We developed a facile protocol for grafting-onto and cross-linking unsaturated-bond-containing common polymers via the formation of masked-ketene-functionalized polymers. The protocol utilizes a cascade functionalization agent 1 that has nitrile N-oxide and masked ketene functionalities. Through the model ligation reactions using 1, it turned out that the 1 facilitates the catalyst-free click introduction of masked ketene moieties to the unsaturated bonds such as C≡N and C=C bonds, capable of undergoing catalyst-free ligation with not only a nucleophilic amine but also a neutral alcohol with low nucleophilicity. On the basis of these results, the catalyst-free grafting reactions of PEG onto EPDM and PAN using 1 were performed to afford the corresponding graft copolymers in excellent conversion yields. In addition, it was also revealed that heating of both PAN and NR with masked ketene moieties at 250 °C for 1 h without catalyst enables the efficient conversion to give the respective cross-linked polymers.
We developed a powerful and highly reliable cascade functionalization technique for constructing sophisticated macromolecular architectures. Central to the technique are the ambident agents having combined functions of a nitrile N-oxide group and an electrophile. The agents proved capable of facile catalyst- and solvent-free functionalization of polymers and further integrations involving cross-linking.
The thermotriggered modification of surfaces was performed under catalyst-free conditions using an orthogonal agent possessing both nitrile N-oxide and Meldrum's acid moieties. The nitrile N-oxide moiety of the orthogonal agent successfully underwent catalyst-free 1,3-dipolar cycloaddition to unsaturated bonds of glass surfaces to produce Meldrum's acid-functionalized surfaces. The subsequent thermal decomposition of Meldrum's acid moiety in the presence of nucleophiles afforded versatile nucleophile-modified surfaces (e.g., wet, waterproof, and photoactive surfaces). Surface characteristics were investigated with the water contact angle, time-of-flight secondary ion mass spectrometry (TOF-SIMS), and X-ray photoelectron spectroscopy (XPS). In addition, the surface modification of silica nanoparticles using the orthogonal agent was also achieved to evaluate the density of the functional group concentration on the surface.
Fluorinated surfaces show favorable physical properties for material applications. However, fluorination processes of bulk surfaces using conventional reagents require skilled techniques and special equipment. Herein, we demonstrate highly efficient surface modification using a new fluorination tool, perfluoroalkyl‐substituted stable nitrile N‐oxide. The nitrile N‐oxide is successfully synthesized in one‐pot by exploiting 1,1‐diphenylnitroethene as the precursor of nitrile N‐oxide. The nitrile N‐oxide exhibits not only high reactivity but also thermal stability, which enables the simple chemical modification of allyl group‐modified rigid surfaces without catalysts or byproducts. The surface is analysed by X‐ray photoelectron spectroscopy, time‐of‐flight secondary ion mass spectrometry, and contact angle measurements, providing clear evidence that the perfluoroalkyl groups are densely integrated on the bulk surface as a result of the efficient covalent bond formation.
A new orthogonal agent containing phototriggered o‐nitrobenzyl (NB) ether and kinetically stabilized nitrile N‐oxide moieties are synthesized and applied to the reliable catalyst‐free functionalization of materials. This orthogonal reagent enables the modification of rubbers and glass surfaces containing unsaturated bonds through the catalyst‐free [2+3] cycloaddition reaction of nitrile N‐oxide to obtain photolabile NB ether‐functionalized materials. The resulting substrates having an NB ether are suitable to undergo photocontrollable reactions with electrophiles for generating various types of functional materials.
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