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Synthesis of Well-Defined Three- and Four-Armed Cage-Shaped Polymers via “Topological Conversion” from Trefoil- and Quatrefoil-Shaped Polymers
This
paper describes a novel synthetic approach for three- and
four-armed cage-shaped polymers based on the topological conversion
of the corresponding trefoil- and quatrefoil-shaped precursors. The
trefoil- and quatrefoil-shaped polymers were synthesized by the following
three reaction steps: (1) the <i>t</i>-Bu-P<sub>4</sub>-catalyzed
ring-opening polymerization of butylene oxide using multiple hydroxy-
and azido-functionalized initiators to produce the three- or four-armed
star-shaped polymers possessing three or four azido groups at the
focal point, respectively, (2) the ω-end modification to install
a propargyl group at each chain end, and (3) the intramolecular multiple
click cyclization of the clickable star-shaped precursors. The topological
conversion from the trefoil- and quatrefoil-shaped polymers to the
cage-shaped polymers was achieved by the catalytic hydrogenolysis
of the benzyl ether linkages that had been installed at the focal
point. The amphiphilic cage-shaped block copolymers together with
the corresponding trefoil- and quatrefoil-shaped counterparts were
synthesized in a similar way using 2-(2-(2-methoxyethoxy)ethoxy)ethyl
glycidyl ether as a hydrophilic monomer and decyl glycidyl ether as
a hydrophobic monomer. Interestingly, significant changes in the critical
micelle concentration and micellar morphology were observed for the
amphiphilic block copolymers upon the topological conversion from
the trefoil- and quatrefoil-shaped to cage-shaped architectures