Use of smart polymers in catalysis

Transformation of SPs, swelling-shrinking, was used to control the activity of the embedded catalysts (Lu et /., 2006,2009a). Metal nanoparticles such as Ag, Au, Rh or Pt were embedded inside the pNIPAM shell and their exposure to the medium meant that their catalytic activity was dependent on the temperature-induced conformational changes of the polymer (Fig. 13.8). 

Metal nanoparticles embedded inside temperature-responsive polymer brushes (Lu et al., 2006) or cross-linked pNlPAM shell (Lu dai,2009a) were tested for the oxidation of alcohols to corresponding aldehydes or ketones (Lu et al., 2009a). The nanoparticles were fully accessible to the reactants at the temperature below the LCST of pNIPAM. Swelling-shrinking could be 

8 Poly(styrene) composite particles consisting of thermosensitive core-shell of pNIPAM in which Ag nanoparticles are embedded. 

The composite particles are suspended in water which swells the thermosensitive network attached to the surface of core particles. In this state the reagents can diffuse freely to the nanoparticles that act as catalysts. At higher temperature T 30°C) the network shrinks and the catalytic activity of the nanoparticles is strongly diminished. Source Reproduced from Lu, Mei, Drechsler and Ballauff (2006). Thermosensitive core-shell particles as carriers for Ag nanoparticles Modulating the catalytic activity by a phase transition in networks. Angewandte Chemie-International Edition, 45, 813-816. Copyright (2005), with permission from John Wiley and Sons.) (Lu etal., 2006). 

Similar particulate systems with a polyelectrolyte polymer core have been developed for the immobilisation of nanoparticles and enzymes (Lu et al, 2009b). In both cases the core of the particles was used for stabilising the catalytic systems, preventing their agglomeration and for easier handling and recovery after the completion of the reaction. In the case of the enzymes, polyelectrolyte polymer core particles present a better way of enzyme immobilisation than immobilisation on solid surfaces. The mild conditions inside the poly electrolyte core preserve the native conformation and biological activity of enzymes. 

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