Controlled Synthesis of a Chitosan‐Based Graft Copolymer Having Polysarcosine Side Chains Using the NCA Method with a Carboxylic Acid Additive

Summary: A novel chitosan derivative with polysarcosine side chains, i.e., chitosan‐ graft ‐polysarcosine [chitosan‐ graft ‐poly( N ‐methylglycine)], was synthesized by ring‐opening polymerization of sarcosine N ‐carboxyanhydride (NCA) with chitosan as a macroinitiator in the presence of carboxylic acids in dimethyl sulfoxide at 27 °C. Degree of substitution ( DS̄ ) for polysarcosine side chains introduced to chitosan was controlled successfully by the feed amount of the additive nicotinic acid ( DS̄ = 0.21–0.71). Independent of DS̄ control, degree of polymerization ( DP̄ ) for polysarcosine side chains was controlled by adjusting feed ratios of NCA monomer to chitosan ( DP̄ = 14–43). Kinetic analysis of the propagation of sarcosine NCA was conducted by measuring CO 2 evolution. Apparent k p values decreased with increased feed amounts of nicotinic acid, supporting the theory that propagation of NCA in the presence of nicotinic acid proceeds via equilibrium between active amine and dormant ammonium species. Propagation mechanism of carboxylic acid‐mediated polymerization of sarcosine N ‐carboxyanhydride. magnified image Propagation mechanism of carboxylic acid‐mediated polymerization of sarcosine N ‐carboxyanhydride.