Asymmetric Polymerization Research Articles

Synthesis of asymmetric imine polymers for highly selective sorting of semiconducting single-walled carbon nanotubes by a two-in-one strategy

An asymmetric imine polymer was obtained by a two-in-one strategy, which shows high selectivity sorting towards semiconductor-SWCNTs and can be removed thoroughly and easily by TFA stimuli.

Chemically Asymmetric Polymers Manipulate the Crystallization of Two-Dimensional Covalent Organic Frameworks to Synthesize Processable Nanosheets.

Nanosheets derived from two-dimensional covalent organic frameworks (2D COFs) are increasingly desirable in various fields. While breakthroughs in the chemical and physical delamination of 2D COFs are rising, precisely regulating the growth of the COF nanosheets has not been realized yet. Herein, we report an effective strategy of polymer-manipulated crystallization to accurately control the growth of COF nanosheets. Chemically asymmetric polyvinylpyrrolidone (PVP) is developed as the manipulator that selectively interacts with the aldehydes and (100) facet to induce anisotropic growth of COFs. The number of PVP constitutional units determines this specific interaction, leading to molecularly thin but thickness-controllable nanosheets with excellent dispersity. We process these nanosheets into robust A4-sized membranes for ultraselective molecular separation. The membrane intercalated with long-chain PVP demonstrates largely improved performance, surpassing the reported COF membranes. This work reports a strategy for anisotropically crystallizing 2D COFs to yield processable nanosheets toward practical applications.

The “solvent” effect of short arms on linear and nonlinear shear rheology of entangled asymmetric star polymers

This study examines the influence of the short arms in model asymmetric 3-arm star polymers, in which the short arm is unentangled while the other two long arms are entangled, on linear and nonlinear shear rheological behavior. As increasing the short arm length of the asymmetric star polymers, the linear viscoelastic rubber plateau decreases, indicating the relaxed short arms act as “solvent” that dilute the star polymers. This idea is examined by the relationship between the plateau moduli of polymer solutions GN(φ) and the corresponding polymer melts GN(1) for entangled linear polymers, GN(φ) = GN(1)φ1+α, where φ is the volume fraction of the polymer. The “solvent” effect of the short arms is also supported by the nonlinear rheology results showing weaker damping function and larger peak strain at stress overshoot. With the above clarification of the short-arm contributions, this work provides a guidance of molecular design for tuning linear and nonlinear rheology of star polymers.

Studies of various properties of different derivatives of asymmetric poly(paraphenylenevinylene) (PPV) polymers for light emitting applications

In this study various poly(paraphenylenevinylene) (PPV) derivatives with different asymmetric alkoxy side-chain lengths were synthesized by a modified Gilch polymerization to improve solubilities and to investigate photoluminescence for light-emitting performance. The optical properties of the monomers and polymers with different alkoxy groups, bonded to the PPV main chain, were examined by UV–Vis and photoluminescence spectroscopy. The UV–Vis spectra showed increases in the intensities of the π-π* transition peaks of asymmetric PPV polymers compared to those of the asymmetric monomers. The excitation and emission wavelengths in the solution states were 467–472 nm and 571–579 nm, respectively. The photoluminescence quantum efficiencies of asymmetric polymers were also investigated and found as being 31–38%, with long excited-state lifetimes of 2.94–3.53 ns. The photoluminescence quantum efficiencies of the asymmetric monomers and polymers were compared. The band gap energy value with respect to emission energies were calculated to be in the range 2.17–2.13 eV for the asymmetric polymers. It was noted that these polymers demonstrated good thermal stabilities and optical and photoluminescence properties, showing great potential in optoelectronic applications. The thermal properties and heat changes in the polymer structures were studied by TGA and DSC. All polymers were amorphous, being stable up to 380 °C. The pre-decay temperature for asymmetric dialkyl monomers was around 169 °C and around 380 °C for the asymmetric dialkyl polymers. Most of the mass losses for asymmetric dialkyl monomers occurred in the range 185–475 °C and 396–512 °C for asymmetric dialkyl polymers. The DSC graphs of these polymers revealed the glass transition temperatures (Tg) 76–113 °C. Thus the PPV derivatives having longer flexible alkyl or alkoxy substituents revealed low Tg or low morphological stabilities. The asymmetric dialkyl PPV polymers showed enthalpies 58.79–123.15 cal/g and entropies 0.176–0.343 cal/g oC.

