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. 2024 Nov 8;13(11):1598–1604. doi: 10.1021/acsmacrolett.4c00675

Efficient Cross-Linking through C–H Bond Insertion of Unfunctionalized Commodity Materials Using Diazirine-Containing Polymers

Mizhi Xu †, Banruo Huang †, Haley K Beech †, Patrick T Getty ‡, Juan Manuel Urueña §, Craig J Hawker †,‡,§,*
PMCID: PMC11580386  PMID: 39513545

Abstract

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The synthesis and application of multifunctional diazirine-containing polymers for on-demand cross-linking of unfunctionalized commodity polymers through C–H bond insertion is demonstrated. While small-molecule diazirine cross-linkers have seen important applications such as plastic compatibilization and photopatterning, the high degree of functionalization of polymer-based diazirine cross-linkers offers promise for enhanced compatibility based on polymer blending and increased efficiency due to controllable multivalency. As a demonstrative example, unfunctionalized linear poly(n-butyl acrylate) (PnBA) can be cross-linked using various polymeric cross-linkers with diazirine contents as low as 0.8 wt % in 1 min under photochemical conditions. With gel fractions up to 95%, tunable rheological behavior is observed with increasing cross-linker loadings, consistent with a transition from entangled branched polymers to a cross-linked network. Moreover, the synthetic stability of the diazirine units can be exploited to prepare diazirine-containing polymers based on a variety of different backbones, from vinyl copolymers to poly(dimethylsiloxane) (PDMS), which allows successful photopatterning using a commercial 3D printer.

Cross-linking is a critical process in enhancing the mechanical properties and stability of polymeric materials.1−4 By introducing cross-links along the backbone of linear polymer chains, thermoplastics could be converted into elastomers or thermosets, resulting in increased impact resistance, tensile strength, and high-temperature performance. This transformation also enhances resistance to chemical or biological degradation, with these properties being crucial for applications spanning from adhesives to medical devices.

Traditionally, unfunctionalized polymers can be cross-linked through e-beam irradiation or by thermal treatment in the presence of organic peroxides.5 These radical-based methods, however, pose significant challenges, including undesired cleavage of the polymer backbone and limited control over the nature and number of cross-linking sites, ultimately compromising the integrity of the material.6 Alternatively, cross-linking methods that leverage specific functional groups face challenges when applied to commodity polymers that are difficult to functionalize or have only C–C and C–H bonds such as polyethylene and polypropylene.7−10

Recent advances in C–H functionalization chemistry have facilitated the development of more efficient and controlled cross-linking techniques.11,12 Specifically, the use of carbenes for direct C–H insertion into the polymer backbone has emerged as a promising strategy. Under mild thermal or photochemical conditions, singlet carbenes can be generated from diazirine or diazo precursors, enabling efficient functionalization and cross-linking.13−17 These carbene-mediated cross-linking strategies have found a diverse array of applications, including plastic compatibilization,18 LED processing,19,20 photopatterning,21−25 and as adhesives.26−29

Despite the potential of small-molecule diazirine and diazo compounds, their application is often hindered by challenges, such as limited structural variability, the need for relatively high loading levels due to their difunctional nature, and potential leaching of unattached cross-linkers. To address the limitations of small-molecule cross-linkers, incorporation of diazirine groups into polymeric structures offers a versatile platform for enhancing cross-linking efficiency and fine-tuning material properties (Figure 1A). In particular, we have recently demonstrated the facile synthesis of diazirine-containing polymers via controlled radical (co)plymerization, which allows the preparation of vinyl polymers with up to ∼50 diazirine units per chain.30

Figure 1.

Figure 1

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(A) Unfunctionalized commodity polymers can be efficiently cross-linked by diazirine-containing polymers via direct C–H insertion of singlet carbenes. (B) Variable backbone structures of polymeric cross-linkers.

This study explores the synthesis and application of multifunctional diazirine-containing polymers for on-demand cross-linking of various unfunctionalized polymers (Figure 1B). Facile access to multifunctional diazirine copolymers enables curing studies on a wide variety of commodity acrylic and siloxane polymers. Analysis of the structure and properties before and after cross-linking demonstrates that a high degree of cross-linking and gel formation could be achieved at minimal diazirine loadings, with oscillatory rheology providing insight into the evolution of a network structure as the diazirine loading is increased. The versatility of this approach is further emphasized by demonstrating the effective cross-linking and photopatterning of commercially relevant acrylate, acrylamide, methacrylate, and siloxane-based systems.

