Structural–dynamical relationship in silica PEG hybrid gels
Résumé
Hybrid organic–inorganic materials have been prepared from mixtures of tetraethoxysilane and poly(ethylene glycol) (PEG) of low molecular mass. These materials are diphasic systems in which silica aggregates, controlling the mechanical properties, are wrapped around by the polymer phase. Strong correlations between the synthesis scheme, the structure and the properties of these materials are evidenced. Solid-state 29Si NMR points out the change of the silica morphology with the nature of the catalyst (acidic, [HCl] or nucleophilic, [NH4F]). In addition, these changes induce strong variations of the thermal properties of the PEG phase. The structural and dynamical inhomogeneities of the PEG are analyzed using 13C NMR and EPR spectroscopies. Near the SiO2 surfaces, hydrogen bonding hinders the motion of the PEG chains, while the bulk of the polymeric phase possesses the same properties as the polymer melt. Thermal analyses (DSC) disclose the difference between materials prepared with the various catalysts which are related to the degree of interpenetration between the two phases.