Selectively Regulating Asymmetric Photopolymerization Via Competition Between Circularly Polarized UV and Visible Light

AbstractCircularly polarized light (CPL) has attracted considerable interest since it can impart chiral bias into photochemical reactions and open up a novel opportunity for synthesizing chiral polymer materials. Despite numerous reports describing the chiral induction effect with single CPL, the synergistic or competitive effect between two types of CPL—i.e., circularly polarized ultraviolet light (CPUV) for triggering asymmetric polymerization while circularly polarized visible light (CPVL) only for accelerating helical chain propagation—is rarely reported. Here, this work demonstrates that the selective regulation on the asymmetric photopolymerization can be realized by the arbitrarily coupled irradiation with CPUV and CPVL, either constructively or destructively. In the former case, further chirality amplification can be achieved. Remarkably, for the latter case, the opposite handed CPVL can bias the polymer helicity during the chain propagation process and thereby overrule the helical preference inducted by CPUV. This work highlights the importance of chiral induction effect in helical chain propagation process and is highly valuable for deeper understanding of helical preference in CPL‐triggered asymmetric photopolymerization.

Synthesis and microphase separation of dendrimer-like block copolymers by anionic polymerization strategies

Anionic polymerization for the preparation of polystyrene-b-polybutadiene is well-established and leads to thermoplastic elastomers on industrial scale. The classical ABA block copolymer (BCP) architecture and composition usually forms a cylindrical morphology in the bulk state. Their anisotropic mechanical properties are, however, unfavorable for many applications. The gyroid microphase is entirely isotropic, but it is only formed in a narrow compositional area of around 35 vol% of the minority polymer block. In the present study, a second-generation dendrimer-like block copolymer structure ((AB)2B)3 is described. This BCP architecture is expected to show a higher curvature on the microphase boundaries, which leads to a larger morphological range for the gyroid phase. Three compositionally different polymers are synthesized by living anionic polymerization strategies and the resulting morphology is analyzed via transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The dendrimer-like BCPs are compared to their less branched analogues, namely the asymmetric star polymers and H-shape stars. The expected influence of the dendrimer-like BCP architecture on the microphase separation is investigated paving the way to a promising synthetic platform for interesting mechanical and optical properties.

Facile synthesis of AA'B- and ABC-type polypept(o)ide miktoarm star polymers utilizing polysarcosine end group functionalization for core introduction

Miktoarm star polymers display asymmetric architectures with combinations of multiple polymeric arms of different chemical nature emanating from a shared core. Their unique structure–property relationships in comparison to linear counterparts (with same molecular weight) make these architectures interesting for the design of novel polymeric species and the development of nanosized delivery systems. However, the synthesis of such structures is often demanding. Based on polypept(o)ides, we herein report on the synthesis of AA'B- and ABC-type miktoarm star polymers by introducing a multifunctional lysine end group to a polysarcosine (pSar) chain end, comprising orthogonal amine-protective groups. Therefore, each polymeric arm could be synthesized separately by living ring-opening polymerization (ROP) of respective N-carboxyanhydrides (NCAs), offering high reaction control and a resulting structure completely based on amino acids. We demonstrate the utility and versatility of this approach by designing a small, asymmetric and big AA'B miktoarm star polymer comprising two pSar arms with chain lengths of ∼50 or ∼150 in different combinations and a poly(Nε-trifluoroacetate-lysine) (pLys(TFA)) arm, as well as an ABC architecture by introducing a poly(γ-benzyl-glutamate) (pGlu(OBn)). 1H NMR, including 1H DOSY experiments, as well as size-exclusion chromatography (SEC) proof the successful and controlled synthesis of asymmetric miktoarm star polymers with precise control over degree of polymerization of the individual arms with narrow molecular weight distributions.

To thread or not to thread? Effective potentials and threading interactions between asymmetric ring polymers.

We use computer simulations to study a system of two unlinked ring polymers, whose length and bending stiffness are systematically varied. We derive the effective potentials between the rings, calculate the areas of minimal surfaces of the same, and characterize the threading between them. When the two rings are of the same kind, threading of a one ring through the surface of the other is immanent for small ring-ring separations. Flexible rings pierce the surface of the other ring several times but only shallowly, as compared to the stiff rings which pierce less frequently but deeply. Typically, the ring that is being threaded swells and flattens up into an oblate-like conformation, while the ring that is threading the other takes a shape of an elongated prolate. The roles of the threader and the threaded ring are being dynamically exchanged. If, on the other hand, the rings are of different kinds, the symmetry is broken and the rings tend to take up roles of the threader and the threaded ring with unequal probabilities. We propose a method how to predict these probabilities based on the parameters of the individual rings. Ultimately, our work captures the interactions between ring polymers in a coarse-grained fashion, opening the way to large-scale modelling of materials such as kinetoplasts, catenanes or topological brushes.

