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Synthesis and Application of Monodisperse Oligo(Oxyethylene)-Grafted Polystyrene Resins for Solid-Phase Organic Synthesis
journal contribution
posted on 2014-07-14, 00:00 authored by Daniel Lumpi, Christian Braunshier, Ernst Horkel, Christian Hametner, Johannes FröhlichIn
a preliminary investigation by our group, we found that poly(styrene-oxyethylene)
graft copolymers (PS-PEG), for example, TentaGel resins, are advantageous
for gel-phase 13C NMR spectroscopy. Because of the solution-like
environment provided by the PS-PEG resins, good spectral quality of
the attached moiety can be achieved, which is useful for nondestructive
on-resin analysis. The general drawbacks of such resins are low loading
capacities and the intense signal in the spectra resulting from the
PEG linker (>50 units). Here, we describe the characterization
of
solvent-dependent swelling and reaction kinetics on a new type of
resin for solid-phase organic synthesis (SPOS) that allows an accurate
monitoring by gel-phase NMR without the above disadvantages. A series
of polystyrene-oligo(oxyethylene) graft copolymers containing monodisperse
PEG units (n = 2–12) was synthesized. A strong
correlation between the linker (PEG) length and the line widths in
the 13C gel-phase spectra was observed, with a grafted
PEG chain of 8 units giving similar results in terms of reactivity
and gel-phase NMR monitoring to TentaGel resin. Multistep on-resin
reaction sequences were performed to prove the applicability of the
resins in solid-phase organic synthesis.