Oligomeric-solvent engineering of hierarchical hydrogen-bonding networks for multifunctional glass interlayers

Domain: chemistry
Published: 2026-03-07
Editorial outcome: minor_revision

Abstract
The properties of polymer gels are governed not only by the crosslinked network but also by the solvent. Conventional small-molecule solvents impose trade-offs among environmental adaptability, cost, and biocompatibility. Here, we employ oligomeric polyethylene glycol as a multifunctional solvent for poly(methacrylic acid) (PMAA), converting the otherwise plastic PMAA network into a transparent, dissipative gel. The oligomeric solvent promotes a hierarchical hydrogen-bonding architecture with broadly distributed strengths, coupling elasticity and viscosity, stabilizing the network, and enabling high energy dissipation for acoustic damping and impact resistance. Meanwhile, thermally reversible hydrogen-bond dissociation provides broad endothermic heat absorption, affording thermal buffering. The gels further exhibit high transparency, robust adhesion, and self-healing. Harnessing the gel as an interlayer, we fabricate laminated glass that integrates light transmission, thermal regulation, sound attenuation, and mechanical protection. This oligomer-solvent strategy offers a practical route to multifunctional, energy-efficient, safer building glazing applications in real-world architecture settings.

Introduction
Polymer gels are soft materials composed of cross-linked polymer networks swollen with a solvent phase1. The polymer network forms the structural backbone, while the solvent occupies the interstitial spaces2. Importantly, the solvent does more than simply fill space. It plays a pivotal role in determining the physicochemical properties, functional performance, and practical applications of the gel. Specifically, (1) solvent molecules infiltrate the polymer network, counteracting elastic retraction of the crosslinks through swelling and thereby preserving macroscopic volume and shape3; (2) solvents critically influence responsiveness of the gel to environmental stimuli (e.g. temperature, pH, light, electric fields) by mediating molecular interactions and phase transitions4; (3) solvents modulate mechanical properties through polymer-solvent interactions5-7; and (4) solvents can serve as functional carriers, enabling drug delivery8, ionic conduction9, and functioning as media for in situ catalysis or material synthesis10,11.

Common gel solvents are typically small molecules such as water or organic liquids12, each with characteristic drawbacks. For instance, hydrogels are flexible and biocompatible but suffer from water crystallization at low temperature and evaporation at high temperature, which narrows the operating window, as well as thermodynamic incompatibility with hydrophobic components13,14. Organogels can mitigate drying and compatibility issues but often exhibit weak polymer-solvent interactions and limited biocompatibility15. Ionic liquids and deep eutectic solvents offer ultralow volatility and useful functionalities, yet they present practical drawbacks including cost, synthetic complexity, biodegradability concerns, composition sensitivity, and high viscosity16-20. These trade-offs motivate solvent strategies that better balance performance, processability, environmental adaptability, and biocompatibility.

Motivated by the inherent limitations of conventional small-molecule solvents, recent efforts have increasingly turned to polymeric liquids as alternative gel solvents. Liu et al.21 introduced poly(n-butyl acrylate) (PBA) fluid into polymer networks, achieving efficient energy dissipation over a broad frequency range. Wang et al.22-24 established PEG as a polymeric solvent platform for gel systems, demonstrating that PEG-based gels can simultaneously exhibit high mechanical strength, self-healing capability, energy dissipation, and 3D printability. Although these studies highlight the versatility of polymeric solvents, their design targets and underlying mechanisms differ from those of the present work. In PEG gels based on P(HEMA-co-AAc)23, enhanced toughness and self-healing primarily originate from solvent-enabled multivalent interactions and increased chain correlations or entanglements. In contrast, polymer-fluid-based damping gels21 achieve tunable dissipation by regulating the relaxation (reptation) dynamics of confined polymeric liquids, leading to molecular-weight-dependent and frequency-shiftable dissipation peaks.

Here, we pursue a distinct molecular design strategy: we select PMAA, whose carboxylic groups intrinsically form strong associative assemblies25 (bulk copolymerization of MAA yields glassy, brittle PMAA, Fig. 1a), and employ PEG-200 as an oligomeric solvent that introduces additional weaker/medium-strength hydrogen-bonding states, thereby broadening the bond-strength distribution within a single interaction family (hydrogen bonding). First, owing to its oligomeric nature, PEG has far greater contour length than small-molecule solvents and more effectively separates adjacent PMAA chains, thereby increasing interchain spacing and free volume26,27. Second, the ether oxygen on PEG bears lone pairs and serves as hydrogen-bonding acceptors, forming multiple bidentate (medium-strength) and monodentate (weak) interactions with the carboxylic groups of PMAA28. In parallel, a fraction of PMAA carboxyl groups associate with each other from cyclic dimers to linear aggregates25,29, supplying the strong-bond tier of the hierarchy (Fig. 1b). Notably, both PEG and PMAA are indispensable for building this hierarchical hydrogen-bonding network. Substituting PEG with H2O results in a glassy, brittle PMAA material rather than a gel (Supplementary Fig. 1), while replacing PMAA with polyacrylic acid (PAAc) suppresses gelation in the PEG/PAAc (PEA) system (Supplementary Fig. 2). This architecture achieves a finely balanced elasticity and viscosity30,31, enabling a gel-like response across an ultra-wide frequency range (Fig. 1c). The elastic component provides high mechanical strength, while the viscous component delivers high damping, with a loss factor (tan δ) approaching 1. This combination confers both noise reduction and impact energy absorption. Simultaneously, the thermally responsive interactions of the PEG/PMAA system enhance thermal regulation. To demonstrate practical utility, we integrated the gel into a laminated-glass prototype and systematically evaluated its multifunctionality (Fig. 1d). The resulting composite exhibits a combination of optical clarity, thermal buffering, acoustic damping, and mechanical robustness. Rather than optimizing isolated properties, this system achieves integrated performance, opening avenues for functional materials in architectural glazing, protective interfaces, and energy-responsive systems.

Results
Hierarchical Hydrogen-bonding Network: Design and Characterization
We characterized the structure of PEM gels across different length scales. Optical transmittance in the 400–800 nm range was measured using an ultraviolet-visible spectrophotometer. All PEM gels exhibit high transparency, with a logo image clearly visible beneath a 2 mm-thick PEM gel film (Fig. 2a).

Successful gel formation was further verified by 1H nuclear magnetic resonance (NMR) spectroscopy (Fig. 2b). The multiple peaks near 3.70 ppm correspond to protons in PEG32, while the peaks at 6.06 ppm and 5.66 ppm arise from MAA. In the PEM gels, all three signals remain but shift downfield, confirming network formation and their participation in hydrogen bond interactions. Fourier transform infrared (FT-IR) spectroscopy further elucidates the chemical composition and interaction mechanism within the PEM gels (Fig. 2c). For neat PEG, absorption peaks at 2876 cm-1 and 2930 cm-1 correspond to symmetrical and asymmetric stretching of –CH groups, while the peak at 1059 cm-1 is assigned to C–O–C stretching33,34. For neat MAA, the characteristic C=O stretching vibration appears near 1700 cm-1. These characteristic peaks are present in all PEM gel samples, confirming the successful incorporation of both components.

To clarify the hierarchical nature of the hydrogen-bonding network, peak deconvolution was performed on the C=O vibration FT-IR spectra. Neat MAA exhibits a prominent carbonyl peak at 1700 cm-1 (Supplementary Fig. 3a), characteristic of strong dimeric hydrogen bonds. Upon PEG incorporation, an additional blue-shifted peak emerges near 1728 cm-1 (Supplementary Fig. 3b-e). This shift arises from the disruption of partial strong PMAA–PMAA dimers and the formation of weaker PEG–PMAA hydrogen bonds, which diminish the electron-withdrawing environment of the carbonyl group35. Peak-area ratio analysis further reveals that the fraction of strongly hydrogen-bonding carbonyl groups increases with MAA content (Supplementary Fig. 3f), underscoring the compositional dependence of hydrogen-bonding interactions within the gel network. Concomitantly, the C–O–C stretching of PEG (1000–1100 cm-1) undergoes pronounced broadening and becomes increasingly asymmetric with rising MAA content, accompanied by the appearance of a shoulder at lower wavenumbers (Supplementary Fig. 4)36,37. This feature signifies the coexistence of free ether oxygen and hydrogen-bonding ether oxygen, reflecting hydrogen bond interactions between PEG ether oxygens and PMAA hydroxyl groups.

To elucidate the thermal evolution of this hierarchical hydrogen-bonding network at the molecular level, temperature-dependent FT-IR spectra of the PEM gel were recorded from 30 to 150 °C. Focusing first on the O–H stretching region of PMAA (Fig. 2d), a gradual blue shift from 3500 to 3515 cm-1 indicates the progressive dissociation of hydrogen-bond aggregates into free carboxyl groups. Two-dimensional correlation spectroscopy (2DCOS) provided higher resolution of these sequential events. While synchronous spectra (Fig. 2e) indicate cooperative spectral changes across the broad 2700–3600 cm-1 range, the asynchronous spectra (Fig. 2f) distinguish sequential thermal events: the spectral response of hydrogen bond O–H groups (~3297 cm-1) precedes that of the weakly associated or free O–H groups (~3596 cm-1), corroborating the progressive thermal disruption of the network.

Further insight is provided by the C=O stretching region (1690–1750 cm-1, Supplementary Fig. 5). The synchronous spectra exhibit positive cross-peaks between the band at ~1700 cm-1 (dimeric PMAA–PMAA hydrogen bonds) and the band at ~1728–1730 cm-1 (free C=O and PEG–PMAA hydrogen bonds), indicating concurrent intensity variations during heating. According to Noda’s rule, the positive synchronous and positive asynchronous correlations at (1700, 1728 cm-1) reveal the specific reaction sequence: the destabilization of hydrogen-bonding PMAA–PMAA carbonyls initiates first, followed by the subsequent development of free or PEG–PMAA carbonyls.

Then, we further investigated hydrogen-bonding interactions between PMAA and PEG chains through molecular dynamics (MD) simulations. Representative simulation snapshots are presented in Fig. 2g. The evolution of hydrogen-bonding numbers over a 100 ps trajectory is shown in Supplementary Fig. 6, and the corresponding average hydrogen-bonding counts are summarized in Fig. 2h. On the one hand, the number of hydrogen bonds between PMAA and PEG is consistently greater than that between PMAA chains, indicating that the introduction of PEG disrupts the dense interchain hydrogen bonds in PMAA and inserts itself as a bridging component. On the other hand, both types of hydrogen bonds increase with higher MAA content, reflecting the growing availability of hydrogen-bonding donors and acceptors within the network. Fig. 2i presents the average hydrogen-bonding lengths. The PMAA–PMAA hydrogen bonds exhibit longer average distances than those between PMAA–PEG, further supporting the notion that PEG effectively inserts between PMAA chains and establishes shorter, more favorable hydrogen bonds as molecular bridges. To complement these findings, binding energies between PMAA–PEG and PMAA–PMAA were calculated via molecular simulation, as shown in Fig. 2j. The binding energy increases with the number of hydrogen bonds in both cases. Notably, the binding energy of PMAA–PMAA is significantly higher than that of PMAA–PEG. This difference is attributed to the formation of strong, multidentate hydrogen-bonding assemblies. Combined with the bond length analysis, these results confirm the hierarchical nature of hydrogen bonding within the PEG–PMAA network.

Furthermore, scanning electron microscopy (SEM) images reveal that the cross sections of PEM gels are flat and smooth, with no observable signs of phase separation (Supplementary Fig. 7). The morphological uniformity is further supported by small-angle X-ray scattering (SAXS) results of the PEM gel (Supplementary Fig. 8). Thermal gravimetric analysis (TGA) demonstrates that PEM gels possess good thermal stability (Supplementary Fig. 9). The glass transition temperature (Tg) of PEM gels increases with increasing MAA content and remains close to room temperature (Supplementary Fig. 10). This trend is attributed to the increasing density of hydrogen bonds within the network. Since viscoelastic material exhibits maximum internal energy dissipation near their Tg, these gels are promising candidates for room-temperature damping applications.

It is worth noting that hierarchical interactions have also been reported in several recent gel systems38-40, such as ion–dipole hybrid gels and deep eutectic solvent–based gels. In these materials, hierarchy is typically introduced through chemical heterogeneity, for example by combining multiple interaction motifs (ionic coordination, ion–dipole coupling, or eutectic complexation) with distinct bonding energies. By contrast, we adopt a fundamentally different molecular design strategy in which hierarchical behavior emerges from a single interaction type—hydrogen bonding—whose strength distribution is continuously broadened through oligomeric-solvent engineering. The finite chain length of oligomeric PEG molecules enables them to function simultaneously as a solvent, spacer, and multidentate hydrogen-bonding bridge, generating hierarchy through topological and length-scale modulation. This strategy provides a conceptually simple and general route to hierarchical viscoelastic networks.

Mechanical Properties, Flaw Insensitivity and Self-Healing
We next investigated the mechanical properties, flaw-insensitivity and self-healing of PEM gels. The mechanical performance was first analyzed through uniaxial tensile testing, and the stress-strain curves for all PEM gels are summarized in Fig. 3a. With increasing MAA content, the fracture stress of PEM gel increases and the yielding behavior becomes more pronounced. Under an applied stress field, network failure proceeds from low to high binding energy. Therefore, the hydrogen bonds within the gel network rupture first, dissipating energy and weakening interchain interactions, which leads to yield initiation. Then the external force is transmitted along the long-entangled chains until the covalent bonds at the crosslink points are broken, causing the disentanglement and interchain slippage. Eventually, excessive covalent bonds are broken to form voids in the network, causing the gel to break. More PMAA chains result in an increased number of hydrogen bonds and chain entanglements, which together enhance both the Young's modulus and toughness of the PEM gels (Supplementary Fig. 11). To further analyze the stress-strain behavior, we applied the Mooney–Rivlin equation (Fig. 3b), expressed as follows41,42:

σred = 2C1 + 2C2 / λ

where σred is the reduced stress, λ is the stretch ratio, C1 is the material constant corresponding to half of the shear modulus, and C2 reflects strain hardening (C2 < 0) or softening (C2 > 0) beyond the Gaussian elasticity regime43. As shown in Supplementary Fig. 12, the Mooney–Rivlin plots reveal that PEM2.2 and PEM2.4 exhibit strain softening across the entire strain range, PEM2 gel shows softening only at high 1/λ and PEM1.8 shows neither strain softening nor hardening. For gels with higher MAA content (particularly PEM2.2 and PEM2.4), strain softening arises from the rupture of interchain hydrogen bonds. In contrast, as the MAA content decreases, the number of hydrogen bonds decreases and chain motion becomes increasingly restricted by chemical crosslinks, making strain softening insignificant (PEM2) or even absent (PEM1.8). Because only a small amount of chemical crosslinker was used, the permanent crosslink density is low, positioning PEM1.8 at the boundary between strain softening and hardening (C2 ≈ 0).