The cross-linking performance of diazirine-containing polymers was initially explored using a blend system comprising an unfunctionalized PnBA as the bulk matrix with varying amounts of poly(n-butyl acrylate-diazirine acrylate) copolymer (PnBA-co-PDzA) added as a cross-linker. Through reversible addition–fragmentation chain-transfer (RAFT) copolymerization, a PnBA-co-PDzA (P1) cross-linker was synthesized containing 10 mol % diazirine acrylate repeating units with a Mn of 52 kDa. Clear blends with a light-yellow color were prepared in a mold by mixing 90–99 wt % of unfunctionalized PnBA (105 kDa) with varied loadings of P1 at 1, 3, 5, and 10 wt % (Figure 2A). Notably, these cross-linker loadings correlated to low contents of the trifluoromethyl diazirinyl group (CF3Dz, highlighted in red in Figure 2A) in the entire blends. CF3Dz contents of 0.1, 0.2, 0.4, and 0.8 wt % were estimated for the four blends, respectively. For consistency in the following discussions, the CF3Dz wt % content in the entire blend will be used primarily to quantify diazirine loadings (see Supporting Information for calculation details). The prepared PnBA blends were then cured either by exposure to 370 nm UV light for 1 min or by heating at 110 °C for 2 h. Homogeneous, solidified samples were observed, suggesting successful cross-linking.

Figure 2.

Figure 2

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(A) UV or thermal curing of PnBA blends with different loadings of cross-linker P1. Photos showing the blend with 0.8 wt % of CF3Dz after UV-curing (left) and thermal-curing (right). (B) Gel fractions of cured PnBA blends with varied loadings of CF3Dz show enhanced curing efficiency with higher cross-linker loadings.

Subsequently, gel fraction measurements were conducted on the cured PnBA samples to quantify the cross-linking efficiency after either thermal or photochemical generation of the reactive carbene units from the starting diazirine groups.3,31 Soluble polymer chains unconnected to the cross-linked network were removed by repeated swelling of cured samples in dichloromethane (DCM) and collection of the soluble fractions. This allows for comparison of gel content across various cross-linker loadings and curing procedures (Figure 2B). When the blend containing a CF3Dz content of 0.1 wt % was subjected to curing conditions, gel fractions of 44% for UV-cured samples and 48% for thermally cured samples were achieved, respectively. The observed gel fractions suggest that at a diazirine loading of 0.1 wt % only partial cross-linking occurred, leaving approximately half of the PnBA as linear or branched architectures. Higher gel fractions were observed for increased P1 loadings, with CF3Dz contents of 0.2 and 0.4 wt %. For the blend with a CF3Dz loading of 0.8 wt %, nearly quantitative cross-linking of the starting linear unfunctionalized PnBA was achieved, resulting in gel fractions of 96% and 97% for UV or thermally cured samples, respectively (Figure 2B). This low CF3Dz loading of 0.8 wt % underscores the advantage of employing a multifunctional polymer containing on average 4–50 diazirine units along the backbone as a cross-linker. These results also suggest that thermal curing typically results in slightly higher gel fractions when compared to UV curing across different cross-linker loadings, presumably due to a higher conversion of the diazirine moiety into carbene intermediates at elevated temperatures and extended curing times (2 h versus 1 min).

It is noteworthy that attempted cross-linking of the same unfunctionalized linear PnBA with a small-molecule, bisdiazirine derivative failed to form a network at the same CF3Dz loading of 0.8 wt % , under either photochemical or thermal conditions (see Supporting Information for details). Only after increasing the bisdiazirine cross-linker to 10 wt %, equivalent to a CF3Dz content of 4.2 wt %, was cross-linking observed in the cured samples. At these high loading levels of small-molecule diazirines, however, a heterogeneous sample was observed under UV conditions, likely due to the rapid and extensive nitrogen evolution and phase separation during the curing process (Figure S10). These findings highlight the advantages of using low loadings of polymer-based diazirine cross-linkers.

Following the determination of gel fractions for cured blends containing varying amounts of diazirine cross-linkers, the impact of curing on mechanical properties was then investigated by photorheology. For experiments with a UV intensity of 25 mW/cm2, a rapid sol–gel transition was observed after ∼1 min of UV irradiation, as indicated by a significant increase in storage modulus (G′) that surpassed loss modulus (G″) (Figure 3). This fast solidification process is fully consistent with the efficient carbene formation from diazirine groups and subsequent cross-linking during photochemical curing.

Figure 3.

