Photo-emulsion Polymerization Research Articles

Continuous Synthesis of Spherical Polyelectrolyte Brushes by Photo-Emulsion Polymerization in a Microreactor.

Nanosized spherical polyelectrolyte brushes (SPBs) are ideal candidates for the preparation of nanometal catalysts, protein separation, and medical diagnostics. Until now, SPBs have been synthesized by photo-emulsion polymerization in a batch reactor, which remains challenging to scale up. This paper reports a successful continuous preparation of SPBs by photo-emulsion polymerization in a self-made microreactor. The effects of residence time, monomer concentration, and feed ratios on the conversion of monomers and SPB structures are systematically investigated by dynamic lighting scattering and transmission electron microscopy. Poly(acrylic acid) (PAA) SPBs obtained in a microreactor exhibiting a narrow size distribution with a short reaction time are very effective in inhibiting the calcium carbonate scale and are comparable to those produced in a batch reactor. This work confirms the feasibility of continuous preparation and scaled-up production of SPBs.

The Design and Preparation of Antibacterial Polymer Brushes with Phthalocyanine Pigments

Phthalocyanine pigments have many problems in waterborne coating applications because of their low polarity, poor dispersion in water, and easy agglomeration properties. In order to solve these problems, the phthalocyanine pigments were encapsulated with a copolymer of methyl methacrylate (MMA) and butyl acrylate (BA) by a mini-emulsion polymerization method. The pigments are effectively dispersed in water and have good compatibility with the resin. Concerning the bacterial reproduction and growth problem for the waterborne system, the resin-encapsulated phthalocyanine pigments were further grafted with antibacterial polymer poly(N-(2-hydroxyethyl) acrylamide) (PHEAA) on its surface using the photoemulsion polymerization technique. Comprehensive properties, including centrifugal stability and chromaticity change, were studied. The polymer encapsulation improved the centrifugal stability of the pigment. The thermogravimetric results showed that the residual mass of C.I. Pigment Green 7 (52.30%) was higher than that of C.I. Pigment Blue 15:3 (30.06%), and the sublimation fastness of PG7 was higher. The TEM results revealed that the shape of the PG7 after encapsulation and grafting was more regular than that of PB15:3. The L* of the pigment decreased after encapsulation but then increased after further grafting. The phthalocyanine pigment composite latex had good antibacterial properties after the grafting of PHEAA.

Tunable Protein Adsorption by Zwitterionic Spherical Poly(CBAA) Brushes Prepared via Photoemulsion Polymerization

Zwitterionic polymer brushes are well-known as excellent hydrophilic and antifouling materials. However, they demonstrate a certain degree of adsorption for proteins and other substances in practical application, and little research has been conducted into this area. Herein, a facile and efficient approach was employed to prepare zwitterionic spherical polymer brushes, polystyrene-poly(2-carboxy-N,N-dimethyl-N-(3′-acrylamidopropyl) ethanaminium inner salt) brushes (PS–PCBAA brushes). Specifically, the preparation process consists of three steps. First, polystyrene (PS) nanospheres were synthesized via conventional emulsion polymerization, and then photoinitiator with terminal double bond was immobilized on the surface of the PS core by copolymerizing with styrene (PS@HMEM). Finally, zwitterionic polymer chains (PCBAA) were grafted onto the surface of PS@HMEM via photoemulsion polymerization. The hydrodynamic diameter and size distribution, morphology, and chemical composition of PS–PCBAA brushes were characterized. The interaction between PS–PCBAA brushes and proteins was investigated by turbidity and size change. The interaction between brushes and proteins was mainly affected by two factors: the electrostatic interaction between polymer chains and proteins, and the transition of zwitterionic polymers from a fouling polymer to a nonfouling polymer. This work provided a simple and environmentally friendly method for constructing zwitterionic materials that showed potential application in the controllable adsorption and desorption of proteins.

Catalytic Activity Comparison of Gold Nanoparticles in Annealed and Quenched Spherical Polyelectrolyte Brushes

Abstract Two kinds of cationic spherical polyelectrolyte brushes (SPB), quenched poly(methacryloxyethyltrimethyl ammonium chloride) brush and annealed poly(2-aminoethyl methacrylate hydrochloride) brush with polystyrene cores (PS-PMETAC and PS-PAEMH), were synthesized by photo-emulsion polymerization. The small and uniform gold nanoparticles (AuNPs) were successfully immobilized in these two SPBs. The chain layer extension of the quenched SPB loaded with AuNPs (SPB-Au) was more complete than that of the annealed SPB-Au in alkaline system. Compared the catalysis of the prepared AuNPs onto the two SPBs, it was found that the catalytic activity of AuNPs in quenched SPB is higher than that in annealed SPB.

