Nanoreactors for Polymerizations and Organic Reactions

Asymmetric Aldol Reactions Catalyzed by Polymeric Self-Assembly with Side-Chain Dipeptide Pendants

To explore the role of proline amide moieties in polymer-supported organocatalysts, side-chain l-proline-l-alanine (Pro-Ala) dipeptide-containing block copolymers were synthesized, and their catalytic potential for the aldol reaction was explored. The dipeptide monomer (Boc-Pro-Ala-HEMA) was polymerized to prepare block copolymers in the presence of hydrophilic poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA) and hydrophobic poly(methyl methacrylate) (PMMA) macro-chain transfer agents. Boc group expulsion from the block copolymers produced double hydrophilic PPEGMA-b-P(Pro-Ala-HEMA) (1b) and amphiphilic PMMA-b-P(Pro-Ala-HEMA) (1c) polymers. The solution behaviors of the polymers were studied by various physical techniques, which showed the formation of self-assembled aggregates of 1c in water and N,N-dimethylformamide (DMF)/water solvent mixtures. These polymers are used as organocatalysts during the aldol reaction of cyclohexanone and 4-nitrobenzaldehyde in different solvent polarities, catalyst loadings, temperatures, and reaction times. This work emphasizes superior catalytic activity of 1c at lower catalyst loadings (5%) while maintaining high conversion (95%) and enantioselectivity (94%) across multiple recycling cycles in DMF/water at a 3:1 ratio (v/v).

Dynamics and Equilibration Mechanisms in Block Copolymer Particles

Self-assembly of block copolymers into interesting and useful nanostructures, in both solution and bulk, is a vibrant research arena. While much attention has been paid to characterization and prediction of equilibrium phases, the associated dynamic processes are far from fully understood. Here, we explore what is known and not known about the equilibration of particle phases in the bulk, and spherical micelles in solution. The presumed primary equilibration mechanisms are chain exchange, fusion, and fragmentation. These processes have been extensively studied in surfactants and lipids, where they occur on subsecond time scales. In contrast, increased chain lengths in block copolymers create much larger barriers, and time scales can become prohibitively slow. In practice, equilibration of block copolymers is achievable only in proximity to the critical micelle temperature (in solution) or the order-disorder transition (in the bulk). Detailed theories for these processes in block copolymers are few. In the bulk, the rate of chain exchange can be quantified by tracer diffusion measurements. Often the rate of equilibration, in terms of number density and aggregation number of particles, is much slower than chain exchange, and consequently observed particle phases are often metastable. This is particularly true in regions of the phase diagram where Frank-Kasper phases occur. Chain exchange in solution has been explored quantitatively by time-resolved SANS, but the results are not well captured by theory. Computer simulations, particularly via dissipative particle dynamics, are beginning to shed light on the chain escape mechanism at the molecular level. The rate of fragmentation has been quantified in a few experimental systems, and TEM images support a mechanism akin to the anaphase stage of mitosis in cells, via a thin neck that pinches off to produce two smaller micelles. Direct measurements of micelle fusion are quite rare. Suggestions for future theoretical, computational, and experimental efforts are offered.

Nanoconfinement in miniemulsion increases reaction rates of thiol–ene photopolymerization and yields high molecular weight polymers

Photoinitiated thiol–ene polymerization was performed in bulk and miniemulsion. We show that the compartmentalization of the reaction inside nanodroplets led to faster reaction kinetics and yielded polymers with higher molecular weight.

Biomimetic controlled radical photopolymerization in a two-dimensional organized environment under visible light

Fast and well-controlled photoinduced atom transfer radical polymerization (photoATRP) in the organized medium of a bilayer activated by visible light under environmentally friendly mild aqueous conditions leads to polymers with predetermined molecular weight and low dispersity. The decisive parameter for photoATRP of monomers in the organized medium was their mobility and orientation with respect to the bilayer and the photoredox catalyst localized in the interstitial layer.

