3 research outputs found
Effective Approach to Cyclic Polymer from Linear Polymer: Synthesis and Transformation of Macromolecular [1]Rotaxane
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
Macromolecular [2]Rotaxanes: Effective Synthesis and Characterization
Macromolecular
[2]rotaxanes, which consist of a polymer chain threading
into a wheel component, were synthesized in high yield and with high
purity. The synthesis was achieved by the ring-opening polymerization
(ROP) of δ-valerolactone (VL) using a hydroxyl-terminated pseudorotaxane
as an initiator with diphenyl phosphate as a catalyst in dichloromethane
at room temperature. The <sup>1</sup>H NMR, gel permeation chromatography
(GPC), and MALDI-TOF-MS measurements
of the resulting poly(δ-valerolactone)s clearly indicate the
presence of the rotaxane structure with the polymer chain, confirming
that the diphenyl phosphate-catalyzed ROP of VL proceeds without deslippage
of the wheel component. The obtained macromolecular [2]rotaxane was
acetylated to afford a nonionic macromolecular [2]rotaxane, in which
only one wheel component is movable from one end to another along
the polymer chain
Thermoresponsive Shuttling of Rotaxane Containing Trichloroacetate Ion
A thermoresponsive rotaxane shuttling system was developed with a trichloroacetate counteranion of an ammonium/crown ether-type rotaxane. Chemoselective thermal decomposition of the ammonium trichloroacetate moiety on the rotaxane yielded the corresponding nonionic rotaxane accompanied by a positional change of the crown ether on the axle. The rotaxane skeleton facilitated effective dissociation of the acid, markedly lowering the thermal decomposition temperature