Narrow or Monodisperse, Highly Cross-Linked, and “Living” Polymer Microspheres by Atom Transfer Radical Precipitation Polymerization

Exploiting the Monomer-Feeding Mechanism of RAFT Emulsion Polymerization for Polymerization-Induced Self-Assembly of Asymmetric Divinyl Monomers

We exploited the monomer-feeding mechanism of reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization to achieve the successful polymerization-induced self-assembly (PISA) of asymmetric divinyl monomers. Colloidally stable cross-linked block copolymer nanoparticles with various morphologies, such as vesicles, were directly prepared at high solids. Morphologies of the cross-linked block copolymer nanoparticles could be controlled by varying the monomer concentration, degree of polymerization (DP) of the core-forming block, and length of the macro-RAFT agent. X-ray photoelectron spectroscopy (XPS) characterization confirmed the presence of unreacted vinyl groups within the obtained block copolymer nanoparticles, providing a landscape for further functionalization via thiol-ene chemistry. Finally, the obtained block copolymer nanoparticles were employed as additives to tune the mechanical properties of hydrogels. We expect that this study not only offers considerable opportunities for the preparation of well-defined cross-linked block copolymer nanoparticles, but also provides important insights into the controlled polymerization of multivinyl monomers.

Precipitation Polymerization: A Powerful Tool for Preparation of Uniform Polymer Particles

Precipitation polymerization (PP) is a powerful tool to prepare various types of uniform polymer particles owing to its outstanding advantages of easy operation and the absence of any surfactant. Several PP approaches have been developed up to now, including traditional thermo-induced precipitation polymerization (TRPP), distillation precipitation polymerization (DPP), reflux precipitation polymerization (RPP), photoinduced precipitation polymerization (PPP), solvothermal precipitation polymerization (SPP), controlled/‘‘living’’ radical precipitation polymerization (CRPP) and self-stabilized precipitation polymerization (2SPP). In this review, a general introduction to the categories, mechanisms, and applications of precipitation polymerization and the recent developments are presented, proving that PP has great potential to become one of the most attractive polymerization techniques in materials science and bio-medical areas.

Preparation of Poly(Ionic Liquid) Microbeads via Cooling-Assisted Phase Separation Method

A simple and large-scale non-chemical preparation of uniform poly(ionic liquid) (PIL) microbeads via a cooling-assisted phase separation (CAPS) method is reported. For this method, PIL bulk is dissolved to form a saturated solution in a mixed solvent composed of good solvent and non-solvent at a relatively high temperature. Then, the uniform PIL microbeads are prepared by cooling the solution to room temperature or a lower temperature in the absence of stabilizer. The size of microbeads can be controlled by adjusting the preparation parameters, including PIL concentration, cooling rate, and agitation state. The scale of preparation can be up to 10 g, and the yield of PIL microbeads is more than 70% or 88% when the solution is cooled to room temperature or 0 °C, respectively. The formation mechanism of PIL microbeads is discussed by tracing the nucleation and growth process by the transmittance of light of the solution during cooling. The application of this CAPS method to other polymer microbeads preparation is finally discussed by choosing different good solvent and non-solvent.

Microsphere Polymers in Molecular Imprinting: Current and Future Perspectives

Molecularly imprinted polymers (MIPs) are specific crosslinked polymers that exhibit binding sites for template molecules. MIPs have been developed in various application areas of biology and chemistry; however, MIPs have some problems, including an irregular material shape. In recent years, studies have been conducted to overcome this drawback, with the synthesis of uniform microsphere MIPs or molecularly imprinted microspheres (MIMs). The polymer microsphere is limited to a minimum size of 5 nm and a molecular weight of 10,000 Da. This review describes the methods used to produce MIMs, such as precipitation polymerisation, controlled/'Living' radical precipitation polymerisation (CRPP), Pickering emulsion polymerisation and suspension polymerisation. In addition, some green chemistry aspects and future perspectives will also be given.

Molecularly Imprinted Nanoparticles for Biomedical Applications

Molecularly imprinted polymers (MIPs) are synthetic receptors with tailor-made recognition sites for target molecules. Their high affinity and selectivity, excellent stability, easy preparation, and low cost make them promising substitutes to biological receptors in many applications where molecular recognition is important. In particular, spherical MIP nanoparticles (or nanoMIPs) with diameters typically below 200 nm have drawn great attention because of their high surface-area-to-volume ratio, easy removal of templates, rapid binding kinetics, good dispersion and handling ability, undemanding functionalization and surface modification, and their high compatibility with various nanodevices and in vivo biomedical applications. Recent years have witnessed significant progress made in the preparation of advanced functional nanoMIPs, which has eventually led to the rapid expansion of the MIP applications from the traditional separation and catalysis fields to the burgeoning biomedical areas. Here, a comprehensive overview of key recent advances made in the preparation of nanoMIPs and their important biomedical applications (including immunoassays, drug delivery, bioimaging, and biomimetic nanomedicine) is presented. The pros and cons of each synthetic strategy for nanoMIPs and their biomedical applications are discussed and the present challenges and future perspectives of the biomedical applications of nanoMIPs are also highlighted.

