Effective Approach to Cyclic Polymer from Linear Polymer:
Synthesis and Transformation of Macromolecular [1]Rotaxane
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Abstract
We report a convenient and scalable
synthesis of cyclic poly(ε-caprolactone)
(PCL) from its linear counterpart based on the rotaxane protocol.
Cyclic PCL was prepared by ring-opening polymerization of ε-caprolactone
(ε-CL) initiated by a pseudo[2]rotaxane initiator in the presence
of diphenylphosphate (DPP) as a catalyst, followed by capping of the
propagation end by using a bulky isocyanate to afford macromolecular
[2]rotaxane. The successive intramolecular cyclization to macromolecular
[1]rotaxane at the polymer terminus proceeded with good yield. The
attractive interaction of the terminal ammonium/crown ether moiety
was removed via N-acetylation. This enabled movement of the crown
ether wheel along the axle PCL chain to the urethane region of the
other terminus in solution state. Size-exclusion chromatography and
2D diffusion-ordered spectroscopy (DOSY) results demonstrated the
formation of cyclic PCL from linear PCL, which is further supported
by thermal property or crystallinity change before and after transformation