SYNTHESIS AND CHARACTERIZATION OF POLYURETHANE-CHITOSAN INTERPENETRATING POLYMER NETWORKS

A polyurethane-chitosan (PU-CH) coating was synthesized from castor-oi l-based PU prepolymer and highly deacetylated and depolymerized chitos an. The films cast with the coating were used for the characterization . X-ray photoelectron spectroscopy, a surface-sensitive technique, ind icated the chemical bonding between the chitosan and PU prepolymer as well as the enrichment of chitosan on the surface of the film PU-CH. E lectron 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 transitio n temperature (T-g1) of the film PU-CH were 10 and 18 degrees C higher than those in the PU film, respectively, and the activation energy (2 7.0 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. I t suggests that the molecular motion in the PU-CH was restricted by gr afted and crosslinked interpenetrating polymer networks (IPNs). The re sults of the differential thermal analysis and thermogravimetric analy sis proved that the thermostability of the film PU-CH was significantl y higher than that of the film PU, and the T-g1 value is in good agree ment with that calculated from ESR. It could be concluded that the IPN s resulted from the chitosan grafting and crosslinking with PU exist i n the film PU-CH. (C) 1998 John Wiley & Sons, Inc.