CO2-Responsive Spherical Polyelectrolyte Brush with Multi-Stimulation for Reversible Protein Immobilization and Release

Multi-responsive materials have received extensive interest in many areas due to their smart characteristics. This paper presents rationally designed multi-responsive spherical polyelectolyte brushes composed of a solid polystyrene (PS) core and a poly (2-(dimethylamino) ethyl methacrylate) (PDMAEMA) shell synthesized by photoemulsion polymerization. Based on dynamic light scattering, Zeta potential, turbidity measurements, isothermal titration calorimetry, and UV-vis spectroscopy, PS-PDMAEMA works as a good potential adsorbent for bovine serum albumin (BSA) for which the maximum adsorption capability could reach up to 5190mg g−1. Moreover, the immobilization and release of protein on the polymer brush could be adjusted with different triggers, including the pH, ionic strength, and temperature. Furthermore, the green gas triggers, CO2 and N2, could be employed in the BSA@ PS-PDMAEMA system by easily bubbling over many cycles without any salt accumulation. The main reason for the observed actions is the brushes could be switched alternately between extended and collapsed states with different stimulations. Upon comparing the circular dichroism spectra of original and released BSA after many cycles of adsorption and release, it’s clear that the protein can retain its initial biological activity after release from the PS-PDMAEMA. This work provides an effective and green way to immobilize and release proteins in biotechnology.

Stabilization of Pickering Emulsions by Hairy Nanoparticles Bearing Polyanions.

Pickering emulsions are increasingly applied in drug delivery, oil–water separation, composite materials preparation, and other fields. However, systematic studies on the stabilization of Pickering emulsions to satisfy the growing application demands in multiple fields with long-term conservation are rare. Compared to conventional solid nanoparticles, polyanion-modified hairy nanoparticles are more stable in practical environments and are investigated in this study. Poly (sodium p-styrenesulfonate) was grafted to a polystyrene (PS) core via a photoemulsion polymerization. A hairy nanoparticle bearing polyanions called poly (sodium p-styrenesulfonate) brush (PS@PSS) was synthesized. The size and uniformity of the Pickering emulsions stabilized by PS@PSS were investigated via a polarizing microscope. The stability of Pickering emulsions were optimized by adjusting critical factors like ultrasonic power and time, standing time, oil phases, salt concentration, and water:oil ratio. Results indicated that the Pickering emulsions could be stabilized by PS@PSS nanoparticles, which showed remarkable and adjustable partial wetting properties. It was found that the optimized conditions were ultrasonic power of 150 W, ultrasonic time of 3 min, salt concentration of 0.1 mM, oil phase of hexadecane, and water:oil ratio of 1:1. The formation and stability of Pickering emulsion are closely related to the hairy poly (sodium p-styrenesulfonate) brush layer on the nanoparticle surface.

Antifouling performance of nano-sized spherical poly(N-hydroxyethyl acrylamide) brush

The biomedical applications of nanoparticles are still impeded by the non-specific adsorption of proteins, cells, or others biological species in vivo/in vitro. In this work, poly(N-hydroxyethyl acrylamide) was hired to modify a solid polymer core, polystyrene (PS) nanoparticles, via surface-initiated photo-emulsion polymerization to form nano-sized spherical poly(N-hydroxyethyl acrylamide) brush (PS@PHEAA). Its antifouling ability and stability were investigated by dynamic light scattering (DLS), turbidimetric titration, and isothermal titration calorimetry (ITC). The size of PS@PHEAA was constant as a function of pH, while slightly changed with ionic strength in single protein solution. ITC data confirmed that protein was slightly adsorbed on PS@PHEAA and the ionic strength influenced the adsorption. All characterizations demonstrated that PHEAA layer reduced the interaction between nanoparticles and proteins. Thus, these nanoparticles ideal candidates for future applications in the biomedical field.

