Synthesis of Macrocyclic Poly(ɛ-caprolactone) by Intramolecular Cross-Linking of Unsaturated End Groups of Chains Precyclic by the Initiation

A twin-tailed tadpole-shaped amphiphilic copolymer of poly(ethylene glycol) and cyclic poly(ε-caprolactone): synthesis, self-assembly and biomedical applications

A tadpole-shaped amphiphilic copolymer containing cyclic PCL and two PEG tails, PEG-b-(c-PCL)-b-PEG, was rationally designed and synthesized.

Advanced Developments in Cyclic Polymers: Synthesis, Applications, and Perspectives

Due to the topological effect, cyclic polymers demonstrate different and unique physical and biological properties in comparison with linear counterparts having the same molecular-weight range. With advanced synthetic and analytic technologies, cyclic polymers with different topologies, e.g. multicyclic polymers, have been reported and well characterized. For example, various cyclic DNA and related structures, such as cyclic duplexes, have been prepared conveniently by click chemistry. These types of DNA have increased resistance to enzymatic degradation and have high thermodynamic stability, and thus, have potential therapeutic applications. In addition, cyclic polymers have also been used to prepare organic-inorganic hybrids for applications in catalysis, e.g. catalyst supports. Due to developments in synthetic technology, highly pure cyclic polymers could now be produced in large scale. Therefore, we anticipate discovering more applications in the near future. Despite their promise, cyclic polymers are still less explored than linear polymers like polyolefins and polycarbonates, which are widely used in daily life. Some critical issues, including controlling the molecular weight and finding suitable applications, remain big challenges in the cyclic-polymer field. This review briefly summarizes the commonly used synthetic methodologies and focuses more on the attractive functional materials and their biological properties and potential applications.

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.

Synthesis of Eight- and Star-Shaped Poly(ε-caprolactone)s and Their Amphiphilic Derivatives

Spirocyclic tin dialkoxides are unique initiators for the ring-expansion polymerization of lactones leading to complex, but well-defined macromolecular architectures. In a first example, epsilon-caprolactone (epsilon CL) was polymerized, followed by the resumption of polymerization of a mixture of epsilon CL and epsilon CL alpha-substituted by a chloride (alpha Cl epsilon CL), so leading to "living" eight-shaped chains. Upon hydrolysis of the alkoxides, a four-arm star-shaped copolyester was formed, whose each arm was grafted by conversion of the chloride units into azides, followed by the Huisgen's [3+2] cycloaddition of alkyne end-capped poly(ethylene oxide) (PEO) onto the azide substituents. The complexity of this novel amphiphilic architecture was increased further by substituting the four-arm interconnecting PCL by an eight-shaped PCL. In a preliminary step, epsilon CL was polymerized followed by a few units of epsilon CL alpha-substituted by an acrylate. The intramolecular photo-crosslinking of the acrylates adjacent to the tin dialkoxides was effective in stabilizing the eight-shaped polyester while preserving the chain growth sites. This quite unusual tetrafunctional macroinitiator was used to copolymerize epsilon CL and alpha Cl epsilon CL, followed by hydrolysis of the alkoxides, conversion of the chloride units into azides and grafting of the four arms by PEO (see above). This architecture reported for the very first time is nothing but a symmetrical four-tail eight-shaped copolyester macromolecule.