Compatibilization efficiency of styrene-butadiene multiblock copolymers inPS/PP blends

The compatibilizing effect of di-, tri-, penta-, and heptablock (two types) copolymers with styrene and butadiene blocks was studied in polystyrene/po lypropylene (PS/PP) 4/1 blends. The structure of PS/PP blends with the addi tion of 5 or 10 wt % of a block copolymer (BC) was determined on several sc ale levels by means of transmission electron microscopy (TEM) and small-ang le X-ray scattering (SAXS). The results of the structure analysis were corr elated with measured stress-transfer properties: elongation at break, impac t, and tensile strength. Despite the fact that the molar mass of the PS blo cks in all the BCs used was about 10,000, that is, below the critical value M* (similar to 18,000) necessary for the formation of entanglements of PS chains, all the BCs used were found to be good compatibilizers. According t o TEM, a certain amount of a BC is localized at the interface in all the an alyzed samples, and this results in a finer dispersion of the PP particles in the PS matrix, the effect being more pronounced with S-B-S triblock and S-B-S-B-S pentablock copolymers. The addition of these two BCs to the PS/PP blend also has the most pronounced effect on the improvement of mechanical properties of these blends. Hence, these two BCs can be assumed to be bett er compatibilizers for the PS/PP (4/1) blend than the S-B diblock as well a s both S-B-S-B-S-B-S and B-S-B-S-B-S-B heptablock copolymers. In both types of PS/PP/BC blends (5 or 10 wt % BC), the BC added was distributed between both the PS/PP interface and the PS phase, and, according to SAXS, it main tained a more or less ordered supermolecular structure of neat BCs. (C) 200 1 John Wiley & Sons, Inc.