Synthesis of Complementary Host- and Guest-Functionalized Polymeric Building Blocks and Their Self-Assembling Behavior

Abstract

New polymers that incorporate paraquat or crown ether moieties as chain ends or central units were synthesized by stable free radical polymerization (SFRP) and atom transfer radical polymerization (ATRP). For SFRP, TEMPO derivatives that contain a functional unit were used as initiators. For ATRP, a copper−amine or copper−bipyridine complex was used as a catalyst with radical initiators from halide derivatives of paraquat and crown ethers. These end- or center-functionalized polymers formed pseudorotaxane complexes with complementary small molecules. They also formed reversible pseudorotaxane polymers: chain-extended, star-shaped homopolymers, and block copolymers. Complexation studies to determine stoichiometry and association constants with thermodynamic parameters were performed by NMR spectroscopy and isothermal microcalorimetric (ITC) titration. The association constants of crown ether derivatives and paraquat compounds in chloroform were measured for the first time: Ka = 2.97 × 103 M−1 for paraquat polystyrene and bis(m-phenylene)-32-crown-10 and Ka = 4.38 × 103 M−1 for paraquat polystyrene and crown ether polystyrene. These are 4−6-fold higher than the association constant of the analogous small molecule host−guest system in acetone.