Synthesis of Side-Chain Polyrotaxane by Radical Polymerizations of Pseudorotaxane Monomers Consisting of Crown Ether Wheel and Acrylate Axle Bearing Bulky End-Cap and Ammonium Group

The mixing of an acrylate 1a bearing secondary ammonium salt moiety and terminal di-tert-butylphenyl group with dibenzo-24-crown-8 (DB24C8) afforded the pseudorotaxane monomer 2a. The association constant Ka was 18 L mol-1 in CDCl3 at 25 °C. An equimolar mixture of 1a and DB24C8 was heated at 60 °C for 20 h in benzene (0.5 M) in the presence of AIBN to give side-chain-type polyrotaxane in 66% yield. The incorporation ratio of the rotaxane unit, which is denoted by R, in the polyrotaxane was 0.42. The R value increased as the polymerization temperature decreased or the dielectric constant of the solvent decreased. The effect of the molar ratio [DB24C8]/[1a] on the R value was complicated since DB24C8 itself enhanced the polarity of the system. The R value increased until [DB24C8]/[1a] reached 1.0 in benzene, chlorobenzene, and 1,2-dichloroethane. When [DB24C8]/[1a] > 1, however, the R value increased gradually as [DB24C8]/[1a] increased in polar solvent such as 1,2-dichloroethane, while the R value rather ...