Topological polymer networks with sliding cross-link points: The "sliding gels". Relationship between their molecular structure and the viscoelastic as well as the swelling properties
Résumé
Topological polymer networks with sliding cross-link points, the "sliding gels" (also called slide-ring gels), are a new class of supramolecular networks based on intermolecularly cross-linked alpha-cyclodextrins/poly(ethylene glycol) polyrotaxane precursors. The cross-link points of such networks are not fixed but can slide along the template chain of the polyrotaxanes. The main parameters governing the sliding gel properties are the number of cyclodextrins per polyrotaxane, the cross-linking density, and the nature of the swelling solvent. Small-angle neutron scattering, swelling measurements, and mechanical spectrometry were used to understand the unusual physical properties and their relation to the molecular structure of the sliding gels. The swelling as well as the viscoelastic properties are found to be solvent dependent reflecting the structural changes of the network. Indeed, in water, the number of cross-link points (topological and physical) increases as opposed to dimethyl sulfoxide (DMSO) leading to higher modulus values, while the persistence length of the sliding gel strands increases in DMSO as opposed to water leading to a shift of the tan(delta) peak, the transition point between the two observed viscoelastic regimes, toward higher frequencies.