To gain deeper insight into the gel network structure, the Rubinstein–Panyukov model was also used to analyze the stress-strain curves. The model is expressed as44:

σ / (λ - λ-2) = Gx + Ge / (0.74λ + 0.61λ-0.5 - 0.35)

where σ is the stress, λ is the stretch ratio, and Gx and Ge represent the shear modulus contributions from crosslinks and entanglements, respectively45. The fitted curves are shown in Supplementary Fig. 13, and the extracted values of Gx and Ge are summarized in Fig. 3c. Clearly, Ge is consistently larger than Gx, and both increase with higher MAA content. This indicates that entanglements dominate the mechanical properties of PEM gels, while the limited number of chemical crosslinks primarily serve to stabilize the network. With increasing PMAA content, hydrogen bonding interactions become more abundant, and the resulting hydrogen-bonding aggregates act in a manner similar to covalent crosslinks. These aggregates not only function as additional crosslinking sites but also promote entanglement by bandaging chains together, thereby suppressing disentanglement during deformation.

The densely packed hydrogen bonds and extensive chain entanglements not only enhance the mechanical strength of the PEM gel but also promote crack passivation. To evaluate the defect tolerance of the gel, a single-edge notch test was conducted using the PEM2 gel as a representative example (Supplementary Fig. 14a). The notched gel exhibited a fracture strain of 3.56 mm/mm, approximately 70% of that of the unnotched sample, demonstrating that the PEM2 gel is relatively insensitive to structural flaws. The corresponding fracture energy was calculated to be 3.52 kJ m-2. In addition, the notched gel was able to lift a 200 g weight without visible crack propagation (Supplementary Fig. 14b), further confirming its flaw-insensitive behavior.

The PEM2 gel also exhibits excellent self-healing capability at room temperature, enabled by the dynamic and reversible nature of its hydrogen bonds. Notably, no external stimuli such as heat or solvents are required to trigger healing. The healing process was monitored in situ using optical microscopy (Supplementary Fig. 15a). Initially, the PEM2 gel was completely severed into two parts, and the width of the crack gradually narrowed over time. After 24 h, the crack was almost fully closed. The mechanical recovery was quantified by uniaxial tensile tests (Supplementary Fig. 15b), and the self-healing efficiency was calculated based on the recovery of fracture strain (Supplementary Fig. 15c). The PEM2 gel reached a self-healing efficiency of 84% after 24 h at room temperature.

Viscoelastic Behavior and Energy Dissipation
The viscoelastic behavior of PEM gels was investigated. To determine the relaxation time, stress relaxation tests were conducted under a fixed strain of 1 mm/mm. As shown in Supplementary Fig. 16, the relaxation time decreases with increasing MAA content, suggesting that dissociation of hydrogen bonds plays a dominant role in stress relaxation. Rheological measurements were performed to characterize the viscoelastic nature of the gels. The shear modulus, defined as the sum of the storage modulus (G') and the loss modulus (G''), reflects the material's combined elasticity and viscous responses. In most cases, when G' exceeds G'', the material behaves as a predominantly elastic solid. Conversely, when G'' exceeds G', viscous behavior dominates, indicating a viscous (sol) state46. As shown in Fig. 3d and Supplementary Fig. 17, all PEM gels exhibit a near-constant gel-like state across an ultra-wide frequency range from 10-4 to 103 Hz, spanning eight orders of magnitude. Within this range, G' and G'' remain comparable, and the loss factor (tan δ) fluctuates around unity (Supplementary Fig. 18). This indicates that PEM gels possess a well-balanced viscoelastic profile: they are capable of dissipating mechanical energy while also maintaining structural recovery without flowing freely30,31. A relevant mechanistic interpretation is provided in Supplementary Fig. 19.

Furthermore, the apparent activation energy of all PEM gels was calculated (Fig. 3e and Supplementary Fig. 20). Each gel exhibited two distinct activation energies, with the high-temperature region showing larger values than the low-temperature region. This behavior can be ascribed to multiple relaxation mechanisms47. At high temperatures (corresponding to low frequencies), hydrogen bonds and covalent crosslinks gradually dissociate, and the activation energy (Ea1) primarily reflects bond dissociation. These values are significantly higher than the typical dimerization energy of -COOH groups (approximately 25-40 kJ mol-1)48. In contrast, at low temperatures (corresponding to high frequencies), relaxation is dominated by chain entanglements, and the activation energy (Ea2) corresponds to the relaxation of long polymer chains.

To gain deeper insight into the damping performance of the PEM gel, dynamic mechanical analysis (DMA) was performed. As shown in Fig. 3f and Supplementary Fig. 21 a-c, both the storage modulus (E′) and loss modulus (E″) decrease markedly with increasing temperature, in agreement with the time–temperature equivalence principle and the rheological observations. The loss factor (tan δ) presents a clear peak near the Tg for all PEM gels, and regions with tan δ > 0.3 are defined as high-damping regions. All PEM gels demonstrate good damping performance across a broad temperature range. Similar to the DSC results, increasing the MAA content shifts Tg to higher temperatures (Supplementary Fig. 21d), reflecting the enhanced strength and density of hydrogen-bonding interactions. The viscoelastic nature of the PEM2 gel was further verified by varying both the tensile rate and the testing temperature (Supplementary Fig. 22). The mechanical response exhibited strong dependencies on both variables: the gel behaved in a hard and brittle manner under high tensile rates and low temperatures, and became soft and tough under low tensile rates and high temperatures. These trends are fully consistent with the time-temperature equivalence principle.

As an intuitive manifestation of the damping capability, energy dissipation serves as a key criterion for evaluating the damping performance of materials. In tensile loading–unloading cycles, the hysteresis loops enlarge with strain (Fig. 3g and Supplementary Fig. 23a-c). The damping capacity, defined as the ratio of dissipated energy to total strain energy, decreases with increasing strain (Fig. 3h and Supplementary Fig. 23d-e). Two factors contribute to this result. First, at small strain, the polymer chains remain coiled, enabling substantial internal friction and interchain sliding, which leads to pronounced energy dissipation and high damping capacity. With increasing strain, chains gradually elongate and orient, reducing available sliding space and thereby lowering frictional dissipation. Second, at small strain, the dynamic and reversible crosslinks within the gel can continuously break and reform, contributing significantly to energy dissipation. With increasing strain, many of these weak interactions are rapidly ruptured and cannot readily reform, thereby diminishing the dissipation capacity. Meanwhile, the network is increasingly supported by the polymer backbone and strong crosslinks, causing the gel network to exhibit more elasticity. Notably, we observed at the same strain, the damping capacity increases with MAA content (Fig. 3i), underscoring the key role of hydrogen bond density in enhancing energy dissipation.

Consistent with tensile observations, large-amplitude oscillatory shear (LAOS) tests further demonstrate the dissipation capability of the PEM gels (Supplementary Fig. 24). All gels exhibit stable elliptical Lissajous loops over 100 cycles, indicating stable linear viscoelastic behavior49. The loop area, corresponding to the dissipated energy per cycle (ΔW), decreases only slightly during cycling, confirming that the reversible hydrogen bonds repeatedly break and reform without structural damage. Moreover, ΔW increases with MAA content, demonstrating that a higher density of hydrogen-bonding interactions enhances energy dissipation.

Furthermore, we emphasize that our oligomeric-solvent engineering strategy is universal. To examine its generality, PEGs with different molecular weights (400, 600, and 800 g mol-1) were employed to prepare PExMy gels. Longer PEG chains act as plasticizers, increasing the distance between PMAA chains and thereby reducing the number of hydrogen bonds formed. As a result, replacing PEG-200 with PEG-400, PEG-600, and PEG-800 in the PEM2 formulation yielded sol-like rather than gel-like products (Supplementary Fig. 25). To obtain comparable gel states, the MAA content was accordingly increased, resulting in the PE400M3, PE600M4, and PE800M5 formulations. All of these gels display high transparency (Supplementary Fig. 26a). Their stress-strain curves confirm robust, gel-like toughness (Supplementary Fig. 26b), and they exhibit excellent damping capacity (Supplementary Fig. 26c). The rheological behavior of PE400M3, PE600M4, and PE800M5 is summarized in Supplementary Fig. 27, showing that all maintain a balance between viscosity and elasticity across an ultra-wide frequency range, with tan δ values approaching 1.

Thermal Management, Impact Protection, and Acoustic Absorption Properties
The hierarchical hydrogen-bonding network in PExMy gels gradually dissociates with increasing temperature, resulting in an overall endothermic response. This feature suggests that PExMy gels hold promise for thermal management applications. To verify their endothermic capability, disc-shaped PExMy gel samples (diameter = 2 cm) were placed on a white substrate and exposed to a xenon lamp for 10 min (1000 W m-2). As shown in Fig. 4a, thermal infrared images reveal maximum surface temperatures of 35.9 ℃, 34.8 ℃, 33.1 ℃, and 31.8 ℃, respectively, despite the ambient temperature exceeding 80 ℃. This confirms the effective heat-buffering ability of the gels. A broad endothermic peak was also observed in the DSC curves of all PExMy gels, attributed to the energy required for dissociation of the hierarchical hydrogen bonds (Fig. 4b). Integration of the DSC curves yielded the corresponding enthalpy values (Fig. 4c), which increased as the MAA content increased, consistent with the higher density of hydrogen bonds formed. To evaluate thermal reversibility, cyclic DSC measurements were conducted using the PE600M4 gel as an example (Supplementary Fig. 28). The heating scan shows a clear endothermic peak, whereas no corresponding exothermic peak appears upon cooling. This behavior reflects the intrinsic nature of the hierarchical hydrogen-bonding network: the endothermic peak originates from the disruption of hierarchical hydrogen-bonding coupled with chain rearrangement. Once they are thermally dissociated, their reformation during cooling is kinetically hindered. Although hydrogen bonds can reform, the slow relaxation dynamics and chain-entanglement constraints prevent recovery of the original organization, resulting in the absence of a distinct exothermic peak.

The excellent damping properties of PExMy gels also make them well suited for impact protection. Their ability to reduce impact force was evaluated using a falling-ball impact test (Fig. 4d), in which steel balls of different weights (25, 50, and 100 g) were dropped freely from a fixed height of 50 cm. Measurement of the impact forces showed that all PExMy gels significantly attenuated the impact of the balls on a steel plate (Supplementary Fig. 29). For example, with the 25 g ball, the polydimethylsiloxane (PDMS) film reduced the impact force by 72.1%, whereas all PExMy gel films reduced it by more than 82.2% (Fig. 4e), demonstrating the high energy absorption of PExMy gels. We further examined protective performance using the PE600M4 gel. A 25 g steel ball was dropped from 50 cm onto a glass slide covered with either PDMS or PE600M4 gel films. Both the unprotected and PDMS-protected glass fractured, whereas the gel-protected glass remained intact (Fig. 4f and Supplementary Movie 1). To visualize the damping effect, PDMS and PE600M4 balls (diameter = 2 cm) were dropped from 30 cm. The elastic PDMS ball rebounded strongly, while the viscoelastic PE600M4 gel showed no rebound (Supplementary Movie 2). In addition to impact resistance, long-term stability is essential for protective applications. Since PExMy gels contain PEG solvent, rheological tests were conducted to assess possible solvent leakage under high pressure50. Samples were held at 50 °C under a normal force of 10 N, with the dynamic modulus recorded every 5 s. After 500 s under continuous pressure, the samples gradually flattened, but no solvent leakage was observed (Supplementary Fig. 30a). The normalized modulus (G' /G'0) slightly increased over time (Supplementary Fig. 30b), confirming the structural stability of the gels under sustained stress.

The damping capability of the gel also extends to the acoustic field. When vibration or noise is transferred from the matrix to the gel, mechanical vibration is dissipated through the motion of polymer chains and chain segments, where intermolecular friction converts the mechanical energy into heat, producing a damping effect. To evaluate acoustic noise reduction, the PE600M4 gel was compared with PDMS and polyvinyl butyral (PVB, a commonly used acoustic film). All materials were prepared as disc samples (diameter = 29 mm, thickness = 8 mm) and tested using an acoustic impedance tube. As shown in Fig. 4g, the PE600M4 gel exhibits excellent broadband sound absorption across 2000–6400 Hz, with absorption coefficients higher than those of PDMS and PVB. In particular, it is most responsive in the 2000–4000 Hz range, reaching a peak absorption coefficient of 0.45 near 3000 Hz. This range largely overlaps with typical environmental noise, offering effective protection for hearing health. Additionally, the impedance ratio of the PE600M4 gel is much less than 1, indicating strong reflection and limited transmission of sound (Fig. 4h). Sound attenuation tests further demonstrated that the PE600M4 gel effectively reduces noise intensity across 2000–6400 Hz, with an average reduction of 60 dB, compared to 42 dB for PVB and 30 dB for PDMS (Fig. 4i).

Application as Multifunctional Glass Interlayers
Windows have long been a key architectural component. In modern buildings, however, they have evolved from simple openings for ventilation and light into multifunctional systems, whose performance directly influences comfort, energy efficiency, and security. High transparency enhances indoor light transmission and reduces reliance on artificial lighting. Heat absorption lowers energy consumption by reducing thermal load. Sound insulation improves the indoor acoustic environment by blocking external noise. Impact resistance protects against glass breakage in high-rise buildings caused by wind pressure or accidental impact, thereby ensuring safety. The PE600M4 gel integrates all of these properties, making it highly suitable as an interlayer for multifunctional architectural glass, hereafter referred to as M-glass (Supplementary Fig. 31). The preparation of M-glass and N-glass is shown in Supplementary Fig. 32.

As glass interlayers, strong glass–interlayer adhesion is essential for the long-term integrity and multifunctional stability of safety glass. Owing to the abundance of hydroxyl groups, the PExMy gel exhibits robust adhesion. When polymerized in situ on glass, the resulting adhesion is too strong to separate the two substrates. To demonstrate this strong adhesion, a circular gel (diameter = 2 cm, thickness = 1 mm) was polymerized in situ between two glass substrates. Upon application of a 500 g load, no adhesive failure was observed (Fig. 5a and Supplementary Movie 3). The laminated structure was capable of lifting a 2 kg weight. The adhesive joint remained fully intact, while fracture occurred in the glass substrate. To avoid asymmetric adhesion arising from differences in polymerization environments at the two interfaces51, PE600M4 gels were polymerized between two PET release films. Adhesive performance was quantitatively evaluated using 90° peel and lap-shear tests. The PE600M4 gel demonstrated strong adhesion on various substrates (Supplementary Fig. 33), achieving an adhesion strength and interfacial toughness on glass as high as 332 kPa and 676 J m-2 (Fig. 5b), respectively. In addition, the gel also exhibited strong yet compliant adhesion to human skin (Supplementary Fig. 34). Cyclic shear of the PE600M4 gel within ±5% strain generated stable dynamic stress responses. The gel could sustain at least 1000 cycles of lap-shearing deformations (Fig. 5c).

