ON THE MULTIPLE MELTING BEHAVIOR OF POLYMORPHIC SYNDIOTACTIC POLYSTYRENE AND ITS BEHAVIOR IN A MISCIBLE STATE

Differential scanning calorimetry (DSC) and X-ray diffraction analysis were performed to study the multiple melting behavior and crystal for ms of neat syndiotactic polystyrene (s-PS) in comparison with its misc ible blends with amorphous atactic polystyrene (a-PS) or poly(2,6-dime thyl-p-phenylene oxide) (PPO). For neat s-PS annealed at 242 to 250 de grees C, three melting peaks of changing intensity were observed (labe led I, II, and III from low to high temperature), while if annealed at high temperatures (254 degrees C or higher) only two melting peaks we re left. The missing peak was determined to be Peak-III for s-PS annea led at high temperatures. For the s-PS/a-PS or s-PS/PPO blends, two me lting peaks were observed, and the missing peak is Peak-II. The missin g Peak-II in the blend systems is attributed to the alpha-modification . Apparently, the condition of s-PS being compatible with a-PS or PPO is unfavorable for generating the alpha-modification upon melt crystal lization. This study also showed that Peak-I is associated with the be ta-modification. Peak-III may be associated with the less stable beta' form, which can be transformed to the beta form upon annealing at hig h temperatures. For the s-PS/a-PS or s-PS/PPO blends upon annealing at higher temperatures, Peak-III quickly decreases, leaving only a singl e melting peak (Peak-I) for the blends. The phenomenon of the decrease of Peak-III crystals in the blend is similar to that for neat s-PS an nealed at high temperatures.