Temperature and pH Dual-Responsive Core-Brush Nanocomposite for Enrichment of Glycoproteins

In this report, we present a novel modular approach to the immobilization of a high density of boronic acid ligands on thermoresponsive block copolymer brushes for effective enrichment of glycoproteins via their synergistic multiple covalent binding with the immobilized boronic acids. Specifically, a two-step, consecutive surface-initiated atom transfer radical polymerization (SI-ATRP) was employed to graft a flexible block copolymer brush, pNIPAm-b-pGMA, from an initiator-functionalized nanosilica surface, followed by postpolymerization modification of the pGMA moiety with sodium azide. Subsequently, an alkyne-tagged boronic acid (PCAPBA) was conjugated to the polymer brush via a Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction, leading to a silica-supported polymeric hybrid material, Si@pNIPAm-b-pBA, with a potent glycol binding affinity. The obtained core-brush nanocomposite was systematically characterized with regard to particle size, morphology, organic content, brush density, and number of immobilized boronic acids. We also studied the characteristics of glycoprotein binding of the nanocomposite under different conditions. The nanocomposite showed high binding capacities for ovalbumin (OVA) (98.0 mg g^-1) and horseradish peroxidase (HRP) (26.8 mg g^-1) in a basic buffer (pH 9.0) at 20 °C. More importantly, by adjusting the pH and temperature, the binding capacities of the nanocomposite can be tuned, which is meaningful for the separation of biological molecules. In general, the synthetic approach developed for the fabrication of block copolymer brushes in the nanocomposite opened new opportunities for the design of more functional hybrid materials that will be useful in bioseparation and biomedical applications.

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

Preparation of Molecularly Imprinted Microspheres by Precipitation Polymerization

Molecularly imprinted polymers (MIPs) gained an expansively growing interest in the past few decades. After an initial, explorative period of preparing MIPs exclusively with bulk polymerization, new polymer synthesis routes have been adapted to overcome the drawbacks of the traditional method. Among these the most appealing is precipitation polymerization that results in nano- and microspheres with narrow size distribution and makes the production of MIPs more straightforward. Here, we describe a precipitation polymerization protocol for a common small molecule template, propranolol that is carried out in the conventional way, in dilute monomer solution. Moreover, a modified precipitation polymerization protocol from concentrated monomer solution is presented for a diclofenac imprinted polymer which makes the synthesis even more versatile and circumvents the disadvantages of the dilute solution conditions.

Enhanced separation and antifouling performance of reverse osmosis membrane incorporated with carbon nanotubes functionalized by atom transfer radical polymerization

TEM and HAADF-STEM-EDS merged elemental mapping images of functionalized MWCNTs, and antifouling mechanism of mixed-matrix RO membranes.

A facile synthesis, structural morphology and fluorescent properties of cross-linked poly(cyclotriphosphazene-co-1,3,5-tri(4-hydroxyphenyl)benzene) hybrid copolymer microspheres

Tunable size synthesis of fluorescent active microspheres with proposed unique chemical structure.

Reflux precipitation polymerization: a new synthetic insight in molecular imprinting at high temperature

Reflux precipitation polymerization was first used to fabricate monodispersed MIP microspheres, indicating electrostatic interaction was important for molecular imprinting at high temperature.

Hydrophilic Hollow Molecularly Imprinted Polymer Microparticles with Photo- and Thermoresponsive Template Binding and Release Properties in Aqueous Media

A facile, general, and efficient approach to prepare hydrophilic hollow molecularly imprinted polymer (MIP) microparticles with photo- and thermoresponsive template binding and release behaviors in aqueous media is described, which includes the preparation of uniform "living" silica submicrospheres bearing surface atom transfer radical polymerization (ATRP)-initiating groups (i.e., alkyl halide groups) via a one-pot sol-gel method, their subsequent grafting of azobenzene (azo)-containing MIP shell and poly(N-isopropylacrylamide)-block-poly(2-hydroxyethyl methacrylate) (PNIPAAm-b-PHEMA) brushes via successive surface-initiated ATRP, and final removal of the silica core. The successful synthesis of such hydrophilic hollow MIP microparticles was confirmed with SEM, FT-IR, water dispersion stability, and static contact angle studies. They proved to show apparently higher template binding capacities than the corresponding solid ones and obvious photo- and thermoresponsive template binding properties in aqueous solutions. Moreover, their pronounced light- and temperature-controlled template release in aqueous media was also demonstrated. In particular, the introduction of PNIPAAm-b-PHEMA brushes onto hollow MIP microparticles imparted them with high surface hydrophilicity both below and above the lower critical solution temperature of PNIPAAm, which paves the way for their applications in such areas as controlled drug/chemical delivery and smart bioanalysis.

