Hydrophilic PEG-based resins

These resins have their roots in the polyacrylamide resins introduced in the 1980s for SPPS using the fluorenylmethoxycarbonyl (Fmoc)-tert-butyl (tBu) strategy. They were developed following the concept that the insoluble support and peptide backbone should have comparable polarities [44]. 

Kempe and Barany [45] developed the CLEAR family, which is based on the copolymerization of branched PEG-containing cross-linkers such as trimethylol-propane ethoxylate triacrylate, which contain various ethylene oxide units, with amino-functionalized monomers such as allylamine or 2-aminoethylmethacrylate. These amino groups constitute the starting points for the solid-phase synthesis. The loadings of these solid supports are affected by the amount of functionalized monomer used for polymerization. Typical loadings are in the range 

l-OAmmolg-1. The CLEAR family supports swell in a broad range of hydro-phobic and hydrophilic solvents and has excellent physical and mechanical properties for both batch-wise and continuous-flow systems. 

The compatibility of all these PEG-based resins with aqueous buffers allows their use for biochemical applications such as on-resin screening of chemical libraries and in the development of affinity chromatography [58-61]. All these families of PEG-based resins, except POEPS, are free of aromatic rings. This feature makes these solid supports highly suitable for a broad range of applications where such rings can react with reagents or/and jeopardize the solid-phase NMR control of the reactions [62]. 

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