Figure 3

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Photorheology (at 1% strain and 1 rad/s frequency) shows rapid cross-linking of the PnBA blend with 0.8 wt % of CF3Dz under UV light (25 mW/cm2).

Oscillatory shear rheology measurements were then conducted to evaluate the mechanical properties of cured samples with varying diazirine contents. For cured blends with CF3Dz contents of 0.2, 0.4, and 0.8 wt %, frequency sweeps conducted at 1% strain shed light onto the structural differences resulting from different cross-linking densities (Figure 4A). For UV-cured blends with CF3Dz contents of 0.2 and 0.4 wt %, slightly higher values of G′ than G″ at low frequencies (<1 rad/s) suggest the existence of highly branched or entangled polymer chains. In contrast, the frequency sweep of a UV-cured blend with a CF3Dz content of 0.8 wt % showed minimal change in G′ across different angular frequencies. These findings, coupled with gel fractions exceeding 95%, indicated near-complete cross-linking with 0.8 wt % loading of diazirine. Similar trends were observed in thermally cured samples (Figure S13). Overall, unfunctionalized PnBA materials could be cross-linked with the formation of a viscoelastic solid in both UV and thermally cured samples through blending with diazirine-containing linear polymers. In these systems, G′ dominates over G″ throughout the examined angular frequency range. It should be noted that the mechanical fragility of cured blends with a CF3Dz content of 0.1 wt % prevented further rheological measurements, likely resulting from insufficient cross-linking at this low loading level.

Figure 4.

Figure 4

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(A) Frequency sweep at 1% strain of UV-cured blends shows increased degree of cross-linking with higher CF3Dz loading. (B) Storage modulus values obtained at 1% strain and 1 rad/s frequency of UV- or thermally cured blends show increased modulus with higher CF3Dz loadings.

To further understand the impact of curing conditions on mechanical properties, the moduli of these cured PnBA samples were compared at a 1 rad/s frequency and 1% strain. A gradual increase in G′ was noted within the series of UV- or thermally cured samples with increasing diazirine loadings (Figure 4B). Notably, a higher storage modulus (G′) was consistently observed in thermally cured samples compared to their UV-cured counterparts at equivalent cross-linker loadings. This higher modulus correlates with the increased gel fraction observed for the thermally cured samples. It is proposed that this small but consistent increase in gel fraction between UV- and thermally cured samples is due to both longer reaction times and enhanced chain mobility at elevated temperatures. Additionally, the initial formation of a yellow color for the UV-cured samples is noteworthy. This color is consistent with a minor side reaction involving the formation of a diazo isomer from the starting diazirine units. The inability of these diazo isomers to generate carbene intermediates may decrease overall carbene content upon irradiation, contributing to the observed differences in properties between UV- and thermally cured samples.14 Upon heating, the yellow color disappears presumably due to the conversion of diazo groups to the desired carbene species, leading to a higher degree of cross-linking.

With the efficient curing of unfunctionalized PnBA being established, the molecular weight impact of the PnBA-co-PDzA cross-linker was then investigated. In addition to P1 (Mn = 52 kDa, 10 mol % functionalization), two PnBA-co-PDzA cross-linkers with Mn = 22 and 11 kDa containing 10 mol % diazirine acrylate units were also prepared. With the same feed ratio of 10 mol % diazirine, these molecular weights correspond to approximately 44, 18, and 9 diazirine groups per chain, respectively. Despite the significant variation in molecular weight, all of these cross-linkers were fully miscible with high molecular weight, unfunctionalized PnBA and could lead to successful curing at a CF3Dz content of 0.8 wt % (10 wt % loading of the polymeric cross-linkers). In each case, high gel fractions exceeding 95% were achieved under both UV and thermal curing conditions (Tables S6 and S7; Figure S14).

While cross-linkers with varied molecular weights afford equally high gel content, the molecular weight of the unfunctionalized PnBA homopolymer was also shown to significantly influence the efficiency of network formation. For example, a blend consisting of an unfunctionalized PnBA with a lower molecular weight (Mn = 25 kDa) yields a gel fraction of 44% when subjected to UV curing (Table S8; Figure S15). This reduction in cross-linking can be attributed to two factors: (1) compared to the PnBA with Mn of 105 kDa, the lower Mn of 25 kDa correlates to an approximately 4-time increase in the number of chains in this blend, leading to less efficient cross-linking, and (2) the chain entanglement is significantly reduced with the lower Mn of 25 kDa, resulting in fewer entanglements being trapped as cross-links after curing.