Synthesis and characterization of pH-responsive nanoscale hydrogels for oral delivery of hydrophobic therapeutics

pH-responsive, polyanionic nanoscale hydrogels were developed for the oral delivery of hydrophobic therapeutics, such as common chemotherapeutic agents. Nanoscale hydrogels were designed to overcome physicochemical and biological barriers associated with oral delivery of hydrophobic therapeutics such as low solubility and poor permeability due to P-glycoprotein related drug efflux. Synthesis of these nanoscale materials was achieved by a robust photoemulsion polymerization method. By varying hydrophobic monomer components, four formulations were synthesized and screened for optimal physicochemical properties and in vitro biocompatibility. All of the responsive nanoscale hydrogels were capable of undergoing a pH-dependent transition in size. Depending on the selection of the hydrophobic monomer, the sizes of the nanoparticles vary widely from 120nm to about 500nm at pH 7.4. Polymer composition was verified using Fourier transform infrared spectroscopy and 1H-nuclear magnetic resonance spectroscopy. Polymer biocompatibility was assessed in vitro with an intestinal epithelial cell model. All formulations were found to have no appreciable cytotoxicity, defined as greater than 80% viability after polymer incubation. We demonstrate that these nanoscale hydrogels possess desirable physicochemical properties and exhibit agreeable in vitro biocompatibility for oral delivery applications.

Preparation of Au/Ag multilayers via layer-by-layer self-assembly in spherical polyelectrolyte brushes and their catalytic activity

Spherical polyelectrolyte brushes (SPBs) consisting of polystyrene (PS) core and poly(2-aminoethyl methacrylate hydrochloride) (PAEMH) shell were prepared by photo-emulsion polymerization. Au nanoparticles (Au-NPs) with controlled size and size distribution were synthesized in situ using SPBs as nanoreactors. Via layer-by-layer deposition technique on the surface of SPBs, nano-composite particles with Au/Ag-NPs bilayer and Au/Ag/Au-NPs trilayer were prepared. The structures of the as-prepared Au/Ag multilayer SPBs were characterized by UV-Vis spectroscopy, TEM, ICP-AES and DLS. The charge reversal of the nano-composite particles observed by zeta potential confirmed the success of layer-by-layer assembly. The Au/Ag-NPs bilayer nano-composite particles showed high catalytic efficiency with an apparent activation energy of about 41.2 kJ/mol in the reduction reaction of 4-nitrophenol to 4-aminophenol in the existence of sodium borohydride monitored. The catalytic activity of Au/Ag-NPs multilayer SPBs close to Au-NPs SPBs and much higher than Ag-NPs SPBs reveals its potential applications in cost-effective catalysts with high-performance.

Preparation of Functional Janus Particles with Response to Magnetic Force

Magnetic Janus particles consisting of iron oxide particles and polystyrene were prepared by miniemulsion polymerization and subsequent seed emulsion polymerization. The polystyrene areas on the Janus particle surface were then functionalized by grafting poly(acrylic acid) (PAA) brushes via photoemulsion polymerization or by coating palladium nanoparticles via a vapor deposition method. The magnetic Janus particles partially grafted with PAA were pH sensitive and able to immobilize proteins. The orientation of Janus particles partially covered with palladium in the wax–water interface could be controlled by an external magnetic force. These functional magnetic Janus particles with superparamagnetism have potential applications in, e.g., controlled interfacial catalysis triggered by a magnetic force.

Encapsulation of Quantum Dot Clusters in Stimuli-Responsive Spherical Polyelectrolyte Brushes

Novel fluorescence-labeled spherical polyelectrolyte brushes consisting of a fluorescent polystyrene (PS) nanocomposite core and a poly(acylic acid) (PAA) brush shell were successfully prepared. Quantum dots (QDs) were well confined in the PS core through hybrid emulsion polymerization. PAA chains were then grafted onto the surface of the fluorescent PS core to form a brush structure through photoemulsion polymerization. The obtained fluorescent spherical polyelectrolyte brushes are highly pH sensitive in addition to their excellent dispersibility in water. Fluorescent nanoclusters were introduced into spherical polyelectrolyte brushes to acquire high sensitive detection in the applications of spherical polyelectrolyte brushes as catalyst tracer, as biosensor, and in protein coding.

