142 Advances in Polymer Science Editorial Board: A. Abe. A.-C ...

Asymmetric Star Polymers Synthesis and Properties 87
Scheme 13
complished using THF as a solvent and short polymerization times. The PVS
block with the unreacted double bonds was used as a multifunctional linking
agent. Subsequent addition of living PS chains produced miktoarm stars of the
type (PS) nPVN, as shown in Scheme 12. Characterization studies revealed that
n=13.
The method adopted for the synthesis of these stars can be considered as a
macromonomer method, since end-reactive vinyl groups were used for the linking
of the PS arms. There is a possibility that the silyl vinyl anion formed after
the addition of the living PS chains reacts with silyl vinyl groups; this effect was
minimized using short VS blocks and a large excess of PS anions.
Similar structures of the AB n type were prepared by Wang et al., A being PS
and B PB or P2VP [32, 33]. Due to the much higher molecular weight of the PS
arm the polymers were called umbrella copolymers. The reaction sequence for
the preparation of the PS(PB) n copolymers is given in Scheme 13. Butadiene was
polymerized anionically in the presence of dipiperidinoethane (dipip) followed
by the addition of styrene. A diblock copolymer having a PS chain and a short