A Review on Recent Progress of Glycan-Based Surfactant Micelles as Nanoreactor Systems for Chemical Synthesis Applications

The nanoreactor concept and its application as a modality to carry out chemical reactions in confined and compartmentalized structures continues to receive increasing attention. Micelle-based nanoreactors derived from various classes of surfactant demonstrate outstanding potential for chemical synthesis. Polysaccharide (glycan-based) surfactants are an emerging class of biodegradable, non-toxic, and sustainable alternatives over conventional surfactant systems. The unique structure of glycan-based surfactants and their micellar structures provide a nanoenvironment that differs from that of the bulk solution, and supported by chemical reactions with uniquely different reaction rates and mechanisms. In this review, the aggregation of glycan-based surfactants to afford micelles and their utility for the synthesis of selected classes of reactions by the nanoreactor technique is discussed. Glycan-based surfactants are ecofriendly and promising surfactants over conventional synthetic analogues. This contribution aims to highlight recent developments in the field of glycan-based surfactants that are relevant to nanoreactors, along with future opportunities for research. In turn, coverage of research for glycan-based surfactants in nanoreactor assemblies with tailored volume and functionality is anticipated to motivate advanced research for the synthesis of diverse chemical species.

Therapeutic Polymersome Nanoreactors with Tumor-Specific Activable Cascade Reactions for Cooperative Cancer Therapy

Therapeutic nanoreactors are of increasing interest in precise cancer therapy, which have been explored to in situ produce therapeutic compounds from inert prodrugs or intrinsic molecules at the target sites. However, engineering a nanoreactor with tumor activable cascade reactions for efficient cooperative cancer therapy remains a great challenge. Herein, we demonstrate a polymersome nanoreactor with tumor acidity-responsive membrane permeability to activate cascade reactions for orchestrated cooperative cancer treatment. The nanoreactors are constructed from responsive polyprodrug polymersomes incorporating ultrasmall iron oxide nanoparticles and glucose oxidase in the membranes and inner aqueous cavities, respectively. The cascade reactions including glucose consumption to generate H₂O₂, accelerated iron ion release, Fenton reaction between H₂O₂ and iron ion to produce hydroxyl radicals (•OH), and •OH-triggered rapid release of parent drugs can be specifically activated by the tumor acidity-responsive membrane permeability. During this process, the orchestrated cooperative cancer therapy including starving therapy, chemodynamic therapy, and chemotherapy is realized for high-efficiency tumor suppression by the in situ consumed and produced compounds. The nanoreactor design with tumor-activable cascade reactions represents an insightful paradigm for precise cooperative cancer therapy.

Facile Synthesis of Chiral Polymers with Defined Architecture via Cooperative Assembly of Confined Templates

Herein is presented the synergistically self-assembled system as biomimetic polymerization media. This approach allows the facile synthesis of chiral amino acid-based polymers with high molecular weight and low dispersity inside of the bilayer of catanionic vesicles by using a conventional radical polymerization under moderate conditions.

Dissipative particle dynamics simulation of multicompartment micelle nanoreactor with channel for reactants

The structural variation of multicompartment micelles is investigated using a dissipative particle dynamics simulation method for nano-reactor application. It turns out that well-defined multicompartment micelles with channel structures can be generated through the self-assembly of triblock copolymers consisting of a hydrophilic (A), a lipophilic (B), and a fluorophobic (C) block arranged in a B–A–C sequence: The corona and core are formed by the hydrophilic A block and the fluorophilic C block, respectively while the channel between the aqueous phase and core is formed by the lipophilic B block and the core. By performing a set of simulations, it is confirmed that channel size can be controlled as a function of the block length ratios between blocks A and B. Furthermore, it is also confirmed that the reactants pass through such channels to reach the micelle core by analyzing the pair correlation functions. By monitoring the change of the number of reactants in the multicompartment micelle, it is revealed that the diffusion of reactants into the core is slowed down as the concentration gradient is decreased. This work provides mesoscopic insight for the formation of multicompartment micelles and transport of reactants for use in the design of micelles as nanoreactors.

