Synthesis and characterization of cyclic and linear helical poly(α‐peptoid)s by N‐heterocyclic carbene‐mediated ring‐opening polymerizations of N‐substituted N‐carboxyanhydrides

• DOI: 10.1002/bip.21597
• Publication Date: 2011-02-03T15:50:54Z
• Authors: Li Guo; Jinhai Li; Zachary Brown; Kushal Ghale; Donghui Zhang
• Keywords: Peptoid; Dispersity; Degree of polymerization

Cyclic poly(alpha-peptoid)s [a.k.a. poly(N-R-glycine)] with chiral aromatic side-chains [R = (R)- or (S)-CHMePh] have been synthesized by N-heterocyclic carbene-mediated ring-opening polymerization of N-substituted N-carboxyanhydrides (N(R-NCA)). Their linear analogs prepared primary amine-initiated the corresponding N(R-NCA). Poly[(R)/(S)-N-CHMePh-glycine] polymer molecular weights (MWs) in range 4-15 kg mol(-1) and low MW distribution (Polydispersity index (PDI) < 1.15) can be readily accessed these methods. high were not obtained due to competitive formation cyclic oligomeric species that result from intramolecular transamidation. Intrinsic viscosity measurements confirm architectural difference between polymers two methods reveals both poly[(S)-N-CHMePh-glycine]s behave as random-coil 0.1M LiBr/Dimethylformamide (DMF) solution. Circular dichroism analysis suggests retain polyproline I helix conformations, analogously previously reported oligomers. Differential scanning calorimetry poly[(S)-N-CHMePh-glycine] are amorphous glass transition temperature (T(g) 122 degrees C) being notably higher than 112 identical MW. These results consistent absence chain ends, causing reduced segmental mobilities.