Boosting Natural Rubber Performance by Backbone Rigid Functionalization

ABSTRACT

Natural rubber relies on irreversible vulcanization to enhance material performance, but the resulting densely crosslinked networks resist breakdown, rendering conventional physical recycling methods ineffective. Developing backbone‐level functionalization strategies that simultaneously improve performance and enable controlled deconstruction remains a fundamental challenge. Here we develop a backbone rigid functionalization (BRF) strategy to install rigid, polar cyclobutane units directly into natural rubber via catalyst‐free [2+2] photocycloaddition. Incorporation of cyclobutane‐fused succinimide units substantially enhances tensile strength and toughness. Simply varying the reaction time enables continuous tuning of material behavior from viscoelastic polymers to elastomers and plastomers. When combined with vulcanization, the polar‐functionalized natural rubber yields high‐performance thermosets with a five‑fold improvement in stress, Young's modulus and toughness relative to conventional vulcanizates. Notably, the cyclobutane‐fused succinimide units undergo force‐triggered cycloreversion upon bulk ball‐milling, enabling vulcanized rubber with on‐demand hydrolytic degradability. This single‐step BRF process provides a practical pathway for accessing high‐performance rubbers with on‐demand degradability.

A backbone rigid functionalization (BRF) strategy is developed to install rigid, polar cyclobutane units directly into natural rubber via catalyst‐free [2+2] photocycloaddition. Incorporation of cyclobutane‐fused succinimide units substantially enhances tensile strength and toughness. This single‐step BRF process provides a practical pathway for accessing high‐performance rubbers with on‐demand hydrolytic degradability.

1. Introduction

Natural rubber, composed predominantly of cis‐1,4‐polyisoprene, is intrinsically soft, tacky, and thermally sensitive, exhibiting limited elastic recovery and mechanical robustness [1]. Traditionally, these deficiencies are overcome through sulfur‐based vulcanization, which permanently converts linear chains into densely crosslinked networks [2]. The incorporation of sulfur crosslinks, inorganic fillers, and metal additives markedly improves mechanical property, durability, and heat resistance (Figure 1a) [3, 4, 5, 6]. However, postconsumer vulcanized rubbers persist in the environment and are notoriously difficult to recycle or reprocess [7, 8], as cleavage of strong C–S and S–S bonds typically requires harsh conditions and generates hazardous byproducts [9]. These limitations highlight a fundamental dilemma: How to enhance the performance of natural rubber while preserving its ability to be reprocessed or degraded. Addressing this challenge demands molecular‐level strategies that reengineer elastomer backbones beyond conventional irreversible crosslinking to create tunable, deconstructable rubbers [10, 11].

FIGURE 1.

Strategies for natural rubber functionalization. (a) Conventional vulcanization of natural rubber. (b) Polar functionalization of rubber via amination. (c) Concept and challenges of polar functionalization of natural rubber via [2+2] photocycloaddition. (d) BRF of natural rubber.

Introducing polar functionality into non‐polar polymer backbones offers a powerful route to diversify material properties and introduce controlled chemical responses [12, 13, 14, 15]. Beyond irreversible vulcanization, incorporating polar functional groups provides opportunities to enhance the material performance of rubber materials [16, 17, 18, 19, 20, 21]. In this context, controlled amine functionalization of polyolefins has attracted growing interest for improving tensile strength, toughness, adhesion, wettability, and so on [22, 23, 24]. Emerging catalytic methods, such as direct C–H amination and alkene hydroamination, have been applied to modify rubber backbones [25, 26, 27, 28, 29, 30, 31] (Figure 1b). Generally, these approaches install flexible, non‐stereoregular substituents that only modestly perturb chain entanglements, offering limited improvement in mechanical properties. What is needed are robust, backbone‐level polar motifs that both reinforce polymer chain interactions and provide a predictable, stimulus‐responsive route to deconstruction [32].

