The thermodynamics (temperature-concentration phase diagram), the crystal structure, and the morphology of systems prepared from syndiotactic polystyrene (sPS) in naphthalene, a solvent solid at room temperature, are reported. From the temperature-concentration phase diagram and from neutron diffraction investigations, it is shown that sPS/naphthalene can form two compounds of differing stoichiometries but having the same diffraction pattern. Time-resolved X-ray diffraction experiments are in agreement with the outcomes of the T-C phase diagram. The morphology of these systems is found to be essentially fibrillar and reminiscent of thermoreversible gels obtained from sPS in low-melting-point solvents.