Model nonlinear block copolymers: Synthesis, characterization, morphology

The synthesis of well-defined, near monodisperse, nonlinear block copolymers of the A(3)B (3-miktoarm star copolymers), A(3)B (4-miktoarm star copolymers), (AB)(2)(BA)(2) (inversed 4-miktoarm star block copolymers), and A(3)BA(3) (bridged miktoarm star copolymers) types is described. A is polyisoprene (PI) and B is polystyrene (PS). The synthetic approach involves the reaction of methyltrichlorosilane or tetrachlorosilane with monofunctional or difunctional macroanions of B under conditions unfavorable to chain coupling or linking, followed by addition of the monofunctional macroanion A. Characterization was carried out by size exclusion chromatography, low-angle laser light scattering, laser differential refractometry, membrane and vapor pressure osmometry, and NMR and UV spectroscopy. Microphase separation was studied by transmission electron microscopy and small-angle x-ray scattering. Comparison with the corresponding linear block copolymers showed that the macromolecular architecture not only strongly affects the morphological domain borders but can introduce new morphologies as well.