NMR Investigation of the Order-Disorder and Rheological Transitions in Styrene-Isoprene Diblock Copolymers

13 C NMR spectroscopy was used to investigate the physical basis of the rheological thermal transition (T rheo ) in symmetric poly(styrene-b-isoprene) (SI) diblock copolymers. Among the studied samples, those with M n = (3-32)×10 3 , which all exhibited two glass transition features (T g,1 and T g,2 ) in their DSC curves, had T rheo values ranging from -10°C to 205°C. The NMR line width data related to the styrene units in the bulk materials show that a strong segregation behavior persists over a wide range of temperature above T rheo