Controlled synthesis of a chitosan-based graft copolymer having polysarcosine side chains using the NCA method with a carboxylic acid additive

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 degrees C. Degree of substitution ((DS) over bar) for polysarcosine side chains introduced to chitosan was controlled successfully by the feed amount of the additive nicotinic acid ((DS) over bar =0.21-0.71). Independent of (DS) over bar control, degree of polymerization ((DP) over bar) for polysarcosine side chains was controlled by adjusting feed ratios of NCA monomer to chitosan ((DP) over bar =14-43). Kinetic analysis of the propagation of sarcosine NCA was conducted by measuring CO2 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.