Hinge-linked polymer gels : a rigid network cross-linked with a rotatable tetrasubstituted ferrocene

A novel polymeric gel is designed and synthesized, based on rotatable 1,1,3,3-tetrakis(4-aminophenyl)ferrocene cross-linking units capable of hinge-like motion. This hinge-linked gel results from an end-to-end reaction between the ferrocene-based cross-linker and a bifunctional poly(amide acid) oligomer. The cross-linking reaction efficiency is estimated by sol fraction analysis based on the Miller-Macosko model. Mechanical properties and rheological measurements show that the hinge-linked gel exhibits good mechanical stability and perfect elastic properties, although the gel cross-linking depends solely on metal-organic coordination at the ferrocenyl center. The hinge-linked network concept presented herein offers a novel design concept, which may be applicable to a variety of polymeric materials such as resins, metal-organic frameworks, and gels.