A major advantage of the polymeric diazirine strategy is the ability to tune the nature of the backbone to allow blending with a wide variety of unfunctionalized linear polymers. Having demonstrated the efficient cross-linking of PnBA, curing studies were then conducted on other commercially important polymers, including poly(methyl acrylate) (PMA), poly(methyl methacrylate) (PMMA), poly(N-isopropylacrylamide) (PNIPAM), and polydimethylsiloxane (PDMS). For the vinyl-based systems, facile RAFT copolymerization of diazirine-containing acrylate or methacrylate monomers with the desired vinyl monomers successfully produced polymeric cross-linkers with 10 mol % of diazirine content and varied backbone structures (Table 1, P2–P4).

Table 1. Gel Fractions of Cross-Linked PMA, PMMA, and PNIPAM.

graphic file with name mz4c00675_0006.jpg

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a

Average values of triplicate experiments.

b

Exposed to 370 nm light for 1 min (PMA) or 5 min (PMMA and PNIPAM).

c

Heating at 110 °C for 2 h.

In all cases, homogeneous blending of the diazirine-containing copolymer with the corresponding unfunctionalized systems proved to be successful. For example, the PMA copolymer (P2) was blended with linear unfunctionalized PMA at a 10 wt % loading (1.0 wt % of CF3Dz), and the blend was subjected to curing conditions. A moderate gel fraction of 56% and a high gel fraction of 91% were achieved through UV and thermal curing, respectively (Table 1). Similar to the results with PnBA, superior cross-linking efficiency was observed with thermal curing, supporting the hypothesis that increased chain mobility and a higher amount of carbene intermediate upon heating also contributed to enhanced cross-linking efficiency. Notably, the discrepancy between UV and thermal curing is particularly pronounced in the case of PMA compared with PnBA, likely due to the higher glass transition temperature for PMA (Tg = 10 °C). To further investigate the influence of Tg on the curing process, a blend of PMMA with the corresponding cross-linker P3 at a 10 wt % loading (1.0 wt % of CF3Dz) was cured (Table 1). Gel fractions of 51% and 87% were observed after UV and thermal curing, respectively, consistent with the lower cross-linking efficiency of the glassy PMMA blend at room temperature, which limits polymer chain mobility (Tg = 110 °C). Additionally, the cross-linking of PNIPAM was examined, owing to its versatile biomedical applications.32,33 Unfunctionalized PNIPAM could be blended with a diazirine-containing PNIPAM copolymer (P4) at a 10 wt % loading (0.8 wt % of CF3Dz) and successfully cured under both UV and thermal conditions, yielding high gel fractions of 78% and 81%, respectively (Table 1). Collectively, these findings illustrate the versatility of diazirine-containing polymers in cross-linking a diverse range of acrylic polymers.

To further expand the scope of polymer backbones, the cross-linking of PDMS systems with diazirine chemistry was examined. Unlike acrylic-based polymeric cross-linkers prepared from radical copolymerization, the required PDMS-based diazirine-containing cross-linkers can be synthesized through the modification of commercially available polysiloxanes. Specifically, a hydrosilylation reaction between the Si–H groups of a commercial PDMS copolymer and an allyl-containing diazirine derivative (1) was employed to produce the desired cross-linker, with nearly quantitative conversion of the Si–H groups to the desired diazirine units (P5, Figure 5A).34,35 Significantly, the compatibility of the diazirine units with hydrosilylation chemistry further demonstrates the synthetic versatility of diazirine building blocks in polymer science. Photo-cross-linking of commercial polysiloxane derivatives was then examined with a view to the growing range of applications for PDMS systems in the fabrication of elastomers and coating materials.36−39

Figure 5.

Figure 5

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(A) Synthesis of diazirine-containing polysiloxane P5 shows previously unattainable compatibility of diazirine compounds with hydrosilylation conditions. (B) Successful photopatterning of the thiol-containing resin with 20 wt % of P5 (1.1 wt % of CF3Dz). Experiments were performed on a commercial Mono3Z2 printer.

The PDMS-based cross-linker P5 was first blended with an unfunctionalized PDMS and subjected to typical UV-curing conditions. However, no cross-linking was observed, likely due to the high bond dissociation energy of the C–H bond in the Si–CH3 groups (Table S12).40 To test this hypothesis, two commercial PDMS copolymers containing more reactive silane groups (Si–H, 4–8%) or thiol groups (S–H, 4–6%) were then blended with P5 and cured by UV irradiation. It is noteworthy that gel fractions of 46% and 58% were achieved for these two blends (Table S12). Compared to unfunctionalized PDMS, the introduction of cross-linkable silane or thiol groups into the PDMS backbone significantly enhanced the ability to cross-link polysiloxane materials.

