed for use at room temperature. Therefore, in the following, we focused on latexes formulated with 20% IBOA. The goal was to control the dissipative properties through chain relaxation mechanisms such as disentanglement or network defects, rather than relying on shifts in the $T_α$ transition.

<table><caption>**Table 2.** Tensile characterization and adhesive performance measured for all samples. Non-crosslinked samples ($X_{gel} < 1$ wt%) are highlighted in red. Samples not obeying the Dahlquist criterion ($G' < 100$ kPa) and the fibrillation criterion ($tan(δ)/G' > 0.5 \times 10^{-5}$) are also highlighted (in orange and yellow/ocher, respectively)</caption><thead><tr><th>Series</th><th>Latex</th><th>G' (kPa)<br>0.1Hz</th><th>tan(δ)/G' @ 0.1Hz<br>x10<sup>-5</sup></th><th>C<sub>soft</sub> (kPa)</th><th>C<sub>hard</sub> (kPa)</th><th>C<sub>soft</sub>/C<sub>hard</sub></th><th>W<sub>adh</sub> (J.m<sup>-2</sup>)</th><th>Shear<br>debonding<br>time (s)</th></tr></thead><tbody><tr><td>A</td><td>ISO20_X1_DDT0</td><td>112</td><td>0.1</td><td>-</td><td>-</td><td>-</td><td>*</td><td>*</td></tr><tr><td>A</td><td>ISO40_X1_DDT0</td><td>168</td><td>0.5</td><td>-</td><td>-</td><td>-</td><td>*</td><td>*</td></tr><tr><td>A</td><td>ISO50_X1_DDT0</td><td>424</td><td>0.48</td><td>-</td><td>-</td><td>-</td><td>*</td><td>*</td></tr><tr><td>A</td><td>ISO60_X1_DDT0</td><td>1.3E5</td><td>3.9E-04</td><td>-</td><td>-</td><td>-</td><td>*</td><td>*</td></tr><tr><td>B</td><td>ISO20_X1_DDT0.4</td><td>31</td><td>2.2</td><td>31</td><td>19</td><td>1.6</td><td>38</td><td>526</td></tr></tbody></table>
<table><tr><td>B</td><td>ISO40_X1_DDT0.4</td><td>83</td><td>0.88</td><td>106</td><td>42</td><td>2.5</td><td>50.0</td><td>600</td></tr><tr><td>B</td><td>ISO50_X1_DDT0.4</td><td>417</td><td>0.37</td><td>293</td><td>145</td><td>2.0</td><td>29</td><td>2640</td></tr><tr><td>B</td><td>ISO60_X1_DDT0.4</td><td>908</td><td>0.21</td><td>699</td><td>646</td><td>1.1</td><td>*</td><td>*</td></tr><tr><td>C</td><td>ISO20_X0.5_DDT0.4</td><td>24</td><td>3.7</td><td>19</td><td>9</td><td>2.1</td><td>85</td><td>375</td></tr><tr><td>C</td><td>ISO40_X0.5_DDT0.4</td><td>100</td><td>0.88</td><td>120</td><td>34</td><td>3.6</td><td>855</td><td>51</td></tr><tr><td>D</td><td>ISO20_X0.2_DDT0.4</td><td>8</td><td>17</td><td>16</td><td>6</td><td>2.4</td><td>31</td><td>9</td></tr><tr><td>D</td><td>ISO20_X0.5_DDT0.4</td><td>24</td><td>3.7</td><td>19</td><td>9</td><td>2.1</td><td>85</td><td>375</td></tr><tr><td>D</td><td>ISO20_X0.7_DDT0.4</td><td>46</td><td>1.6</td><td>61</td><td>17</td><td>3.5</td><td>90</td><td>447</td></tr><tr><td>D</td><td>ISO20_X1_DDT0.4</td><td>31</td><td>2.2</td><td>31</td><td>19</td><td>1.6</td><td>38</td><td>526</td></tr><tr><td>E</td><td>ISO20_X1_DDT0.2</td><td>78</td><td>0.55</td><td>50</td><td>60</td><td>0.8</td><td>29</td><td>600</td></tr><tr><td>E</td><td>ISO20_X1_DDT0.4</td><td>31</td><td>2.2</td><td>31</td><td>19</td><td>1.6</td><td>38</td><td>526</td></tr><tr><td>E</td><td>ISO20_X1_DDT0.7</td><td>14</td><td>7.0</td><td>39</td><td>6</td><td>6.2</td><td>106</td><td>167</td></tr><tr><td>E</td><td>ISO20_X1_DDT1.0</td><td>6</td><td>26</td><td>13</td><td>3</td><td>4.2</td><td>31</td><td>9</td></tr><tr><td>F</td><td>ISO20_X0.5_DDT0.2</td><td>72</td><td>0.72</td><td>63</td><td>28</td><td>2.3</td><td>89</td><td>660</td></tr><tr><td>F</td><td>ISO20_X0.5_DDT0.4</td><td>24</td><td>3.7</td><td>19</td><td>9</td><td>2.1</td><td>85</td><td>375</td></tr><tr><td>F</td><td>ISO20_X0.5_DDT0.7</td><td>5</td><td>41</td><td>29</td><td>6</td><td>4.8</td><td>46</td><td>3</td></tr><tr><td>F</td><td>ISO20_X0.5_DDT1.0</td><td>2</td><td>190</td><td>-</td><td>-</td><td>-</td><td>28</td><td>2</td></tr><tr><td>G</td><td>ISO20_X0.2_DDT0.1</td><td>73</td><td>0.52</td><td>87</td><td>13</td><td>6.9</td><td>337</td><td>4410</td></tr><tr><td>G</td><td>ISO20_X0.2_DDT0.2</td><td>62</td><td>0.79</td><td>86</td><td>6</td><td>14.2</td><td>194</td><td>6600</td></tr><tr><td>G</td><td>ISO40_X0.2_DDT0.1</td><td>162</td><td>0.45</td><td>180</td><td>68</td><td>2.6</td><td>31</td><td>&gt; 20000</td></tr><tr><td>G</td><td>ISO40_X0.2_DDT0.2</td><td>123</td><td>0.56</td><td>93</td><td>18</td><td>5.1</td><td>529</td><td>1080</td></tr></table>

