Polyrotaxane Networks Formed via Rotaxanation Utilizing Dynamic Covalent Chemistry of Disulfide

Abstract

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 1 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 1 H 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.