M-glass is highly transparent, with clear visibility of objects behind it (Fig. 5d). UV-vis measurements confirmed that its light transmittance remains above 70% (Fig. 5e), satisfying building glass requirements, though slightly lower than N-glass due to absorption by the gel. To simulate practical use, M-glass and N-glass were assembled into glass chambers for comparative testing. First, their thermal management performance was assessed (Supplementary Fig. 35). A thermometer was placed inside each chamber, while a separate device monitored the blank control group. Temperatures were recorded hourly from 10:00 to 19:00. As shown in Fig. 5f, the temperature inside the M-glass room was consistently lower than in the N-glass and blank groups. When the ambient temperature was below 25 ℃, differences between groups were minimal, but above 25 ℃, M-glass displayed pronounced heat absorption. At 2:00 pm, the temperature in the M-glass chamber was 2.6℃ lower than outside, consistent with the DSC results (Fig. 4b), which revealed an endothermic peak at around 25 ℃. Thus, M-glass effectively lowers indoor temperature to a more comfortable level. Sound reduction was next evaluated (Fig. 5g and Supplementary Movie 4). A loudspeaker played white noise at an average of 87 dB for 60 s in the absence of any glass room. With N-glass installed, the average loudness dropped to 63 dB, while M-glass further reduced it to 51 dB (Fig. 5h), indicating enhanced noise-blocking capability. Finally, impact resistance was tested by dropping a 100 g ball from a height of 30 cm onto the glass rooms. As shown in Fig. 5i and Supplementary Movie 5, N-glass shattered completely upon impact, whereas M-glass sustained only minor localized damage, confirming its protective function. High-speed imaging shows the PE600M4 gel protects glass from impact by dissipating stress at the outer layer, preserving the glass’s structural integrity (Supplementary Fig. 36 and Supplementary Movie 6).

To demonstrate the practical applicability of M-glass, we subjected it to representative environmental stressors: UV irradiation to simulate solar exposure, cyclic heating to mimic high-temperature conditions, and water rinsing to emulate rainfall. Under all conditions, the M-glass consistently maintained high optical transparency (Supplementary Fig. 37), effective heat absorption, sound-insulation capability (Supplementary Fig. 38 and Supplementary Movie 7), and robust impact resistance (Supplementary Fig. 39 and Supplementary Movie 8), demonstrating excellent stability and functional reliability under realistic environmental scenarios.

Conventional PVB and EVA interlayers often require high-pressure autoclaves or irreversible thermal crosslinking to achieve optical transparency; without such treatment, trapped air, crystallinity, or phase inhomogeneity causes light scattering. Instead, we emphasize that the proposed gel-based interlayer represents a distinct and complementary strategy for laminated glass fabrication, prioritizing manufacturing simplicity, optical reliability, interfacial adaptability, and processing flexibility (Supplementary Table 2).

Methods
Materials
Methacrylic acid (MAA), polyethylene glycol (PEG, molecular weight of 200, 400, 600, and 800), acrylic acid (AAc), and 2-hydroxy-2-methylpropiophenone (HMPP) were provided by Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). N,N’-methylene bisacrylamide (MBAA) was purchased from Kelong Chemical Reagent Factory (Chengdu, China). PVB tape was purchased from Xiangrui Factory (Jiangsu, China). Glue A and Glue B (Dow Corning DC184) used for the preparation of PDMS elastomers were supplied by Dow Corning Co. Ltd (Shanghai, China). All reagents were used as received without further purification.

Preparation of PExMy gels
The gels were prepared through one-pot free-radical polymerization. As a representative procedure, PEG-200 (0.01 mol), MAA (0.018, 0.02, 0.022, or 0.024 mol), MBAA (0.1 mol% relative to MAA), and HMPP (0.2 mol% relative to MAA) were mixed as the precursor solution. The precursor was injected into a PTFE reaction cell and polymerized under UV irradiation (365 nm, 60 W) for 45 min. The resulting gels were denoted as PExMy, where x represents the molecular weight of PEG, and y represents the molar ratio of MAA to PEG. Unless otherwise specified, the PEG-200My gels (abbreviated as PEMy) were used as the representative samples for tests and characterizations. For comparison, pure PMAA was prepared by bulk polymerization, a PMAA hydrogel was obtained by replacing PEG with H2O, and a PEA gel was synthesized by substituting MAA with AAc, while keeping all other polymerization conditions identical. The detailed compositions are summarized in Supplementary Table 1.

Preparation of PDMS elastomer
PDMS elastomer was synthesized by mixing Glue A and Glue B at a mass ratio of 10:1, followed by thorough degassing to remove air bubbles. The mixture was cast into a PTFE mold and cured in an oven at 60 ℃ for 3 h to obtain the PDMS elastomer.

Characterizations
Transmittance spectra of approximately 2 mm gel films were recorded on a Shimadzu UV-Vis spectrophotometer. Fourier transform infrared (FTIR) spectroscopy spectra were acquired on a Thermo Fisher Scientific spectrometer (USA); gel samples were measured in attenuated total reflectance (ATR) mode, and liquid samples were prepared using KBr pellets. Variable-temperature IR spectra (30-150 °C, 3 °C min−1) were collected in transmission mode (Nicolet iS10, Thermo Fisher Scientific, USA) using ZnSe windows. 1H nuclear magnetic resonance (NMR) spectra were recorded on a Bruker spectrometer (Germany) at 298 K using D2O as solvent. Gel microstructures were observed using a Thermo Fisher Scientific scanning electron microscope (SEM). Thermal gravimetric analysis (TGA) was performed on a NETZSCH analyzer (Germany) from 45-800℃ at 10 ℃ min-1 under N2 atmosphere. Differential scanning calorimetry (DSC) curves were obtained using a MettlerS calorimeter (USA) from -30-150℃ at 5 ℃ min-1 under N2 atmosphere. Dynamic mechanical analysis (DMA) was performed in tensile mode at 0.1% strain from -20-150℃ at 3 ℃ min-1. Small-angle X-ray scattering (SAXS) measurements were performed on a Xeuss system (France) with 50 keV X-ray energy (wavelength: 1.54189 Å), and a sample-to-detector distance of 2841.36 mm. 2D SAXS patterns were recorded on a PILATUS3 300K detector and analyzed using Foxtrot Academic Edition software. Rheology tests were conducted using an Anton Paar rheometer (Austria). Frequency sweeps (1-100 Hz) were performed at 1% strain, with a normal force of 5 N. Temperature was varied from 5-95 °C at 10 °C min−1. Master curves at 25 ℃ were generated via time-temperature superposition.

Molecular Dynamics (MD) Simulation
An amorphous cell containing 5 PMAA chains and 50 PEG molecules was constructed. Simulations were performed with the COMPASS Ⅱ force field in the Forcite module (Materials Studio). The cell was annealed five times (300-500 K) under NVE conditions, followed by 5 ns of NPT simulation (298 K, 1 atm, with a 5 fs timestep). The maximum hydrogen-acceptor distance was set to 2.5 Å for hydrogen bond analysis.

Tensile Testing
Gel samples polymerized in dumbbell-shaped molds (16 × 4 × 3 mm3) were tested using an Instron universal testing machine (USA) with a 500 N load cell. Uniaxial tensile tests were conducted at 100 mm min-1 unless otherwise specified. Young's modulus was calculated from the initial linear region of stress-strain curves. Rate dependence was examined at various tensile velocities, and temperature dependence was examined at different test temperatures. For cyclic loading-unloading, dissipated energy (hysteresis) was determined by integrating the area between loading and unloading curves.

Single-Edge Notch Test
Rectangular gel samples (20 × 5 × 3 mm3) were prepared. Notched samples contained a 1 mm central notch, while unnotched samples were intact. Uniaxial tensile tests were run at room temperature at 100 mm min-1. Fracture energy was calculated using52:

G = W(λb)c / √λb (3)

where c is the notch length, λb is the strain at crack initiation in the notched sample, and W (λb) is the strain energy density of the unnotched sample at the same strain.

Stress Relaxation Test
Dumbbell-shaped samples (16 × 4 × 3 mm3) were stretched to a fixed strain (1 mm/mm) and held for 10 min. Stress relaxation followed:

σ = σ0 e-t/τ (4)

where σ0 is the initial stress and τ is the relaxation time.

Large Amplitude Oscillatory Shear (LAOS) Tests
The LAOS tests were carried out using an Anton Paar rheometer at 25 °C. Under an applied sinusoidal stress input (σ = σ₀ sin ωt), the gels exhibited a corresponding strain response (ε = ε₀ sin (ωt − δ)), where δ denotes the phase lag. The enclosed area of the resulting stress-strain hysteresis loop reflects the energy dissipation per cycle.

Falling-Ball Test
Impact resistance was measured using a falling-ball tester (LICHEN, China). Steel balls (25, 50, and 100 g) were dropped from 50 cm onto gel-covered target discs, and the resulting impact force was recorded.

Acoustic Testing
Acoustic performance was evaluated with an impedance tube (4206-T, HBK, UK) in the frequency range of 500-6400 Hz. Disc samples (29 mm in diameter and 8 mm thick) were tested under normal incidence. The sound absorption coefficient, impedance ratio, and transmission loss were measured.

Adhesion Testing
Adhesion properties were evaluated by 90° peel and lap-shear tests using an Instron universal testing machine at room temperature. For the 90° peel test, gel samples (25 × 15 × 1 mm3) backed with polyimide film were adhered to the substrates at a peel rate of 100 mm min-1. For lap-shear tests, gel samples (10 × 5 × 1 mm3) were sandwiched between two substrates to form a laminated structure and loaded at a testing speed of 100 mm min-1. To demonstrate the adhesion performance of the gel, the PE600M4 gel was temporarily attached to the experimenter’s hand and then carefully removed. The surface morphology of the gel was subsequently examined under an optical microscope (Leica, Germany). The hand shown in Supplementary Fig. 34 belongs to one of the authors. Written informed consent for both participation in the experiment and publication of the image was obtained.

