From high molecular weight precursor polyrotaxanes to supramolecular sliding networks. The 'sliding gels'

This paper presents the synthesis and characterization of an original class of supramolecular networks, the ' sliding ' gels. In this new class of network materials the crosslink points are not fixed but sliding. The molecular structure is based on intermolecularly crosslinked alpha-cyclodextrins/poly(ethylene-glycol) precursor polyrotaxanes. A synthetic method was developed to obtain various high molecular weight precursor polyrotaxanes with various amounts of alpha-cyclodextrins (alpha-CD) per template chain (the so-called degree of complexation, N). The crosslinking reaction of the precursor polyrotaxanes was carried out with the divinyl-sulfone allowing an efficient and good control of the crosslinking density. This control permitted to obtain various network materials with unusual physical/mechanical properties depending on the crosslinker amount and on N. The unusual properties originate from the sliding character of the crosslink points, in these new network materials, which induces a variable and eventually controllable mean mass distribution of the entanglement length. The mechanical spectroscopy and theological experiments showed two viscoelastic regimes evidencing the molecular mechanism of the change of the mean mass distribution between the crosslink points due to the sliding of alpha-CD rings on the template PEG chain. (c) 2005 Elsevier Ltd. All rights reserved.