Synthesis of Nanocomposites from Pd0 and a Hyper-Cross-Linked Functional Resin Obtained from a Conventional Gel-Type Precursor

Hyper-cross-linked resins stemming from a gel-type poly-chloro- methylated poly(styrene- co -divinylben- zene) resin (GT) have been investigat- ed by a multi-methodological approach based on elemental analysis, scanning electron microscopy, X-ray microanaly- sis, and solvent absorption. The hyper- cross-linking of the parent resin was ac- complished by Friedel–Crafts alkyla- tion of the phenyl rings of the resins with the chloromethyl groups. This pro- duced a permanent pore system com- prising both micropores ( < 2.0 nm in diameter) and mesopores (2.2 nm). The chloromethyl groups that did not react in the hyper-cross-linking step were transformed into methylmercaptan groups and the latter were then con- verted into sulfonic groups by oxida- tion with hydrogen peroxide. By this procedure the extensive permanent po- rosity of the parent unsulfonated hyper-cross-linked polymer (HGT) was retained by the sulfonated polymer (HGTS). The final exchange capacity of HGTS was determined to be 0.36 mmolg 1 . HGTS was easily meta- lated with Pd II and the subsequent re- duction of the metal centers with either aqueous sodium borohydride, formal- dehyde, or dihydrogen produced three Pd 0 /HGTS nanocomposites. The metal nanoparticles had diameters in the 1– 6 nm range for all the nanocomposites, as determined by TEM, but with some- what different distributions. When formaldehyde was used, more than 90% of the nanoparticles were less than 3 nm and their radial distribution throughout the polymer beads was quite homogeneous. These findings show that with this reducing agent the metal nanoparticles are generated within the pore system of the polymer matrix, hence their size is controlled by the dimensions of the pores of the pol- ymeric support