Hydrodynamic properties of model 3‐miktoarm star copolymers

The synthesis of well‐defined, nearly monodispersed, 3‐miktoarm (from the greek word μlkτós meaning mixed) star copolymer of the A₂B type is described. A and B is either polystyrene (PS), polybutadiene (PBd), or polyisoprene (PI). The sequential controlled addition of living anionic B and A chains to methyltrichlorosilane leads to narrow molecular weight distribution miktoarm star copolymers with homogeneous composition. Characterization was carried out by size exclusion chromatography, low‐angle laser light scattering, laser differential refractometry, membrane and vapor pressure osmometry, nuclear magnetic resonance and ultraviolet spectroscopy. Analysis of [η], R_H and R_v of the A₂B and one A₂B₂ miktoarm copolymers, suggests that a small expansion of the copolymer occurs either in a good solvent for both species or in a Θ solvent for one of them, as compared with the corresponding star homopolymers. This is in contrast to results obtained on linear block copolymers, and is due to the increased occurrence of heterocontacts in the miktoarm starshaped architecture. © 1995 John Wiley & Sons, Inc.