A versatile synthetic strategy for macromolecular cages: intramolecular consecutive cyclization of star-shaped polymers

Cage-Shaped Polymers Synthesis: A Comprehensive State-of-the-Art

Researchers have dedicated their efforts for the creation of a wide choice of complex and precise macromolecular architectures over the past 100 years. Among them, cyclic polymers benefit from their absence of terminal chains and from their singular topology to minimize their hydrodynamic volume in solution, increase their chemical stability, limit their number of possible conformations as well as a reduce their propensity to crystallize or to form entanglements in comparison to their acyclic counterparts. While monocyclic structures have already been widely investigated and reviewed, reports on more complex polycyclic structures are rare. In this regard, cage-shaped polymers-consisting of at least three polymer chains covalently interconnected through strictly two junction points-have received little attention over the past two decades. Although their synthesis is a worthy challenge, only a few synthetic methodologies of polymer cages were successfully developed so far. Thus, this review intends to highlight the key concepts of the conception of cage-shaped polymers in addition to propose an actual and exhaustive state-of-art concept of their synthesis to rationally promote the next-generation synthesis strategies.

Highly Ordered Nanoscale Film Morphologies of Block Copolymers Governed by Nonlinear Topologies

Among many properties of cyclic block copolymers, the notable domain spacing (d-spacing) reduction offers nonlinear topology as an effective tool for developing block copolymers for nanolithography. However, the current consensus regarding the topology-morphology correlation is ambiguous and in need of more studies. Here we present the morphological investigation on nanoscale films of cyclic and tadpole-shaped poly(n-decyl glycidyl ether-block-2-(2-(2-methoxyethoxy)ethoxy)ethyl glycidyl ether)s and their linear counterpart via synchrotron grazing-incidence X-ray scattering. All copolymers form phase-separated nanostructures, in which only the nonlinear copolymers form highly ordered and unidirectional nanostructures. Additionally, d-spacings of cyclic and tadpole-shaped block copolymers are 49.3-53.7% and 25.0-32.5% shorter than that of their linear counterpart, respectively, exhibiting greater or comparable d-spacing reductions against the experimentally and theoretically achieved values from the literature. Overall, this study demonstrates that cyclic and tadpole topologies can be utilized in developing materials with miniaturized dimensions, high structural ordering, and unidirectional orientation for various nanotechnology applications.

One-Shot Intrablock Cross-Linking of Linear Diblock Copolymer to Realize Janus-Shaped Single-Chain Nanoparticles

Developing an efficient and versatile process to transform a single linear polymer chain into a shape-defined nanoobject is a major challenge in the fields of chemistry and nanotechnology to replicate sophisticated biological functions of proteins and nucleic acids in a synthetic polymer system. In this study, we performed one-shot intrablock cross-linking of linear block copolymers (BCPs) to realize single-chain nanoparticles (SCNPs) with two chemically compartmentalized domains (Janus-shaped SCNPs). Detailed structural characterizations of the Janus-shaped SCNP composed of polystyrene-block-poly(glycolic acid) revealed its compactly folded conformation and compartmentalized block localization, similar to the self-folded tertiary structures of natural proteins. Versatility of the one-shot intrablock cross-linking was demonstrated using several different BCP precursors. In addition, the Janus-shaped SCNP produce miniscule microphase-separated structures.

The power of architecture – cage-shaped PEO and its application as a polymer electrolyte

First reported gram-scale synthesis of a four-arm cage-shaped poly(ethylene oxide) polymer and its pioneering application as polymer electrolyte.

Correlations of nanoscale film morphologies and topological confinement of three-armed cage block copolymers

Three-armed cage block copolymers composed of immiscible blocks in near equivalent volume fractions formed topologically controlled sub-10 nm cylindrical and lamellar nanostructures in nanoscale films.

Topologically controlled phase transitions and nanoscale film self-assemblies of cage poly(ε-caprolactone) and its counterparts

Here we report the first quantitative investigation of nanoscale film morphologies of a cage-shaped poly(ε-caprolactone) and its counterparts in star, cyclic, and linear topologies through synchrotron grazing incidence X-ray scattering analysis.