Preparation and characterization of poly(MMA-EGDMA-AMPS) microspheres by soap-free emulsion polymerization

The poly(methyl methacrylate-ethylene glycol dimethacrylate-2-acrylamido-2-methylpropanesulfonic acid) [poly(MMA-EGDMA-AMPS)] microsphere was produced by a soap-free emulsion polymerization of MMA, EGDMA and AMPS. The chemical composition, morphology, particle size distribution and properties of the obtained microspheres were characterized by energy dispersive spectrometer (EDS), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), a laser particle analyzer and thermogravimetric analysis (TGA). Results showed that the microspheres had a high-quality spherical morphology, irrespective of the components, and their particle sizes mainly ranged from 10 μm to 70 μm. The microspheres were thermally stable up to 190°C. As the AMPS loading was increased, the synthetic yield rate decreased and the water uptake increased. The optimum synthetic yield rate and water uptake were obtained at a 2.0 wt% AMPS. In addition, the selected microspheres with a diameter of approximately 25 μm provided an effective plugging, and the plugging rate was up to 80%. This study demonstrated that the plugging behavior of microspheres was due to their deformation, migration and aggregating properties in the plugging process, which made them potential materials for modifying the porous reservoir to enhance oil recovery in petroleum engineering.

Atom transfer radical polymerization to fabricate monodisperse poly[glycidyl methacrylate-co-poly (ethylene glycol) methacrylate] microspheres and its application for protein affinity purification

Poly[glycidyl methacrylate-co-poly (ethylene glycol) methacrylate] microspheres for the first time were successfully synthesized by atom transfer radical polymerization (ATRP) method at room temperature. The co-polymerization approach was investigated to delicately control the microsphere morphology and size-distribution by reaction conditions including solvent percentage, monomer loading and rotation speed. The results show that the average size of the microspheres is ∼5.7 μm with coexistence of epoxy, hydroxyl and ether groups, which provide plentiful functional sites for protein anchoring. The mechanism of the microsphere formation is proposed. The microsphere successfully demonstrates its unique application for affinity purification of proteins, in which the functional epoxy group facilitates a simple and efficient protein covalent immobilization to purify immunoglobulin G on the microspheres, while the hydrophilic poly (ethylene glycol) motif can repulse nonspecific protein adsorption for good specificity. This microspheres can be used in broad protein biosensors due to their abundant functional groups and high surface to volume ratio.

Recent Advances in Macromolecularly Imprinted Polymers by Controlled Radical Polymerization Techniques

Molecularly imprinted polymers (MIPs) are synthetic receptors with tailor-made recognition sites for the target molecules. Their high molecular recognition ability, good stability, easy preparation, and low cost make them highly promising substitutes for biological receptors. Recent years have witnessed rapidly increasing interest in the imprinting of biomacromolecules and especially proteins because of the great potential of these MIPs in such applications as proteome analysis, clinical diagnostics, and biomedicine. So far, some useful strategies have been developed for the imprinting of proteins and controlled radical polymerization techniques have proven highly versatile for such purpose. This mini-review describes recent developments in the controlled preparation of proteins-imprinted polymers via such advanced polymerization techniques.

Hydrophilic molecularly imprinted polymers for selective recognition of polycyclic aromatic hydrocarbons in aqueous media

A hydrophilic molecularly imprinted polymer (H-MIP) for phenanthrene has been synthesized with higher selectivity in aqueous solution than the traditional MIP.

Monodisperse highly cross-linked “living” microspheres prepared via photoinitiated RAFT dispersion polymerization

Monodisperse highly Cross-linked “Living” microspheres were synthesized via photoinitiated RAFT dispersion polymerization of MMA using a bifunctional monomer or a trifunctional monomer as the cross-linker.

Amphiphilic polyoxometalate-paired polymer coated Fe₃O₄: magnetically recyclable catalyst for epoxidation of bio-derived olefins with H₂O₂

An amphiphilic composite with magnetic Fe3O4 core and dodecylamine-modified polyoxometalate-paired poly(ionic liquid) shell was synthesized and characterized by (1)H NMR, thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, UV-vis spectroscopy, X-ray diffraction (XRD), and digital microscopy. Catalytic tests for H2O2-based epoxidation of bioderived olefins, along with comparisons to various counterparts, demonstrate well that this newly designed catalyst exhibits high activity and selectivity, coupled with convenient magnetic recovery, and effective regeneration. The unique amphiphilic catalyst structure and the intramolecular charge transfer between amino groups and heteropolyanions are revealed to be responsible for the catalyst's excellent performances in epoxidation reactions.