Heavy metal ions removal by nano-sized spherical polymer brushes

Nano-sized spherical polymer brushes (SPBs) consisting of both a polystyrene (PS) core and a brush shell of poly(acrylic acid) (PAA), poly(N-acrylcysteamine) (PSH), or poly(N-acrylcysteamine-co-acrylic acid) (P(SH-co-AA)), were prepared by photo-emulsion polymerization. The core-shell structure was observed by dynamic light scattering and transmission electron microscopy. Due to the strengthened Donnan effect, the PAA brush can adsorb heavy metal ions. Effects of the contact time, thickness of PAA brush and pH value on the adsorption results were investigated. Due to the coordination between the mercapto groups and heavy metal ions as well as the electrostatic interactions, SPBs with mercapto groups are capable to remove heavy metal ions selectively from aqueous solutions. The order of adsorption capacity of the heavy metal ions by SPBs with mercapto groups is: Hg2+ ≈ Au3+ > Pb2+ > Cu2+ > Ni2+. The adsorbed heavy metal ions can be eluted from SPB by aqueous HCl solution, and the SPBs can be recovered. After three regenerations the recovered SPBs still maintain their adsorption capacity.

Tunable, responsive nanogels containing t-butyl methacrylate and 2-(t-butylamino)ethyl methacrylate

We present the synthesis and characterization of a series of pH-responsive hydrogel nanoparticles based on crosslinked 2-(diethylaminoethyl) methacrylate and poly(ethylene glycol) methyl ether methacrylate (P(DEAEMA-g-PEGMA)). Variants of this polymer were created using t-butyl methacrylate (P(DEAEMA-co-TBMA-g-PEGMA)) or t-butylaminoethyl methacrylate (P(DEAEMA-co-TBAEMA-g-PEGMA)). The synthesis of these materials was accomplished using a facile photoemulsion polymerization. Polymer composition was verified using 1H NMR spectroscopy and closely approximates the copolymer composition estimated from reactivity ratios. Particle formulations possess a dry diameter of 50–65 nm as determined by transmission electron microscopy and collapsed hydrodynamic diameter of 70–100 nm as determined by dynamic light scattering. Dynamic light scattering and pyrene fluorescence spectroscopy were used to probe the pH-dependent phase transition in the hydrogel nanoparticles from collapsed hydrophobe to swollen hydrophile. The inclusion of t-butyl methacrylate served to depress the nanogel pKa and critical pH for phase transition to <6.9 while the inclusion of t-butylamino methacrylate had the opposite effect. We show that these hydrogel nanoparticles possess tunable physicochemical properties that can be adjusted by changing copolymer composition.

Binding between Proteins and Cationic Spherical Polyelectrolyte Brushes: Effect of pH, Ionic Strength, and Stoichiometry

Cationic spherical polyelectrolyte brushes (SPBs) were synthesized by photoemulsion polymerization, consisting of a polystyrene core with a diameter around 80 nm and a poly(2-aminoethylmethacrylate hydrochloride) (PAEMH) shell with a thickness from 10 to 50 nm densely grafted on the core surface. The binding of various proteins onto SPBs was observed by turbidimetric titration, dynamic light scattering (DLS), zeta potential, and isothermal titration calorimetry (ITC). The binding, aggregation, and releasing of proteins by SPB can be tuned by modulating pH. The pH regions of binding for bovine serum albumin (BSA), β-lactoglobulin (BLG), and papain onto SPBs are markedly different and tunable by ionic strength and stoichiometry between protein and SPB. Binding energetics, affinity, and amount of various proteins onto cationic SPBs were determined by ITC. These findings lay the foundation for SPB applications in the protein purification and selective immobilization of different proteins, enzymes, and antibodies.

Polycationic nanoparticles synthesized using ARGET ATRP for drug delivery

This work provides a systemic comparison for ARGET ATRP and UV-initiated polycationic nanoparticles for drug delivery and a guide to deciding which type of polycationic nanoparticles have the best properties for specific applications. Polycationic nanoparticles were synthesized using a previously developed UV-initiated photoemulsion polymerization or a newly developed ARGET ATRP synthesis technique. The effect of the ratio of hydrophobic monomer in the feed was evaluated. Increasing the feed ratio of hydrophobic monomer was necessary to maintain biocompatibility and pH-responsive membrane disruptive characteristics when switching from the UV-initiated polymerization to ARGET ATRP. The resulting polycationic nanoparticles have utility as drug delivery carriers for hydrophobic drugs and/or nucleic acids.

