The phase transitions occurring in bulk samples of the syndiotactic polystyrene-toluene complex were monitored by X-ray diffraction and infrared spectral measurements during heating. For this purpose we have chosen the delta form samples with different thickness so that the diffusion time of solvent molecules in the sample was changed. By heating the sample, the delta form transferred to the gamma form in the temperature range 100-130 degrees C, irrespective of the thickness of starting delta form samples. In a thin sample the evaporation of solvent occurred easily after the solvent was excluded from the delta form by heating, resulting in the formation of the gamma form and then the alpha form at higher temperature. But, the thicker sample was found for the first time to give higher content of the beta form in addition to the transformation of the gamma to alpha form. In this case the solvent molecules excluded from the delta form crystal lattice are remained in the amorphous region and enhance the formation of the beta form in a relatively low-temperature region. In this way, depending on the relative content of residual solvent, the formation behavior of the beta form was found to be largely different.