Poly ethylene glycol -Polystyrene Graft Polymers

Poly(ethylene glycol)-Polystyrene Graft Polymers... 

Poly(ethylene glycol) grafted on crosslinked polystyrene (PEG-PS) resin has often been used as a polymer support for chiral catalysts of reactions performed in aqueous media. Peptides immobilized to PEG-PS resin have been developed and used as a catalyst for direct asymmetric aldol reactions in aqueous media (Scheme 3.19) [42]. When tripeptide-supported PEG-PS 67 was used as chiral catalyst in the reaction between 70 and acetone, the corresponding aldol product 69 was obtained with 73% ee. Kudo further developed the one-pot sequential reaction of acidic deacetalization and enanhoselective aldol reaction by using an Amberhte and PEG-ST-supported peptide catalyst 67 [43]. The enantioenriched aldol product 72 was obtained in 74% isolated yield from acetal 70 in a one-pot reaction (Scheme 3.20). 

The membrane surfaces have also been grafted or coated with polyacrylamide, poly(acrylic acid) [70, 71], poly(vinyl alcohol) and cellulose derivatives [72]. Another possibility for improving the membrane properties is the use of polymer blends. Blends of PVDF/PVP [73, 74], PVDF/poly(ethylene glycol) (PEG) [75], PVDF/sulfonated polystyrene [76], PVDF/poly(vinyl acetate) [77] and PVDF/ poly(methyl methacrylate) [78] have been used in the preparation of micropor-ous membranes. 

Glycopeptide 31 was synthesized in a custom-made, fully automatic continuous-flow peptide synthesizer constructed essentially as described elsewhere (19). A resin consisting of a cross-linked polystyrene backbone grafted with poly(ethylene glycol) chains (TentaGel , Rapp Polymer, Germany) and functionalized with the Rink amide linker (p-[a-(fluoren-9-ylmethoxyformamido)-2,4-dimethoxybenzyl]phenoxyacetic acid, Nova-biochem, Switzerland) was used for the syntheses. DMF was distilled before use. 

The extremely low friction achieved on PLL(20)-g[2.9]-PEG(5) films in SFA experiments is not a unique property of this specific copolymer but has also been observed for other grafted poly(ethylene glycol) films as well as for other polymer-brush systems in a good solvent, such as grafted polystyrene in toluene. The osmotic pressure, which leads to strong repulsive forces as the polymer brushes are compressed, effectively prevents the direct contact of the solid surfaces. At comparable solid surface separations, thin films of water or aqueous salt solutions have been shown to retain a shear fluidity characteristic of the bulk liquid. In a control experiment, this was also observed in 10 mM HEPES buffer solution (data not shown). 

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