Reconfiguration of Langmuir Monolayers of Thermo-Responsive Branched Ionic Polymers with LCST Transition.

Thermo-responsive ionic polymers have the ability to form adaptive and switchable morphologies, which may offer enhanced control in energy storage and catalytic applications. Current thermo-responsive polymers are composed of covalently attached thermo-responsive moieties, restricting their mobility and global dynamic response. Here, we report the synthesis and assembly at the water-air interface of symmetric and asymmetric amphiphilic thermo-responsive branched polymers with weakly ionically bound arms of amine-terminated poly(N-isopropylacrylamide) (PNIPAM) macro-cations. As we observed, symmetric branched polymers formed multimolecular nanosized micellar assemblies, whereas corresponding asymmetric polymers formed large, interconnected worm-like aggregates. Dramatic changes in localized and large-scale chemical composition confirmed the reversible adsorption and desorption of the mobile PNIPAM macro-cations below and above the low critical solution temperature (LCST) and their non-uniform redistribution within polymer monolayer. Increasing the temperature above LCST led to the formation of large interconnected micellar aggregates because of the micelle-centered aggregation of the hydrophobized PNIPAM macro-cationic terminal chains in the aqueous subphase. Overall, this work provides insights into the dynamic nature of the chemical composition of branched ionic polymers with weakly ionically bound thermo-responsive terminal chains and its effect on both morphology and local/surface chemistry of monolayers at LCST transition.

CuH-catalyzed consecutive hydrosilylation/dehydrocoupling polymerization of difunctional hydroxyketones with dihydrosilanes for syntheses of chiral poly(silyl ether)s

The development of structurally diverse chiral polymers via asymmetric polymerization of prochiral monomers is the frontier in polymeric chemistry. Herein, the easy-to-operate and efficient CuH-catalyzed consecutive asymmetric hydrosilylation/dehydrocoupling polymerization of difunctional hydroxyketone monomers with dihydrosilanes has been developed, providing the chiral poly(silyl ether)s. This polymerization features atom economy, low catalyst loading, broad substrate scope, mild condition, high stereoselectivity and reactivity. The results of DSC revealed poly(silyl ether)s exhibited good thermal properties.

Asymmetric Miktoarm Star Polymers as Polyester Thermoplastic Elastomers

Asymmetric Miktoarm Star Polymers as Polyester Thermoplastic Elastomers

Asymmetric Cationic Polymerization of Benzofuran through a Reversible Chain-Transfer Mechanism: Optically Active Polybenzofuran with Controlled Molecular Weights

Benzofuran (BzF) is a prochiral, 1,2-disubstituted, unsymmetric cyclic olefin that can afford optically active polymers by asymmetric polymerization, unlike common acyclic vinyl monomers. Although asymmetric cationic polymerization of BzF was reported by Natta et al. in the 1960s, the polymer structure has not been clarified, and there are no reports on molecular weight control. Herein, we report dual control of the optical activity and molecular weight of poly(BzF) using thioether-based reversible chain-transfer agents for asymmetric cationic polymerization with β-amino acid derivatives as chiral additives and aluminum chloride as a catalyst. This asymmetric moderately living cationic polymerization leads to an increase in molecular weight and specific optical rotation with monomer conversion. In addition, asymmetric block polymers consisting of opposite absolute configurational segments were synthesized using both enantiomers sequentially as chiral additives. Finally, a comprehensive analysis of the polymerization products and the model reaction revealed that the optical activity of poly(BzF) originates from the threo-diisotactic structure, which occurs by regio-, trans-, and enantioselective propagation.

Corrigendum to ‘Absolute asymmetric polymerizations in solution needing no physical chiral source’ [Polymer 245 (2022) 124673

Corrigendum to ‘Absolute asymmetric polymerizations in solution needing no physical chiral source’ [Polymer 245 (2022) 124673

Inside Cover: Synthesis of Chiral Covalent Organic Frameworks via Asymmetric Organocatalysis for Heterogeneous Asymmetric Catalysis (Angew. Chem. Int. Ed. 25/2022)

A universal organocatalytic asymmetric polymerization approach for the synthesis of chiral covalent organic frameworks (CCOFs) under ambient conditions is developed by Bing-Jian Yao, Yu-Bin Dong et al. in their Research Article (e202115044). With a chiral 2-methylpyrrolidine catalyst, a series of tris(N-salicylideneamine)-derived β-ketoenamine CCOFs were constructed from prochiral monomers via Schiff-base condensation. The metalated CCOFs promote asymmetric A3-coupling reactions at a gram-scale level in a fixed-bed model reactor.