Cyclic Lap-Shear Test
Cyclic lap-shear tests were performed on gel samples (20 × 50 × 1 mm3) sandwiched between two glass substrates. The tests were conducted at a loading rate of 100 mm min-1 with the shear strain controlled within ±5%.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this work, the authors introduce oligomeric polyethylene glycol (PEG-200) as a “solvent” for poly(methacrylic acid) (PMAA) to engineer hierarchical hydrogen-bond networks that couple elasticity and viscosity. They argue this architecture yields transparent, dissipative gels with (i) room-temperature broadband viscoelastic damping (tan δ ≈ 1 over many decades of frequency via TTS), (ii) impact resistance, (iii) thermal buffering due to endothermic H-bond dissociation, (iv) adhesion/self-healing, and (v) optical clarity. These combined properties enable application as a multifunctional laminated glass interlayer, and the concept is further extended to higher-molecular-weight PEGs by adjusting composition to maintain gel-like behavior. The study is promising and near the bar for publication in this journal. However, several aspects require clarification, additional quantification, and expanded controls to strengthen the mechanistic claims and application relevance:\n1. While the concept of oligomeric solvents is novel, several recent works (e.g., on ion-dipole hybrid gels or deep eutectic solvent gels) also report hierarchical interactions. The authors should explicitly differentiate their approach in terms of molecular design strategy rather than performance alone.\n2. PEG-200 is framed as a “solvent.” Given it is a low-MW polymeric liquid with strong H-bonding to PMAA, many readers will view it as a plasticizer/cosolvent. The authors should clearly define how this “oligomeric solvent” differs from traditional small-molecule solvents such as water, particularly in terms of molecular interaction, volatility, and hydrogen-bonding behavior. Comparative experiments with water-based PMAA gels would clarify this distinction.\n3. The authors mention that the concept extends to higher-MW PEGs, yet the influence of PEG molecular weight on the hierarchical hydrogen-bond architecture is unclear. Please clarify how varying PEG chain length affects hydrogen-bond density, phase homogeneity, and mechanical behavior. Comparative FTIR or rheological data could strengthen this section.\n4. The hierarchical hydrogen-bond network is central to the paper, yet the supporting data (FTIR, DSC, MD simulations) are largely indirect. Incorporating more quantitative validation such as temperature-dependent NMR, 2D-IR or other spectroscopic techniques would strengthen the mechanistic claim of multi-tiered hydrogen bonds.\n5. It remains uncertain whether the observed endothermic transitions are reversible. Please include cyclic DSC results to confirm the reversibility of hydrogen-bond dissociation and reassociation during heating–cooling cycles. This would provide stronger evidence for the proposed thermal buffering mechanism.\n6. The demonstration of the “M-glass” system is interesting, yet its long-term stability under realistic conditions (humidity, UV exposure, and thermal cycling) has not been discussed. Such data—or at least an informed discussion—are essential to evaluate its suitability for real-world glazing applications.\n7. For the falling-ball tests and glass-room drop tests, please add: replicates, error bars, and statistical treatment of impact force reductions.\n8. Common glass interlayers include PVB and EVA. Please provide matched-thickness benchmarking against these commercial materials to contextualize performance. Clarify failure modes of the composite glass (glass cracking patterns, gel deformation) using high-speed images or post-impact observations.", "reviewer_2": "This manuscript presents a PEG oligomer-based gel with functionalities in thermal regulation, sound attenuation, and mechanical protection. While the reported properties are interesting, the core concept — polymer oligomer solvent-based gels — is not novel. PEG-based “PEGgels” and related systems have been extensively studied in recent years, with detailed mechanistic, mechanical, and functional analyses already published (e.g., Nat. Commun. 2021, 12, 3610; Adv. Mater. 2022, 34, 2107791; Sci. Adv. 2025, 11, eadv5292). These works already have covered thermal stability, tunable mechanics, self-healing, energy dissipation, and protective applications. The authors highlight thermal regulation and glass interlayer application as new angles, but the overall novelty of this work requires further clarification based on the previous work. In other words, the use of PEG oligomers as solvent/structural components in gels is well-established. The manuscript does not convincingly demonstrate how this system advances beyond existing PEGgel literature, particularly in terms of mechanism or application scope. Therefore, I don’t think the manuscript in current form is ready for publication in Nat. Commun..\nSome other issues are as below:\n1. The comparison to starfish stiffness modulation is misleading. Starfish employ complex, reversible, biologically regulated systems (blood pressure, peptides); the PEM gel simply softens via PEG plasticization — a fundamentally different and far less sophisticated mechanism.\n2. Page 12, Line 261. The explanations about elasticity and viscosity (consistent damping factor) across broad temperatures lack scientific theories or experiment support, authors can refer to some previous work (e.g. Nat. Commun. 2021, 12(1), 3610).\n3. Figure 3h. Typically, to evaluate the damping capacity of materials at varied tensile strains, the tensile tests are performed at separated strain cycles instead of consecutive cycles.\n4. The explanations on the spectroscopy should be more comprehensive. How is the formation of H-bonds between PEG and MAA resulting in the blueshift? What about the corresponding shift for PEG.\n5. The manuscript introduces asymmetric adhesion without explaining its functional purpose, to me it appears to offer only drawbacks.\n6. Missing figure captions and wrongly assigned figure numbers for figures S8 and after.", "reviewer_3": "The manuscript by Li et al. reports a polymeric material composed of poly(methacrylic acid) (PMAA) swollen in poly(ethylene glycol) (PEG), forming a gel-like network that exhibits properties including high energy dissipation, acoustic damping, self-healing, adhesiveness, and impact resistance. These properties arise from the interaction between PEG macromolecules and the PMAA network. The material and its performance are well characterized, and the authors demonstrate several proof-of-concept applications. Overall, the experimental work is solid and the results are of potential interest.\nHowever, the presentation of prior work is incomplete and somewhat misleading. The concept of using PEG as a macromolecular solvent was first introduced by Wang Z. et al. (Adv. Mater. 2022, “Tough, Transparent, 3D-Printable, and Self-Healing Poly(ethylene glycol)-Gel (PEGgel)”), where the fundamental principles, transparency, self-healing, and exceptional mechanical properties were already demonstrated. Subsequent studies, including Wang M. et al., Nature 2024, have further explored applications and properties of PEG–polymer hybrid materials.\nThe authors should therefore revise the Abstract and Introduction to properly acknowledge this prior work and avoid implying that the present study introduces the concept for the first time (e.g., phrases such as “our oligomeric-solvent engineering strategy” or “we introduce oligomeric PEG into a PMAA network to construct a gel system that addresses key limitations of traditional solvent-based gels” are misleading).\nWith appropriate correction of the contextual framing, this manuscript would represent a valuable contribution to the field highlighting the advantages and further applications of an already established concept."}, "author_response": "Dear Reviewers,\nThank you very much for reviewing our manuscript entitled “Bioinspired Oligomeric-Solvent\nEngineering of Hierarchical Hydrogen-Bond Networks for Multifunctional Glass Interlayers”\n(Manuscript ID: NCOMMS-25-73988). We sincerely appreciate your time and the constructive\ncomments provided.\nIn response to your valuable suggestions, we have carefully revised the manuscript and made\nsubstantial improvements. All revisions have been highlighted in red in the revised manuscript, and\ndetailed point-by-point responses to each comment are provided below.\nThank you again for your insightful feedback, which has greatly helped us improve the quality and\nclarity of the manuscript. We believe that the revised version is significantly improved compared to\nthe original submission.\nSincerely,\nRong Ran\nOn behalf of all authors\nResponse to the reviewers’ comments\nReviewer #1:\nIn this work, the authors introduce oligomeric polyethylene glycol (PEG-200) as a “solvent” for\npoly(methacrylic acid) (PMAA) to engineer hierarchical hydrogen-bond networks that couple\nelasticity and viscosity. They argue this architecture yields transparent, dissipative gels with (i) room-\ntemperature broadband viscoelastic damping (tan δ ≈ 1 over many decades of frequency via TTS), (ii)\nimpact resistance, (iii) thermal buffering due to endothermic H-bond dissociation, (iv) adhesion/self-\nhealing, and (v) optical clarity. These combined properties enable application as a multifunctional\nlaminated glass interlayer, and the concept is further extended to higher-molecular-weight PEGs by\nadjusting composition to maintain gel-like behavior. The study is promising and near the bar for\npublication in this journal. However, several aspects require clarification, additional quantification,\nand expanded controls to strengthen the mechanistic claims and application relevance:\nResponse: We appreciate the reviewer for this positive and insightful assessment of our manuscript.\nIn response to the reviewer’s comments, we have thoroughly revised the Manuscript and Supporting\nInformation to strengthen the mechanistic interpretation of the hierarchical hydrogen-bonding network,\n1\nprovide additional quantitative analyses where appropriate, and expand control experiments to better\nsubstantiate the structure–property–function relationships.\nBelow, we address each specific point raised by the reviewer in detail.\n1.While the concept of oligomeric solvents is novel, several recent works (e.g., on ion–dipole hybrid\ngels or deep eutectic solvent gels) also report hierarchical interactions. The authors should explicitly\ndifferentiate their approach in terms of molecular design strategy rather than performance alone.\nResponse: We thank the reviewer for highlighting this important point. We agree that hierarchical\ninteractions have been reported in several recent gel systems, including ion–dipole hybrid gels and\ndeep eutectic solvent–based gels. However, we emphasize that the central novelty of our work lies in\nthe molecular design strategy, rather than in the observation of hierarchical interactions per se.\nSpecifically, the hierarchical hydrogen-bonding network in our system does not arise from mixing\nmultiple types of strong interactions (e.g., ionic coordination, ion–dipole coupling, or eutectic\ncomplexes). Instead, it emerges from a single interaction motif—hydrogen bonding—whose strength\ndistribution is broadened by the introduction of an oligomeric solvent with finite chain length. In this\noligomeric-solvent strategy, PEG does not function as a functional additive or co-network former, but\nas an oligomeric solvent that simultaneously (i) dilutes and spatially separates PMAA chains, (ii)\nbridges neighboring chains through multidentate hydrogen bonding, and (iii) preserves chain\nentanglement and mobility over extended length scales.\nThis design principle is fundamentally distinct from ion-dipole or eutectic gel approaches, where\nhierarchy is typically introduced through chemical heterogeneity (multiple bond chemistries, ions, or\neutectic components). In contrast, our approach achieves hierarchy through topological and length-\nscale modulation of a single hydrogen-bonding chemistry, enabled by the oligomeric nature of the\nsolvent. This difference leads to a qualitatively different viscoelastic landscape, characterized by a\ncontinuous spectrum of relaxation times rather than discrete relaxation modes.\nTo clarify this distinction, we have revised the Introduction and Discussion to explicitly compare\nthese design strategies and to articulate how oligomeric-solvent engineering represents a\ncomplementary, conceptually simpler route to hierarchical networks. The updated discussion revised\non page 8 of the manuscript.\nPage 8: “It is worth noting that hierarchical interactions have also been reported in several recent gel\n2\nsystems38-40, such as ion–dipole hybrid gels and deep eutectic solvent–based gels. In these materials,\nhierarchy is typically introduced through chemical heterogeneity, for example by combining multiple\ninteraction motifs (ionic coordination, ion–dipole coupling, or eutectic complexation) with distinct\nbonding energies. By contrast, we adopt a fundamentally different molecular design strategy in which\nhierarchical behavior emerges from a single interaction type—hydrogen bonding—whose strength\ndistribution is continuously broadened through oligomeric-solvent engineering. The finite chain length\nof oligomeric PEG enables it to function simultaneously as a solvent, spacer, and multidentate\nhydrogen-bonding bridge, generating hierarchy through topological and length-scale modulation.\nThis strategy provides a conceptually simple and general route to hierarchical viscoelastic networks.”\n2.PEG-200 is framed as a “solvent.” Given it is a low-MW polymeric liquid with strong H-bonding to\nPMAA, many readers will view it as a plasticizer/cosolvent. The authors should clearly define how\nthis “oligomeric solvent” differs from traditional small-molecule solvents such as water, particularly\nin terms of molecular interaction, volatility, and hydrogen-bonding behavior. Comparative experiments\nwith water-based PMAA gels would clarify this distinction.\nResponse: We thank the reviewer for raising this important point. PEG functions as an oligomeric\nsolvent, which is fundamentally different from conventional small-molecule solvents such as water. In\nthis work, PEG oligomeric solvent serves two functions. First, owing to their oligomeric nature, PEG\nchains possess a substantially greater contour length than small-molecule solvents and can more\neffectively separate adjacent PMAA chains, thereby increasing interchain spacing and free volume.\nSecond, the ether oxygen atoms along the PEG backbone bear lone pairs and act as hydrogen-bond\nacceptors, forming multiple bidentate (medium-strength) and monodentate (weak) interactions with\nthe carboxylic groups of PMAA. As a result, the introduction of oligomeric PEG broadens the\nhydrogen-bond strength distribution and enables the construction of a hierarchical hydrogen-bonding\nnetwork.\nTo illustrate this distinction, we performed a comparison in which PEG-200 was replaced by water\nat the same molar ratio (e.g., PEM : 0.02 mol MAA and 0.01 mol PEG or water). Because of the much\n2\nsmaller molecular weight of water, this substitution corresponds to the addition of only 0.18 g of water.\nUnder these conditions, the resulting material shows little difference from bulk polymerized PMAA\nand remains a white, hard, and brittle plastic sheet (Fig. S1). This result indicates that simply matching\n3\nthe molar ratio cannot reproduce the role played by PEG in the PE M system. More importantly, even\nx y\nwhen the water content is increased, water cannot replicate the function of PEG. Although water\nmolecules can form hydrogen bonds with PMAA via their hydroxyl groups, they exist as discrete, non-\nbridging species. Consequently, water primarily competes for and occupies the carbonyl groups of\nPMAA, weakening interchain PMAA–PMAA hydrogen bonding rather than constructing a stable\nbridging network. In contrast, PEG chains can simultaneously interact with PMAA chains, thereby\nenabling effective chain separation and network connectivity.\nTaken together, these results demonstrate that PEG oligomers act as an “oligomeric solvent” that\nuniquely combines molecular bridging and plasticization effects. This dual functionality\nfundamentally distinguishes PEG oligomers from traditional small-molecule solvents such as water.\nThe updated results are now presented in Fig. S1, with the corresponding discussion revised on page\n5 of the manuscript.\nFig. S1. Photographs show that substituting PEG with H O at the same molar ratio (PMMA hydrogel:\n2\n0.02 mol MAA and 0.01 mol H O) produces a white, hard, and brittle plastic sheet rather than a\n2\nhydrogel. This result indicates that matching the molar ratio alone is insufficient to reproduce the role\nof PEG in the PE M system. H O disrupts PMAA–PMAA hydrogen bonding but fails to establish a\nx y 2\nstable bridging network, whereas PEG oligomers can simultaneously interact with multiple PMAA\nchains, enabling effective chain separation and network connectivity.