Radical Miniemulsion Polymerization Research Articles

Hairy nanoparticles by atom transfer radical polymerization in miniemulsion

Polymer nanoparticles with various architectures and functionalities are promising materials in numerous fields. Miniemulsion polymerization is one of the suitable pathways to prepare polymer nanoparticles since each droplet could act as a “nanoreactor”. A “smart” atom transfer radical polymerization (ATRP) catalytic system comprising Cu-TPMA/DS− (TPMA = tris(2-pyridylmethyl)amine, DS−= dodecyl sulfate anion) ion pair catalyst was efficiently applied in miniemulsion ATRP at low catalyst concentrations. Herein, hairy nanoparticles consisting of hydrophobic poly(n-butyl methacrylate) (P(BMA/EGDMA), EGDMA = ethylene glycol dimethacrylate) network “core” and hydrophilic oligo(ethylene oxide) methyl ether methacrylate (OEOMA) chains as “hair” were prepared by miniemulsion ATRP and a successive chain extension by aqueous ATRP from the particle surface. The addition of an inimer, 2-(α-bromoisobutyryloxy)ethyl methacrylate (HEMA-iBBr) to the P(BMA/EGDMA) network introduced more ATRP initiation sites for ATRP of OEOMA, enabling adjustment of the particle size from >400 nm to <150 nm. The miniemulsion system remained stable after the one pot synthesis of P(BMA/EGDMA)-g-POEOMA and P(BMA/EGDMA/HEMA-iBBr)-g-POEOMA, and the resulting polymer nanoparticles were re-dispersed in water for further modification. A zwitterionic monomer, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA), was grafted from P(BMA/EGDMA/HEMA-iBBr)-g-POEOMA. The resulting hairy nanoparticles provide an avenue for the design and preparation of novel nanostructured materials.

Thermally reprocessable bio-based polymethacrylate vitrimers and nanocomposites

Vitrimers are covalently cross-linked polymeric materials that can be processed upon heating wherein triggerable polymer networks shuffle chemical bonds through exchange reactions without losing their network integrity. In this work, we apply vitrimers to develop recyclable thermosets derived from materials with relatively high bio-source content. We explore the reaction between β-ketoesters derived from commercially available (2-acetoacetoxy) ethyl methacrylate (AAEMA) incorporated within isobornyl methacrylate (IBOMA, from pine sap), and a bi-functional amine (Priamine, derived from vegetable oils) to synthesize catalyst-free vitrimers. Controlled radical miniemulsion polymerization was also used to synthesize the water-borne copolymer analogs. Vitrimer nanocomposites were obtained by the incorporation of amine‐functionalized polyhedral oligomeric silsesquioxane (POSS–NH2) at different loadings (0, 5, 10 and 20 wt%). Incorporation of 20 wt% POSS-NH2 improved tensile modulus (from 96 to 176 MPa), tensile strength (from 2.5 to 5 MPa) and decomposition temperature (225–255 °C), and slowed down the relaxation rate and increased apparent activation energy of stress relaxation compared to the neat vitrimer. We further show that the vitrimers studied here and the nanocomposites containing vinylogous urethane cross-linking networks can be un-cross-linked by dissolving in excess mono-functional amine at 65 °C or recycled by grinding and remolding at 125 °C without compromising the mechanical properties.

Nanocomposite of Graphene Oxide Encapsulated in Polymethylmethacrylate (PMMA): Pre-Modification, Synthesis, and Latex Stability

The compatibility of graphene oxide with its dispersion medium (polymer) plays a critical role in the formation of nanocomposite materials with significant property improvements. Environmentally friendly miniemulsion polymerization, which allows a formation of nanoencapsulation in an aqueous phase and high molecular weight polymer/composite production is one promising method. In this study, we screened a series of amphiphilic modifiers and found that the quaternary ammonium (ar-vinyl benzyl) trimethyl ammonium chloride (VBTAC) pending carbon double bonds could effectively modify the graphene oxide (GO) to be compatible with the organophilic monomer. After that, free radical miniemulsion polymerization successfully synthesized stable latex of exfoliated poly (methyl methacrylate) (PMMA)/ GO nanocomposite. The final latex had an extended storage life and a relatively uniform particle size distribution. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) analysis of this latex and its films indicated successful encapsulation of exfoliated nano-dimensional graphene oxide inside a polymer matrix.