* These samples could not be tested as they did not adhere to any surface.

3. Impact of gel fraction on viscoelastic and adhesive properties with series D, E and F.
The amount of network defects in the adhesives is primarily indicated by their gel fraction. To explore this, we investigated the viscoelastic and adhesive properties by tuning both the crosslinker and CTA contents in the formulations. A particular interest was given to series D, which was formulated with 0.42 wt% DDT and crosslinker contents ranging from 0.2 to 1.0 wt%. Additionally, series E and F were produced with DDT concentrations ranging from 0.16 to 1.0 wt%, and crosslinker contents of 1.0 and 0.5 wt%, respectively. These three series overall represent a variation in gel fraction from 0 to 88%.

Dynamic rheology mastercurves (Fig. 7), and in particular the tan(δ) curves, give already a clear overview of the network features. Series D ranges from a non-crosslinked sample (ISO20-X0.2_DDT0.4) with tan(δ) >>1 and near-terminal flow behavior at low frequencies, to ISO20-X1_DDT0.4, which exhibits a $X_{gel}$ of 72% and demonstrates moderate dissipation (this sample was previously discussed in series B). A similar trend is observed when reducing the amount of DDT in series E, and in series F, although the changes occur at a much faster rate.
<figure><img src="image_11.png" /><figcaption>**Figure 7.** Mastercurves for series D (tuning A1 content, 20 wt% IBOA and 0.4 wt% DDT) (a, b), E (tuning DDT content, 20 wt% IBOA and 1 wt% A1) (c, d) and F (tuning DDT content, 20 wt% IBOA and 0.5 wt% A1) (e, f).</figcaption></figure>
For all significantly crosslinked samples ($X_{gel} > 1$ wt%), the upturns of $G'$ values at low frequencies indicate plateau values ranging from 1 to 10 kPa, which correlate well with the gel fractions (Fig. S9 in the Supporting Information). The most highly crosslinked sample, such as ISO20_X1_DDT0.2, showed relatively low dissipation with $tan(\delta)$ values about 0.4 and only marginally met the $tan(\delta)/G' > 0.5$ Pa$^{-1}$ criterion. However, most other samples demonstrated highly dissipative behavior, distinct from the $T_α$ transition, with $tan(\delta)$ values between 0.5 and 1 in the 0.1-10 rad s$^{-1}$ frequency range. We also noted that samples with the lowest DDT amount (e.g. ISO20_X1_DDT0.2 and ISO20_X0.5_DDT0.2), exhibited particularly large dissipations, with relatively flat $tan(\delta)$ profiles spanning over several decades of frequency.
<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /></figure>