\nPage 5: “Notably, both PEG and PMAA are indispensable for building this hierarchical hydrogen-\nbonding network. Substituting PEG with H O results in a glassy, brittle PMAA material rather than a\n2\ngel (Fig. S1), while replacing PMAA with polyacrylic acid (PAAc) suppresses gelation in the\nPEG/PAAc (PEA) system (Fig. S2).”\n3. The authors mention that the concept extends to higher-MW PEGs, yet the influence of PEG\nmolecular weight on the hierarchical hydrogen-bond architecture is unclear. Please clarify how varying\nPEG chain length affects hydrogen-bond density, phase homogeneity, and mechanical behavior.\nResponse: We thank the reviewer for this insightful comment. In our system, increasing the PEG chain\nlength does not compromise the phase homogeneity of the PE M gels, as evidenced by their\nx y\nconsistently high optical transparency (Fig. S26a). However, longer PEG chains increase the spatial\nseparation between adjacent PMAA chains, which reduces the proportion of strong, short-range\nPMAA–PMAA hydrogen bonds while increasing the fraction of relatively weak, long-range PMAA–\nPEG hydrogen bonds.\nTo verify this effect, we synthesized PE M gels at a fixed MAA/PEG molar ratio (x = 2) using\nx 2\nPEGs of different molecular weights (400, 600, and 800 g/mol). All formulations (PE M , PE M ,\n400 2 600 2\nand PE M ) formed sol-like rather than gel-like materials (Fig. S25), indicating longer PEG chains\n800 2\nhinder the formation of strong hydrogen bonds. Notably, PE M retains partial mechanical integrity\n400 2\nand does not fully flow upon inversion, whereas PE M behaves entirely as a viscous solution.\n800 2\nThis progressive loss of structural integrity confirms that increasing PEG chain length weakens the strong\nhydrogen-bond density, shifting the network toward weaker PMAA–PEG interactions.\nTo obtain self-supporting gels with higher molecular weight PEGs, the MAA content was increased\nto compensate for the reduced density of strong hydrogen bonds. When adjusted accordingly, PE M ,\n400 3\nPE M , and PE M all exhibited robust gel-like behavior. As shown in Fig. S26b, their stress–strain\n600 4 800 5\ncurves demonstrate enhanced mechanical strength, confirming that the increased MAA content\neffectively restores strong hydrogen bonding. Moreover, the damping capacity (Fig. S26c) and\nrheological measurement results (Fig. S27) further confirm that the chain length of PEG does not\ncompromise the damping performance of the gel. These results collectively show that, despite\nvariations in PEG chain length, the gels consistently form a hierarchical hydrogen-bonding network,\nwith PEG oligomers serving as molecular bridges. The updated results are now presented in Fig. S25,\nwith the corresponding discussion revised on page 13 of the manuscript.\nPage 13: “Furthermore, we also emphasize that our oligomeric-solvent engineering strategy is\nuniversal. To examine its generality, PEGs with different molecular weights (400, 600, and 800 g/mol)\nwere employed to prepare PE M gels. Longer PEG chains act as plasticizers, increasing the distance\nx y\nbetween PMAA chains and thereby reducing the number of hydrogen bonds formed. As a result,\nreplacing PEG-200 with PEG-400, PEG-600, and PEG-800 in the PEM formulation yielded sol-like\n2\nrather than gel-like products (Fig. S25). To obtain comparable gel states, the MAA content was\n5\naccordingly increased, resulting in the PE M , PE M , and PE M formulations. All of these gels\n400 3 600 4 800 5\ndisplay high transparency (Fig. S26a). Their strain-stress curves confirm robust, gel-like toughness\n(Fig. S26b), and they exhibit excellent damping capacity (Fig. S26c). The rheological behavior of\nPE M , PE M , and PE M is summarized in Fig. S27, showing that all maintain a balance\n400 3 600 4 800 5\nbetween viscosity and elasticity across an ultra-wide frequency range, with tanδ values approaching\n1.”\nFig. S25. Photographs of PE M , PE M , and PE M gels. The PE M sample retains partial mechanical\n400 3 600 4 800 5 400 2\nintegrity and does not fully flow upon inversion, whereas the PE M sample behaves entirely as a viscous solution.\n800 2\nThis progressive loss of structural integrity confirms that increasing the PEG chain length weakens the strong\nhydrogen-bonding density and toward to weaker PMAA–PEG hydrogen-bonding.\n4. The hierarchical hydrogen-bond network is central to the paper, yet the supporting data (FTIR, DSC,\nMD simulations) are largely indirect. Incorporating more quantitative validation such as temperature-\ndependent NMR, 2D-IR or other spectroscopic techniques would strengthen the mechanistic claim of\nmulti-tiered hydrogen bonds.\nResponse: We sincerely thank the reviewer for this insightful and constructive comment. We agree\nthat rigorous validation of the proposed hierarchical hydrogen-bonding network is essential. In\nresponse, we have incorporated systematic FT-IR analysis combined with temperature-dependent two-\ndimensional infrared (2D-IR) spectroscopy to directly elucidate the hierarchical hydrogen-bonding\nnetwork in the gel.\nFirst, the coexistence of hydrogen bonds with distinct strengths was confirmed by FT-IR\nspectroscopy. Neat MAA exhibits a dominant carbonyl peak at ~1700 cm-1 (Fig. S3a), which is\ncharacteristic of strong dimeric PMAA–PMAA hydrogen bonds. Upon incorporation of PEG, an\nadditional blue-shifted carbonyl peak emerges at ~1728 cm-1 (Fig. S3b–e). This shift reflects the\npartial disruption of strong PMAA–PMAA dimers and the formation of weaker PEG–PMAA hydrogen\nbonds.\nImportantly, quantitative peak-area ratio analysis demonstrates that the relative fraction of strongly\nhydrogen-bonded carbonyl groups increases monotonically with increasing MAA content (Fig. S3f),\nproviding direct evidence for the composition-dependent hierarchy of hydrogen-bond interactions\nwithin the gel.\nConsistent signatures are also observed in the PEG segment. The C–O–C stretching band of PEG\n(1000–1100 cm-1) exhibits pronounced broadening and increasing asymmetry with rising MAA\ncontent, accompanied by the emergence of a low-wavenumber shoulder (Fig. S4). This spectral\nevolution signifies the coexistence of free ether oxygens and hydrogen-bonded ether oxygens,\nconfirming the formation of PEG–PMAA hydrogen bonds and further supporting the heterogeneous\nhydrogen-bonding environment.\nSecond, the thermal evolution of the hierarchical hydrogen-bond network was directly probed by\ntemperature-dependent FT-IR and 2D correlation infrared spectroscopy. FT-IR spectra of the PEM\n2\ngel were collected during heating from 30 to 150 °C. In the O–H stretching region of PMAA (Fig. 2d),\na gradual blue shift from ~3500 to ~3515 cm-1 is observed, indicating progressive dissociation of\nhydrogen-bonding aggregates into weaker associated or free carboxyl groups.\nTo resolve the sequential nature of these thermal events, two-dimensional correlation spectroscopy\n(2DCOS) was employed. The synchronous spectrum (Fig. 2e) reveals cooperative spectral changes\nacross the broad 2700–3600 cm-1 region, confirming the collective response of hydrogen-bonded\nspecies to thermal perturbation. More critically, the asynchronous spectrum (Fig. 2f) distinguishes the\norder of molecular events: the response of strongly hydrogen-bonded O–H groups (~3297 cm-1)\nprecede that of weakly associated or free O–H groups (~3596 cm-1), directly evidencing stepwise\nthermal dissociation of hydrogen bonds with different strengths.\nAdditional mechanistic insight is obtained from the carbonyl stretching region (1690–1750 cm-1,\nFig. S5). The synchronous 2D-IR spectrum shows positive cross-peaks between the ~1700 cm-1 band\n(dimeric PMAA–PMAA hydrogen bonds) and the ~1728–1730 cm-1 band (free or PEG–PMAA-\nassociated carbonyls), indicating correlated intensity changes upon heating. According to Noda’s rule,\nthe presence of both positive synchronous and positive asynchronous cross-peaks at (1700, 1728 cm-\n1) establishes a well-defined sequence: the disruption of strong PMAA–PMAA hydrogen bonds occurs\nfirst, followed by the emergence of weaker or free carbonyl species. This spectroscopic evidence\nunambiguously confirms the hierarchical and discontinuous nature of the hydrogen-bond network.\nCollectively, these results provide direct experimental validation of the proposed multi-tiered\nhydrogen-bonding mechanism, thereby substantially strengthening the mechanistic foundation of the\nmanuscript. The updated results are now presented in Fig. 2d-f, Fig. S3-S5, with the corresponding\ndiscussion revised on page 7 of the manuscript.\nFig. 2. Characterizations and simulations revealing hierarchical hydrogen-bonding in PEM gels. d.\ny\nTemperature-dependent FTIR spectra of PEM gel upon heating from 30 to 150 oC (10 oC intervals). e, f. Synchronous\n2\nand asynchronous 2DCOS spectra of the PEM gel. Red regions indicate positive intensities, while blue regions\n2\nrepresent negative ones.\nFig. S3. Peak fitting analysis of the carbonyl stretching vibration [v(C=O)] at 1700 cm-1. a. Pure MAA. b-e.\nPEM gel, y= 1.8, 2, 2.2, and 2.4. f. Corresponding area fractions of the fitted carbonyl peak.\ny\ny\nFig. S5. Synchronous and asynchronous 2DCOS spectra of the PEM gel. Red regions indicate positive\n2\nintensities, while blue regions represent negative ones.\nPage 7: “Fourier transform infrared (FT-IR) spectroscopy further elucidate the chemical composition\nand interaction mechanism within the PEM gels (Fig. 2c). For neat PEG, absorption peaks at 2876\ny\ncm-1 and 2930 cm-1 correspond to symmetrical and asymmetric stretching of –CH groups, while the\n2\npeak at 1059 cm-1 is assigned to C–O–C stretching33,34. For neat MAA, the characteristic C=O\nstretching vibration appears near 1700 cm-1. These characteristic peaks are present in all PEM gel\ny\nsamples, confirming the successful incorporation of both components.\nTo clarify the hierarchical nature of the hydrogen-bonding network, peak deconvolution was\nperformed on the C=O vibration FT-IR spectra. Neat MAA exhibits a prominent carbonyl peak at 1700\ncm-1 (Fig. S3a), characteristic of strong dimeric hydrogen bonds. Upon PEG incorporation, an\nadditional blue-shifted peak emerges near 1728 cm-1 (Fig. S3b-e). This shift arises from the disruption\nof partial strong PMAA–PMAA dimers and the formation of weaker PEG–PMAA hydrogen bonds,\nwhich diminish the electron-withdrawing environment of the carbonyl group35. Peak-area ratio\nanalysis further reveals that the fraction of strongly hydrogen-bonding carbonyl groups increases with\nincreasing MAA content (Fig. S3f), underscoring the compositional dependence of hydrogen-bonding\ninteractions within the gel network. Concomitantly, the C–O–C stretching of PEG (1000–1100 cm-1)\nundergoes pronounced broadening and becomes increasingly asymmetric with rising MAA content,\naccompanied by the appearance of a shoulder at lower wavenumbers (Fig. S4)36,37. This feature\nsignifies the coexistence of free ether oxygen and hydrogen-bonding ether oxygen, reflecting hydrogen\nbond interaction between PEG ether oxygens and PMAA hydroxyl groups.\nTo elucidate the thermal evolution of this hierarchical hydrogen-bonding network at the molecular\nlevel, temperature-dependent FT-IR spectra of the PEM gel were recorded from 30 to 150 °C.\ncm-1 indicates the progressive dissociation of hydrogen bond aggregates into free carboxyl groups.\nTwo-dimensional correlation spectroscopy (2DCOS) provided higher resolution of these sequential\nevents. While synchronous spectra (Fig. 2e) indicate cooperative spectral changes across the broad\n2700–3600 cm-1 range, the asynchronous spectra (Fig. 2f) distinguish sequential thermal events: the\nspectral response of hydrogen bond O–H groups (~3297 cm-1) precede that of the weakly associated\nor free O–H groups (~3596 cm-1), corroborating the progressive thermal disruption of the network.\nFurther insight is provided by the C=O stretching region (1690–1750 cm-1, Fig. S5). The synchronous\nspectra exhibit positive cross-peaks between the band at ~1700 cm-1 (dimeric PMAA–PMAA hydrogen\nbonds) and the band at ~1728–1730 cm-1 (free C=O and PEG–PMAA hydrogen bonds), indicating\nconcurrent intensity variations during heating. According to Noda’s rule, the positive synchronous and\npositive asynchronous correlations at (1700, 1728 cm-1) reveals the specific reaction sequence: the\ndestabilization of hydrogen-bonding PMAA–PMAA carbonyls initiates first, followed by the\nsubsequent development of free or PEG–PMAA carbonyls.”\n5. It remains uncertain whether the observed endothermic transitions are reversible. Please include\ncyclic DSC results to confirm the reversibility of hydrogen-bond dissociation and reassociation during\nheating–cooling cycles. This would provide stronger evidence for the proposed thermal buffering\nmechanism.\nResponse: We thank the reviewer for this valuable suggestion. In response, we have conducted cyclic\n10\ndifferential scanning calorimetry (DSC) measurements to explicitly evaluate the thermal reversibility\nof the endothermic transition, using the PE M gel as a representative example (Fig. S28).\n600 4\nDuring the heating scan, a pronounced endothermic transition is observed, whereas no\ncorresponding exothermic peak appears upon cooling. This result indicates that the thermal process is\nnot fully reversible under the applied heating–cooling conditions. Such behavior is consistent with the\nintrinsic characteristics of the hierarchical hydrogen-bonding network in the gel. Specifically, the\nendothermic peak originates from the disruption of hierarchical hydrogen-bonding coupled with chain\nrearrangement. Once them are thermally dissociated, their reformation during cooling is kinetically\nhindered. Although hydrogen bonds can reform, the slow relaxation dynamics and chain-entanglement\nconstraints prevent recovery of the original organization, resulting in the absence of a distinct\nexothermic peak. The updated results are now presented in Fig. S28, with the corresponding discussion\nrevised on page 14 of the manuscript.\nFig. S28. Cyclic DSC curve of the PE M gel between -30 to 150℃. The heating scan shows a clear endothermic\n600 4\npeak, whereas no corresponding exothermic peak appears upon cooling. This behavior reflects the intrinsic nature of the hierarchical hydrogen-bonding network: the endothermic\n11\npeak originates from the disruption of hierarchical hydrogen-bonding coupled with chain\nrearrangement. Once them are thermally dissociated, their reformation during cooling is kinetically\nhindered. Although hydrogen bonds can reform, the slow relaxation dynamics and chain-entanglement\nconstraints prevent recovery of the original organization, resulting in the absence of a distinct\nexothermic peak.”\n6. The demonstration of the “M-glass” system is interesting, yet its long-term stability under realistic\nconditions (humidity, UV exposure, and thermal cycling) has not been discussed. Such data—or at\nleast an informed discussion—are essential to evaluate its suitability for real-world glazing\napplications.\nResponse: We appreciate the reviewer’s important comment regarding the long-term stability of the\nM-glass system under realistic service conditions. In response, we have expanded the discussion and\nincluded representative environmental stability tests designed to simulate real-world environmental in\npractical applications.\nSpecifically, the M-glass was subjected to UV irradiation to simulate solar exposure, cyclic heating\nto mimic high-temperature condition, and water rinsing to emulate rainfall. Following these treatments,\nthe M-glass consistently retained high optical transparency (Fig. S37), effective heat-absorption\ncapability, and sound-insulation performance (Fig. S38 and Movie S7), as well as robust impact\nresistance (Fig. S39 and Movie S8). These results indicate that the M-glass exhibits good\nenvironmental tolerance and functional stability against representative UV, thermal, and humidity,\nsupporting its suitability for real-world in practical applications. The updated results are now presented\nin Fig. S37-39, and Movie S7, S8 with the corresponding discussion revised on page 18 of the\nmanuscript.\nPage 18: “To demonstrate the practical applicability of M-glass, we subjected it to representative\nenvironmental stressors: UV irradiation to simulate solar exposure, cyclic heating to mimic high-\ntemperature condition, and water rinsing to emulate rainfall. Under all conditions, the M-glass\nconsistently maintained high optical transparency (Fig. S37), effective heat-absorption, sound-\ninsulation capability (Fig. S38 and Movie S7), and robust impact resistance (Fig. S39 and Movie S8),\ndemonstrating excellent stability and functional reliability under realistic environmental scenarios.”\nfor 2 h and cooled to room temperature), and rinsed under running water to mimic UV exposure, high-temperature\ncondition, and rain condition, respectively. Thermal infrared images and photographs of all M-glass exposure to a\nxenon lamp. Scale bar: 2 cm.\nFig. S38. a-c. Experimental setup for sound measurement under UV, heat, and rain condition, respectively. Scale bar:\n4 cm. d. Loudness variation of the blank group, original M-glass room, M-glass room under UV condition, heat\ncondition, and rain condition.\nFig. S39. Photographs showing the M-glass under UV condition, heat condition, and rain condition after the impact\nof a 100 g steel ball dropped from a height of 30 cm. Scale bar: 2 cm.