Synthesis and Morphological Behavior of Model 6-Miktoarm Star Copolymers, PS(P2MP)₅, of Styrene (S) and 2-Methyl-1,3-Pentadiene (P2MP)

Three 6-miktoarm star (6μ-star) copolymers [PS(P2MP) 5 ] of styrene (S) and 2-methyl-1,3-pentadiene (2MP) were synthesized by anionic polymerization and controlled chlorosilane chemistry, using high vacuum techniques. In all cases [ M w = 103 kg/mol, [S] = 44% (v/v); M w = 91.1 kg/mol, [S] = 53% (v/v); M w = 224 kg/mol, [S] = 92% (v/v)] the P2MP exhibited high 1,4-microstructure (∼99%). Molecular characterization (size-exclusion chromatography, membrane osmometry, low-angle laser light scattering, and NMR) revealed high molecular weight/composition homogeneity, and structural analysis (differential scanning calorimetry, transmission electron microscopy, and small-angle X-ray scattering) showed highly ordered patterns. The deviations from predictions based on Milner's morphological model are much more pronounced than that of PS(P2MP) 2 and PS(P2MP) 3 miktoarm stars, which we attribute to greater crowding of the arms for these highly branched molecules.