<figure><img src="image_14.png" /></figure>

<figure><img src="image_15.png" /></figure>

<figure><img src="image_16.png" /></figure>

<figure><img src="image_17.png" /><figcaption>**Figure 8:** Stress-strain tensile curves and Mooney reduced plots for series D (a, b), E (c, d) and F (e, f). \*Noisy data occurring for extremely high strains (λ>30) were cut, they barely affect the Mooney reduced representation.</figcaption></figure>
The impact of tuning the gel fraction was particularly evident when investigating the nonlinear
properties during tensile tests (Fig. 8). For all series, increasing the gel fraction – either by
decreasing the amount of crosslinker or decreasing the molar mass of the precursors – resulted in
an increase in the Young’s modulus. This trend aligns with linear rheology analyses, where an
increase of the G’ modulus was visible for samples with higher gel fractions. Moreover, the
impact of increasing the gel fraction was even more pronounced on the large strain region. Strain
hardening was directly correlated with the gel fraction, occurring at lower strain values and
higher stress levels. This was quantified by an increase in C<sub>hard</sub> (Fig. S10 in the Supporting
Information).

Series D and E show an optimal adhesion energy, which results from an enhanced modulus
and a more extended fibrillation plateau, achieved by either increasing the amount of crosslinker
or decreasing the amount of DDT. The optimal gel fraction for these properties is about 50-70 %
(Fig. 9 and 10a).
<figure><img src="image_18.png" /><figcaption>**Figure 9.** Probe tack tests (25 °C, 100 µm thick films, probe speed 10 µm min⁻¹) conducted for series D (a), E (b) and F (c).</figcaption></figure>
<figure><img src="image_19.png" /><figcaption>**Figure 10.** Comparison of a) adhesion energy and b) shear debonding times (50 °C, 100 µm thick films, 13.6 N shear force) for series D, E and F.</figcaption></figure>

Samples with lower gel fractions typically exhibited high initial tackiness but a limited ability to form fibrils, which was also reflected in insufficient strain hardening during tensile tests. In contrast, samples with higher gel fractions, displayed improved strain hardening but lower dissipative behavior, less fibril formation, and debonding through interfacial failure. The photo of the debonding profile, shown in Fig. S11 in the Supporting Information, is typical of interfacial failure, with cavities forming at the surface of the sample, leading to surface crack propagation. For comparison, samples undergoing proper fibrillation revealed cavities expanding
within the bulk of the material until producing fibrils, allowing efficient energy dissipation before reaching adhesive debonding. Notably, 'fingering' was also visible during the fibrillation process, prior to final detachment

Series F, which contained a lower amount of crosslinkers, exhibited similar behavior to the other series, with the exception that it maintained very good adhesion energy even at gel fractions up to 80% (e.g., sample ISO_X0.5_DDT0.2). The probe tack profile for this sample revealed a double fibrillation plateau, indicating that some fibrils fractured under elongation while others remained intact. This allowed the sample to achieve strains approaching 950%, resulting in enhanced adhesive energy.

Good correlations can be found between the adhesion energies and the $C_{soft}/C_{hard}$ ratio obtained from tensile tests. A $C_{soft}/C_{hard}$ ratio around 2 was found to offer a good compromise between adhesion and shear holding time. Lower ratios rather correlate with increased debonding times at the expense of poor adhesion, while higher ratios generally indicated good adhesion but faster debonding times. In terms of shear holding time (Fig 10b), increasing the gel fraction up to 60% consistently led to improved debonding times, which reached values close to 20 minutes in all cases.

One noteworthy outcome of this study is the identification of optimal structural features that combine both high adhesion and high shear holding time. The ideal formulation should yield a gel fraction in the 60-80% range, with very low crosslink density, ideally achieving plateau moduli as low as 10 kPa at low frequencies. This low crosslink density should be offset by a high density of entanglements to favor large dissipations at low frequencies.

