Primary Amine‐Initiated Polymerizations of Alanine‐NCA and Sarcosine‐NCA

Abstract

Abstract Summary: Sarcosine‐ N ‐carboxyanhydride (Sar‐NCA), L ‐alanine‐NCA and D,L ‐alanine‐NCA were polymerized with benzylamine as initiator in three different solvents: dichloromethane (CH 2 Cl 2 ), 1,4‐dioxane and dimethylformamide (DMF). The isolated polyaminoacids were characterized by 1 H NMR spectroscopy and MALDI‐TOF mass spectrometry. High conversions and degrees of polymerization $\overline {DP}$ s close to the monomer‐initiator (M/I) ratios were found for all polypeptides. For polysarcosine which was soluble under the given reaction conditions a narrow monomodal frequency distribution was found. In contrast, a broad frequency distribution was observed, when L ‐alanine NCA was polymerized in dioxane and DMF. These results were attributed to a partial precipitation of oligopeptides in the β ‐sheet structure, which reduces the reactivity of endgroups for steric reasons. The polymerizations of D,L ‐alanine‐NCA showed features in between the extremes of Sar‐NCA and L ‐Ala‐NCA. Schematic illustration of the secondary structures formed in a primary amine initiated polymerization of L ‐Ala‐NCA. image Schematic illustration of the secondary structures formed in a primary amine initiated polymerization of L ‐Ala‐NCA.