Synthesis and Characterization of Model 4-Miktoarm Star Co- and Quaterpolymers

The synthesis of well-defined, nearly monodisperse, 4-miktoarm (from the Greek word μικτος meaning mixed) star co- and quaterpolymers of the A₂B₂ and ABCD types, is described. A is polystyrene, B polybutadiene, C polyisoprene, and D poly(4-methylstyrene). The synthetic approach involves the reaction of tetrachlorosilane with the active chain end centers of the first arm under conditions unfavorable to chain coupling or linking, followed by a stoichiometric addition (titration) of the living polymer of the second or the third arm, and finally by an excess of the living polymer of the last arm. The sequence of addition of the different living polymers and the monitoring of the progress of the linking reaction by size-exclusion chromatography (SEC) are the key for successful synthesis. Characterization was carried out by SEC, low-angle laser light scattering, laser differential refractometry, membrane and vapor pressure osmometry, and NMR spectroscopy.