Compatabilization of polystyrene polypropylene blends by styrene-butadieneblock copolymers with differing polystyrene block lengths

Compatibilization of polystyrene/polypropylene (PS/PP) blends, by use of a series of butadiene-styrene block copolymers was studied by means of small- angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). T he compatibilizers used differ in molar mass and the number of blocks. It w as shown that the ability of a block copolymer (BC) to participate in the f ormation of an interfacial layer land hence in compatibilization) is closel y associated with the molar mass of styrene blocks. If the styrene blocks a re long enough to form entanglements with the styrene homopolymer in the me lt, then the BC is trapped inside this phase of the PS/PP blends, and its m igration to the PS/PP interface is difficult. In this case, the BC does not participate in the formation of the interfacial layer nor, consequently, i n the compatibilization process. On the other hand, the BC's with the molar mass of the PS blocks below the critical value are proved to be localized at the PS/PP interface. This preferable entrapping of some styrene-butadien e BC's in the PS phase of the PS/PP blend is, of course, connected to the d iffering miscibility of the BC blocks with corresponding components of this blend. Although the styrene block is chemically identical to the styrene h omopolymer in the blend, the butadiene block is similar to the PP phase. (C ) 1999 John Wiley & Sons, Inc.