Two types of crystalline syndiotactic polystyrene units are observed in these styrene-p-methylstyrene copolymers. The low-temperature crystalline form is observed in copolymers containing 2 weight percent or less 4-methylstyrene, and the high-temperature crystalline form is observed in copolymers containing 3 to 7 weight percent 4-methylstyrene. Quantitative analysis of styrene-4-methylstyrene copolymers can be performed with the use of infrared spectroscopy and an infrared absorption band intensity ratio technique.
