Preparation and performance of Pd particles encapsulated in block copolymer nanospheres as a hydrogenation catalyst

Triblock nanospheres with hydroxylated polyisoprene (PHI) coronas, cross-linked poly(2-cinnamoyloxyethyl methacrylate) shells, and poly(acrylic acid) (PAA) cores were prepared following a method described previously. Equilibrating such nanospheres with a PdCl2 solution in methanol enabled the loading of Pd2+ into the PAA cores of the nanospheres. After the excess PdCl2 in the methanol phase was removed, Pd(II) inside the nanosphere cores was reduced with hydrazine to yield Pd nanoparticles. Such encapsulated Pd particles were dispersed in methanol or water, which solubilized PHI. Like Pd black, the nanosphere-encapsulated Pd nanoparticles catalyzed the hydrogenation of alkenes. The need for the reactant(s) to diffuse into and products to diffuse out of the encapsulating nanospheres expectedly slowed the catalytic reactions. The more interesting aspect had been in our ability to modify the activity of the Pd catalyst via changing the pH and thus the conformation of the encapsulating polymer chains.