Figure-Eight-Shaped and Cage-Shaped Cyclic Polystyrenes

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.

Expanding Cyclic Topology-Based Biomedical Polymer Panel: Universal Synthesis of Hetero-"8"-Shaped Copolymers and Topological Modulation of Polymer Degradation

8-Shaped copolymers with two macrocycles connected together represent an interesting cyclic topology-derived polymer species due to the simultaneous incorporation of two cyclic moieties and the reported unique physical and chemical properties. To provide a proof-of-concept for a broad readership on biomedical polymers, a well-defined hetero-8-shaped amphiphilic copolymer, cyclic-poly(oligo(ethylene glycol)monomethyl ether methacrylate)-b-cyclic PCL (cPOEGMA-b-cPCL) is synthesized by an elegant integration of intrachain click cyclization and interchain click coupling. The potential of the self-assembled micelles of cPOEGMA-b-cPCL for controlled drug release is evaluated by in vitro drug loading and drug release, cellular uptake, cytotoxicity, and degradation studies. Most importantly, the micelles based on cPOEGMA-b-cPCL show much slower degradation profiles than the previously reported linear counterpart, POEGMA-b-PCL and tadpole-shaped analog, PEG-b-cPCL because of the presence of cyclic hydrophilic POEGMA segment. Therefore, this study not only develops a robust strategy for a universal precise synthesis of well-defined hetero-8-shaped copolymers based on diverse vinyl and ring-structured monomers, but also reveals the first modulation of polymer degradation property by topological control of the nondegradable moiety in the polymer construct through advanced macromolecular engineering.

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.

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.

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.

Modulation of cyclic topology toward enhanced drug delivery, from linear and tadpole-like to dumbbell-shaped copolymers

In this study, an efficient strategy for the synthesis of dumbbell-shaped amphiphilic copolymers with cyclic moieties as the two bells was developed and the enhanced performance of dumbbell-shaped copolymers for controlled drug release because of the simultaneous introduction of two macrocycles was disclosed.

Micelles with Cyclic Poly(ε-caprolactone) Moieties: Greater Stability, Larger Drug Loading Capacity, and Slower Degradation Property for Controlled Drug Release

Polymer topology exerts a significant effect on its properties and performance for potential applications. Cyclic topology and its derived structures have been recently shown to outperform conventional linear analogues for drug delivery applications. However, an amphiphilic tadpole-shaped copolymer consisting of a cylic hydrophobic moiety has rarely been explored. For this purpose, a tadpole-shaped amphiphilic diblock copolymer of poly(ethylene oxide)-b-(cyclic poly(ε-caprolactone)) (mPEG-b-cPCL) was synthesized successfully via ring-opening polymerization (ROP) of ε-CL using a mPEG-based macroinitiator with both a hydroxyl and an azide termini and subsequent intrachain Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAc) click cyclization. A comparison study on the self-assembly behaviors, in vitro drug loading and drug release profiles, and degradation properties of the resulting mPEG-b-cPCL (C) with those of the linear counterpart (mPEG-b-PCL, L) revealed that mPEG-b-cPCL micelles are a better formulation than the micelles formed by the linear counterparts in terms of micelle stability, drug loading capacity, and the degradation property. Interestingly, compared to the single degradation of L, C exhibited a slower two-stage degradation process including the topological change from tadpole shape to linear conformation and the subsequent degradation of a linear polymer. This study therefore uncovered the topological effect of a hydrophobic moiety on the properties of the self-assembled micelles and developed a complementary alternative to enhance the micelle stability by introducing a cyclic hydrophobic segment.

Universal Synthetic Strategy for the Construction of Topological Polystyrenesulfonates: The Importance of Linkage Stability during Sulfonation

Polystyrenesulfonate (PSS), as one of the most important categories of polyelectrolytes, has received increasing attention due to its great potential in the applications of energy- and biomedical-related fields. However, most of the previous studies only focused on linear PSS and its derivatives, but little attention was paid to nonlinear topological PSSs. So far, the synthesis of nonlinear PSSs with well-defined structures is still a challenging task, and the main obstacle lies in the stability issue of functional chemical linkages during the sulfonation process of polystyrene (PS) precursors, such as the carbon-oxygen-containing linkages. Herein, by rationally designing the chemical structure of the functional linkage, we introduce a versatile and efficient strategy for the preparation of topological PSSs. Specifically, by embedding firm triazole linkages (without carbon-oxygen linkages) into the backbone structure of cyclic and hyperbranched PS precursors, the backbone and functional linkages are found to present excellent chemical stability under certain sulfonation conditions, which eventually lead to the successful preparation of cyclic and hyperbranched PSSs. By using two sets of PSS samples with varied molar masses, the scaling relations between the number of repeating units and the sedimentation coefficient are established for both linear and cyclic PSSs. We believe that our proposed synthetic strategy is universal and could be extended to the synthesis of other types of topological PSSs.

The effect of chain architecture on the phase behavior of A4B4 miktoarm block copolymers

Well-defined miktoarm (polystyrene)₄-(polylactic acid)₄ ((PS)₄-(PLA)₄) block copolymers were synthesized and their phase behaviors were compared with linear PS-b-PLA block copolymers, in which the miktoarm architecture enhanced the phase segregation.

Solution self-assembly of poly(3-hexylthiophene)–poly(lactide) brush copolymers: impact of side chain arrangement

Solution self-assembly of P3HT-containing copolymers was tailored effectively via bottlebrush architecture, particularly by tuning its side chain arrangement as well as copolymer composition.

Molecular Weight Distribution of Living Chains in Polystyrene Prepared by Atom Transfer Radical Polymerization

Living and dead chains of a polystyrene synthesized by atom transfer radical polymerization were separated and characterized by high performance liquid chromatography (HPLC), size exclusion chromatography (SEC), NMR, and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The bromine end group in the living chain was quantitatively converted to a hydroxyl end group via first azidation and subsequent copper-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction with propargyl alcohol. The living chains bearing a polar end group are fully resolved from the unmodified dead chains by HPLC separation using a bare silica stationary phase. Molecular weight distributions (MWD) of the living and dead chain are characterized by SEC and MALDI-MS. The MWD of the living chains is close to a Poisson distribution. Interestingly, the elution peak of the living chains in the HPLC separation split into two. The peak split is attributed to the diastereomeric structure of the chain end by NMR and MALDI-MS analyses.