Entropic surface segregation from athermal polymer blends: Polymer flexibility vs bulkiness.

We examine athermal binary blends composed of conformationally asymmetric polymers of equal molecular volume next to a surface of width ξ. The self-consistent field theory (SCFT) of Gaussian chains predicts that the more compact polymer with the shorter average end-to-end length, R0, is entropically favored at the surface. Here, we extend the SCFT to worm-like chains with small persistence lengths, ℓp, relative to their contour lengths, ℓc, for which R0≈2ℓpℓc. In the limit of ℓp ≪ ξ, we recover the Gaussian-chain prediction where the segregation depends only on the product ℓpℓc, but for realistic polymer/air surfaces with ξ ∼ ℓp, the segregation depends separately on the two quantities. Although the surface continues to favor flexible polymers with smaller ℓp and bulky polymers with shorter ℓc, the effect of bulkiness is more pronounced. This imbalance can, under specific conditions, lead to anomalous surface segregation of the more extended polymer. For this to happen, the polymer must be bulkier and stiffer, with a stiffness that is sufficient to produce a larger R0 yet not so rigid as to reverse the surface affinity that favors bulky polymers.

Synthesis of Chiral Covalent Organic Frameworks via Asymmetric Organocatalysis for Heterogeneous Asymmetric Catalysis.

A general and efficient organocatalytic asymmetric polymerization approach for the synthesis of chiral covalent organic frameworks (CCOFs) has been developed. With a chiral 2-methylpyrrolidine catalyst, a series of tris(N-salicylideneamine)-derived β-ketoenamine-CCOFs are directly constructed from prochiral aldehyde- and primary amine-monomers. The adopted aminocatalytic asymmetric Schiff-base condensation herein is performed under ambient conditions with clear green synthetic advantages over the conventional acid-catalysed solvothermal methods. The obtained β-ketoenamine-CCOFs can be further metalated by a solid-state coordination approach, and the resulting CuII @CCOFs can highly promote an asymmetric A3 -coupling reaction. Specifically, a CuII @CCOF@chitosan aerogel was fabricated as a highly efficient fixed-bed model reactor for scaled-up catalysis. The concept of aminocatalytic asymmetric polymerization might open a new way for constructing the CCOFs via asymmetric organocatalysis.

Synthesis of Chiral Covalent Organic Frameworks via Asymmetric Organocatalysis for Heterogeneous Asymmetric Catalysis

AbstractA general and efficient organocatalytic asymmetric polymerization approach for the synthesis of chiral covalent organic frameworks (CCOFs) has been developed. With a chiral 2‐methylpyrrolidine catalyst, a series of tris(N‐salicylideneamine)‐derived β‐ketoenamine‐CCOFs are directly constructed from prochiral aldehyde‐ and primary amine‐monomers. The adopted aminocatalytic asymmetric Schiff‐base condensation herein is performed under ambient conditions with clear green synthetic advantages over the conventional acid‐catalysed solvothermal methods. The obtained β‐ketoenamine‐CCOFs can be further metalated by a solid‐state coordination approach, and the resulting CuII@CCOFs can highly promote an asymmetric A3‐coupling reaction. Specifically, a CuII@CCOF@chitosan aerogel was fabricated as a highly efficient fixed‐bed model reactor for scaled‐up catalysis. The concept of aminocatalytic asymmetric polymerization might open a new way for constructing the CCOFs via asymmetric organocatalysis.

Absolute asymmetric polymerizations in solution needing no physical chiral source

Absolute asymmetric polymerizations, which do not need chiral compounds, are very limited. In addition, they involve spontaneously formed supramolecular compounds, or they need circularly polarized light, and the resulting polymers are often insoluble showing no chiral information at the molecular level. Here we have achieved five kinds of real absolute asymmetric polymerizations of achiral acetylene monomers showing no CD in solution to yield soluble high MW chiral polymers showing CD peaks in solution. These polymerizations did not contain spontaneously formed chiral crystals of monomers or did not use circularly polarized light. A new mechanism we propose here for this new unusual polymerization will give us clues to a better understanding of the reason for the homochirality of our world.

Three-Component Asymmetric Polymerization toward Chiral Polymer

Three-Component Asymmetric Polymerization toward Chiral Polymer

Progress review of asymmetric polymers for organic solar cells

This review summarizes the recent advances of asymmetric donor polymers developed using a symmetry-breaking strategy, including polymers with asymmetric side chains and polymers with asymmetric backbones.