NOVEL 2-DIMENSIONALLY PERIODIC NONCONSTANT MEAN-CURVATURE MORPHOLOGIES OF 3-MIKTOARM STAR TERPOLYMERS OF STYRENE, ISOPRENE, AND METHYL-METHACRYLATE

The morphology of a family of four 3-miktoarm star terpolymers of poly styrene (PS), polyisoprene (PI), and polymethyl methacrylate (PRIMA) w as studied. For three of the samples, the molecular weight of the PMMA block was systematically varied while that of the PS and PI blocks we re held fixed. In the fourth sample, the PS and PMMA blocks were appro ximately of the same molecular weight and the PI was the majority comp onent. In all terpolymers, the system displayed a three-phase, two-dim ensionally periodic microstructure of an inner PI column with a surrou nding PS annulus in a matrix of PMMA. For the two samples with the lon ger PMMA blocks (218 and 186 kg/mol), the PI-PS and PS-PMMA interfaces were cylindrical, whereas a unique nonconstant mean curvature (non-CM C) concentric diamond prism shape of the PI and PS microdomains occurr ed for the sample with the lowest molecular weight PMMA block (144 Kg/ mol) as well as the polymer with the longer PI block. In these star te rpolymers there are three chemically different chains emanating from t he same junction point. The interaction parameter between PS and PMMA is relatively low, whereas that between PI and PMMA. is the highest. T he star molecular architecture gives the molecule the ability to ''cho ose'' which arms directly interact in the microphase segregate state. In the present systems, the junctions lie on the PIPS interface causin g partial mixing of the PS and PMMA blocks, while minimizing the highl y unfavorable contact between the PI and PMMA blocks.