\n13\n7. For the falling-ball tests and glass-room drop tests, please add: replicates, error bars, and statistical\ntreatment of impact force reductions.\nResponse: We thank the reviewer for this constructive suggestion. In response, we have incorporated\nthe corresponding replicates, error bars, and statistical analyses for both the falling-ball and glass-room\ndrop tests. Each measurement was performed in triplicate (n = 3), and the data are presented as mean\n± standard deviation (SD). The updated results are now presented in Fig. 4e and Fig. S29.\nFig. 4e. Summary of impact force reduction rates for steel balls of different weights dropped from a fixed height of\n50 cm. Data are presented as the mean values ± SD, n = 3 independent samples. Source data are provided as a Source\nData file.\nFig. S29. Force profiles during falling-ball impacts and the reduction of impact forces by PE M gel coatings\nx y\nwith steel balls of different weights. Data are presented as the mean values ± SD, n = 3 independent samples. Source\ndata are provided as a Source Data file.\n14\n8. Common glass interlayers include PVB and EVA. Please provide matched-thickness benchmarking against these\ncommercial materials to contextualize performance. Clarify failure modes of the composite glass (glass cracking patterns,\ngel deformation) using high-speed images or post-impact observations.\nResponse: We thank the reviewer for the valuable suggestions. We acknowledge that PVB and EVA\nare widely used in glass interlayers; however, their performance and optical transparency are\nintrinsically coupled to specific processing routes.\nConventional PVB interlayers rely on prefabricated thermoplastic films followed by high-\ntemperature, high-pressure autoclave processing. This process is essential to induce viscous flow,\neliminate trapped air, ensure intimate interfacial contact, and suppress light scattering. Without such\nthermal–pressure treatment, PVB-laminated glass typically exhibits insufficient optical transmittance.\nEVA interlayers, while not requiring autoclave pressure, similarly depend on elevated-temperature\nlamination and irreversible thermal crosslinking of preformed films to achieve optical clarity and\nmechanical integrity. In the absence of adequate thermal curing, residual crystallinity and phase\ninhomogeneity in EVA lead to significant light scattering, preventing glass-grade transparency.\nIn contrast, the interlayer reported in this work is fabricated through direct injection of a low-\nviscosity liquid precursor between glass substrates, followed by in situ polymerization. This process\nenables complete wetting of the glass surfaces and intrinsic optical homogeneity from the outset,\nwithout the need for prefabricated films, high-temperature autoclaves, or post-lamination thermal\ncuring.\nOwing to this fundamentally different processing paradigm and optical formation mechanism,\ndirect matched-thickness benchmarking against PVB or EVA films—which inherently require thermal\nlamination to become optically functional—is not pursued. Instead, we emphasize that the proposed\ngel-based interlayer represents a distinct and complementary strategy for laminated glass fabrication,\nprioritizing manufacturing simplicity, optical reliability, interfacial adaptability, and processing\nflexibility (Table S2).\nRegarding failure modes, we have now included high-speed impact imaging (Fig. S36 and Movie\nS6). Upon impact by a falling ball, the bare glass fractured immediately, whereas the glass protected\nby the PE M gel remained fully intact, with no detectable damage to either component. So, the\n600 4\nfracture of M-glass originates from stress concentration at its outer layer upon impact. In contrast, the\n15\nexcellent damping capability of the gel effectively dissipates the impact energy, preventing its\ntransmission to the inner glass layer and thereby maintaining the structural integrity of the entire M-\nglass. The updated results are now presented in Fig. S36, Table S2, and Movie S6, with the\ncorresponding discussion revised on page 18-19 of the manuscript.\nSupplementary Table 2. Comparison between the proposed in situ gel interlayer and conventional\ncommercial glass interlayers.\nParameter PVB EVA This work\nInterlayer form Polymer film Polymer film Liquid precursor\nFilm stacking + Film stacking + Direct injection + UV\nConstruction method\nautoclave thermal curing polymerization\nProcessing High Heating treatment\nRoom temperature\ntemperature (typically >120 °C) (thermal crosslinking)\nHigh (autoclave\nProcessing pressure Low or none None\nrequired)\nAchieved after\nAchieved after thermal Intrinsic from in situ\nOptical transparency thermal–pressure\ncuring polymerization\ntreatment\nGood (liquid wetting\nLimited (solid–solid\nInterfacial adaptability Limited and in suit\ncontact)\npolymerization)\nManufacturing\nHigh Moderate Low\ncomplexity\nEquipment\nAutoclave Heated laminator Ultraviolet lamp\nrequirement\nPE M gel remained fully intact, with no detectable damage to either component. So, the fracture of M-glass\n600 4\noriginates from stress concentration at its outer layer upon impact. In contrast, the excellent damping capability of\nthe gel effectively dissipates the impact energy, preventing its transmission to the inner glass layer and thereby\nmaintaining the structural integrity of the entire M-glass.\nPage 18: “Finally, impact resistance was tested by dropping a 100 g ball from a height of 30 cm onto\nthe glass rooms. As shown in Fig. 5i and Movie S5, N-glass shattered completely upon impact, whereas\nM-\nglass sustained only minor localized damage, confirming its protective function. High-speed\nimaging shows the PE M gel protects glass from impact by dissipating stress at the outer layer,\n600 4\npreserving the glass’s structural integrity. (Fig. S36 and Movie S6).”\nPage 19: “Conventional PVB and EVA interlayers often requiring high-pressure autoclaves or\nirreversible thermal crosslinking to achieve optical transparency; without such treatment, trapped air,\ncrystallinity, or phase inhomogeneity causes light scattering. Instead, we emphasize that the proposed\ngel-based interlayer represents a distinct and complementary strategy for laminated glass fabrication,\nprioritizing manufacturing simplicity, optical reliability, interfacial adaptability, and processing\nflexibility (Table S2).”\nThis manuscript presents a PEG oligomer-based gel with functionalities in thermal regulation, sound\nattenuation, and mechanical protection. While the reported properties are interesting, the core concept\n— polymer oligomer solvent-based gels — is not novel. PEG-based “PEGgels” and related systems\nhave been extensively studied in recent years, with detailed mechanistic, mechanical, and functional\nanalyses already published (e.g., Nat. Commun. 2021, 12, 3610; Adv. Mater. 2022, 34, 2107791; Sci.\nAdv. 2025, 11, eadv5292). These works already have covered thermal stability, tunable mechanics,\nself-healing, energy dissipation, and protective applications. The authors highlight thermal regulation\nand glass interlayer application as new angles, but the overall novelty of this work requires further\nclarification based on the previous work. In other words, the use of PEG oligomers as solvent/structural\ncomponents in gels is well-established. The manuscript does not convincingly demonstrate how this\nsystem advances beyond existing PEGgel literature, particularly in terms of mechanism or application\nscope. Therefore, I don’t think the manuscript in current form is ready for publication in Nat. Commun..\nResponse: We thank the reviewer for pointing out these important prior studies. We agree that using\npolymer/oligomer fluids as the liquid phase of gels has been explored and has produced valuable\ninsights and functionalities, including PEG-based gels and polymer-fluid-gel damping concepts.\nHowever, we emphasize that our manuscript advances beyond this literature in (i) molecular design\nstrategy, (ii) mechanistic signature of dissipation, and (iii) application integration.\n(i) Molecular design strategy (how hierarchy is generated).\nThe reported PEGgel work (Adv. Mater. 2022, 34, 2107791) uses a P(HEMA-co-AAc) matrix and\nhighlights multivalent solvent-mediated interactions (notably abundant weak C–H···O hydrogen\nbonding) to enable toughness, self-healing, and printability. In contrast, our system is built on a PMAA\nbackbone that intrinsically forms strong carboxylic-acid assemblies (dimers/aggregates) and then uses\nPEG-200 to introduce additional weaker/medium-strength H-bonding states. This creates a single-\ninteraction-family hierarchy (hydrogen bonding) with a broadened strength distribution, rather than\nrelying on comonomer-enabled network chemistry. In our manuscript, we further show that PMAA is\nessential for gelation in PEG, whereas replacing MAA with AAc prevents gelation (PEG/PAAc)\n(Figure S2), underscoring the distinct molecular requirement of the PMAA platform.\ncontaining precursor solution. This because the alpha-methyl substituent increases hydrophobicity\nand stabilizes strong carboxyl to carboxyl associations1,2. However, PAAc lacks the alpha-methyl\ngroup, prevents gelation in the PEA system, consistent with the loss of the strong-bond tier in the\nabsence of robust self-association among carboxyl groups. Scale bar: 2 cm.\n(ii) Mechanistic signature (what produces broadband damping).\nThe polymer-fluid-gel framework in Nat. Commun. 2021, 12, 3610 achieves controllable\ndissipation by tuning the reptation/relaxation time of confined polymer fluids, with relaxation time\nscaling with the molecular weight of the polymer fluid (reptation model) and producing frequency-\ndependent peaks that can be shifted by design. Our work targets a fundamentally different regime: we\naim for nearly frequency-independent damping (tan δ ≈ 1 across many decades via TTS) arising from\na continuous spectrum of reversible hydrogen-bond association/dissociation events. We support this\nhierarchical H-bond mechanism using spectroscopic deconvolution/sequence analysis and MD results\nthat quantify hydrogen-bond numbers, bond lengths, and binding energies for PMAA–PMAA versus\nPMAA–PEG interactions.\n(iii) Application scope (integrated laminated-glass interlayer vs. single-function\nprotection/damping).\nRecent APFG work (Sci. Adv. 2025, 11, eadv5292) achieves broad-temperature damping and\nimpact protection using PEG-based polymer-fluid gels combined with Fe³⁺-diffusion surface ionic\ncrosslinking to form an armor-core structure. Our manuscript instead demonstrates a transparent,\nadhesive, self-healable interlayer whose multifunctionality is intrinsically coupled to reversible\nhydrogen bonding: (1) viscoelastic damping, (2) impact energy absorption, and importantly (3) thermal\nbuffering via endothermic H-bond dissociation, integrated into a laminated glass prototype. This\n“multifunction-in-one-interlayer” building-glazing scenario is not addressed in the cited studies, which\nprimarily focus on toughness/printability or damping-protection under wide temperatures via armor-\n19\ncore/ionic strengthening.\nTo make these distinctions explicit, we have revised the manuscript to position our work relative\nto PEGgel and polymer-fluid-gel literature, emphasizing that our key advance is oligomeric-solvent\nengineering of a PMAA-specific hierarchical hydrogen-bond landscape that enables simultaneous\noptical clarity + broadband damping + thermal buffering + interlayer adhesion in a single material\nsystem. The updated introduction revised on page 3 of the manuscript.\nPage 3: “Motivated by the inherent limitations of conventional small-molecule solvents, recent efforts\nhave increasingly turned to polymeric liquids as alternative gel solvents. Liu et al.21 introduced poly\n(n-butyl acrylate) (PBA) fluid into polymer networks, achieving efficient energy dissipation over a\nbroad frequency range. Wang et al.22-24 first established PEG as a polymeric solvent platform for gel\nsystems, demonstrating that PEG-based gels can simultaneously exhibit high mechanical strength,\nself-healing capability, energy dissipation, and 3D printability. Although these studies highlight the\nversatility of polymeric solvents, their design targets and underlying mechanisms differ from those of\nthe present work. In PEG gels based on P(HEMA-co-AAc)23, enhanced toughness and self-healing\nprimarily originate from solvent-enabled multivalent interactions and increased chain correlations or\nentanglements. In contrast, polymer-fluid-based damping gels21 achieve tunable dissipation by\nregulating the relaxation (reptation) dynamics of confined polymer liquids, leading to molecular-\nweight-dependent and frequency-shiftable dissipation peaks.\nHere, we pursue a distinct molecular design strategy: we select PMAA, whose carboxylic groups\nintrinsically form strong associative assemblies25 (bulk copolymerization of MAA yields glassy, brittle\nPMAA, Fig. 1a), and employ PEG-200 as an oligomeric solvent that introduces additional\nweaker/medium-strength hydrogen-bonding states, thereby broadening the bond-strength distribution\nwithin a single interaction family (hydrogen bonding). First, owing to its oligomeric nature, PEG has\nfar greater contour length than small-molecule solvents and more effectively separate adjacent PMAA\nchains, thereby increasing interchain spacing and free volume26,27. Second, the ether oxygen on PEG\nbear lone pairs and serve as hydrogen-bonding acceptors, forming multiple bidentate (medium-\nstrength) and monodentate (weak) interactions with the carboxylic groups of PMAA28. In parallel, a\nfraction of PMAA carboxyl groups associate with each other from cyclic dimers to linear\naggregates25,29, supplying the strong-bond tier of the hierarchy. (Fig. 1b). Notably, both PEG and\nPMAA are indispensable for building this hierarchical hydrogen-bonding network. Substituting PEG\n20\nwith H\nwith polyacrylic acid (PAAc) suppresses gelation in the PEG/PAAc (PEA) system (Fig. S2). This\narchitecture achieves finely balance elasticity and viscosity30,31, enabling a gel-like response across an\nultra-wide frequency range (Fig. 1c). The elastic component provides high mechanical strength, while\nthe viscous component delivers high damping, with a loss factor (tan δ) approaching 1. This\ncombination confers both noise reduction and impact energy absorption. Simultaneously, the thermally\nresponsive interactions of the PEG/PMAA system enhance thermal regulation. To demonstrate\npractical utility, we integrated the gel into a laminated-glass prototype and systematically evaluated\nits multifunctionality (Fig. 1d). The resulting composite exhibits combination of optical clarity, thermal\nbuffering, acoustic damping, and mechanical robustness. Rather than optimizing isolated properties,\nthis system achieves integrated performance, opening avenues for functional materials in architectural\nglazing, protective interfaces, and energy-responsive systems.”\n21\n1. The comparison to starfish stiffness modulation is misleading. Starfish employ complex, reversible,\nbiologically regulated systems (blood pressure, peptides); the PEM gel simply softens via PEG\nplasticization — a fundamentally different and far less sophisticated mechanism.\nResponse: We thank the reviewer for this insightful comment and fully agree with the concern raised.\nStiffness regulation in starfish relies on complex, reversible, and biologically regulated mechanisms\nthat are not directly comparable to the physicochemical behavior of our synthetic system. Accordingly,\nall biomimetic references to starfish have been removed. The revised manuscript now focuses\nexclusively on the role of PEG oligomers as molecular bridges that separate polymer chains and\nconstruct a hierarchical hydrogen-bonding network, thereby eliminating any potentially misleading\nbiological analogy.\n2. Page 12, Line 261. The explanations about elasticity and viscosity (consistent damping factor) across\nbroad temperatures lack scientific theories or experiment support, authors can refer to some previous\nwork (e.g. Nat. Commun. 2021, 12(1), 3610).\nResponse: We thank the reviewer for this insightful comment. We agree that a clearer theoretical\nframework is necessary to rationalize the observed quasi-constant damping behavior over broad\nfrequency and temperature ranges.\nof hierarchical relaxation mechanisms, analogous in principle to polymer-fluid-gel systems reported\npreviously (e.g., Nat. Commun. 2021, 12, 3610), while emphasizing the fundamental differences in\nphysical origin.\nIn our PEG/PMAA system, the balanced viscoelastic response does not arise from confined\npolymer fluid reptation, but from a hierarchical hydrogen-bonding network that introduces multiple,\noverlapping relaxation modes. Specifically, strong PMAA–PMAA hydrogen bonds provide long-lived\nelastic constraints, medium-strength PMAA–PEG interactions contribute intermediate relaxation, and\nweak hydrogen bonds together with chain entanglements enable fast energy dissipation. The\ncoexistence and continuous exchange among these relaxation processes lead to comparable storage\nand loss moduli across a wide frequency window, resulting in a loss factor fluctuating around unity.