Host-Guest Driven Copolymerization of Tetraphosphonate Cavitands

The outstanding complexing properties of tetraphosphonate cavitands towards N-methylpyridinium salts were exploited to realise a new class of linear and cyclic AABB supramolecular polymers through host-guest interactions. The effectiveness of the selected self-association processes was tested by 1HNMR studies, whereas microcalorimetric analyses clarified the binding thermodynamics and revealed the possibility of tuning entropic contributions by acting on the flexibility of the guest linker. Although the formation of linear polymeric chains for a rigid system was demonstrated by X-ray analysis, the presence of a concentration-dependent ring-chain equilibrium was indicated by solution viscosity measurements in the case of a very flexible ditopic BB guest co-monomer. Supramolecular alternating copolymers: Cyclic and linear AABB supramolecular copolymers were prepared by connecting complementary monomeric units through host-guest interactions. Thermodynamic and topological control of this process was achieved by controlling the flexibility of the ditopic guest spacer, solvent and concentration. The structure of the alternating copolymer formed by self-assembly of a bis(tetraphosphonate cavitand) and methyl viologen is shown.