The gelation and crystallization processes in solution of syndiotactic polystyrene ill toluene and toluene + carbon dioxide fluid mixutures were studied in a variable-volume view-cell system over a pressure range from 7 to 50 MPa for polymer concentrations up to 25 wt % and for CO2 concentrations up to 43 wt% All the solutions in toluene and in toluene + CO2 Mixtures up to 16 wt % CO2 displayed only a sol-gel boundary. Solutions with 28 wt % CO2 displayed also a liquid-liquid phase boundary. Solutions in 43% CO2 displayed instead a fluid-solid crystallization boundary along with a liquid-liquid phase boundary. Consequences of the phase separation path on the eventual morphology and the crystal state of the polymer were investigated. When Solutions are cooled to room temperature while maintaining pressure constant during, which the sol-gel boundary is crossed first. the resulting morphology is fibrillar and the polymer displays the 6 crystal form with,I trace amount of the beta form. When the solutions are depressurized instead, holding the temperature constant during which liquid-liquid phase boundary is crossed first, with further cooling the polymer-rich phase (PRP) leads to a stacked-lamellar morphology with the beta crystal form. The polymer-lean phase (PLP) leads to a mixed morphology with lamellar layers connected with fibrils and the polymer displays a mixed crystal Structure consisting of the delta + beta polymorphs. In the absence of gelation at high CO2 levels, the crystallization leads to only the beta polymorph. A mechanistic framework is provided to account for the formation of these different polymorphs front the different phase separation paths followed.