Next, photopatterning experiments were conducted using a low-viscosity blend based on a commercial PDMS copolymer (Mn = 7 kDa) containing 4–6% thiol groups. A clear blend was prepared by mixing 80 wt % of the commercial PDMS copolymer with 20 wt % of P5 (1.1 wt % of CF3Dz). Using a commercial Mono3Z2 3D printer, a square-void-in-circle pattern was successfully fabricated by irradiating the PDMS blend with 365 nm light for 5 min (Figure 3B). The demonstration of efficient photopatterning highlights the utility of diazirine-containing polymers in the fabrication of silicone materials, paving the way for future 3D printing applications.

In summary, this study describes the synthesis and application of diazirine-containing polymers for the efficient cross-linking of unfunctionalized vinyl- and siloxane polymers. Through the analysis of the gel content and mechanical characterization of the polymer networks, thermal and photochemical curing of a variety of blends based on commodity polymers at different cross-linker loadings was examined. Impressive gel fractions exceeding 95% are achieved with a diazirine content of 0.8 wt % upon 1 min UV irradiation for linear PnBA systems. Furthermore, the versatility of diazirine-containing polymers is highlighted by the effective blending and cross-linking of other vinyl polymers such as PMA, PMMA, and PNIPAM. Significantly, a diazirine-containing polysiloxane cross-linker could be synthesized via hydrosilylation, facilitating tunable cross-linking of commercially available linear silicone derivatives. The successful photopatterning of these silicone resin blends using a commercial 3D printer showcases the practicality and potential of diazirine-containing polymers in advanced materials design and fabrication.

Acknowledgments

This work was supported via U.S. Army Research Office contract W911NF-19-D-0001 for the Institute for Collaborative Biotechnologies. The research made use of shared facilities of the UC Santa Barbara Materials Research Science and Engineering Center (MRSEC, NSF DMR-2308708), a member of the Materials Research Facilities Network (http://www.mrfn.org). The research on photopatterning was performed in the Additive Manufacturing facility of BioPACIFIC Materials Innovation Platform (NSF DMR-1933487).

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsmacrolett.4c00675.

  • Detailed experimental procedures, characterization (NMR, SEC, rheology), and gel fraction measurements (PDF)

Author Contributions

# M.X. and B.H. contributed equally. CRediT: Mizhi Xu conceptualization, writing - original draft; Banruo Huang conceptualization, writing - original draft; Haley K. Beech investigation, writing - review & editing; Patrick T. Getty investigation, writing - review & editing; Juan Manuel Urueña investigation; Craig J. Hawker conceptualization, funding acquisition, supervision, writing - original draft, writing - review & editing.

The authors declare no competing financial interest.

Supplementary Material

mz4c00675_si_001.pdf (1.1MB, pdf)

