We prepared novel semi-interpenetrating polymer network (semi-IPN) materials by mixing poly(ester urethane), synthesized by the polymerization reaction between poly(ethylene glycol adipate) and toluene diisocyanate in the presence of 2,2-bis(hydroxyl methyl) propionic acid as an extender, with nitrokonjac glucomannan (NKGM) in tetrahydrofuran and then by crosslinking and curing the mixture at 60degreesC for 1.5 h. Miscibility and the properties of the sheets were studied by Fourier transition infrared spectroscopy, wide-angle X-ray diffraction, differential scanning calorimetry (DSC), and scanning electron microscopy. The results indicate that strong interactions between poly(ester urethane) and NKGM in the semi-IPN sheets occurred, leading to good miscibility between the two polymers in the whole region of component ratios. When the content of NKGM was 10%, the tensile strength and breaking elongation of the serni-IPN sheet were simultaneously enhanced to 35 MPa and 960%, respectively, compared with pure polyurethane. The DSC curves showed a low softening temperature for the poly(ester urethane), which resulted in the high elongation. By changing the NKGM amount from 10 to 90%, we prepared a series of composite materials from an elastomer to tough plastics. (C) 2003 Wiley Periodicals, Inc.