Physical properties of poly(ethylene glycol) (PEG)-based resins for combinatorial solid phase organic chemistry: A comparison of PEG-cross-linked andPEG-grafted resins

Three series of poly(ethylene glycol) (PEG)-based polymers were synthesized and characterized with respect to their physical properties. Polyoxyethyle ne-polyoxypropylene (POEPOP), polyoxyethylene-polyoxetane (SPOCC), and poly oxyethylene-polystyrene (POEPS-3) were synthesized respectively by anion po lymerization, cation polymerization, and radical polymerization. Both bulk and suspension modes were used to synthesize the polymers from derivatized PEG monomers (PEG 400, PEG 900, and PEG 1500). The three supports were comp ared with two commercially available PEG-grafted supports (TentaGel S OH, A rgoGel-OH) and two polystyrene supports (aminomethylated polystyrene [PS-NH 2] and macroporous aminomethylated polystyrene [PLAMS]) with respect to the ir swelling properties, loading, NMR spectral quality, as well as solvent a nd reagent accessibility. Loadings of 0.3-0.7 mmol/g were obtained for the PEG-based resins. Swelling of the PEG-based resins was determined to be hig her than that of the PEG-grafted resins and polystyrene supports. The PEG-b ased resins gave better resolved high-resolution NMR spectra than the PEG-g rafted resins when examined by magic angle spinning nanoprobe (MAS) NMR spe ctroscopy. Moreover, fluorescence quenching of polymer bound 2-amino-benzoa te by protonation with p-toluenesulfonic acid showed moderate to fast diffu sion through the polymer depending on the solvent and the polymer matrix.