Thermo-mechanical properties linked to rheological features in high molecular weight SEBS copolymers: Effect of styrene content and ethylene/butylene proportion

Novel results on the thermomechanical and rheological properties of poly (Styrene-b-Ethylene-co-Butylene-b-Styrene) (SEBS) copolymers of molecular weight close to Mw = 200,000 g/mol, with varying styrene content and ethylene/butylene proportion, are presented. DSC and DMTA tests reveal that only the sample which contains more ethylene than butylene in PEB midblock chains is able to crystallize. Small amplitude oscillatory flow measurements show evidence of PEB entanglements, although the chains are anchored to PS cylinder domains. Increasing butylene proportion in PEB leads to a decrease of the entanglement density. Entanglements and microphase segregation bring about a very elastic behaviour which produces "plug-flow", leading to smooth extrudates, in extrusion flow experiments.