#### 4. Optimized formulations combining high adhesion and shear holding time (series G).
A final series G was thus synthesized by using a very low amount of DDT (< 0.2 wt%), promoting the formation of high molar mass, entangled polymer chains. Simultaneously, the amount of crosslinker was kept to a minimum (< 0.2 wt%) to maintain a certain fraction of network defects, with a targeted gel fraction below 80 wt% (See Table 1). Additionally, two samples with increased T~g~ were produced by incorporating 40 wt% of IBOA.

The mastercurves (Fig. 11) show as expected T~α~ transitions at high frequencies, which vary with the fraction of IBOA. However, the secondary transition at lower frequencies is significantly broadened due to the high molar mass of the network defects, resulting in highly dissipative behavior extending to very low frequencies. In practice, it is not possible to properly determine the G' plateau value. Instead, a downturn in the loss factor at very low frequencies suggests that these sample may be permanently crosslinked. Gel fractions ranging from 55 to 78% were later confirmed. It was observed that both the Dahlquist and fibrillation criteria (tan(δ)/G'~0.1 Hz~ > 0.5 Pa⁻¹) were barely met.

Tensile testing (Fig. 12) showed strong strain hardening for samples with 0.1 wt% DDT, achieving nominal stresses above 1 MPa. In contrast, samples with 0.2 wt% DDT showed poor strain hardening, with the absence of a σ~R~ minimum in the Mooney reduced stress plot, typically indicative of non-crosslinked materials. The resulting C~soft~/C~hard~ ratios ranged from intermediate values (2.6 for ISO40_X0.2_DDT0.1) to values in the 0.8-14.2 range for other samples, suggesting a trade-off between high adhesion and poor shear holding times.
<figure><img src="image_20.png" /><figcaption>**Figure 11.** Mastercurves of series G (tuning IBOA and DDT contents, 0.2 wt% A1): a) storage and loss moduli, b) tan(δ).</figcaption></figure>

<figure><img src="image_21.png" /><figcaption>**Figure 12.** Tensile test results for series G: a) stress-strain plot, b) Mooney reduced plot</figcaption></figure>
In contradiction with these predictions, both probe tack and shear tests showed very good performance in comparison to other series (Table 2). We found again that samples with 40 wt% IBOA displayed either cohesive debonding with extremely good shear holding time (>5h30) and very poor adhesion (ISO40_X0.2_DDT0.1), or adhesive debonding with excellent adhesion (530 J m⁻²) and correct shear holding time (ISO40_X0.2_DDT0.2). In contrast, samples with 20 wt% IBOA displayed more balanced properties, outperforming all other series. These samples, ISO20_X0.2_DDT0.2 and ISO20_X0.2_DDT0.1, displayed extended fibrillation plateaus during probe tack testing, resulting in high adhesion energies (340 and 194 J m⁻² resp., Fig. 13 and Table 2). Additionally, shear tests showed adhesive debonding with long debonding times (1h13 and 1h50).

<figure><img src="image_22.png" /><figcaption>**Figure 13.** Tack tests for series G</figcaption></figure>

**5. Correlation between composition of polyacrylates and adhesive performance**

In most tests discussed in this paper (series A-F), well-established criteria relating the viscoelastic properties to adhesive performance provided an adequate way to discriminate
between samples that were either too rigid or too lightly crosslinked. However, we found that these criteria underestimated the performance of optimized samples (series G), where network entanglements were maximized while maintaining an overall gel fraction within the 60-80% range. A limitation of our findings is that adhesive performance can be highly dependent on the timescales of the experiments (e.g., the vertical displacement speed during probe tack tests or the applied weight during shear tests). Additionally, we caution that direct comparisons of tack/shear performance balances should be sometimes exerted with caution, especially for samples with higher T<sub>g</sub> that show poor adhesion and good shear holding time. Since the shear tests were conducted at 50 °C to accelerate debonding times while the tack tests were run at room temperature, it is likely that the high T<sub>g</sub> samples may have shown poorer shear holding time at lower temperature due to poor adhesion to the substrate.

We also highlight that the simple physical parameters characterizing the structure of the networks: T<sub>g</sub>, M<sub>w</sub> of precursors and gel fraction, offer an empirical yet effective correlation with the adhesive performance. To further illustrate this, contour graphs of adhesion performance were constructed using the M<sub>w</sub> and gel fraction axes, specifically for samples with 20wt% IBOA (Fig. 14).

