Synthesis of Main-Chain-Type Polyrotaxanes by New Click Polymerization Using Homoditopic Nitrile N-Oxides via Rotaxanation-Polymerization Protocol

Main-chain-type poly[2]rotaxanes (9 and 12) and poly[3]rotaxanes (10 and 13) were synthesized by a new click polymerization using unstable and stable homoditopic nitrite 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 nitrite N-oxide 8' was generated in situ through the reaction of the corresponding hydroxamoyl chloride 8 with molecular sieves 4 angstrom. The click polymerization of diethynyl-functionalized [2]rotaxane 5 and [3]rotaxane monomer 7 with 8' 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 nitrite 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 H-1 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.