STRUCTURAL-DYNAMICAL RELATIONSHIP IN SILICA PEG HYBRID GELS

Hybrid organic-inorganic materials have been prepared from mixtures of tetraethoxysilane and poly(ethylene glycol) (PEG) of low molecular ma ss. These materials are diphasic systems in which silica aggregates, c ontrolling the mechanical properties, are wrapped around by the polyme r phase. Strong correlations between the synthesis scheme, the structu re and the properties of these materials are evidenced. Solid-state Si -29 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 t he PEG phase. The structural and dynamical inhomogeneities of the PEG are analyzed using C-13 NMR and EPR spectroscopies. Near the SiO2 surf aces, hydrogen bonding hinders the motion of the PEG chains, while the bulk of the polymeric phase possesses the same properties as the poly mer melt. Thermal analyses (DSC) disclose the difference between mater ials prepared with the various catalysts which are related to the degr ee of interpenetration between the two phases.