Sodium benzoate (SB), a conventional nucleating agent of a-phase isotactic polypropylene (iPP) was discovered to induce the creation of beta-phase iPP under certain crystalline conditions. Polarized optical microscopy (POM) and wide angle X-ray diffraction (WAXD) were carried out to verify the versatile nucleating activity of SB and investigate the influences of SB's content, isothermal crystallization temperature, and crystallization time on the formation of beta-phase iPP. The current experimental results indicated that, under isothermal crystallization conditions, SB showed peculiar nucleating characteristics on inducing iPP crystallization which were different from those of the commercial P form nucleating agent (TMB-5). The content of P crystal form of iPP nucleated with SB (PP/SB) increased initially with the increase of crystallization temperature, nucleating agent (SB) percentage or crystallization time, reached a maximum value, and then decreased as the crystallization temperature, nucleating agent percentage or crystallization time further increased. While the content of beta crystal form of iPP nucleated with TMB-5 (PP/TMB-5) showed a completely different changing pattern with the crystallization conditions. The obvious difference of the two kinds of nucleating agents on inducing iPP crystallization can be explained by the versatile nucleating ability of SB. (c) 2008 Wiley Periodicals, Inc.