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

Abstract

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 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′ was generated in situ through the reaction of the corresponding hydroxamoyl chloride 8 with molecular sieves 4 Å. 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 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 1H 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.