A novel flame retardant, tetra(5,5-dimethyl1,3- dioxaphosphorinanyl-2-oxy) neopentane (DOPNP), was synthesized successfully, and its structure was characterized by FT-IR, (1)H NMR, and (31)P NMR. The thermogravimetric analysis (TGA) results demonstrate that DOPNP showed a good char-forming ability. Its initial decomposition temperature was 236.4 degrees C based on 1% mass loss, and its char residue was 41.2 wt % at 600 degrees C, and 22.9 wt % at 800 degrees C, respectively. The flame retardancy and thermal degradation behavior of novel intumescent flame-retardant polypropylene (IFR-PP) composites containing DOPNP were investigated using limiting oxygen index (LOI), UL-94 test, TGA, cone calorimeter (CONE) test, and scanning electron microscopy (SEM). The results demonstrate that DOPNP effectively raised LOI value of IFR-PP. When the loading of IFR was 30 wt %, LOI of IFR-PP reached 31.3%, and it passed UL-94 V-0. TGA results show that DOPNP made the thermal decomposition of IFR-PP take place in advance; reduced the thermal decomposition rate and raised the residual char amount. CONE results show that DOPNP could effectively decrease the heat release rate peak of IFR-PP. A continuous and compact char layer observed from the SEM further proved the flame retardance. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3430-3439, 2011