“Silica-graft-polyamidoamine hybrid materials: effect of constraints on the polymer mobility”

Organic-inorganic hybrid materials with excellent heavy metal ions
chelating properties are synthesized by covalent bonding of multifunctional
polymers of polyamidoamine (PAA) type onto silica. Two series of polyamidoaminesilica
hybrid materials differing in the PAA chemical structure are prepared and
their thermal properties are investigated. Differential Scanning Calorimetry (DSC)
is used to study the effects of chain immobilization and ion chelation on the
glass-transition temperature (Tg) of the polymers. The Tg of PAA-hybrid materials
is elevated with respect to ungrafted PAAs, but when the linear and the
corresponding hybrid PAAs are in the complex form with metal ions such as Cu2+ and
Co2+, the materials arrive to the decomposition temperature and no Tg is detected.
To highlight the effect of metal ion on the molecular mobility of these systems,
an oligomeric plasticizer is added. The behaviour in the T g region is analyzed
and discussed in term of Tool-Narayanaswamy- Moynihan (TNM) model. In particular
the apparent activation energy [Δh*) is used to discuss overall segmental cooperativity
in order to better understand the effect of complex formation on
structural mobility.