Progress in the Preparation of Functional and (Bio)Degradable Polymers via Living Polymerizations

This review presents the latest developments in (bio)degradable approaches and functional aliphatic polyesters and polycarbonates prepared by typical ring-opening polymerization (ROP) of lactones and trimethylene carbonates. It also considers several recent innovative synthetic methods including radical ring-opening polymerization (RROP), atom transfer radical polyaddition (ATRPA), and simultaneous chain- and step-growth radical polymerization (SCSRP) that produce aliphatic polyesters. With regard to (bio)degradable approaches, we have summarized several representative cleavable linkages that make it possible to obtain cleavable polymers. In the section on functional aliphatic polyesters, we explore the syntheses of specific functional lactones, which can be performed by ring-opening copolymerization of typical lactone/lactide monomers. Last but not the least, in the recent innovative methods section, three interesting synthetic methodologies, RROP, ATRPA, and SCSRP are discussed in detail with regard to their reaction mechanisms and polymer functionalities.

Programmed folding into spiro-multicyclic polymer topologies from linear and star-shaped chains

The development of precise folding techniques for synthetic polymer chains that replicate the unique structures and functions of biopolymers has long been a key challenge. In particular, spiro-type (i.e., 8-, trefoil-, and quatrefoil-shaped) polymer topologies remain challenging due to their inherent structural complexity. Herein, we establish a folding strategy to produce spiro-type multicyclic polymers via intramolecular ring-opening metathesis oligomerization of the norbornenyl groups attached at predetermined positions along a synthetic polymer precursor. This strategy provides easy access to the desired spiro-type topological polymers with a controllable number of ring units and molecular weight while retaining narrow dispersity (Ɖ < 1.1). This effective strategy marks an advancement in the development of functionalized materials composed of specific three-dimensional nanostructures.

Synergy of Macrocycles and Macromolecular Topologies: An Efficient [34]Triazolophane-Based Synthesis of Cage-Shaped Polymers

The development of complex topologies such as macromolecular cages constitutes a fascinating aspect of polymer chemistry. In the present work, a novel strategy involving self-closing bifunctional end-groups, which under specific conditions, are allowed to assemble themselves into a predefined thermodynamically favored macrostructure, was designed to fulfill the topological conversion of star-shaped polymers to their respective cage-shaped polymers. A series of four different well-defined four-arm star-shaped poly(ε-caprolactone) polymers varying in molar masses were successfully synthesized, end-functionalized, and closed into cage-shaped polymers by formation of [3₄]triazolophane macrocycle units. The obtained cage-shaped polymers feature interesting properties that depend drastically on the chain length of the arms and seem to differ from previous reported polymer cages.

Ring-expansion cationic cyclopolymerization for the construction of cyclic cyclopolymers

A “cyclic cyclopolymer” was successfully synthesized via ring-expansion cationic cyclopolymerization with a cyclic initiator by using a divinyl ether carrying a gem-dimethyl group on the spacer as the monomer.

Synthesis of stimuli-responsive nanosized ring-like colloids and cyclic polymers via a dual-template approach

Ring-like particles have received considerable attention due to their unique interior cavity and properties. However, the preparation of stimuli-responsive nanosized rings with internal size smaller than 100 nm remains unexplored likely due to the challenges encountered in their synthesis. The successful fulfillment of this target will not only significantly enrich the family of ring-like nanoparticles but also build a connection that bridges ring-like nanoparticles and cyclic polymers. For this purpose, we report in this study a controlled synthesis of stimuli-responsive ring-like colloids and cyclic polymers using both star-shaped polymers and β-cyclodextrin (β-CD) as the dual templates. The first template comprising star-shaped polymers generated a ring-like structure and adoption of β-CD as the second template further restricted the ring thickness to the height of a β-CD, leading to the generation of stimuli-responsive nanosized ring-like colloids with ring thickness less than 1 nm, which shifted the ring-like structure to cyclic polymers with reversible cross-linked disulfide bridges. The reported "dual-template" approach is thus a valuable alternative to the current synthetic strategies toward stimuli-responsive ring-like colloids and cyclic polymers.

Installing a functional group into the inactive ω-chain end of PMMA and PS-b-PMMA by terminal-selective transesterification

Various functional groups were incorporated into the inherently inactive ω-chain end of polymethacrylate-based polymers by terminal-selective transesterification.