The [2+2] photocycloaddition is a well‐established and powerful method for constructing cyclobutane rings [33]. Given that natural rubber consists of repeating cis‐alkene units, we envisaged its direct [2+2] photocycloaddition with a polar alkene as a route to introduce polar functional groups (Figure 1c). Beyond imparting polarity, this method simultaneously incorporates rigid cyclobutane units into the polymer backbone. Introducing four‐membered rings into polyolefin repeat units has been demonstrated to restrict bond rotation along the backbone, thereby enhancing thermal and mechanical properties by reducing the conformational freedom (entropy) of polymer chains [34, 35]. To date, only one example has demonstrated the use of UV‐induced Paterno–Büchi [2+2] cycloaddition with aldehydes to introduce oxetane groups into the side chains of an unsaturated styrene–isoprene–styrene copolymer [36]. However, applying [2+2] photocycloaddition to the polar functionalization of unsaturated polymer backbones remains unexplored, primarily due to the tendency of photoirradiation to induce uncontrolled interchain cross‐linking [37, 38]. Therefore, achieving selective [2+2] photocycloaddition with polar olefins while suppressing self‐crosslinking of the rubber backbone is critical.

Here we report a backbone rigid functionalization (BRF) strategy that utilizes a [2+2] photocycloaddition of maleimides to introduce rigid, polar cyclobutane‐fused succinimide units into the backbone of natural rubber (Figure 1d). The reaction proceeds at room temperature, reaches up to 28 mol% functionalization in 10 min, and requires no catalyst or sacrificial reagents. Incorporation of these bicyclic polar units substantially enhances tensile strength and toughness. Simply varying the reaction time enables continuous tuning of material behavior from viscoelastic polymers to elastomers and plastomers. When combined with vulcanization, the polar‐functionalized natural rubber yields high‐performance thermosets with five‐fold improved strength and toughness relative to conventional vulcanizates. Moreover, because the bicyclic cyclobutane units are mechanoresponsive and undergo force‐triggered cycloreversion [39, 40, 41, 42, 43, 44], the resulting materials exhibit on‐demand degradability upon bulk ball‐milling. This single‐step BRF process therefore provides a practical pathway to high‐performance, on‐demand degradable rubbers.

2. Results and Discussion

Initially, we explored [2+2] photocycloaddition for natural rubber functionalization (Table S1). In the presence of a photocatalyst, rapid gelation of natural rubber solution occurred. To suppress homocoupling of the cis‐alkene moieties in natural rubber, we subsequently investigated catalyst‐free [2+2] photocycloaddition. Among various polar olefins screened, only N‐alkyl maleimides exhibited both high reactivity and effective suppression of excessive cross‐linking, attributed to their distinctive triplet self‐excitation capability upon irradiation [45, 46]. A small‐molecule model reaction of 2‐methyl‐2‐butene with N‐methyl maleimide (M1) confirmed the efficient [2+2] photocycloaddition to form cyclobutane‐fused succinimide units (Figures S1–S4). For systematic evaluation of reaction parameters on functionalization efficiency and material properties, we selected commercially available cis‐1,4‐polyisoprene (PI) and M1 as model substrates (Figure 2a). A solution of PI and M1 (0.50 equiv to the cis‐alkene units) in DCM was irradiated in a photoreactor with a 500 W medium‐pressure mercury lamp. Polymers obtained at different irradiation times were purified and subsequently characterized to determine their degree of functionalization ratios (DOF by ¹H NMR) and molecular weight (M _w by size exclusion chromatography, SEC). Prolonged irradiation time from 2 to 10 min increased the polar functionalization ratio from 6 to 28 mol%, with a concomitant increase in M _w and Đ (Figure 2b, and Table S2). Notably, this fast BRF strategy proceeds in high reaction efficiency without requiring any catalysts or additives at room temperature. Replacing the 500 W mercury lamp with a 10 W 365 nm LED still afforded a substantial DOF of 21 mol% for PI, which is beneficial for the operation and scalability of this BRF strategy (Table S3). For the rubber with a functionalization ratio of 28 mol% (PIF‐28), the formation of cyclobutane‐fused succinimide structure on the polymer backbone was confirmed by NMR and fourier‐transform infrared spectroscopy attenuated total reflectance (FTIR‐ATR) analyses. The ¹H NMR spectrum showed characteristic resonance of the N–CH₃ signal at 2.98 ppm (s), while carbonyl (C═O) resonances of cyclic imides appeared in the range of 174–180 ppm of its ¹³C NMR spectrum (Figure 2c). The FTIR‐ATR spectrum of PIF‐28 exhibited two characteristic absorption bands at 1765 and 1693 cm⁻¹ (Figure S5), which are assigned to the C═O stretching vibration of the cyclic imide groups [43].

FIGURE 2.

BRF of natural rubber with N‐methyl maleimide. (a) Reaction scheme and property evolution upon BRF. (b) Evolution of DOF and M _w with reaction time. (c) ¹H and ¹³C NMR of PIF‐28. (d) DSC traces. (e) Rheological frequency sweeps. (f) Stress‐strain curves of PIF‐12, PIF‐19, PIF‐23, and PIF‐28. (g) SEM images of PI and PIF‐28.

