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 K a was 18 L mol -1 in CDCl 3 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 decreased in less polar solvent such as benzene. The copolymerization of 2a and styrene afforded the corresponding copolymer. The composition of the rotaxane unit could be controlled by the feed ratio of styrene, while the ratio of complexation of the ammonium group, i.e., rotaxane content to total acrylate, remained almost constant. The acylative neutralization of the resulting polyrotaxane afforded a nonionic polyrotaxane.