Synthesis and characterization of polyurethane–chitosan interpenetrating polymer networks

A polyurethane–chitosan (PU–CH) coating was synthesized from castor-oil-based PU prepolymer and highly deacetylated and depolymerized chitosan. The films cast with the coating were used for the characterization. X-ray photoelectron spectroscopy, a surface-sensitive technique, indicated the chemical bonding between the chitosan and PU prepolymer as well as the enrichment of chitosan on the surface of the film PU–CH. Electron spin resonance (ESR) spectroscopy using the nitroxyl radical 4-hydroxy-2,2,6,6-tetramethyl piperidine-1-oxyl (4-hydroxy-TEMPO) as a reporter group was used to study the chain mobility in the film PU–CH. It was observed that T_50G of the probe and the first glass transition temperature (T_g1) of the film PU–CH were 10 and 18°C higher than those in the PU film, respectively, and the activation energy (27.0 kJ mol⁻¹) of tumbling for the probe covalently bonded with PU–CH was 12.8 kJ mol⁻¹ higher than that of the probe with the film PU. It suggests that the molecular motion in the PU–CH was restricted by grafted and crosslinked interpenetrating polymer networks (IPNs). The results of the differential thermal analysis and thermogravimetric analysis proved that the thermostability of the film PU–CH was significantly higher than that of the film PU, and the T_g1 value is in good agreement with that calculated from ESR. It could be concluded that the IPNs resulted from the chitosan grafting and crosslinking with PU exist in the film PU–CH. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1321–1329, 1998