Volume Transition and Adhesion Force of Nanosized Bifunctional Spherical Polyelectrolyte Brushes Observed by Dynamic Light Scattering and Atomic Force Microscopy

Stimuli-responsive nanoparticles have attracted considerable interest due to their enormous potential applications. In this paper, nanosized bifunctional spherical polyelectrolyte brushes (BSPBs) were prepared through grafting random copolymer chains from N-isopropylacrylamide (NIPA) and acrylic acid (AA) onto polystyrene core by photoemulsion polymerization. The pH- and thermo-responses of the BSPB with different ratio of NIPA and AA were investigated by dynamic light scattering. Atomic force microscopy (AFM) was employed to in situ monitor the pH response of the morphology and surface adhesion of BSPB as well as to visualize BSPB individually or as monolayer in air and liquid. The brush-like shell was illegible in electron microscopy images but clearly observed in AFM images. The results demonstrated that AFM was a powerful tool for in situ observing the stimulus-response of brushes on the surface of nanoparticles.

Spherical Polyelectrolyte Brushes on Colloidal Poly(butadiene) Particles

Abstract A novel method to prepare spherical polyelectrolyte brushes (SPB) on the surface of colloidal poly(butadiene) (PB) core without having to use initiators with C=C double bond to attach covalently on the core surface was reported. Making use of the abundant double bonds in PB, spherical poly(acrylic acid) (PAA) bushes were grown from PB core surface by direct thermo-initiated emulsion polymerization using KPS as initiator. The thickness of SPB increased significantly upon increasing pH and decreasing the ionic strength. The grafting density of SPB with PB core was estimated from the relationship between the brush thickness and ionic strength based on the modified Daoud-Cotton model. The grafting density of SPB prepared by thermo-initiated emulsion polymerization (0.122 nm-2) is higher that that of SPB by photo-emulsion polymerization (0.105 nm-2). Using SPB with PB core as nanoreactors, nickel and silver nanoparticles were prepared by reduction of Ni 2+ and Ag + absorbed inside SPB as counterions. Relatively high catalytic activities for the reduction of p-nitrophenol by NaBH4 were observed for SPB immobilized Ni or Ag nanoparticles.

Spherical polymer brushes with vinylimidazolium-type poly(ionic liquid) chains as support for metallic nanoparticles

We present here the synthesis of spherical polyelectrolyte brushes by photo-emulsion polymerization with a solid polystyrene core (diameter ∼ 100 nm) onto which chains of vinylimidazolium-type poly(ionic liquid)s have been densely grafted. The as-synthesized brush particles were employed as nanoreactors for the generation and immobilization of metal nanoparticles. Transmission electron microscopy characterization shows that Au and Pd nanoparticles with diameter of 2.1 ± 0.2 nm and 2.5 ± 0.3 nm are homogeneously embedded inside the PIL brushes, respectively. The study of swelling behavior of the brush particles before and after metal deposition indicates obviously ion-specific effect. The composite particles exhibit a long-term colloidal stability in aqueous solutions as well as in ionic liquids. Catalytic activity of the as-synthesized metal nanocomposite particles is investigated by using the reduction of 4-nitrophenol with NaBH4 as a model reaction, which can be compared directly with reported systems. In addition, it is found that the rate constant kapp of PIL-metal nanocatalyst could be modulated by salt concentration.

Self-Assembly of Nano-Sized Spherical Polyelectrolyte Brushes on Different Substrates as Observed by AFM

Nano-sized spherical poly (acrylic acid) (PAA) brushes (SPB) were prepared on the surface of colloidal polystyrene (PS) particles by photo-emulsion polymerization. Atomic force microscopy (AFM) was employed to observe the assembly of SPB on substrates of silicon, gold and mica with various surface properties and to determine the morphological information including particle size, shape and core-shell structure of SPB. We found that the surface polarity, electrostatic interactions between SPB and substrate surface and among SPB and capillary forces during sample drying affect the SPB assembly on substrate surface and their morphology.

Synthesis of thermo- and pH-sensitive polyelectrolyte brushes by combining thermo-controlled emulsion polymerization and photo-emulsion polymerization

Bifunctional spherical polyelectrolyte brushes (SPBs) with tunable thermo- and pH-sensitivity are synthesized by combining thermo-controlled emulsion polymerization and photo-emulsion polymerization. They consist of a spherical polystyrene core and a shell of mixed brushes of poly(N-isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAA) whose composition can be easily modulated by the dose of monomers. The kinetics of SPB synthesis as well as their size change with temperature and pH is determined by dynamic light scattering (DLS). The scanning electron microscopy (SEM) images show that the bifunctional SPBs have a defined spherical morphology with a narrow size distribution.