MISCIBILITY, MICROSTRUCTURE, AND DYNAMICS OF BLENDS CONTAINING BLOCK-COPOLYMER .1. MISCIBILITY OF BLENDS OF HOMOPOLYSTYRENE WITH STYRENE-BUTADIENE BLOCK-COPOLYMERS

The miscibilities of blends of homopolystyrene/styrene-butadiene/styre ne (PS/SBS) and PS/SB-4A (4-arm star block copolymer) have been studie d by dynamic mechanical analysis (DMA) and C-13 CPMAS NMR techniques. The results indicate that the miscibilities of these two blends depend on the molecular weight of PS (M(PS)) and are almost independent of t he molecular architecture of the studied block copolymers. It is also found that there exists an optimum range of M(PS) which will give rise to well-improved mechanical properties of the blends. The reason sugg ested for this phenomenon is that the intermolecular entanglement inte raction plays a critical role. It is also found that even when the rat io value of M(PS)/M(bPS) (molecular weight of PS block in SB block cop olymers) is as high as 1.2 for PS/SB-4A and 1.5 for PS/SBS, PS is stil l miscible with the PS block microdomains very well. Meanwhile, when M (PS) is much higher than M(bPS), the blends of PS/SBS and PS/SB-4A are still partially miscible.