TentaGel® resins are grafted copolymers consisting of a low crosslinked polystyrene matrix on which polyethylene glycol (PEG or POE) is grafted via an ethyl ether group which increases stability towards acid treatment and minimizes PEG-leaching. These copolymers are pressure stable. TentaGel® resins have high diffusion rates and excellent swelling in a wide range of solvents from e.g. toluene to water. 4-Formyl-3-Methoxy Phenol (FMP-Linker) coupled to TentaGel® Resins.