In this work, a two phase crystallization model based on the extension of the Kolmogoroff approach was proposed and verified by comparison with experimental isothermal and nonisothermal crystallization data of Syndiotactic Polystyrene (sPS) in a very wide range of cooling rates, up to 600 degrees C/s. To investigate the effects of high cooling rate on the sPS crystalline structure, a homemade apparatus was adopted. The morphology in solid samples was analyzed by densitometry, IR spectroscopy, and X-rays diffraction. The coupling of these techniques allows the determination of the fractions of different crystalline phases. In agreement with melt-crystallization studies of sPS proposed by different authors, either alpha and beta forms could be produced depending on the thermal history of the sample. Results show that the stable beta form is favored for specimens solidified at higher temperature or under low cooling rates, whereas alpha and mesomorphic forms are favoured at low temperature or high cooling rates. The proposed multi-phase crystallization kinetics model successfully described all the range of experimental data. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1757-1766, 2010