Nitrocellulose (NC), a rigid natural polymer, was modified by gradient interpenetrating polymer networks containing poly(ethylene glycol dimethacrylate) (PEGDMA) to obtain both high strength and large toughness across the thickness from surface to the core of samples. PEGDMA content decreased with distance from the surface to core of nitrocellulose with a gradient of poly(ethylene glycol dimethacrylate) (NC/grad. PEGDMA) determined by elemental chemical analysis. The distribution of the guest component across the NC/grad. PEGDMA semi-IPNs sample thickness was reciprocal function. SEM micrographs of NC/grad. PFGDMA semi-IPNs revealed that, when the content of guest component was about 23%, the gradient system showed almost single phase morphology. At the same time, the tensile test results showed that NC/grad. PEGDMA featured both higher tensile strength and larger toughness. (c) 2007 Wiley Periodicals, Inc.