Molecular Chain Movements and Transitions of SEBS above Room Temperature Studied by Moving-Window Two-Dimensional Correlation Infrared Spectroscopy

The temperature-dependent molecular chain movements and transitions of polystyrene- block -poly(ethylene- co -1-butene)- block -polystyrene block copolymer (SEBS) above room temperature were studied by in-site infrared spectroscopy combined with moving-window two-dimensional (MW2D) correlation spectroscopy. Some complex molecular chain movements and transitions of SEBS were revealed with the linear incremental temperature increasing (30−166 °C). The melting point of the extraordinary weak crystal of −(CH 2 −CH 2 )− n in the poly(ethylene- co -1-butene) block (EB) is determined at 48 °C. The heat enthalpy relaxation of polystyrene block (S) of SEBS, which is induced by the framework movement of the side benzene ring and the melting of the weak crystal in the polystyrene block, is observed around 72−80 °C from the MW2D correlation spectrum. The glass transition temperature of the polystyrene block is determined around 120 °C. From the MW2D correlation spectrum, we discover that, around 120 °C, the chain segment movement of polystyrene block occurs before that of poly(ethylene- co -1-butene) block in phase interface. At 142 °C, the fundamental chains of the disperse phase (S block) center initiate to entirely move and this type of movement drives a fraction of the disperse phase (S block) to deform from an incomplete shape to a sphere. This corresponds to the entirely viscous flow temperature of the fundamental chains of the disperse phase.