The crystal polymorphism and phase transition mechanisms upon specific annealing schemes imposed on either neat syndiotactic polystyrene (sPS) or its miscible blends with atactic polystyrene (aPS) were examined using Fourier transform infrared (FT-IR) and wide-angle X-ray diffraction (WAXD). The neat sPS or blends were made in such ways that they started as either initially an amorphous/quenched material or solvent-treated to contain initially some trace crystalline gamma-form. Cold crystallization imposed on the initially quenched/amorphous sPS led to the random-coil chains being crystallized into initially a mesomorphic form and subsequently into a more perfect crystalline alpha'-form. IR spectroscopy characterization confirmed a series of structural changes with respect to the annealing temperature imposed on initially quenched/amorphous sPS and revealed a transition from a mesomorphic form to a crystalline alpha'-form via a nucleation and growth process. Conversely, cold crystallization imposed on the initially quenched miscible blends (sPS/aPS) did not involve a mesomorphic form but developed directly into a crystalline alpha- and/or beta-form upon further annealing to higher temperatures. However, the transition behavior was similar between the solvent-cast neat sPS and solvent-cast sPS/aPS blend upon annealing to higher temperatures. The solvent (1,1,2,2-tetrachloroethane)-induced gamma-form in the sPS/aPS blend or neat sPS samples, upon heating to temperatures above 200 degreesC, both exhibited crystal reorganization of the melted crystalline gamma-form originally present, which led to formation of the crystalline alpha'-form. The mechanisms and causes for the different routes of phase transitions in neat sPS or its miscible blends were discussed and analyzed.