\nThis interpretation is experimentally supported by:\n(i) Time–temperature superposition master curves showing G′ ≈ G″ over nearly eight orders of\nmagnitude in frequency.\n(ii) Two distinct apparent activation energies extracted from rheological analysis, corresponding to\nbond-dissociation-dominated and entanglement-dominated relaxation regimes.\n(iii) Temperature-dependent FTIR and 2D correlation spectroscopy revealing stepwise dissociation\nof hydrogen bonds with different strengths rather than a single glass-transition-controlled process.\nWe have revised the manuscript to clarify this theoretical connection and to more explicitly link\nour experimental observations to established viscoelastic relaxation principles (Pages S11–S12 and\nFig. S19).\nFig. S19. Internal network state of PE M gels under different shear frequency.\nx y\ntemperature-independent viscoelastic response of PEM gels within the framework of time–\ny\ntemperature equivalence and relaxation-spectrum theory.\nIn viscoelastic polymer networks, the macroscopic balance between elasticity and viscosity is\ngoverned by the superposition of multiple relaxation modes with distinct characteristic times. When\nthese relaxation modes are narrowly distributed, energy dissipation is localized near the glass\ntransition, leading to a sharp peak in tan δ. In contrast, a broad and overlapping relaxation spectrum\ncan give rise to a nearly constant loss factor over extended frequency and temperature ranges.\nIn PEM gels, such a broad relaxation spectrum originates from the hierarchical hydrogen-\ny\nbonding network combined with chain entanglements. At low frequencies (or equivalently high\ntemperatures, Fig. S19a), weak and medium-strength hydrogen bonds dissociate first, increasing chain\nmobility and releasing long network strands. Although the effective density of elastic constraints\ndecreases due to bond dissociation, the liberated chains simultaneously form additional topological\nentanglements. This compensatory mechanism preserves the balance between energy storage and\ndissipation, preventing a transition to purely viscous flow. At intermediate frequencies (Fig. S19b),\npartial rupture of weak hydrogen bonds occurs while strong PMAA–PMAA hydrogen bonds and\nchemical crosslinks remain intact. In this regime, hydrogen-bond dissociation and entanglement\nformation coexist dynamically, establishing a steady-state viscoelastic response in which the\nrelaxation times of different modes overlap. As a result, both G′ and G″ remain comparable in\nmagnitude. At high frequencies (or low temperatures, Fig. S19c), molecular motion is increasingly\nconstrained, suppressing chain reptation and entanglement relaxation. However, the dominance of\nstrong hydrogen bonds and physical crosslinking effectively “freezes” the network on the experimental\ntimescale, sustaining elastic energy storage. Consequently, although individual relaxation processes\nare restricted, the collective contribution of long-lived elastic modes compensates for the reduced\nviscous dissipation.\nOverall, the hierarchical hydrogen-bond architecture generates a continuous distribution of\nrelaxation times spanning bond dissociation, chain sliding, and entanglement relaxation. The\nsuperposition of these modes underlies the observed G′ ≈ G″ and tan δ ≈ 1 behavior across an ultra-\nwide frequency and temperature window, analogous in principle to multi-relaxation damping systems,\nyet achieved here through dynamic supramolecular interactions rather than confined polymer fluids.”\n3. Figure 3h. Typically, to evaluate the damping capacity of materials at varied tensile strains, the\ntensile tests are performed at separated strain cycles instead of consecutive cycles.\nResponse: We thank the reviewer for this helpful comment. In accordance with the reviewer’s\nrecommendation, the damping capacities previously derived from consecutive cyclic tensile tests have\nbeen removed. Independent single-cycle tensile tests were instead conducted at each fixed strain, and\nthe damping capacity was recalculated for each individual strain.\nIn addition, large-amplitude oscillatory shear (LAOS) measurements were conducted to further\nevaluate the energy dissipation behavior of the PEM gels (Fig. S24). All samples exhibit stable,\ny\nelliptical stress–strain Lissajous loops over 100 cycles, indicating a linear viscoelastic response under\nthe applied conditions. The enclosed loop area, corresponding to the dissipated energy per cycle (ΔW),\nshows only a slight decrease during repeated cycling, suggesting that the reversible hydrogen bonds\nundergo repeated dissociation and reformation without causing permanent structural damage.\nMoreover, ΔW systematically increases with increasing MAA content, demonstrating that a higher\ndensity of hydrogen-bonding interactions leads to enhanced energy dissipation. The updated results\nare now presented in Fig. 3g, Fig. 3h, Fig. S23, and Fig. S24 with the corresponding discussion\nrevised on page 13 of the manuscript.\nFig. 3. Mechanical properties and viscoelastic behavior of PEM gels. g. Tensile load-unload cycle curves of the\ny\nPEM gel at different fixed strain. h. Summary of energy dissipation values and damping capacity of the PEM gel\n2 2\nwith different tensile strains. i. Summary of energy dissipation values and damping capacity of all PEM gel at strain\ny\nof 1mm/mm. Data are presented as the mean values ± SD, n = 3 independent samples. Source data are provided as a\nSource Data file.\ny\ndissipation values and damping capacity of PEM gel samples with different tensile load-unload cycle. Data are\ny\npresented as the mean values ± SD, n = 3 independent samples. Source data are provided as a Source Data file.\nFig. S24. Large amplitude oscillatory shear (LAOS) tests of the PEM gels. The hysteresis loops are elliptical,\ny\nindicating all gel are located in the linear viscoelastic region with 10% strain4,5. The hysteresis loop area represents\nmechanical energy converted to heat during each cycle and the area decreases only slightly after 100 cycles.\nPage 13: “As an intuitive manifestation of the damping capability, energy dissipation serves as a key\ncriterion for evaluating the damping performance of materials. In tensile loading–unloading cycles,\nthe hysteresis loops enlarge with strain (Fig. 3g and S23a-c). The damping capacity, defined as the\nratio of dissipated energy to total strain energy, decreases with increasing strain (Fig. 3h and S23d-\ne). There are two factors contributing to this result. First, at small strain, the polymer chains remain\ncoiled, enabling substantial internal friction and interchain sliding, which leads to pronounced energy\ndissipation and high damping capacity. With increasing strain, chains gradually elongate and orient,\nreducing available sliding space and thereby lowering frictional dissipation. Second, at small strain,\nthe dynamic and reversible crosslinks within the gel can continuously break and reform, contributing\nsignificantly to energy dissipation. With increasing strain, many of these weak interactions are rapidly\nruptured and cannot readily reform, thereby diminishing the dissipation capacity. Meanwhile, the\nnetwork is increasingly supported by the polymer backbone and strong crosslinks, causing the gel\nnetwork to exhibit more \"elasticity\". Notably, we observed at same strain, the damping capacity\nincreases with MAA content (Fig. 3i), underscoring the key role of hydrogen bond density in enhancing\nenergy dissipation.\nConsistent with tensile observations, large-amplitude oscillatory shear (LAOS) tests further\ndemonstrate the dissipation capability of the PEM gels (Fig. S24). All gels exhibit stable elliptical\ny\nLissajous loops over 100 cycles, evidencing stable linear viscoelastic behavior49. The loop area,\ncorresponding to the dissipated energy per cycle (ΔW), decreases only slightly during cycling,\nconfirming that the reversible hydrogen bonds repeatedly break and reform without structural damage.\nMoreover, ΔW increases with MAA content, demonstrating higher density of hydrogen-bonding\nenhances energy dissipation.”\n4. The explanations on the spectroscopy should be more comprehensive. How is the formation of H-\nbonds between PEG and MAA resulting in the blueshift? What about the corresponding shift for PEG.\nResponse: We thank the reviewer for this constructive comment. We have expanded the FT-IR\nspectroscopy discussion to clarify the origin of the observed peak shifts and to provide a more\ncomprehensive interpretation of the hydrogen-bonding interactions between PEG and MAA.\nFurthermore, we have incorporated systematic FT-IR analysis combined with temperature-dependent\ntwo-dimensional infrared (2D-IR) spectroscopy to directly elucidate the hierarchical hydrogen-\nbonding network in the gel.\nThe blue shift observed for the C=O stretching vibration of MAA originates from the\ntransformation of hydrogen-bonding environments upon PEG incorporation. In neat MAA, C=O\n26\npredominantly form cyclic, symmetrical PMAA–PMAA dimers through strong O–H···O=C···H–O\nhydrogen bonds. These strong dimeric interactions significantly withdraw electron density from the\nC=O, weaken the C=O bond, and consequently shift the stretching vibration to lower wavenumbers\n(typically around ~1700 cm-1, Fig. S3a).\nUpon the introduction of PEG, part of PMAA–PMAA dimers is disrupted and replaced by PEG–\nPMAA hydrogen bonds, in which the ether oxygen of PEG serves as the hydrogen-bond acceptor and\nthe MAA hydroxyl group as the donor. Compared with the highly ordered PMAA–PMAA dimers,\nPEG–PMAA hydrogen bonds are weaker and less symmetric. So, the electron-withdrawing effect on\nthe carbonyl group is reduced, leading to an increase in C=O bond strength and a corresponding shift\nof the stretching vibration toward higher wavenumbers. This manifests as the emergence of an\nadditional blue-shifted peak near ~1728 cm-1(Fig. S3b-e). Furthermore, quantitative peak-area ratio\nanalysis demonstrates that the relative fraction of strongly hydrogen-bonded carbonyl groups increases\nmonotonically with increasing MAA content (Fig. S3f), providing direct evidence for the composition-\ndependent hierarchy of hydrogen-bond interactions within the gel.\nCorrespondingly, changes are also observed in the PEG vibrational signatures. The C–O–C\nstretching band of PEG (1000–1100 cm-1) undergoes pronounced broadening and becomes\nincreasingly asymmetric with increasing MAA content, accompanied by the appearance of a shoulder\nat lower wavenumbers (Fig. S4). Rather than exhibiting a distinct peak shift, this behavior reflects the\ncoexistence of free and hydrogen-bonded ether oxygen environments. The shoulder at lower\nwavenumbers is attributed to PEG ether oxygens engaged in hydrogen bonding with PMAA hydroxyl\ngroups, while the main band corresponds to non-interacting or weakly interacting ether oxygens. This\nspectral evolution signifies the coexistence of free ether oxygens and hydrogen-bonded ether oxygens,\nconfirming the formation of PEG–PMAA hydrogen bonds and further supporting the heterogeneous\nhydrogen-bonding environment.\nThen, the thermal evolution of the hierarchical hydrogen-bond network was directly probed by\ntemperature-dependent FT-IR and 2D correlation infrared spectroscopy. FT-IR spectra of the PEM\n2\ngel were collected during heating from 30 to 150 °C. In the O–H stretching region of PMAA (Fig. 2d),\na gradual blue shift from ~3500 to ~3515 cm-1 is observed, indicating progressive dissociation of\nhydrogen-bonding aggregates into weaker associated or free carboxyl groups.\nTo resolve the sequential nature of these thermal events, two-dimensional correlation spectroscopy\n(2DCOS) was employed. The synchronous spectrum (Fig. 2e) reveals cooperative spectral changes\nacross the broad 2700–3600 cm-1 region, confirming the collective response of hydrogen-bonded\nspecies to thermal perturbation. More critically, the asynchronous spectrum (Fig. 2f) distinguishes the\norder of molecular events: the response of strongly hydrogen-bonded O–H groups (~3297 cm-1)\nprecede that of weakly associated or free O–H groups (~3596 cm-1), directly evidencing stepwise\nthermal dissociation of hydrogen bonds with different strengths.\nAdditional mechanistic insight is obtained from the carbonyl stretching region (1690–1750 cm-1,\nFig. S5). The synchronous 2D-IR spectrum shows positive cross-peaks between the ~1700 cm-1 band\n(dimeric PMAA–PMAA hydrogen bonds) and the ~1728–1730 cm-1 band (free or PEG–PMAA-\nassociated carbonyls), indicating correlated intensity changes upon heating. According to Noda’s rule,\nthe presence of both positive synchronous and positive asynchronous cross-peaks at (1700, 1728 cm-\n1) establishes a well-defined sequence: the disruption of strong PMAA–PMAA hydrogen bonds occurs\nfirst, followed by the emergence of weaker or free carbonyl species. This spectroscopic evidence\nunambiguously confirms the hierarchical and discontinuous nature of the hydrogen-bond network.\nCollectively, these results provide direct experimental validation of the proposed multi-tiered\nhydrogen-bonding mechanism, thereby substantially strengthening the mechanistic foundation of the\nmanuscript. The updated results are now presented in Fig. 2d-f, Fig. S3-S5, with the corresponding\ndiscussion revised on page 7 of the manuscript.\nFig. 2. Characterizations and simulations revealing hierarchical hydrogen-bonding in PEM gels. d.\ny\nTemperature-dependent FTIR spectra of PEM gel upon heating from 30 to 150 oC (10 oC intervals). e, f. Synchronous\n2\nand asynchronous 2DCOS spectra of the PEM gel. Red regions indicate positive intensities, while blue regions\n2\nrepresent negative ones.\nPEM gel, y= 1.8, 2, 2.2, and 2.4. f. Corresponding area fractions of the fitted carbonyl peak.\ny\nFigure S4. Enlarged FT-IR spectra in the C–O–C stretching region (1000–1100 cm-1) of neat PEG and PEM gels.\ny\nFig. S5. Synchronous and asynchronous 2DCOS spectra of the PEM gel. Red regions indicate positive\n2\nintensities, while blue regions represent negative ones.\nand interaction mechanism within the PEM gels (Fig. 2c). For neat PEG, absorption peaks at 2876\ny\ncm-1 and 2930 cm-1 correspond to symmetrical and asymmetric stretching of –CH groups, while the\n2\npeak at 1059 cm-1 is assigned to C–O–C stretching33,34. For neat MAA, the characteristic C=O\nstretching vibration appears near 1700 cm-1. These characteristic peaks are present in all PEM gel\ny\nsamples, confirming the successful incorporation of both components.\nTo clarify the hierarchical nature of the hydrogen-bonding network, peak deconvolution was\nperformed on the C=O vibration FT-IR spectra. Neat MAA exhibits a prominent carbonyl peak at 1700\ncm-1 (Fig. S3a), characteristic of strong dimeric hydrogen bonds. Upon PEG incorporation, an\nadditional blue-shifted peak emerges near 1728 cm-1 (Fig. S3b-e). This shift arises from the disruption\nof partial strong PMAA–PMAA dimers and the formation of weaker PEG–PMAA hydrogen bonds,\nwhich diminish the electron-withdrawing environment of the carbonyl group35. Peak-area ratio\nanalysis further reveals that the fraction of strongly hydrogen-bonding carbonyl groups increases with\nincreasing MAA content (Fig. S3f), underscoring the compositional dependence of hydrogen-bonding\ninteractions within the gel network. Concomitantly, the C–O–C stretching of PEG (1000–1100 cm-1)\nundergoes pronounced broadening and becomes increasingly asymmetric with rising MAA content,\naccompanied by the appearance of a shoulder at lower wavenumbers (Fig. S4)36,37. This feature\nsignifies the coexistence of free ether oxygen and hydrogen-bonding ether oxygen, reflecting hydrogen\nbond interaction between PEG ether oxygens and PMAA hydroxyl groups.\nTo elucidate the thermal evolution of this hierarchical hydrogen-bonding network at the molecular\nlevel, temperature-dependent FT-IR spectra of the PEM gel were recorded from 30 to 150 °C.\ncm-1 indicates the progressive dissociation of hydrogen bond aggregates into free carboxyl groups.\nTwo-dimensional correlation spectroscopy (2DCOS) provided higher resolution of these sequential\nevents. While synchronous spectra (Fig. 2e) indicate cooperative spectral changes across the broad\n2700–3600 cm-1 range, the asynchronous spectra (Fig. 2f) distinguish sequential thermal events: the\nspectral response of hydrogen bond O–H groups (~3297 cm-1) precede that of the weakly associated\nor free O–H groups (~3596 cm-1), corroborating the progressive thermal disruption of the network.\nFurther insight is provided by the C=O stretching region (1690–1750 cm-1, Fig. S5). The\nsynchronous spectra exhibit positive cross-peaks between the band at ~1700 cm-1 (dimeric PMAA–\nbonds), indicating concurrent intensity variations during heating. According to Noda’s rule, the\npositive synchronous and positive asynchronous correlations at (1700, 1728 cm-1) reveals the specific\nreaction sequence: the destabilization of hydrogen-bonding PMAA–PMAA carbonyls initiates first,\nfollowed by the subsequent development of free or PEG–PMAA carbonyls.”\n5. The manuscript introduces asymmetric adhesion without explaining its functional purpose, to me it\nappears to offer only drawbacks.