Nonionic surfactants based on amphiphilic polyphosphonate copolymers prepared via anionic ring-opening copolymerization

Nonionic surfactants are omnipresent in our everyday life and used in modern drug delivery. The synthesis of degradable surfactants is crucial to simplify the purification of final products or reduce polymer waste. Here, we present the synthesis of a new amphiphilic 2-n-dodecyl-2-oxo-1,3,2-dioxaphospholane, a monomer for the anionic ring-opening polymerization towards poly(ethylene alkyl phosphonate)s. The novel monomer is copolymerized with 2-ethyl-2-oxo-1,3,2-dioxaphospholane to produce well-defined, water-soluble, and surface-active copolymers with molar masses up to 18,400 g mol−1, dispersities between 1.2 and 1.3, and critical aggregation concentrations below 0.07 g L−1. The reactivity ratios of the two comonomers indicate a random monomer incorporation with r1 = 1.46 and r2 = 0.68. Adjusting the comonomer ratio changes the amphiphilicity of the resulting copolymers. They are applied in the free radical miniemulsion polymerization to produce well-defined nanoparticles. The intrinsic hydrolytic degradability of polyphosphonates makes these polymers interesting candidates for use in, emulsion stabilization for drug delivery or cosmetics.

Temporally Controlled Ultrasonication‐Mediated Atom Transfer Radical Polymerization in Miniemulsion

Temporally Controlled Ultrasonication‐Mediated Atom Transfer Radical Polymerization in Miniemulsion

Temporally Controlled Ultrasonication‐Mediated Atom Transfer Radical Polymerization in Miniemulsion

AbstractDue to the increasing requirement for more environmentally and industrially relevant approaches in macromolecules synthesis, ultrasonication‐mediated atom transfer radical polymerization (sono‐ATRP) in miniemulsion media is applied for the first time to obtain precisely defined poly(n‐butyl acrylate) (PBA) and poly(methyl methacrylate) (PMMA) homopolymers, and poly(n‐butyl acrylate)‐block‐poly(tert‐butyl acrylate) (PBA‐b‐PtBA) and poly(n‐butyl acrylate)‐block‐poly(butyl acrylate) (PBA‐b‐PBA) copolymers. It is demonstrated in the reaction setup with strongly hydrophilic catalyst copper(II) bromide/tris(2‐pyridylmethyl)amine (CuIIBr2/TPMA) responsible for two principal mechanisms – interfacial and ion‐pair catalysis reflecting single‐catalyst approach. This solution turns out to be an excellent tool in controlled preparation of well‐defined polymers with narrow molecular weight distribution (up to Ð = 1.28) and preserves chain‐end functionality (DCF = 0.02% to 0.32%). Temporal control over the polymer chain growth is successfully conducted by turning the ultrasonication on/off. Taking into consideration long OFF stage (92.5 h) during ultrasonication‐induced polymerization in miniemulsion, synthesis is efficiently reinitiated without any influence on controlled characteristics maintaining the precise structure of received PBA homopolymers, confirmed by narrow molecular weight distribution (Ð = 1.26) and high retention of chain‐end functionality (DCF = 0.01%). This procedure constitutes an excellent simple and eco‐friendly approach in preparation of functional polymeric materials.

Ceria/polymer nanocontainers for high-performance encapsulation of fluorophores.

We report the synthesis of high-performance organic–inorganic hybrid fluorescent nanocapsules comprising a polymer shell armored with an inorganic layer and a liquid core containing a fluorophore. The polymeric capsules are synthesized by free radical miniemulsion polymerization and contain covalently bound carboxylate surface functionalities that allow for the binding of metal ions through electrostatic interaction. A cerium(IV) oxide nanoparticle layer, formed in situ at the surface of the hybrid nanocapsules, acts as oxygen scavenger and keeps external reactive molecular oxygen from entering into the capsules, eventually resulting in a reduction of the photooxidation of encapsulated fluorescent molecules. This approach shows an increase in the fluorescence of the model organic fluorophore terrylene diimide by avoiding the ground-state molecular oxygen to react with electronically excited states of the fluorescent hydrocarbon molecule.