Fluorescent boronic acid polymer grafted on silica particles for affinity separation of saccharides

Boronic acid affinity gels are important for effective separation of biological active cis-diols, and are finding applications both in biotech industry and in biomedical research areas. To increase the efficacy of boronate affinity separation, it is interesting to introduce repeating boronic acid units in flexible polymer chains attached on solid materials. In this work, we synthesize polymer brushes containing boronic acid repeating units on silica gels using surface-initiated atom transfer radical polymerization (ATRP). A fluorescent boronic acid monomer is first prepared from an azide-tagged fluorogenic boronic acid and an alkyne-containing acrylate by Cu(I)-catalyzed 1,3-dipolar cycloaddition reaction (the CuAAC click chemistry). The boronic acid monomer is then grafted to the surface of silica gel modified with an ATRP initiator. The obtained composite material contains boronic acid polymer brushes on surface and shows favorable saccharide binding capability under physiological pH conditions, and displays interesting fluorescence intensity change upon binding fructose and glucose. In addition to saccharide binding, the flexible polymer brushes on silica also enable fast separation of a model glycoprotein based on selective boronate affinity interaction. The synthetic approach and the composite functional material developed in this work should open new opportunities for high efficiency detection, separation, and analysis of not only simple saccharides, but also glycopeptides and large glycoproteins.

Efficient Synthesis of Molecularly Imprinted Polymers with Enzyme Inhibition Potency by the Controlled Surface Imprinting Approach

A facile, general, and highly efficient approach to prepare uniform core-shell molecularly imprinted polymer (MIP) particles with enzyme inhibition potency is described for the first time, which involves the combined use of molecular imprinting and controlled/"living" radical polymerization (CRP) techniques as well as surface-anchoring strategy. The thickness of the enzyme-imprinted surface layers of the core-shell MIP microspheres had a significant influence on their binding properties, and only those with their thickness comparable with the diameters of the targeted enzymes could afford enzyme-MIPs with optimal specific bindings. The as-prepared enzyme-MIPs were found to have homogeneous binding sites and high template binding capacities, affinity, and selectivity, and they proved to show much higher enzyme inhibition potency than the small inhibitor by 3 orders of magnitude (i.e., the enzyme inhibition constant of every binding site of the MIP microspheres was about one-thousandth of that of the small inhibitor), mainly due to the formation of strong long-range secondary interactions between enzymes and imprinted pockets. In addition, the general applicability of our strategy was confirmed.

reliable Synthesis of Monodisperse Microparticles: Prevention of Oxygen Diffusion and Organic Solvents Using Conformal Polymeric Coating onto Poly(dimethylsiloxane) Micromold

An effective polymeric thin film deposited by initiated chemical vapor deposition (iCVD) process was presented and its application as a barrier film on the PDMS micromold blocking the penetration of oxygen and organic solvents was investigated. With this barrier film, we were able to synthesize monodisperse polymeric particles of sizes down to 3 μm, which has been reported to be extremely challenging with bare PDMS micromold. The polymeric barrier film on the PDMS micromold enabled this successful synthesis of microparticles by effectively blocking the diffusion of oxygen, which is a well-known radical quencher in radical polymerization, through the PDMS micromold. Furthermore, the iCVD barrier film substantially decreased the penetration of various organic solvents such as acetone, tert-butanol, PDMS oil, and decane as well as organic substances including fluorescent molecules like rhodamine B and fluorescein isothiocyanate (FITC). Therefore, the polymeric barrier film coated on PDMS micromold via iCVD process will broaden the application of PDMS to microfluidic area for the synthesis of smaller microparticles with various organic substances.

Azobenzene-containing molecularly imprinted polymer microspheres with photo- and thermoresponsive template binding properties in pure aqueous media by atom transfer radical polymerization

A facile, general, and highly efficient approach to obtain azobenzene (azo)-containing molecularly imprinted polymer (MIP) microspheres with both photo- and thermoresponsive template binding properties in pure aqueous media is described for the first time, which involves the first synthesis of "living" azo-containing MIP microspheres with surface-immobilized alkyl halide groups via atom transfer radical precipitation polymerization (ATRPP) and their subsequent modification via surface-initiated atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAAm). The successful grafting of poly(NIPAAm) (PNIPAAm) brushes onto the obtained MIP microspheres was confirmed by FT-IR, SEM, water dispersion stability and static contact angle studies, and template binding experiments. The introduction of PNIPAAm brushes onto the azo-containing MIP microspheres significantly improved their surface hydrophilicity and imparted thermoresponsive properties to them, leading to their pure water-compatible and thermoresponsive template binding properties. In addition, the binding affinity of the imprinted sites in the grafted azo-containing MIP microspheres was found to be photoresponsive toward the template in pure water, and this photoregulation process proved to be highly repeatable under photoswitching conditions.