The rubbers with varied functionalization ratios (PIF‐6 to PIF‐28) exhibit an evident transition from a viscous, flowable state to a tough, solid‐state material. This transformation may originate from two complementary factors: (1) main‐chain stiffening induced by the rigid four‐membered cyclobutane rings [34]; and (2) the physical cross‐linking resulting from non‐covalent interactions among polar units [47, 48]. Recognizing that rubber can cross‐link upon light irradiation, we conducted light‐induced experiments on PI in the absence of M1 (Table S4). By varying the reaction time, we obtained two rubbers with increased M _w (PI‑C‑1 and PI‑C‑2). To quantitatively elucidate the influence of this polar functionalization on material properties, the thermal and mechanical behaviors of the polymers were systematically characterized using differential scanning calorimetry (DSC), rheometer, and uniaxial tensile tests. DSC analyses were first conducted on the series of polymers, including pristine PI and PIF‐6 to PIF‐28 (Figure 2d). The glass transition temperature (T _g) of PI was observed at −61.5 °C. Despite their different M _w, PI‑C‑1 and PI‑C‑2 exhibited neglectable T _g changes compared to PI (Figure S6). The T _g of the functionalized rubbers exhibited a continuous increase, ranging from −56.8 to 19.6 °C with increasing functionalization ratio. This systematic increase in T _g originates from the reduced chain segmental mobility, which is caused by the rigid cyclobutane structures and the non‐covalent interactions introduced by the polar units.

Small‐amplitude oscillatory shear tests performed at 25 °C and 1% strain further confirmed the improvement in material properties, which may be attributed to the enhancement of chain rigidity and/or non‐covalent interactions [49]. The frequency dependence of the storage modulus (G′) and loss modulus (G′′) are shown in Figure 2e. For pristine PI, G′′ predominated over G′ across the entire frequency range, characteristic of a viscoelastic liquid. PIF‐6 exhibited a crossover point where G′ surpassed G′′ at approximately 20 rad/s, signaling the onset of elastic dominance at higher frequencies. With increasing functionalization, the elastic behavior becomes more pronounced, as evidenced by the downward shift of the crossover point to 1 rad/s in PIF‐12. Notably, for PIF‐19, PIF‐23, and PIF‐28, G′ consistently exceeded G′′ throughout the frequency sweep, demonstrating solid‐like, elastic behavior. Comparison of the modulus values and trends for PI‑C‑1, PI‑C‑2, PIF‑6, and PIF‑28 shows that the high M _w PI‑C‑2 exhibits a lower modulus than that of PIF‑6 and substantially lower than that of PIF‑28 (Figure S7), indicating that slight cross‐linking contributes only marginally to the enhancement of mechanical properties. The plateau value of G′ increased markedly from 10⁴ to 10⁶ Pa with increasing polar unit content. The observed rheological transition from viscous (PI and PIF‐6) to elastic (PIF‐12 and PIF‐28) behavior demonstrates that main‐chain rigid polar units effectively restrict polymer chain mobility, resulting in a markedly enhanced storage modulus.

PIF‐12, PIF‐19, PIF‐23, and PIF‐28 were molded into dumbbell‐shaped specimens via melt‐pressing for uniaxial tensile testing. The corresponding stress‐strain curves are presented in Figures 2f and S8. PIF‐12 exhibited a stress of 0.04 ± 0.01 MPa with a strain at break of 2278% ± 96%. As the polar unit content increased, PIF‐19 demonstrated an enhanced strength of 0.65 ± 0.02 MPa accompanied by a reduced strain of 1978% ± 49%. To investigate the elastic properties, PIF‐19 was extended step by step up to different strains (Figure S9). After a strain of 700%, the strain recovery value (SR) was 54%. A further increase to 23 mol% resulted in a substantial improvement in tensile stress to 3.30 ± 0.15 MPa, accompanied by a decrease in strain to 976% ± 93% and a reduction in elasticity, with an SR of 50% (Figure S10). Further increasing the functionalization ratio to 28 mol% shifted the material behavior from an elastomer toward a plastomers, achieved a fracture stress of 6.11 ± 0.22 MPa with a strain of 709% ± 30%. The thermal reprocessability of PIF‐28 is evidenced by the repeatable stress‐strain curves and retained mechanical properties after multiple processing cycles (Figure S11). The fracture surfaces of PI and PIF‐28 were examined using cryogenic high‐resolution scanning electron microscopy (Figure 2g). The fracture surface of unfunctionalized PI appeared smooth and featureless. In contrast, PIF‐28 exhibited a wavy, ductile fracture morphology with no evidence of macroscopic phase separation.

