Polyrotaxane Networks Formed via Rotaxanation Utilizing Dynamic Covalent Chemistry of Disulfide

Polyrotaxane networks were synthesized from a mixture of poly(crown ether)s (2-5) as a trunk polymer and dumbbell-shaped bifunctional secondary ammonium salt 6 bearing a disulfide linkage and bulky end caps as a cross-linking agent in the presence of a catalytic amount of benzenethiol via a reversible thiol-disulfide interchange reaction. Trunk polymers 2-4 were prepared by copolymerization of bis(hydroxymethyl)dibenzo-24-crown-8-ether I and comonomers. Poly(crown ether) 5 bearing a poly(tetrahydrofuran) (PTHF) spacer was also synthesized from 1 and PTHF with 4,4'-methylenebis(phenyl isocyanate) (MDI) in N,N-dimethylacetamide (DMAc) at room temperature. The treatment of these poly(crown ether)s (2-5) with axle component 6 in the presence of benzenethiol gave the corresponding polyrotaxane networks (7-10) in quantitative yields. We confirmed the cross-linking process by monitoring the H-1 NMR spectral change during the polymerization. Thermal properties, swelling, and dynamic viscoelasticity of these polyrotaxane networks were evaluated. Polyrotaxane network 10 bearing 5 afforded higher swelling and elasticity than those of other networks because of the flexibility of the trunk polymer as wheel components.