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

Asymmetric Star Polymers Synthesis and Properties 97
Scheme 23
Fig. 2. Asymmetric PB stars with functional end-groups
2.2.2
Asymmetric w-Functionalized Polymers
Three-arm PB stars having arms of equal molecular weight but with different
functional end-groups were prepared [58]. One or two functional dimethylamine
groups were introduced using the functional initiator 3-dimethylaminopropyllithium
(DMAPLi) [59–61]. Post polymerization reactions were carried out to transform
the dimethylamine groups to zwitterions of the sulfobetaine type (Fig. 2).
The method used for the synthesis was similar to the one developed by Pennisi
and Fetters for the synthesis of asymmetric stars, having different molecular
weight arms. The synthesis of the three-arm stars with one of them end-functionalized
with dimethylamine end-group is outlined in Scheme 24. A solution
of living amine-functionalized PB, prepared using DMAPLi as initiator was added
to a large excess of methyltrichlorosilane (Si-Cl/C-Li~100/1) in order to synthesize
the methyldichlorosilane end-capped N-functionalized PB. The excess
silane was removed under reduced pressure. The polymer was repeatedly redissolved
and dried. Purified benzene was distilled into the reactor to redissolve the
silane-capped arm. Finally a slight excess of the unfunctionalized arms, prepared
using sec-BuLi as initiator, was reacted with the macromolecular linking