Dynamic mechanical analysis (DMA) was conducted on PIF‐19, PIF‐23, and PIF‐28 over a range of temperatures (Figure S12). At low temperatures, PIF‐19 and PIF‐23 exhibited comparable storage modulus (E′), whereas PIF‐28 showed a higher modulus. With increasing temperature, the moduli of all samples decreased, but followed distinct trends, indicating that the rigid cyclobutane units effectively restrict segmental mobility. Notably, PIF‐19 displayed a crossover where the loss modulus (E′′) exceeded E′ at high temperatures, characteristic of a viscoelastic liquid. In contrast, PIF‐23 and PIF‐28 maintained E′ > E′′ across the entire temperature range, which might be attributable to the physical cross‐linking effect of the polar succinimide units that reinforce the network via noncovalent interactions. These observations strongly indicate that the polar bicyclic cyclobutane units substantially enhance non‐covalent interactions, thereby increasing the cohesive energy and toughness of PI. Additionally, the polar units significantly enhanced surface hydrophilicity. Water contact angle (WCA) measurements confirmed this trend, with the WCA decreasing from 108.8° (pristine PI) to 82.9° (PIF‐28) as functionalization increases (Figure S13).

The catalyst‐ and additive‐free [2+2] photocycloaddition relies on the triplet activation of N‐alkyl maleimides upon irradiation, leading to the incorporation of succinimide groups in high yields and stereoselectivity (Figure 3a) [46]. To evaluate the versatility of this functionalization protocol, we extended its application to a series of maleimide derivatives bearing n‐octyl (M2), cyclohexyl (M3), benzyl (M4), 2‑methoxyethyl (M5), and 2‑hydroxyethyl (M6) substituents (Figure 3b and Table S5). Saturated alkyl derivatives M2 and M3 achieved a functionalization ratio of 23 mol%, suggesting the high reactivity reported for N‑alkyl maleimides. In contrast, M4‐M6 showed lower degrees of functionalization, which can be explained by the potential quenching of triplet intermediates by phenyl group and heteroatoms [45]. DSC analyses of the functionalized rubbers demonstrated that substituent structure influences thermal properties (Figure 3c). Low functionalization ratios (PIFc, PIFd, and PIFe) have only a slight effect on T _g. For PIFa‐23 and PIFb‐23, T _g rose markedly to −22.1 and −11.4 °C, respectively. To establish the correlation between substituent structure and mechanical properties, uniaxial tensile tests were performed on rubbers with identical functionalization levels, including PIF‐23 (methyl), PIFa‐23 (n‐octyl), and PIFb‐23 (cyclohexyl) (Figures 3d, S14, and S15). Extending the N‐alkyl groups from methyl to n‑octyl enhanced chain flexibility, lowering stress, increasing strain, and slightly reducing toughness. In contrast, the cyclohexyl substituent in PIFb‑23 introduced steric hindrance and rigidity, which enlarged inter‑chain spacing and simultaneously improved toughness and strain while preserving tensile strength and Young's modulus. These findings confirm this BRF strategy as a versatile route compatible with diverse maleimide monomers. It enables the tuning of PI mechanical properties by varying N‐alkyl groups and offers a foundation for developing graft copolymers via hydroxyl‐functionalized units [50].

FIGURE 3.

Diverse BRF of rubbers. (a) Reaction scheme for the [2+2] photocycloaddition between rubbers and maleimide monomers. (b) Functionalization efficiency of PI using various maleimide monomers. (c) DSC traces of the rubbers functionalized with different maleimide monomers. (d) Mechanical performance comparison of PIF‐23/PIFa‐23/PIFb‐23. (e) Functionalization efficiency of synthetic rubbers. (f) Comparison of DSC traces for commercial rubbers pristine and functionalized with M1. (g) Comparison of toughness of pristine and functionalized rubbers.

