Gel-Type Support

Figure 6. Schematic representation of the micro- and nanoscale morphology of nanoclustered metal catalysts supported on gel-type (a) and macroreticular (b) resins [13]. The nanoclusters are represented as black spots. Level 1 is the representation of the dry materials. Level 2 is the representation of the microporous swollen materials at the same linear scale swelling involves the whole mass of the catalyst supported on the gel-type resin (2a) and the macropore walls in the catalyst supported on macroreticular resin (2b). The metal nanoclusters can be dispersed only in the swollen fractions of the supports, hence their distribution throughout the polymeric mass can be homogeneous in the gel-type supports, but not in the macroreticular ones (3a,b). In both cases, the metal nanoclusters are entangled into the polymeric framework and their nano-environment is similar in both cases, as shown in level 4.

This so-called phosphodiester method [92] was later also performed on cross-linked polystyrene [93], macroporous 25% cross-linked polystyrene [94], silica [95], poly(-vinyl alcohol) [96,97], proteins [98], PEG [99], and polyacrylamide [100]. This extensive evaluation of different supports stemmed from the observation that cross-linked polystyrene or other gel-type supports were not ideal for the preparation of phospho-... 

Pepsyn by DVB polyacrylamide (Figures la and 2a) gel-type support, beaded shape [41-43]... 

In the swollen state the gel-type supports can best be described as polymeric solutions and the reactions take place on solubilized polymer chains within each bead, which act as small, individual reaction vessels. Depending on the degree of crosslinking and the degree of swelling, the polymer chains are more or less flexible, a fact that affects the reaction rates. The mass transport of reactants to the reactive sites inside the polymer beads is driven by... 

A great variety of resins and solid supports are available for combinatorial work (151). Gel-type supports are popular and consist of a flexible polymeric matrix to which is attached functional groups capable of binding small... 

The original pin support was poly(acrylic acid) grafted onto inert polyethylene, where the carboxylic acid moieties were capped with mono Boc-protected ethyl-enediamine [79]. PS and the extremely hydrophilic polyhydroxyethyl methacrylate and poly(methacrylic add/dimethylacrylamide) were also grafted on [81]. The last grafted support in the Multipin concept is the so-called Lanterns [80], where the actual solid support is PS, which can be functionalized in a similar way to PS gel-type supports. 

Gel-type supports. Gel-type supports are most often used for solid-phase synthesis and feature equal distribution of functional groups throughout a highly solvated and inert polymer network ideal for the assembly of large molecules. The support capacity can be adjusted to afford problem-free synthesis and a high yield per volume of resin. The polymer network is flexible, and the resin can expand or exclude solvent to accommodate the growing molecule within the gel. There are four types of gel resins ... 

Gel-type supports Highly solvated polymers with an equal distribution of functional groups, for example, polystyrene, polyacrylamide (hydrophilic alternative to polystyrene), and poly(ethylene glycol) (PEG). 

---