HYDRODYNAMIC PROPERTIES OF MODEL 3-MIKTOARM STAR COPOLYMERS

The synthesis of well-defined, nearly monodispersed, 3-miktoarm (from the greek word mu LK tau OS meaning mixed) star copolymer of the A(2)B type is described. A and B is either polystyrene (PS), polybutadiene (PBd), or polyisoprene (PI). The sequential controlled addition of liv ing anionic B and A chains to methyltrichlorosilane leads to narrow mo lecular weight distribution miktoarm star copolymers with homogeneous composition. Characterization was carried out by size exclusion chroma tography, low-angle laser light scattering, laser differential refract ometry, membrane and vapor pressure osmometry, nuclear magnetic resona nce and ultraviolet spectroscopy. Analysis of [eta], R(H) and R(v) of the A(2)B and one A(2)B(2) miktoarm copolymers, suggests that a small expansion of the copolymer occurs either in a good solvent for both sp ecies or in a theta solvent for one of them, as compared with the corr esponding star homopolymers. This is in contrast to results obtained o n linear block copolymers, and is due to the increased occurrence of h eterocontacts in the miktoarm starshaped architecture. (C) 1995 John W iley and Sons, Inc.