\nResponse: We thank the reviewer for this thoughtful comment. We clarify that the asymmetric\nadhesion observed in the preliminary samples is not an intended functional feature, but rather an\nartifact arising from the specific polymerization conditions employed during early-stage\ncharacterization. In these samples, one surface of the gel was in contact with PTFE, while the opposite\nsurface was exposed to air, resulting in distinct interfacial environments and consequently asymmetric\nsurface adhesion.\nImportantly, this asymmetric adhesion is not relevant to the intended application of the material.\nFor practical use as a glass interlayer, the precursor solution is injected directly between two glass\nsubstrates and polymerized in situ. Under these conditions, both interfaces are formed under identical\nenvironments, leading to symmetric and significantly enhanced adhesion. As demonstrated in Movie\nS3, the in situ–polymerized gel adheres so strongly on the glass surfaces that cannot be separated\nwithout damage. A circular gel (diameter = 2 cm, thickness = 1 mm) was polymerized in situ between\ntwo glass substrates. Upon application of a 500 g load, no adhesive failure was observed (Fig. 5a).\nRemarkably, the laminated structure was capable of lifting a 2 kg weight. The adhesive joint remained\nfully intact, while fracture occurred in the glass substrate (Movie S3).\nTo enable quantitative evaluation of adhesion properties, we polymerized the precursor solution\nbetween PET release films, ensuring identical interfacial conditions on both sides of the gel. Adhesive\nperformance was quantitatively evaluated using 90° peel and lap-shear tests. Notably, the PE M gel\n600 4\nexhibited strong adhesion across various substrates (Fig. S34), achieving an adhesion strength and\ninterfacial toughness on glass as high as 332 kPa and 676 J m-2, respectively (Fig. 5b). In addition, the\ngel demonstrated strong yet compliant adhesion to human skin (Fig. S35).\nFurthermore, cyclic lap-shear tests conducted within ±5% strain revealed stable dynamic stress\n31\nresponses, with the gel sustaining at least 1000 cycles of shear deformation without interfacial failure\n(Fig. 5c), confirming the robustness and durability of the gel–glass interface. The updated results are\nnow presented in Fig. 5a-c, Fig. S33 and Movie S3, with the corresponding discussion revised on page\n17 of the manuscript.\nFig. 5. Multifunctional laminated glass composite enabled by oligomeric-solvent-containing PMAA gels. a.\nPhotographs showing the interlayer region (circled) remaining intact during lifting of a 50 g weight. Scale bar: 2\ncm. b. Summary of adhesion strength ang interfacial toughness of PE M gel samples on different substrates. b.\n600 4\nLap-shear stress curve during the repeated loading-unloading cycles.\nFig. S33. Adhesion performance of the PE M gel. a. Photographs demonstrating a square PE M gel (1×1 cm2)\n600 4 600 4\nadhered firmly to various substrates. On glass, polyethylene terephthalate (PET), and copper, the adhesion was\nsufficient to readily lift a 200 g weight. Although adhesion on rubber was slightly weaker, it remained effective. Scale\nbar: 4 cm. b. 90° peeling curves of the PE M gel on various substrates. c. Shear adhesion stress-displacement\n600 4\ncurves of the PE M gel on various substrates.\n600 4\nPage 17: “As glass interlayers, strong glass–interlayer adhesion is essential for the long-term integrity\nand multifunctional stability of safety glass. Owing to the abundance of hydroxyl groups, the PE M\nx y\ngel exhibits robust adhesion. When polymerized in situ on glass, the resulting adhesion is too strong\nto separate them. To demonstrate this strong adhesion, a circular gel (diameter = 2 cm, thickness = 1\nmm) was polymerized in situ between two glass substrates. Upon application of a 500 g load, no\nadhesive failure was observed (Fig. 5a and Movie S3). Remarkably, the laminated structure was\n32\ncapable of lifting a 2 kg weight. The adhesive joint remained fully intact, while fracture occurred in\nthe glass substrate. To avoid asymmetric adhesion arising from differences in polymerization\nenvironments at the two interfaces51, PE M gels were polymerized between PET release film.\n600 4\nAdhesive performance was quantitatively evaluated using 90° peel and lap-shear tests, the PE M\n600 4\ngel demonstrated strong adhesion on various substrates (Fig. S33), achieving an adhesion strength\nand interfacial toughness on glass as high as 332 kPa and 676 J m-2 (Fig. 5b), respectively. In addition,\nthe gel also exhibited strong yet compliant adhesion to human skin (Fig. S34). Cyclically shearing of\nthe PE M gel within ±5% strain generated stable dynamic stress responses, the gel could sustain at\n600 4\nleast 1000 cycles of lap-shearing deformations (Fig. 5c).”\n6. Missing figure captions and wrongly assigned figure numbers for figures S8 and after.\nResponse: We sincerely thank the reviewer for the careful examination of the manuscript. We\napologize for the missing figure captions and the incorrect figure numbering starting from Fig. S8. All\ncaptions have now been restored, and the figure numbering has been carefully checked and corrected\nthroughout the revised Supplementary Information.\nReviewer #3:\nThe manuscript by Li et al. reports a polymeric material composed of poly(methacrylic acid) (PMAA)\nswollen in poly(ethylene glycol) (PEG), forming a gel-like network that exhibits properties including\nhigh energy dissipation, acoustic damping, self-healing, adhesiveness, and impact resistance. These\nproperties arise from the interaction between PEG macromolecules and the PMAA network. The\nmaterial and its performance are well characterized, and the authors demonstrate several proof-of-\nconcept applications. Overall, the experimental work is solid and the results are of potential interest.\nHowever, the presentation of prior work is incomplete and somewhat misleading. The concept of using\nPEG as a macromolecular solvent was first introduced by Wang Z. et al. (Adv. Mater. 2022, “Tough,\nTransparent, 3D-Printable, and Self-Healing Poly(ethylene glycol)-Gel (PEGgel)”), where the\nfundamental principles, transparency, self-healing, and exceptional mechanical properties were\nalready demonstrated. Subsequent studies, including Wang M. et al., Nature 2024, have further\nexplored applications and properties of PEG–polymer hybrid materials.\nThe authors should therefore revise the Abstract and Introduction to properly acknowledge this prior\n33\nwork and avoid implying that the present study introduces the concept for the first time (e.g., phrases\nsuch as “our oligomeric-solvent engineering strategy” or “we introduce oligomeric PEG into a PMAA\nnetwork to construct a gel system that addresses key limitations of traditional solvent-based gels” are\nmisleading).\nWith appropriate correction of the contextual framing, this manuscript would represent a valuable\ncontribution to the field highlighting the advantages and further applications of an already established\nconcept.\nResponse: We sincerely thank the reviewer for the careful evaluation of our manuscript and for\npointing out the important prior work on PEG-based macromolecular solvent systems. We fully agree\nthat the concept of using PEG as a macromolecular solvent was first introduced by Wang Z. et al. (Adv.\nMater. 2022, 34, 2107791).\nWe apologize for the inappropriate wording in the original Abstract and Introduction. Following\nthe reviewer’s suggestion, we have revised the Abstract and Introduction to explicitly cite these\npioneering studies and to clearly position our work as building upon and extending the established\nmacromolecular solvent concept, rather than introducing it.\nWe would like to clarify that the novelty of the present work does not lie in introducing PEG as a\nmacromolecular solvent, but rather in the following three aspects:\n(i) Molecular design strategy (how hierarchy is generated).\nThe reported PEGgel work (Adv. Mater. 2022, 34, 2107791) uses a P(HEMA-co-AAc) matrix and\nhighlights multivalent solvent-mediated interactions (notably abundant weak C–H···O hydrogen\nbonding) to enable toughness, self-healing, and printability. In contrast, our system is built on a PMAA\nbackbone that intrinsically forms strong carboxylic-acid assemblies (dimers/aggregates) and then uses\nPEG-200 to introduce additional weaker/medium-strength H-bonding states. This creates a single-\ninteraction-family hierarchy (hydrogen bonding) with a broadened strength distribution, rather than\nrelying on comonomer-enabled network chemistry. In our manuscript, we further show that PMAA is\nessential for gelation in PEG, whereas replacing MAA with AAc prevents gelation (PEG/PAAc)\n(Figure S2), underscoring the distinct molecular requirement of the PMAA platform.\ncontaining precursor solution. This because the alpha-methyl substituent increases hydrophobicity\nand stabilizes strong carboxyl to carboxyl associations1,2. However, PAAc lacks the alpha-methyl\ngroup, prevents gelation in the PEA system, consistent with the loss of the strong-bond tier in the\nabsence of robust self-association among carboxyl groups. Scale bar: 2 cm.\n(ii) Mechanistic signature (what produces broadband damping).\nOur work targets a fundamentally different regime: we aim for nearly frequency-independent\ndamping (tan δ ≈ 1 across many decades via TTS) arising from a continuous spectrum of reversible\nhydrogen-bond association/dissociation events. We support this hierarchical H-bond mechanism using\nspectroscopic deconvolution/sequence analysis and MD results that quantify hydrogen-bond numbers,\nbond lengths, and binding energies for PMAA–PMAA versus PMAA–PEG interactions.\n(iii) Application scope (integrated laminated-glass interlayer vs. single-function\nprotection/damping).\nOur manuscript demonstrates a transparent, adhesive, self-healable interlayer whose\nmultifunctionality is intrinsically coupled to reversible hydrogen bonding: (1) viscoelastic damping,\n(2) impact energy absorption, and importantly (3) thermal buffering via endothermic H-bond\ndissociation, integrated into a laminated glass prototype. This integrated functionality distinguishes the\npresent system from prior PEG-based gels that primarily target single-function mechanical protection\nor damping applications.\nTo make these distinctions explicit, we have revised the Abstract and Introduction. We now\nemphasize that our key advance is oligomeric-solvent engineering of a PMAA-specific hierarchical\nhydrogen-bond landscape that enables simultaneous optical clarity + broadband damping + thermal\nbuffering + interlayer adhesion in a single material system. The updated introduction revised on page\n3 of the manuscript.\nPage 3: “Motivated by the inherent limitations of conventional small-molecule solvents, recent efforts\n35\nhave increasingly turned to polymeric liquids as alternative gel solvents. Liu et al.21 introduced poly\n(n-butyl acrylate) (PBA) fluid into polymer networks, achieving efficient energy dissipation over a\nbroad frequency range. Wang et al.22-24 first established PEG as a polymeric solvent platform for gel\nsystems, demonstrating that PEG-based gels can simultaneously exhibit high mechanical strength,\nself-healing capability, energy dissipation, and 3D printability. Although these studies highlight the\nversatility of polymeric solvents, their design targets and underlying mechanisms differ from those of\nthe present work. In PEG gels based on P(HEMA-co-AAc)23, enhanced toughness and self-healing\nprimarily originate from solvent-enabled multivalent interactions and increased chain correlations or\nentanglements. In contrast, polymer-fluid-based damping gels21 achieve tunable dissipation by\nregulating the relaxation (reptation) dynamics of confined polymer liquids, leading to molecular-\nweight-dependent and frequency-shiftable dissipation peaks.\nHere, we pursue a distinct molecular design strategy: we select PMAA, whose carboxylic groups\nintrinsically form strong associative assemblies25 (bulk copolymerization of MAA yields glassy, brittle\nPMAA, Fig. 1a), and employ PEG-200 as an oligomeric solvent that introduces additional\nweaker/medium-strength hydrogen-bonding states, thereby broadening the bond-strength distribution\nwithin a single interaction family (hydrogen bonding). First, owing to its oligomeric nature, PEG has\nfar greater contour length than small-molecule solvents and more effectively separate adjacent PMAA\nchains, thereby increasing interchain spacing and free volume26,27. Second, the ether oxygen on PEG\nbear lone pairs and serve as hydrogen-bonding acceptors, forming multiple bidentate (medium-\nstrength) and monodentate (weak) interactions with the carboxylic groups of PMAA28. In parallel, a\nfraction of PMAA carboxyl groups associate with each other from cyclic dimers to linear\naggregates25,29, supplying the strong-bond tier of the hierarchy. (Fig. 1b). Notably, both PEG and\nPMAA are indispensable for building this hierarchical hydrogen-bonding network. Substituting PEG\n36\nwith H\nwith polyacrylic acid (PAAc) suppresses gelation in the PEG/PAAc (PEA) system (Fig. S2). This\narchitecture achieves finely balance elasticity and viscosity30,31, enabling a gel-like response across an\nultra-wide frequency range (Fig. 1c). The elastic component provides high mechanical strength, while\nthe viscous component delivers high damping, with a loss factor (tan δ) approaching 1. This\ncombination confers both noise reduction and impact energy absorption. Simultaneously, the thermally\nresponsive interactions of the PEG/PMAA system enhance thermal regulation. To demonstrate\npractical utility, we integrated the gel into a laminated-glass prototype and systematically evaluated\nits multifunctionality (Fig. 1d). The resulting composite exhibits combination of optical clarity, thermal\nbuffering, acoustic damping, and mechanical robustness. Rather than optimizing isolated properties,\nthis system achieves integrated performance, opening avenues for functional materials in architectural\nglazing, protective interfaces, and energy-responsive systems.”\n37"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The revised manuscript is suitalbe for publication.", "reviewer_2": "The authors have thoroughly addressed the reviewers' critiques by significantly enhancing the mechanistic evidence through additional FT-IR, 2D-COS, and MD simulation data, which explicitly validate the hierarchical hydrogen-bonding network. They have also clearly acknowledged relevant prior work and differentiated their work from prior PEG-gel studies by emphasizing the single-interaction-family design and broadened damping performance, supported by new environmental stability tests and quantitative impact analyses. The revisions have strengthened the manuscript's novelty, data completeness, and practical relevance, making it suitable for publication."}, "author_response": "Dear Reviewers,\nThank you very much for reviewing our manuscript entitled “Oligomeric-Solvent Engineering of\nHierarchical Hydrogen-Bond Networks for Multifunctional Glass Interlayers” (Manuscript ID:\nNCOMMS-25-73988A). We sincerely appreciate your time and the constructive comments provided.\nWe are particularly grateful for your careful assessment and constructive feedback throughout the\nreview process, which have been instrumental in improving the rigor, clarity, and overall quality of the\nmanuscript. Your insightful comments have significantly strengthened the presentation and impact of\nour study.\nThank you again for your valuable contributions and support.\nSincerely,\nRong Ran\nOn behalf of all authors\nResponse to the reviewers’ comments\nReviewer #1: The revised manuscript is suitalbe for publication.\nResponse: We sincerely thank reviewer for the careful re-evaluation of our revised manuscript and for\nthe positive assessment. We greatly appreciate your constructive comments throughout the review\nprocess, which have significantly improved the clarity and quality of the work.\nReviewer #2: The authors have thoroughly addressed the reviewers' critiques by significantly\nenhancing the mechanistic evidence through additional FT-IR, 2D-COS, and MD simulation\ndata, which explicitly validate the hierarchical hydrogen-bonding network. They have also\nclearly acknowledged relevant prior work and differentiated their work from prior PEG-gel\nstudies by emphasizing the single-interaction-family design and broadened damping\nperformance, supported by new environmental stability tests and quantitative impact analyses.\nThe revisions have strengthened the manuscript's novelty, data completeness, and practical\nrelevance, making it suitable for publication.\nResponse: We sincerely thank the reviewer for the thorough evaluation and highly encouraging\ncomments. We greatly appreciate your recognition of the additional mechanistic analyses, including\nthe FT-IR, 2D-COS, and MD simulation results, as well as your acknowledgment of our efforts to\nP\nA\nG\nE\nclarify the distinction from prior PEG-gel studies and to strengthen the environmental stability and\nquantitative impact assessments. Your constructive feedback has been invaluable in improving the\nrigor, clarity, and overall quality of the manuscript.\nP\nA\nG\nE"}]

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