SYNTHESIS, CHARACTERIZATION, AND MORPHOLOGY OF MODEL GRAFT-COPOLYMERSWITH TRIFUNCTIONAL BRANCH-POINTS

Well-defined graft copolymers with polyisoprene backbones and polystyr ene branches, having trifunctional branch points, of the type S2IS2 (H -shaped) and (SI)I(SI) (pi-shaped) were synthesized by anionic polymer ization high-vacuum techniques. The synthetic strategy involves the pr eparation of the outer parts of the molecules, carrying one reactive S i-Cl bond, followed by coupling with difunctional living poly(isopreny llithium) chains. In this way, the number and placement of the branche s can be precisely controlled. Molecular characterization of the fract ionated samples by size exclusion chromatography with UV and RI detect ion, membrane osmometry, low-angle laser light scattering, and H-1-NMR spectroscopy confirmed that the materials exhibit narrow molecular we ight distributions and low compositional heterogeneity. The strongly m icrophase-separated morphologies of these two samples were characteriz ed using TEM and SAXS. The pi architecture with a PS volume fraction o f 0.21 was found to form body-centered cubic spheres, while the H arch itecture with a PI volume fraction of 0.64 was found to form a lamella r morphology. The observed morphology for these architectures was rati onalized by formally dividing the pi and H architectures into componen t simple (single) graft block copolymers which were mapped onto Milner 's morphology diagram for simple graft copolymers.