Blends of styrene-butadiene-styrene triblock copolymer and isotactic polypropylene: morphology and thermomechanical properties

A set of blends of styrene-butadiene-styrene triblock copolymer (SBS) and i sotactic polypropylene (i-PP) in a composition range 0-100% polypropylene b y weight was prepared in a twin screw extruder. The morphology of the blend s has been studied by transmission electron microscopy. The blends present phase separation, Dynamic mechanical measurements show an improvement of th e mechanical properties of SBS when i-PP is the dispersed phase. This reinf orcing effect can be observed even at high temperatures when i-PP is in the rubbery state. The mechanical properties of the blends have been interpret ed using Takayanagi's block model. The melting and crystallization behaviou r of the i-PP in the blends has been studied by differential scanning calor imetry. The fractionated crystallization phenomenon has been observed in th e blends where i-PP forms the dispersed phase. The results are consistent w ith the morphology shown by the blends, in particular, with its phase inver sion, which occurs at a composition near to 50% i-PP. (C) 2000 Society of C hemical Industry.