POLYSTYRENE-POLY(PROPYLENE IMINE) DENDRIMERS - SYNTHESIS, CHARACTERIZATION, AND ASSOCIATION BEHAVIOR OF A NEW CLASS OF AMPHIPHILES

A new class of amphiphilic macromolecules has successfully been synthe sized by creating well-defined diblock copolymers of polystyrene (PS, M(n) = 3.2 x 10(3), M(w)/M(n) = 1.04) with poly(propylene imine) dendr imers. A polystyrene core molecule with a primary amine end-group was prepared by a quantitative three-step modification procedure of acid-f unctionalized polystyrene. On this core molecule, five different gener ations from PS-dendr-NH2 up to PS-dendr-(NH2)(32) were constructed in high yields. The molecular structure of the block copolymers was analy zed in detail with NMR and IR spectroscopy and electrospray mass spect rometry. With conductivity measurements and monolayer pressure-area is otherm determinations, we observed generation-dependent amphiphilic be havior. Dynamic light scattering and transmission electron microscopy showed that amphiphile geometry had a distinct effect on aggregation b ehavior; this is in qualitative agreement with Israelachvili's theory. Critical association concentrations determined with the pyrene probe luminescence technique were as low as 5 x 10(-7) M. The amphiphiles pr esented here, therefore, show a resemblance to traditional block copol ymers with regard to size and stability, and are similar to surfactant s with respect to tuning of the shape.