Synthesis and characterization of Helix-coil block copoly(α-peptoid)s

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Helix-coil block copoly(α-peptoid)s [i.e., polyOS-TV-CHMePh-glycine)- b-poly(Af-Bu-glycine) (PNEPG-b-PNBG)] have been synthesized by N-heterocyclic carbene (NHC)-mediated sequential ring-opening polymerizations (ROP) of the corresponding TV-substituted TV-carboxyanhydride monomers (NCHMePh- NCA and N-NCA). The helical block degree of polymerization (DP) has been kept constant, whereas the coil block DP has been varied by changes to the ratio of the second monomer to initiator (i.e., [NBu-NCA]0:[NHC] 0). SEC analysis reveals an increase of polymer molecular weight (MW) as the [NBu-NCA]0:[NHC]0 ratio is increased, confirming the formation of block copoly(α-peptoid)s having reasonably narrow molecular weight distribution (PDI =1.15-1.26). The copolymer structure has been verified by 1H and 13C{1H} NMR spectroscopy. Polymer MWs obtained by 1H NMR analysis agree with the theoretical MWs for living polymerization. Circular dichroism (CD) analysis reveals that all block copoly(a-peptoid)s exhibit enhanced helical conformational stability than the PNEPG homopolymers, as manifested by the larger mean residual ellipticity (MRE) in the former. The degree of enhancement depends on the copolymer composition. © 2011 American Chemical Society.

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ACS Symposium Series

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