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

Asymmetric Star Polymers Synthesis and Properties 95
Scheme 22
The PDMS was characterized by rather broad molecular weight distributions
(I~1.4) and so fractionation was performed, before continuing to the following
synthetic steps, in order to reduce the polydispersity of the final product. As in
the previous two cases the polymethacrylate branch cannot be isolated and
checked independently.
A similar synthetic route was adopted by Stadler et al. for the synthesis of
(PS)(PB)(PMMA) stars [54] as shown in Scheme 21. Living PS chains were endcapped
with 1-(4-bromomethylphenyl)-1-phenyl ethylene to produce the macromonomer.
The capping reaction with DPE was employed in order to reduce
the reactivity of the PSLi chain ends thus avoiding several side reactions (transmetallation,
addition to the double bond of the DPE derivative). The next step
involved the linking of living PB chains, prepared in THF at –10 °C to the end
double bond of the macromonomer. This produces a new active center which
was used to initiate the polymerization of MMA leading to the formation of the
desired product.