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

Abstract

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.

Synthesis of Eight‐shaped Poly(ethylene oxide) by the Combination of Glaser Coupling with Ring‐opening Polymerization

“…Among them, eightshaped copolymers are the simplest, composed of two cyclic sub-chains, which might be used as a model (co)polymer for theoretical research, as well as be endowed with some special properties and applications. The eight-shaped (co)polymers may be constructed by several methods, for example, an electrostatic selfassembly and covalent fixation process was used to give eight-shaped poly(tetrahydrofuran) (PTHF) [11,12] and poly(styrene) (PS), [13] the intramolecular photo-crosslinking of pendant unsaturations was used to give eightshaped poly(e-caprolactone) (PCL), [14] the reaction between acetal and styrenyl functions was used to give eight-shaped poly(chloroethyl vinyl ether) (PCEVE), [15] the coupling reaction between living dicarbanions with tetrachlorosilane was used to give eight-shaped PS [16] and polyisoprene (PI), [17] the ''click'' reaction between alkyne and azide groups [18] and the reaction between amine and glutaric acid was used to give eight-shaped PS. [19] In addition, the atom The eight-shaped poly(ethylene oxide) (PEO) is synthesized by a combination of Glaser coupling with ring-opening polymerization (ROP).…”

Well‐Defined Miktocycle Eight‐Shaped Copolymers Composed of Polystyrene and Poly(ε‐caprolactone): Synthesis and Characterization

“…Due to unique “endless” topology, the cyclic polymers display novel physical properties different from their linear analogs, such as small hydrodynamic volumes, low intrinsic viscosities, high glass transition temperature, and unique interfacial and fluorescence properties 1–4. Therefore, the synthesis and characterizations of the cyclic polymers have often attracted interests of polymer chemists, and various cyclic polymers have been successfully synthesized 5–8. Most of the studies on cyclic polymers focused on the synthesis and characterization of single cyclic polymers9–20 and only a few literatures reported the preparation of multiple cyclic copolymers, in which almost all of the studies are restricted to the bicyclic polymers including number‐eight‐, theta‐, and manacle‐shaped polymers 8, 21–25.…”

Construction of Linear Polymers, Dendrimers, Networks, and Other Polymeric Architectures by Copper‐Catalyzed Azide‐Alkyne Cycloaddition “Click” Chemistry

“…In recent years CuAAC has been utilized by a number of groups for modular ligation of linear polymers with other molecules to give novel graft/brush polymers, [64][65][66][67][68][69][70][71][72][73][74] star polymers, [75][76][77][78][79][80][81][82][83] and other architectures. [84,85] Since these can be considered as modification rather than construction applications of CuAAC (see Scheme 2), we only highlight a few interesting examples in this review, with apologies to those omitted because of space considerations. First, Lecomte and coworkers have presented novel tadpoleshaped (Scheme 16) [84] and eight-shaped [85] polymers using a cyclic tin(IV) dialkoxide initiator for controlled ring-opening polymerization of e-caprolactones (CL) including an a-chlorinated monomer.…”

“…[84,85] Since these can be considered as modification rather than construction applications of CuAAC (see Scheme 2), we only highlight a few interesting examples in this review, with apologies to those omitted because of space considerations. First, Lecomte and coworkers have presented novel tadpoleshaped (Scheme 16) [84] and eight-shaped [85] polymers using a cyclic tin(IV) dialkoxide initiator for controlled ring-opening polymerization of e-caprolactones (CL) including an a-chlorinated monomer. Conversion of the chlorine groups to azides and subsequent CuAAC with alkyne-PEG yielded complicated structures with potentially novel properties including unexplored modes of self-assembly.…”