The structural variation of multicompartment micelles is investigated using a dissipative particle dynamics simulation method for nano-reactor application.

Cooperation of Amphiphilicity and Smectic Order in Regulating the Self-Assembly of Cholesterol-Functionalized Brush-Like Block Copolymers

Nanoparticle morphology significantly affects the application of nanometer-scale materials. Understanding nanoparticle formation mechanisms and directing morphological control in nanoparticle self-assembly processes have received wide attention. Herein, a series of brush-like amphiphilic liquid crystalline block copolymers, PChEMA _m- b-POEGMA _n, containing cholesteryl mesogens with different hydrophobic/hydrophilic block ratios were designed and synthesized. The self-assembly behaviors of the resulting PChEMA _m- b-POEGMA _n block copolymers in different solvents (tetrahydrofuran/H₂O, 1,4-dioxane/H₂O, and N, N-dimethylformamide) were investigated in detail. Desirable micellar aggregates with well-organized architectures, including short cylindrical micelles, nanofibers, fringed platelets, and ellipsoidal vesicles with smectic micellar cores, were observed in 1,4-dioxane/H₂O with an increasing hydrophobic block ratio. Although both amphiphilicity and smectic order governed the self-assembly, these two factors were differently balanced in the different solvents. This unique supramolecular system provides a new strategy for the design of advanced functional nanomaterials with tunable morphologies.

Pillararene-based self-assembled amphiphiles

Pillararenes are a unique group of supramolecular macrocycles, presenting important features and potential applications on account of their intrinsic structural properties and functionality. Developing pillararene-based self-assembled amphiphiles (PSAs) is an efficient approach to translate pillararenes into functional systems and materials for facilitating their practical applications. In this review article, we highlight recent significant advancements in PSAs. A new standard according to the number, solubility, and amphiphilicity of building blocks is employed for dividing PSAs into different categories. The fabrication of PSAs based on various building blocks and supramolecular interactions, and the formation of amphiphile-based self-assemblies are then discussed based on this standard. Furthermore, interesting stimulus-responsiveness to various factors, such as pH, redox, temperature, light, ionic effect, and host-guest competition, generated by the functional groups on various building blocks is summarized, and the corresponding supramolecular interactions in PSAs and their self-assemblies are elaborated. In addition, some important applications of PSAs and their assemblies are discussed. This review not only provides fundamental findings on the construction of PSAs, but also foresees future research directions in this rapidly developing area.

Asymmetric epoxidation of unfunctionalized olefins accelerated by thermoresponsive self-assemblies in aqueous systems

A thermoresponsive self-assembled nanoreactor, comprising a hydrophilic PNIPAAm shell and a hydrophobic chiral salen Mn^III complex core, exhibits unprecedented efficiency and facile reusability in asymmetric epoxidation of unfunctionalized olefins in pure water without using any organic solvents.

A triazine-phosphite polymeric ligand bearing cage-like P,N-ligation sites: an efficient ligand in the nickel-catalyzed amination of aryl chlorides and phenols

A reusable polymeric material containing P,N-ligation sites was prepared by a facile one-step route for application in transition-metal catalysis as a reusable P,N-ligand.

Dissipative particle dynamics simulation study of poly(2-oxazoline)-based multicompartment micelle nanoreactor

We investigate multicompartment micelles for nanoreactor applications, using the DPD simulation method to characterize the internal structure and the distribution of the reactant.

Temperature-Directed Self-Assembly of Multifunctional Polymeric Tadpoles

Multicompartment tadpole nano-objects are a rare and intriguing class of structures with potential in a wide range of applications. Here, we demonstrate the synthesis of chemically multifunctional polymer tadpoles made at high weight fractions of polymer (>10 wt %). The tadpoles are synthesized using two different thermoresponsive MacroCTAs with either alkyne or pyridyldisulfide end-groups, allowing chemical functionality in the head, tail, or both. Water-soluble molecules or polymers were coupled to either the head, tail or both without a change in tadpole configuration. In addition, the tadpoles can be dried, rehydrated, and stored in water for 5 months without a change in shape. This method represents a new and an important synthetic development in the design of nano-objects.