References

  1. Engle L. P.; Wagener K. B. A Review of Thermally Controlled Covalent Bond Formation in Polymer Chemistry. J. Macromol. Sci. Part C Polym. Rev. 1993, 33 (3), 239–257. 10.1080/15321799308021436. [DOI] [Google Scholar]
  2. Nielsen L. E. Cross-Linking-Effect on Physical Properties of Polymers. J. Macromol. Sci. Part C Polym. Rev. 1969, 3 (1), 69–103. 10.1080/15583726908545897. [DOI] [Google Scholar]
  3. Danielsen S. P. O.; Beech H. K.; Wang S.; El-Zaatari B. M.; Wang X.; Sapir L.; Ouchi T.; Wang Z.; Johnson P. N.; Hu Y.; Lundberg D. J.; Stoychev G.; Craig S. L.; Johnson J. A.; Kalow J. A.; Olsen B. D.; Rubinstein M. Molecular Characterization of Polymer Networks. Chem. Rev. 2021, 121 (8), 5042–5092. 10.1021/acs.chemrev.0c01304. [DOI] [PubMed] [Google Scholar]
  4. Weerasinghe M. A. S. N.; Dodo O. J.; Rajawasam C. W. H.; Raji I. O.; Wanasinghe S. V.; Konkolewicz D.; De Alwis Watuthanthrige N. Educational Series: Turning Monomers into Crosslinked Polymer Networks. Polym. Chem. 2023, 14 (39), 4503–4514. 10.1039/D3PY00912B. [DOI] [Google Scholar]
  5. Miller A. A. A Kinetic Analysis for the Free-radical Crosslinking of Saturated Polymers. J. Polym. Sci. 1960, 42 (140), 441–454. 10.1002/pol.1960.1204214012. [DOI] [Google Scholar]
  6. Munier C.; Gaillard-Devaux E.; Tcharkhtchi A.; Verdu J. Durability of Cross-Linked Polyethylene Pipes under Pressure. J. Mater. Sci. 2002, 37, 4159–4163. 10.1023/A:1020091920606. [DOI] [Google Scholar]
  7. Tillet G.; Boutevin B.; Ameduri B. Chemical Reactions of Polymer Crosslinking and Post-Crosslinking at Room and Medium Temperature. Prog. Polym. Sci. 2011, 36 (2), 191–217. 10.1016/j.progpolymsci.2010.08.003. [DOI] [Google Scholar]
  8. Mavila S.; Eivgi O.; Berkovich I.; Lemcoff N. G. Intramolecular Cross-Linking Methodologies for the Synthesis of Polymer Nanoparticles. Chem. Rev. 2016, 116 (3), 878–961. 10.1021/acs.chemrev.5b00290. [DOI] [PubMed] [Google Scholar]
  9. Chen J.; Garcia E. S.; Zimmerman S. C. Intramolecularly Cross-Linked Polymers: From Structure to Function with Applications as Artificial Antibodies and Artificial Enzymes. Acc. Chem. Res. 2020, 53 (6), 1244–1256. 10.1021/acs.accounts.0c00178. [DOI] [PubMed] [Google Scholar]
  10. Geng Z.; Shin J. J.; Xi Y.; Hawker C. J. Click Chemistry Strategies for the Accelerated Synthesis of Functional Macromolecules. J. Polym. Sci. 2021, 59 (11), 963–1042. 10.1002/pol.20210126. [DOI] [Google Scholar]
  11. Boaen N. K.; Hillmyer M. A. Post-Polymerization Functionalization of Polyolefins. Chem. Soc. Rev. 2005, 34 (3), 267–275. 10.1039/b311405h. [DOI] [PubMed] [Google Scholar]
  12. Williamson J. B.; Lewis S. E.; Johnson R. R.; Manning I. M.; Leibfarth F. A. C-H Functionalization of Commodity Polymers. Angew. Chem., Int. Ed. 2019, 58 (26), 8654–8668. 10.1002/anie.201810970. [DOI] [PubMed] [Google Scholar]
  13. Aglietto M.; Alterio R.; Bertani R.; Galleschi F.; Ruggeri G. Polyolefin Functionalization by Carbene Insertion for Polymer Blends. Polymer 1989, 30 (6), 1133–1136. 10.1016/0032-3861(89)90093-1. [DOI] [Google Scholar]
  14. Lepage M. L.; Simhadri C.; Liu C.; Takaffoli M.; Bi L.; Crawford B.; Milani A. S.; Wulff J. E. A Broadly Applicable Cross-Linker for Aliphatic Polymers Containing C-H Bonds. Science 2019, 366 (6467), 875–878. 10.1126/science.aay6230. [DOI] [PubMed] [Google Scholar]
  15. Musolino S. F.; Mahbod M.; Nazir R.; Bi L.; Graham H. A.; Milani A. S.; Wulff J. E. Electronically Optimized Diazirine-Based Polymer Crosslinkers. Polym. Chem. 2022, 13 (25), 3833–3839. 10.1039/D2PY00687A. [DOI] [Google Scholar]