Enzyme-Deoxygenated Low Parts per Million Atom Transfer Radical Polymerization in Miniemulsion and Ab Initio Emulsion.

The development of robust oxygen-tolerant reversible deactivation radical polymerization (RDRP) systems can dramatically simplify synthesis of well-defined polymers without redundant deoxygenation procedures. Herein, we broaden the application of oxygen-tolerant RDRP from homogeneous aqueous and organic solutions to dispersed media. The glucose oxidase (GOx) degassed atom transfer radical polymerization (ATRP) was conducted in miniemulsion and ab initio emulsion systems using various catalyst regeneration methods: ARGET, ICAR, photo, and eATRP. All of these polymerization procedures led to polymers with predetermined molecular weight, low dispersity, and high chain-end functionality. Emulsion ATRP on a larger scale with preserved control was also successful. Circular dichroism (CD) studies demonstrated that the anionic surfactant, sodium dodecyl sulfate (SDS), did not damage the secondary structure of GOx. This confirms the versatility of the GOx system for various low ppm ATRP methods. GOx-assisted oxygen removal in the synthesis of hydrophobic polymers is reported for the first time. The low cost of deoxygenation reagents and the ability to scale up the procedure suggest the potential for industrial production, especially for emulsion polymerization.

Mathematical modeling of reverse atom transfer radical polymerization in miniemulsion

In this work, we study the reverse atom transfer radical polymerization in miniemulsion using a water-soluble initiator. This study is motivated by the technological advantages of performing polymerizations in dispersed systems, and the attractive possibilities of controlled radical polymerization techniques to produce tailor made polymers. A mathematical model for this system is presented. The model predicts average molecular properties as well as the full molecular weight distribution (MWD) for different experimental conditions. The method of moments is applied for calculating average properties and the probability generating function (pgf) technique is used to model the MWD. The model is based on the mass balance equations of the reacting species. It takes into account the reactions in both the aqueous and organic phases and the mass transfer between them. Predicted conversions, average molecular weights, polydispersity indexes and MWDs for different experimental conditions agree well with experimental data reported in the literature.

Amphiphilic Ferrocene-Containing PEG Block Copolymers as Micellar Nanocarriers and Smart Surfactants.

An important and usually the only function of most surfactants in heterophase systems is stabilizing one phase in another, for example, droplets or particles in water. Surfactants with additional chemical or physical handles are promising in controlling the colloidal properties by external stimuli. The redox stimulus is an attractive feature; however, to date only a few ionic redox-responsive surfactants have been reported. Herein, the first nonionic and noncytotoxic ferrocene-containing block copolymers are prepared, carrying a hydrophilic poly(ethylene glycol) (PEG) chain and multiple ferrocenes in the hydrophobic segment. These amphiphiles were studied as redox-sensitive surfactants that destabilize particles as obtained in miniemulsion polymerization. Because of the nonionic nature of such PEG-based copolymers, they can stabilize nanoparticles even after the addition of ions, whereas particles stabilized with ionic surfactants would be destabilized by the addition of salt. The redox-active surfactants were prepared by the anionic ring-opening polymerization of ferrocenyl glycidyl ether, with PEG monomethyl ether as the macroinitiator. The resultant block copolymers with molecular weights (Mn) between 3600 and 8600 g mol-1 and narrow molecular weight distributions (Mw/Mn = 1.04-1.10) were investigated via 1H nuclear magnetic resonance and diffusion ordered spectroscopy, size exclusion chromatography, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Furthermore, the block copolymers were used as building blocks for redox-responsive micelles and as redox-responsive surfactants in radical polymerization in miniemulsion to stabilize model polystyrene nanoparticles. Oxidation of iron to the ferrocenium species converted the amphiphilic block copolymers into double hydrophilic macromolecules, which led to the destabilization of the nanoparticles. This destabilization of nanoparticle dispersions may be useful for the formation of coatings and the recovery of surfactants.

Electrochemical Atom Transfer Radical Polymerization in Miniemulsion with a Dual Catalytic System.

