Synthesis and characterization of ABC-type star and linear block copolymers of styrene, isoprene, and 1,3-cyclohexadiene

Mikto three-arm, ABC-type star copolymers of styrene, isoprene, and 1,3-cyclohexadiene were synthesized by anionic polymerization using 1,3-bis(1-phenylvinyl) benzene (MDDPE) as linking precursor. A polystyrene macromonomer was prepared by monoaddition of polystyryllithium toward MDDPE. The resulting macromonomer was coupled with polyisoprenyllithium through the remaining double bond in MDDPE moiety, forming a diblock copolymer of styrene and isoprene. The diblock copolymer possessed a living center of diphenylethyllithium, which subsequently initiated the polymerization of a small amount of isoprene (seeding) and 1,3-cyclohexadiene. It was found that, without the seeding process, diphenylethyllithium was not able to initiate the polymerization of 1,3-cyclohexadiene. The resulting macromonomer and star polymers were characterized by gel permeation chromatography, matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry, and H-1 NMR spectroscopy. In addition, linear ABC-type triblock copolymers of the corresponding monomers with different sequences were also synthesized. Microphase separation of the linear and star copolymers was investigated by differential scanning calorimetry and transmission electron microscopy.