Interfacial tension-hindered phase transfer of polystyrene-b-poly(ethylene oxide) polymersomes from a hydrophobic ionic liquid to water

We examine the phase transfer of polystyrene-b-poly(ethylene oxide) (PS-PEO) polymersomes from a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]), into water. The dependence of the phase transfer on the molecular weight and PEO volume fraction (fPEO) of the PS-PEO polymersomes was systematically studied by varying the molecular weight of PS (10,000-27,000 g/mol) as well as by varying the volume fraction of PEO (fPEO) between 0.1 and 0.3. We demonstrate a general boundary for the phase transfer in terms of a reduced tethering density for PEO (σPEO), which is independent of the molecular weight of the hydrophobic PS. The reduced PEO tethering density was controlled by changing the polymersome size (i.e., increased polymersome sizes increase σPEO), confirming that it is the driving force in the transfer of PS-PEO polymersomes at room temperature. The phase transfer dependence on σPEO was also analyzed in terms of the free energy of polymersomes in the biphasic system. The quality of the aqueous phase, which affects the interfacial tension of the PS membrane, influenced the phase transfer. We systematically reduced the interfacial tension by adding a water-selective solvent, THF, which has a similar effect to increasing σPEO. The results indicate that the interfacial tension between the membrane and water plays an important role in the phase transfer with the corona and that the phase transfer can be controlled either by the dimensions of the polymersomes or by the suitability of the solvent for the membrane. The interfacial tension-hindered phase transfer of polymersomes in the biphasic water-[EMIM][TFSI] system will inform the design of temperature-sensitive and reversible nanoreactors and the separation of polydisperse particles according to size by tuning the quality of the solvent.

Rapid synthesis of ultrahigh molecular weight and low polydispersity polystyrene diblock copolymers by RAFT-mediated emulsion polymerization

An environmentally friendly emulsion technique produces uniform nanoparticles with precise control over molecular weight and particle size.

Study on an integrated process combining ozonation with ceramic ultra-filtration for decentralized supply of drinking water

An integrated process was specifically developed for the decentralized supply of drinking water from micro-polluted surface water in the rural areas of China. The treatment process combined ozonation with ceramic ultra-filtration (UF), coagulation for pre-treatment and granular activated carbon filtration. A flat-sheet ceramic membrane was used with a cut-off of 60 nm and the measurement of 254 mm (length) × 240 mm (width) × 6 mm (thickness). Ozonation and ceramic UF was set up whthin one reactor. The experimental results showed that the removal efficiencies of the dissolved organic carbon (DOC) and the formation potential of trihalomethanes (THMs), haloacetic acids (HAAs) and ammonia were 80%, 76%, 70% and 90%, respectively; that the turbidity of the product water was below 0.2 NTU and the particle count number (particles larger than 2 μm) was less than 50 counts per mL. The result also showed that all the pathogenic microorganisms were retained by the ceramic and that UF. Ozonation played a critical role in the control of membrane fouling and the removal of contaminants. Exactly, the membrane fouling can be controlled in situ with 3 mg L(-1) ozone at the permeate flux of 80 L m(-2) h(-1), yet the required dosage of ozone was dependent on the quality of the raw water. Therefore, this study is able to provide a highly compacted system for decentralized supply of high-quality drinking water in terms of both chemical and microbiological safety for the rural areas in China.

Nitroxide-mediated microemulsion polymerization of n-butyl acrylate: decoupling of target molecular weight and particle size

Independent control of molecular weight and particle size can be achieved in nitroxide mediatedn-butyl acrylate microemulsion polymerization.