The presence of abundant unsaturated C═C bonds in other commercial synthetic rubbers also provides opportunities for extending our BRF strategy beyond natural rubber. Three major synthetic rubbers, cis‐polybutadiene (PBD), polychloroprene (CR), and styrene‐butadiene‐styrene triblock copolymer (SBR) were tested under the optimized reaction conditions. Each rubber was mixed with M1 in DCM and irradiated for 10 min under the standard conditions (Table S6). ¹H NMR analyses revealed characteristic N–CH₃ signals, confirming the successful occurrence of the [2+2] photocycloaddition (Figures S16–S18). It has been reported that the differences in chain‐entanglements and viscosities may affect the efficiency of a post‐polymerization modification reaction [24]. However, high functionalization ratios were achieved in all three cases: 15 mol% for PBD (PBDF‑15), 20 mol% for CR (CRF‑20), and 16 mol% for SBR (SBRF‑16) (Figure 3e). DSC analysis revealed dramatic changes in thermal behavior (Figure 3f). While PBD showed a melting transition (T _m) at −9.5 °C, the functionalized rubber (PBDF‑15) only showed a T _g at 63.8 °C. Similarly, the T _m of CR disappeared after polar cyclobutane functionalization, leaving a single T _g at 24.0 °C. The pristine SBR showed no clear thermal transition in the measured range, whereas the functionalized rubber SBRF‑16 observed a well‐defined T _g at 23.1 °C. The observed changes in the DSC traces originate from rigid, polar cyclobutane‐fused succinimide units, which enhance interactions through polarity and disrupt chain packing via their four‐membered ring structure.

The significant differences in backbone structures would lead to different responses in thermal transitions and mechanical reinforcement after BRF. To evaluate the impact of the M1 functionalization on mechanical properties, rubber samples (before and after reaction) were melt‐processed into specimens for uniaxial tensile testing (Figures S19–S21). The functionalization led to substantial mechanical enhancements: PBDF‑15 exhibited a 23.2‑fold increase in stress, a 10.6‑fold increase in Young’s modulus, and a 11.6‐fold increase in toughness; CRF‑20 showed the most dramatic improvements (141‑fold in Young's modulus, 2.3‑fold in toughness); and SBRF‑16 achieved over 3.0‑fold increases in both stress and toughness (Figures 3g and S22). These experimental results collectively demonstrate the broad applicability of this BRF strategy across different commercial rubbers. The incorporated polar cyclobutane units are crucial for the property enhancement. They simultaneously strengthen intermolecular interactions and alter chain conformation, leading to improved mechanical performance.

To investigate how polar cyclobutane functionalization affects vulcanized rubber, we selected PI and PIF‑12 for vulcanization using a standard industrial formulation [51] (Figure 4a and Table S7). A slight increase in T _g was observed in both cases after vulcanization (Figure S23). The mechanical properties of vulcanized samples (V‐PI and V‐PIF‑12) were then compared with PIF‑12 via uniaxial tensile testing (Figures 4b and S24). The stress‑strain curves reveal that PIF‑12 is weak and highly extensible. Both vulcanized samples show similar elongation at break, as chain mobility is constrained by the permanent chemical cross‑links introduced during vulcanization. Remarkably, V‐PIF‑12 outperforms V‐PI by more than six‑fold in stress, Young's modulus and toughness. Although strand extension by force‐coupled cycloreversion of nonscissile mechanophores may contribute to the network toughening [52, 53, 54], we attribute the substantial enhancement primarily to additional physical cross‑links via non‐covalent interactions by the polar units (Figure 4a, red dashed lines). Toluene equilibrium swelling experiments further confirmed the formation of a network structure. The gel fractions of V‐PI and V‐PIF‐12 were comparable (0.93 and 0.87, respectively). Meanwhile, V‐PIF‐12 exhibited increased cross‐link density and decreased swelling ratio with increasing polar functionalization (Table S8). These results indicate that the introduced polar groups have minimal impact on vulcanization while effectively enhancing interchain interactions. These physical cross‑links synergize with the chemical vulcanization network, leading to a comprehensive reinforcement of the material. Therefore, the BRF strategy represents a viable route to enhance the performance of vulcanized rubber.

FIGURE 4.

Vulcanization and on‐demand degradation. (a) Comparison of the network structures before and after vulcanization: PI and PIF‑12. (b) Mechanical performance comparison of V‐PI/PIF‐12/ V‐PIF‐12. (c) General method for chemical degradation of polar cyclobutane unit. (d) Photographs of V‐PI and V‐PIF‐12 before ball‐milling. (e) Photographs of V‐PI′ and V‐PIF‐12′ after ball‐milling. (f) Photographs of V‐PI′ and V‐PIF‐12′ after hydrolysis and dissolved in THF. (g) Quantitative analysis of remaining insoluble network V‐PI′ and V‐PIF‐12′ after acid hydrolysis at different ball‐milling activation times. (h) SEC traces of V‐PI′ and V‐PIF‐12′ after acid hydrolysis at different ball‐milling activation times. (i) ¹H NMR spectra of V‐PI′ and V‐PIF‐12′ after hydrolysis.

