Rheology of Polystyrene-block-poly[ethylene-co-(ethylene-propylene)]-block-polystyrene Tri-block Copolymer/Paraffinic Oil Blends - Effect of Oil Molecular Weight on the Order-Disorder Transition

Blend systems of Polystyrene-block-poly(ethylene-co-(ethylene-propylene)-block-polystyrene(SEEPS) tri-block copolymer and three kinds of paraffinic oil having different molecular weight (MW) were prepared. Styrene content of the SEEPS was 30 wt%. The oils used in this study were Oil-1 (MW=750 g/mole), Oil-2 (540 g/mole), and Oil-3 (410 g/mole). Dynamic viscoelastic properties, the storage (G') and loss modulus (G"), of the blends were measured as a function of temperature (T) and angular frequency (ω). SEEPS/oil = 100/0 and 75/25 (in weight) blends exhibited gel-like behavior over the entire experimental T window below 300°C. On the contrary, the viscoelastic properties of SEEPS/oil = 50/50 and 25/75 blends depended on the MW of oil. For the SEEPS/Oil-1 = 50/50 and 25/75 blends having high MW oil, the clear order-disorder transition (ODT) was observed showing a sudden change of G' at elevating T and the ODT temperature (T ODT ) was found to shift to lower T with increase in oil content. For the SEEPS/Oil-2 = 50/50 blend having medium MW oil, the ODT was observed very clearly, but could not be observed for the 25/75 blend. For the SEEPS/Oil-3 blends having low MW oil, the ODT was not observed showing that there is a rather gradual decrease in G' with T. It was found that the viscoelastic properties of SEEPS/oil blends changed with the content and MW of oil.