<figure><img src="image_23.png" /></figure>
**Figure 14.** 2D-contour plots of adhesion energy (a) and shear debonding time (b) depending on $M_w$ of precursors and gel fraction of the networks, evaluated for samples with 20 wt% IBOA.

While this representation should certainly be extended with additional data at high $M_w$ values, it does suggest that optimal formulations for PSA are obtained for systems with high density of entanglements. The main challenge in synthesizing such samples is that maintaining a proper control over the gel fraction becomes more difficult since even very small extents of branching or lack of control over the crosslinking reaction may lead to strong deviation of properties.

While probe tack and shear holding time values are difficult to compare directly with other reports due to different experimental conditions (e.g. geometries of tack, temperatures and test speeds), an interesting parallel can be drawn with the results given by Tobing and Klein for solution and emulsion-based polyacrylate PSAs.²⁷ They found that gel-free poly(BA-co-AA) copolymers demonstrated optimal tack adhesion for $M_w/M_e$ ratios about 10. The shear holding power, initially extremely poor, could be dramatically enhanced by crosslinking with aluminum acetyl acetonate, yet at the expense of tack performances divided by 3. Notably, the measure of molecular weight between crosslinks $M_c$ from swelling experiments showed rather tightly crosslinked networks, with $M_c/M_e$ values ranging from 3 to 4.

Similar analyses of our networks crosslinked with latent silane comonomers (See Table S2 and calculation details using the Flory-Rehner equation in the Supporting Information) showed that, in all cases, except for the overly crosslinked series A and sample ISO20_X1_DDT0.2 from series E, the $M_c$ values are considerably higher than the entanglement molecular weight for P(nBA), 21 kg mol⁻¹, by a factor of 5 to 25. This suggests that the networks are sparsely crosslinked, with entanglements contributing significantly.
We also emphasize that alternative architectures that do not respond to our findings have also recently been reported to show excellent adhesive behaviors. For instance, Bon and coworkers showed that low molar mass but highly branched chains synthesized with both a high amount of crosslinkers and CTAs could indeed show high peel and tack energies. However, the resistance to debonding under long-term shear stress was not explored in this study.⁵⁶

## Conclusions

Throughout this work, a large number of formulations of all-acrylic PSAs were synthesized and carefully studied to understand the impact of key parameters – such as $T_g$, $M_w$ of linear precursors and $X_{gel}$ of the final crosslinked network - on adhesive performance. Among these parameters, $T_g$ emerged as the most critical. Any formulation leading to $T_g$ above -10 °C led to either poor performance or an imbalance between high adhesion and high shear holding time. The optimal balance was achieved in highly entangled networks with $X_{gel}$ in the 60-80% range, which ensured highly dissipative relaxations while maintaining cohesive properties.

## ASSOCIATED CONTENT

**Supporting Information.** Materials, Details about syntheses and experimental characterization, extended characterization of the samples.

## Corresponding Author

*damien.montarnal@univ-lyon1.fr

*costantino.creton@espci.fr
**Data Availability**

All data discussed in this manuscript is available upon reasonable request to the authors.

**Author Contribution**

**Julie Bratasanu**: Formal analysis, Investigation, Methodology, Writing – original draft, Writing – review and editing; **Victoria Aguilar**: Formal analysis, Investigation, Methodology, Writing – review and editing; **Leila Issoufou Alfari**: Writing – review and editing; **Mathieu Leocmach**: Funding acquisition, Supervision, Writing – review and editing; **Benoit Mahler**: Supervision, Writing – review and editing; **Eric Drockenmuller**: Methodology, Supervision, Writing – review and editing; **Elodie Bourgeat-Lami**: Formal analysis, Methodology, Supervision, Writing – review and editing; **Matteo Ciccotti**: Formal analysis, Methodology, Supervision, Writing – review and editing; **Costantino Creton**: Conceptualization, Funding acquisition, Formal analysis, Methodology, Supervision, Writing – review and editing; **Damien Montarnal**: Conceptualization, Formal analysis, Funding acquisition, Project administration, Supervision, Writing – original draft, Writing – review and editing.

**ACKNOWLEDGMENT**

We gratefully acknowledge funding from the Agence Nationale de la Recherche (ANR, grant VITRIPSA, ANR-21-CE06-0025) for financial support.

We gratefully acknowledge Thibaut Guichard, Shafina Mougamadou and Léa Rozel for their
contribution to the experimental analysis.

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