The stable three‐dimensional network formed through vulcanization is highly resistant to breakdown, rendering conventional physical recycling methods ineffective. Therefore, efforts have been devoted to utilizing the unsaturated C═C bonds for the chemical deconstruction of rubbers [10, 55, 56, 57, 58, 59, 60]. Cyclobutane‐fused succinimide units are known to be mechanoresponsive, and hydrolysable imide groups can be introduced into the backbone via mechanochemical activation [42, 43, 61, 62]. Therefore, the fused succinimide units in V‐PIF‑12 could undergo force‐induced cycloreversion to introduce cleavable imide groups into the main chain, enabling subsequent acid hydrolysis to efficiently degrade the cross‑linked polymer into telechelic oligomers (Figure 4c). To evaluate this BRF strategy for degrading waste vulcanized rubber, control ball‐milling experiments were performed on V‐PI and V‐PIF‑12 (Figure 4d, e). After ball‐milling at 60 Hz for 120 min, the activated polymer network V‐PI′ yielded an insoluble residue in THF after acid treatment. In contrast, hydrolysis of the activated polymer network V‐PIF‑12′ produced a clear THF solution (Figure 4f).

The degradation efficiency was quantified by analyzing the insoluble solid residues and soluble products (Figures S25, S26, Tables S9 and S10). Under identical hydrolysis conditions, the insoluble fraction of V‐PI remained nearly constant with increasing ball‐milling time, whereas that of V‐PIF progressively decreased. After 120 min of ball‐milling, the insoluble fraction of V‐PI′ remained >96% (Figure 4g, orange line). In sharp contrast, the insoluble content of V‐PIF‑12′ dropped to 16%, attributable mainly to inorganic additives from the vulcanization recipe (Figure 4g, green line). The SEC profile of V‐PI′ products showed negligible change over time (Figure S28). For V‐PIF‑12′, the increasing intensity of oligomer peaks in the low‑molecular‑weight region with longer ball‑milling time resulted from the sustained force‐induced cycloreversion of cyclobutane units (Figures 4h and S29). Moreover, ¹H NMR of hydrolyzed V‐PIF‑12′ revealed characteristic olefinic resonances at 6.56 and 7.00 ppm (m), and carboxylic acid proton at 10.87 ppm (bs) (Figure 4i). Quantitative ¹H NMR analysis revealed 59% ring‐opening of the cyclobutane‐fused succinimide mechanophores in V‐PIF‑12′ (Figure S30). Moreover, high‐resolution electrospray ionization mass spectrometry (HR‐ESI‐MS) analysis of the small‐molecule products identified several characteristic telechelic oligomers (A1‐A6) derived from hydrolyzed acyclic imide units of V‐PIF‑12′ (Table S11 and Figure S31). These results confirm the efficient hydrolytic degradation to telechelic oligomers, providing direct evidence for the mechanophore activation in the vulcanized rubber backbone. Overall, the polar cyclobutane units installed via the BRF strategy enable the controllable, on‑demand degradation of vulcanized rubber.

3. Conclusion

We have demonstrated a tunable and efficient method for the direct BRF of natural and synthetic rubbers via [2+2] photocycloaddition with maleimides. This strategy installs rigid, polar cyclobutane‐fused succinimide units into the polymer backbone, which substantially enhances the mechanical properties of rubbers. Meanwhile, such units are mechanoresponsive and undergo force‐triggered cycloreversion upon bulk ball‐milling, enabling vulcanized rubber with on‐demand hydrolytic degradability. We anticipate that this functionalization protocol will offer a novel and practical solution for enhancing the performance of rubber materials.

Author Contributions

Minghang Ji: investigation, writing – original draft, and validation. Shan Tang: supervision, funding acquisition, writing – review and editing, conceptualization, and writing – original draft.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Supporting File: anie73099‐sup‐0001‐SuppMat.pdf.

Dedicated to the 130^th anniversary of Shanghai Jiao Tong University.

Data Availability Statement

The data that supports the findings of this study are available in the supporting information of this article.