Synthesis and Morphological Behavior of Model Linear and Miktoarm Star Copolymers of 2-Methyl-1,3-Pentadiene and Styrene

Three linear diblock copolymers (PS- b -P2MP), two 3-miktoarm [PS(P2MP) 2 ] copolymers, and two 4-miktoarm star copolymers [PS(P2MP) 3 ] of styrene (S) and 2-methyl-1,3-pentadiene (2MP) were synthesized by anionic polymerization/high vacuum techniques and controlled chlorosilane chemistry. Molecular characterization of the samples was carried out by size exclusion chromatography (SEC), membrane osmometry (MO), low-angle laser light scattering (LALLS), and 1 H NMR spectroscopy, and indicated a high degree of molecular and compositional homogeneity. All samples had approximately the same total M̄ w (∼100 000), different compositions, and high 1,4-microstructure for the P2MP blocks. The morphological behavior was determined via transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and differential scanning calorimetry (DSC). The experimental results were compared with those found for PS/PI block copolymer systems and with Milner's theoretical prediction. Significant discrepancies were found. Also, it is the first time that two morphologies (lamellae/double gyroid) coexist in a neat material, and especially in a 4-miktoarm star copolymer.