MODEL BLOCK-GRAFT COPOLYMER VIA ANIONIC LIVING POLYMERIZATION - PREPARATION AND CHARACTERIZATION OF VINYLSILANE)-GRAFT-POLYISOPRENE]-BLOCK-POLYSTYRENE

A model graft copolymer that has well-defined length, number, and posi tion of grafts was prepared via anionic living polymerization. (4-Viny lphenyl)dimethylvinylsilane (VS) was anionically polymerized by cumylc esium in THF at -78 degrees C for 20 min under a pressure of 10(-5) mm Hg, and subsequent addition of styrene (St) yielded a PVS-b-PSt block copolymer that could be used as a backbone molecule. PVS has a silylvi nyl group on the side chain that converts chemical links between backb one and grafts. Isoprene (Is) was anionically polymerized to yield liv ing polyisoprene, and the resultant PIs(-)Cs(+) and PIs(-)Li(+) soluti ons were added to THF and benzene solutions of PVS-b-PSt, respectively . After 24 h, backbone coupling was terminated to yield vinylsilane-gr aft-polyisoprene]-block-polystyrene. The three graft copolymers were p repared. Molecular characterization was carried out by GPC measurement , osmometry, and sedimentation pattern. The M(n) and M(w)/M(n) values of the backbone, grafts, and graft copolymers were determined. The num ber of grafts per backbone molecule was found to be 10.(0), 10.(9), an d 12.(5) for the three graft copolymers, and the position of the graft s was set to the end of the backbone molecule. Spacing and its distrib ution of the graft points on a backbone molecule were also discussed. Three benzene-cast films formed clear microphase-separated structures, such as spherical and lamellar structures. The composition dependence on the morphology of the graft copolymers was found to differ from th at of common block copolymers. These results suggest that the apparent volume fraction of grafts is much larger than the real volume fractio n, because the grafts became crowded in the vicinity of the backbone m olecule.