  16. Yang S.; Yi S.; Yun J.; Li N.; Jiang Y.; Huang Z.; Xu C.; He C.; Pan X. Carbene-Mediated Polymer Cross-Linking with Diazo Compounds by C-H Activation and Insertion. Macromolecules 2022, 55 (9), 3423–3429. 10.1021/acs.macromol.2c00527. [DOI] [Google Scholar]
  17. Yi S.; Yang S.; Xie Z.; Yun J.; Pan X. Carbene-Mediated Polymer Modification Using Diazo Compounds under Photo or Thermal Activation Conditions. ACS Macro Lett. 2024, 13 (6), 711–718. 10.1021/acsmacrolett.4c00222. [DOI] [PubMed] [Google Scholar]
  18. Clarke R. W.; Sandmeier T.; Franklin K. A.; Reich D.; Zhang X.; Vengallur N.; Patra T. K.; Tannenbaum R. J.; Adhikari S.; Kumar S. K.; Rovis T.; Chen E. Y.-X. Dynamic Crosslinking Compatibilizes Immiscible Mixed Plastics. Nature 2023, 616 (7958), 731–739. 10.1038/s41586-023-05858-3. [DOI] [PubMed] [Google Scholar]
  19. Dey K.; Chowdhury S. R.; Dykstra E.; Koronatov A.; Lu H. P.; Shinar R.; Shinar J.; Anzenbacher P. Diazirine-Based Photo-Crosslinkers for Defect Free Fabrication of Solution Processed Organic Light-Emitting Diodes. J. Mater. Chem. C 2020, 8 (34), 11988–11996. 10.1039/D0TC02317E. [DOI] [Google Scholar]
  20. Dey K.; Roy Chowdhury S.; Dykstra E.; Lu H. P.; Shinar R.; Shinar J.; Anzenbacher P. Effect of Bis-Diazirine-Mediated Photo-Crosslinking on Polyvinylcarbazole and Solution-Processed Polymer LEDs. ACS Appl. Electron. Mater. 2021, 3 (8), 3365–3371. 10.1021/acsaelm.1c00354. [DOI] [Google Scholar]
  21. Burgoon H.; Cyrus C.; Skilskyj D.; Thoresen J.; Ebner C.; Meyer G. A.; Filson P.; Rhodes L. F.; Backlund T.; Meneau A.; Cull T.; Afonina I. Photopatterning of Low Dielectric Constant Cycloolefin Polymers Using Azides and Diazirines. ACS Appl. Polym. Mater. 2020, 2 (5), 1819–1826. 10.1021/acsapm.0c00043. [DOI] [Google Scholar]
  22. Wu C.; Li C.; Yu X.; Chen L.; Gao C.; Zhang X.; Zhang G.; Zhang D. An Efficient Diazirine-Based Four-Armed Cross-linker for Photo-patterning of Polymeric Semiconductors. Angew. Chem., Int. Ed. 2021, 60 (39), 21521–21528. 10.1002/anie.202108421. [DOI] [PubMed] [Google Scholar]
  23. Zheng Y.-Q.; Liu Y.; Zhong D.; Nikzad S.; Liu S.; Yu Z.; Liu D.; Wu H.-C.; Zhu C.; Li J.; Tran H.; Tok J. B.-H.; Bao Z. Monolithic Optical Microlithography of High-Density Elastic Circuits. Science 2021, 373 (6550), 88–94. 10.1126/science.abh3551. [DOI] [PubMed] [Google Scholar]
  24. Lu S.; Fu Z.; Li F.; Weng K.; Zhou L.; Zhang L.; Yang Y.; Qiu H.; Liu D.; Qing W.; Ding H.; Sheng X.; Chen M.; Tang X.; Duan L.; Liu W.; Wu L.; Yang Y.; Zhang H.; Li J. Beyond a Linker: The Role of Photochemistry of Crosslinkers in the Direct Optical Patterning of Colloidal Nanocrystals. Angew. Chem., Int. Ed. 2022, 61 (23), e202202633 10.1002/anie.202202633. [DOI] [PubMed] [Google Scholar]
  25. Fan W.; Hong N.; Sun Q.; Li M.; Fu W. Thermo-Curable and Photo-Patternable Polysiloxanes and Polycarbosiloxanes by a Facile Piers-Rubinsztajn Polycondensation and Post-Modification. Polym. Chem. 2022, 13 (15), 2187–2194. 10.1039/D2PY00234E. [DOI] [Google Scholar]
  26. Wang J.; Karami P.; Ataman N. C.; Pioletti D. P.; Steele T. W. J.; Klok H.-A. Light-Activated, Bioadhesive, Poly(2-Hydroxyethyl Methacrylate) Brush Coatings. Biomacromolecules 2020, 21 (1), 240–249. 10.1021/acs.biomac.9b01196. [DOI] [PubMed] [Google Scholar]
