Applicability and productivity of new click chemistry that exploits a nitrile N-oxide as a 1,3-dipole in polymer synthesis were demonstrated by the polymerization of diynes with a homo ditopic aromatic nitrile N-oxide. The nitrile N-oxide was synthesized in situ by the reaction of the corresponding hydroxamoyl chloride with molecular sieves 4 Å. The click polymerization of various ditopic diynes and the nitrile N-oxide efficiently produced polyisoxazoles in high yields. The homo ditopic nitrile N-oxide was also useful for the connection of bisacetylene-terminated polymers to give multiblock copolymers in very high yield. The resulting polyisoxazoles agree well with the structural assignment obtained by the 1H and 13C NMR analyses. The generated polyisoxazoles showed improved thermal stability due to the presence of isoxazole moieties. The molecular diversity of the obtained polyisoxazoles was confirmed by the selective transformations of the isoxazole moieties into β-aminoenone or β-aminoalcohol moieties with high conversion rates. The thermal decomposition temperature of the transformed polymers was lower than that of the polyisoxazoles because of the formations of abundant amino and hydroxyl groups. Furthermore, the functionality of poly(β-aminoalcohol) was proven by quantitatively cross-linking the polymers by treatment with terephthalaldehyde or methylene diphenyl diisocyanate.

New click chemistry is demonstrated. Click polymerization proceeded via 1,3-dipolar polycycloaddition of homo-ditopic nitrile oxides to bifunctional terminal olefinic and acetylenic monomers as dipolarophiles. Molecular sieves (MS 4A) served as an efficient promoter for the polymerization to afford polyisoxazolines and polyisoxazoles in high yields.

A general method for the one-pot synthesis of stable polymer nitrile N-oxides was developed by a combination of 1,1-diphenylnitroethene with a living anionic polymer. The polymer nitrile N-oxide served as a facile and effective grafting tool for use with polymers containing unsaturated bonds in a catalyst-free and solvent-free [2+3] cycloaddition.

rotaxanes (9 and 12) and poly [3]rotaxanes (10 and 13) were synthesized by a new click polymerization using unstable and stable homoditopic nitrile N-oxides according to rotaxanation and polymerization protocol. Rotaxane monomers were prepared from ethynyl-functionalized crown ether and sec-ammonium salt via the typical urethane end-capping protocol. The homoditopic nitrile N-oxide 8 0 was generated in situ through the reaction of the corresponding hydroxamoyl chloride 8 with molecular sieves 4 A ˚. The click polymerization of diethynyl-functionalized [2]rotaxane 5 and [3]rotaxane monomer 7 with 8 0 efficiently proceeded in the absence of a catalyst to afford well-defined polyrotaxanes 9 and 10 containing a polyisoxazole backbone in high yields. The polymerization of a newly developed kinetically stabilized homoditopic nitrile N-oxide 11 with rotaxane monomers yielded well-defined polyrotaxanes 12 and 13 in high yields under similar conditions. The structures of poly[2]rotaxanes (9 and 12) and poly[3]rotaxanes (10 and 13) were confirmed by 1 H NMR, SEC, and IR analyses. The properties of polyrotaxanes such as solubility and thermal stability were evaluated. These polyrotaxanes showed relatively high thermal stability and good film-forming property based on their good solubility toward ordinary organic solvents.

A kinetically stabilized homoditopic nitrile N-oxide was prepared for a catalyst-free click polymerization that efficiently proceeded via 1,3-dipolar cycloaddition with several bifunctional alkyne, alkene, and nitrile monomers. The polymerization afforded the corresponding polymers with high molecular weights and yields.

Intramolecular 1,3-dipolar cycloaddition of 2-phenoxybenzonitrile N-oxides to benzene rings, accompanied by dearomatization, formed the corresponding isoxazolines in high yields. The X-ray single-crystal structure analysis revealed that the reaction formed the cis-adduct as a single isomer. The substituents on the benzene rings markedly affected the reaction rate, yield, and structure of the final product.

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