Progressive macromolecular self-assembly: from biomimetic chemistry to bio-inspired materials

Macromolecular self-assembly (MSA) has been an active and fruitful research field since the 1980s, especially in this new century, which is promoted by the remarkable developments in controlled radical polymerization in polymer chemistry, etc. and driven by the demands in bio-related investigations and applications. In this review, we try to summarize the trends and recent progress in MSA in relation to biomimetic chemistry and bio-inspired materials. Our paper covers representative achievements in the fabrication of artificial building blocks for life, cell-inspired biomimetic materials, and macromolecular assemblies mimicking the functions of natural materials and their applications. It is true that the current status of the deliberately designed and obtained nano-objects based on MSA including a variety of micelles, multicompartment vesicles, and some hybrid and complex nano-objects is at their very first stage to mimic nature, but significant and encouraging progress has been made in achieving a certain similarity in morphologies or properties to that of natural ones. Such achievements also demonstrate that MSA has played an important and irreplaceable role in the grand and long-standing research of biomimetic and bio-inspired materials, the future success of which depends on mutual and persistent efforts in polymer science, material science, supramolecular chemistry, and biology.

Core cross-linked micelle-based nanoreactors for efficient photocatalysis

Stable nanoscale cross-linked polymer micelles containing Ru complexes (Ru-CMs) were prepared from monomethoxy[poly(ethylene glycol)]-block-poly(L-lysine) (MPEG-PLys) and [(bpy)2Ru(fmbpy)](PF6)2 (bpy=bipyridine, fmbpy=5-formy-5'-methyl-2,2'-bipyridine). To stabilize the micelles, bifunctional glutaraldehyde was used as a cross-linker to react with the free amino groups of the PLys block. After that, the Ru-CMs showed very good stability in common solvents. The Ru-CMs showed photocatalytic activity and selectivity in the oxidation of sulfides that were as high as those of the well-known [Ru(bpy)3(PF6)2] complex, because the micelles were swollen in the methanol-sulfide mixture. Moreover, because of the nanoscale size of the particles and their high stability, the Ru-CM photocatalysts can be readily recovered by ultrafiltration and reused without loss of photocatalytic activity. This work highlights the potential of using cross-linked micelles as a platform for developing highly efficient heterogeneous photocatalysts for a number of important organic transformations.

Thermoresponsive Polymer-Supported l-Proline Micelle Catalysts for the Direct Asymmetric Aldol Reaction in Water

l-Proline moieties bound to a thermoresponsive polymer nanoreactor efficiently directed the asymmetric aldol reaction in water with excellent yields and enantioselectivity (ee). The reactions were efficient at higher temperatures in direct contrast to the low yields and ee values found when the reaction was carried out in a DMF/water mixture due to the location of the l-proline moieties within the hydrophobic pocket inside the core of the nanoreactors. This ideal environment formed for catalysis allows control over the water content as well as enhancing interactions between the carboxylic acid of l-proline and the aldehyde substrate. The nanoreactors were disassembled to fully water-soluble polymers by lowering the temperature to below the lower critical solution temperature (LCST) of the polymer, resulting in precipitation of the product in near pure form. The product was isolated by centrifugation and the polymer/water solution reused in additional catalytic cycles by heating the polymer above its LCST and thus reforming the nanoreactors. Although a small decrease in yield after five cycles was observed, the selectivity (anti/syn ratio and ee) remained high.

Advances in nanoreactor technology using polymeric nanostructures

Site isolation, compartmentalization and substrate specificity are a few of the characteristics responsible for the catalytic efficiency demonstrated by enzymes in natural systems. In efforts to mimic these highly efficient systems, research has been directed towards macromolecular chemistry. Robust polymer assemblies can create a favorable and isolated environment around the catalytic site allowing specific and sometimes incompatible reactions to take place within this protected reaction pocket. Further exploring the use of 'smart' polymers, control over both the catalytic activity and substrate specificity is achieved. In addition, polymeric systems provide the opportunity for recycling of the active catalysts, further enhancing the advantages of polymer supported catalytic systems.