  27. Simhadri C.; Bi L.; Lepage M. L.; Takaffoli M.; Pei Z.; Musolino S. F.; Milani A. S.; DiLabio G. A.; Wulff J. E. Flexible Polyfluorinated Bis-Diazirines as Molecular Adhesives. Chem. Sci. 2021, 12 (11), 4147–4153. 10.1039/D0SC06283A. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Lepage M. L.; Takaffoli M.; Simhadri C.; Mandau R.; Gashti M. P.; Nazir R.; Mohseni M.; Li W.; Liu C.; Bi L.; Falck G.; Berrang P.; Golovin K.; Milani A. S.; DiLabio G. A.; Wulff J. E. Influence of Topical Cross-Linking on Mechanical and Ballistic Performance of a Woven Ultra-High-Molecular-Weight Polyethylene Fabric Used in Soft Body Armor. ACS Appl. Polym. Mater. 2021, 3 (11), 6008–6018. 10.1021/acsapm.1c01301. [DOI] [Google Scholar]
  29. Ellis E.; Djordjevic I.; Bin Mohd Ali M. N.; Steele T. W. J. Carbene-Based Bioadhesive Blended with Amine, Thiol, and Acrylate Liquid Additives. ACS Appl. Polym. Mater. 2023, 5 (2), 1440–1452. 10.1021/acsapm.2c01658. [DOI] [Google Scholar]
  30. Huang B.; Xu M.; Hawker C. J. Synthesis and Reactivity of Diazirine-Containing Polymers via Controlled Radical Polymerization. Macromolecules 2024, 57 (9), 4536–4543. 10.1021/acs.macromol.4c00443. [DOI] [Google Scholar]
  31. Rajawasam C. W. H.; Dodo O. J.; Weerasinghe M. A. S. N.; Raji I. O.; Wanasinghe S. V.; Konkolewicz D.; De Alwis Watuthanthrige N. Educational Series: Characterizing Crosslinked Polymer Networks. Polym. Chem. 2024, 15 (4), 219–247. 10.1039/D3PY00914A. [DOI] [Google Scholar]
  32. Guan Y.; Zhang Y. PNIPAM Microgels for Biomedical Applications: From Dispersed Particles to 3D Assemblies. Soft Matter 2011, 7 (14), 6375–6384. 10.1039/c0sm01541e. [DOI] [Google Scholar]
  33. Ansari M. J.; Rajendran R. R.; Mohanto S.; Agarwal U.; Panda K.; Dhotre K.; Manne R.; Deepak A.; Zafar A.; Yasir M.; Pramanik S. Poly(N-Isopropylacrylamide)-Based Hydrogels for Biomedical Applications: A Review of the State-of-the-Art. Gels 2022, 8 (7), 454. 10.3390/gels8070454. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Hofmann R. J.; Vlatković M.; Wiesbrock F. Fifty Years of Hydrosilylation in Polymer Science: A Review of Current Trends of Low-Cost Transition-Metal and Metal-Free Catalysts, Non-Thermally Triggered Hydrosilylation Reactions, and Industrial Applications. Polymers 2017, 9 (10), 534. 10.3390/polym9100534. [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Lukin R. Yu.; Kuchkaev A. M.; Sukhov A. V.; Bekmukhamedov G. E.; Yakhvarov D. G. Platinum-Catalyzed Hydrosilylation in Polymer Chemistry. Polymers 2020, 12 (10), 2174. 10.3390/polym12102174. [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Shit S. C.; Shah P. A Review on Silicone Rubber. Natl. Acad. Sci. Lett. 2013, 36 (4), 355–365. 10.1007/s40009-013-0150-2. [DOI] [Google Scholar]
  37. Mazurek P.; Vudayagiri S.; Skov A. L. How to Tailor Flexible Silicone Elastomers with Mechanical Integrity: A Tutorial Review. Chem. Soc. Rev. 2019, 48 (6), 1448–1464. 10.1039/C8CS00963E. [DOI] [PubMed] [Google Scholar]
  38. Reynolds V. G.; Mukherjee S.; Xie R.; Levi A. E.; Atassi A.; Uchiyama T.; Wang H.; Chabinyc M. L.; Bates C. M. Super-Soft Solvent-Free Bottlebrush Elastomers for Touch Sensing. Mater. Horiz. 2020, 7 (1), 181–187. 10.1039/C9MH00951E. [DOI] [Google Scholar]
  39. Xie R.; Mukherjee S.; Levi A. E.; Reynolds V. G.; Wang H.; Chabinyc M. L.; Bates C. M. Room Temperature 3D Printing of Super-Soft and Solvent-Free Elastomers. Sci. Adv. 2020, 6 (46), eabc6900 10.1126/sciadv.abc6900. [DOI] [PMC free article] [PubMed] [Google Scholar]
  40. Walsh R. Bond Dissociation Energy Values in Silicon-Containing Compounds and Some of Their Implications. Acc. Chem. Res. 1981, 14 (8), 246–252. 10.1021/ar00068a004. [DOI] [Google Scholar]

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