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

98 N. Hadjichristidis, S. Pispas, M. Pitsikalis, H. Iatrou, C. Vlahos
Scheme 24
agent leading to the formation of three-arm stars with one dimethylamine endgroup.
Subsequent reaction with cyclopropane sultone transformed the dimethylamine
groups into zwitterions.
The synthesis of stars with two functional end-amine groups, 2N-3-PB were
prepared in a similar manner. The living unfunctionalized arm was reacted with
an excess of methyltrichlorosilane followed after the removal of the excess silane
by addition of a small excess of the functionalized living arms to the unfunctionalized
chlorosilane-capped arm. When the arm molecular weight was lower than
ca. 10 4 the amount of coupled byproduct of the reaction with the excess silane
was very large (>10%). This result, together with the fact that all the arms have
the same molecular weight, makes the separation of the byproduct from the desired
star impossible. In order to minimize the coupling reaction the living polymer
was end-capped with 1,1-diphenylethylene (DPE). This capping reaction,
accelerated by the addition of a small quantity of THF, reduces the amount of the
coupled product to acceptable levels (