An electrochemical approach was used to control atom transfer radical polymerization (ATRP) of n-butyl acrylate (BA) in miniemulsion. Electropolymerization required a dual catalytic system, composed of an aqueous phase catalyst and an organic phase catalyst. This allowed shuttling the electrochemical stimulus from the working electrode (WE) to the continuous aqueous phase and to the dispersed monomer droplets. As aqueous phase catalysts, the hydrophilic Cu complexes with the ligands N,N-bis( 2-pyridylmethyl)-2-hydroxyethylamine (BPMEA), 2,2'-bipyridine (bpy), and tris(2-pyridylmethyl)amine (TPMA) were tested. As organic phase catalysts, the hydrophobic complexes with the ligands bis(2-pyridylmethyl)-octadecylamine (BPMODA) and bis[2-(4-methoxy-3,5-dimethyl)-pyridylmethyl]octadecylamine (BPMODA*) were evaluated. Highest rates and best control of BA electropolymerization were obtained with the water-soluble Cu/BPMEA used in combination with the oil-soluble Cu/BPMODA*. The polymerization rate could be further enhanced by changing the potential applied at the WE. Differently from traditional ATRP systems, reactivity of the dual catalytic system did not depend on the redox potential of the catalysts but instead depended on the hydrophobicity and partition coefficient of the aqueous phase catalyst.

Nanoprecipitation–Miniemulsion polymerization combined method: A novel approach to synthesis drug loaded nanoparticles with tunable characteristics

In this research polystyrene nanoparticles (NPs) were synthesized using a novel straightforward approach based on the nanoprecipitation and miniemulsion polymerization. Nanoprecipitation or solvent shifting method was applied to prepare primary emulsions. For this purpose, oil phase consisting of solution of styrene, alcohol and polylactide oligomer as a cosurfactant, was added to aqueous phase consisting of water and surfactant. Primary emulsions were easily formed as a result of water-alcohol interdiffusion. Afterwards polystyrene NPs were synthesized by free radical miniemulsion polymerization process. Effect of variety of parameters, such as initiator nature (water-soluble or oil-soluble), cosurfactant, styrene to alcohol and alcohol to water ratio, on polymerization yield and NPs characteristics were investigated. Sodium 11-acryloyl-aminoundecanoate was tested as an amphiphilic polymerizable surfactant to synthesize polystyrene NPs with surface functional groups. Moreover, to examine the applicability of proposed approach for drug immobilization, rifampicin as a hydrophobic anti tubercular model drug was investigated. NPs characteristics were analyzed using scanning electron microscopy, light scattering and zeta potential measurements. Consequently, it was shown that nanoprecipitation–miniemulsion polymerization approach can be considered as a straightforward, low energy emulsification method to synthesize polymeric NPs with tunable characteristics.

Decrease of methyl methacrylate miniemulsion polymerization rate with incorporation of plant oils

Miniemulsion polymerization reactions of methyl methacrylate were conducted in the presence of plant oils, in order to investigate the effect of different types (linseed oil and andiroba oil) and amounts of oils on the polymerization reaction rates and on the molecular weight of the produced polymers. A decrease in the reaction rate, that was proportional to the number of double bonds present in the triglycerides, was observed. Polymers with lower molecular weights were obtained when triglycerides with higher number of double bonds were used. The experimental data were analyzed with a mathematical model developed to represent the kinetics of these reactions, including the kinetic mechanisms associated to free radical miniemulsion polymerization with an oil‐soluble initiator, and the model was able to predict the variation in the polymerization reaction rate depending on the type and amount of the plant oil.Practical applications: Plant oils can be incorporated to polymer latex by free radical miniemulsion polymerization partially substituting petroleum derived monomers. As most plant oils are highly hydrophobic, they act as co‐stabilizers preventing diffusional degradation increasing the stability of the colloidal dispersion. The growing polymer chain can react with the double bonds of the triglyceride molecules resulting in grafting. The grafting increases the compatibility between the polymer and the plant oil. However, the polymer molecular weight and the reaction rate decrease when the amount of unsaturated oil increases. A mathematical model was developed taking into account both addition and chain transfer mechanisms to describe the grafting reactions with the plant oils. The model can predict the variation in the polymerization reaction rate depending on the type and concentration of the plant oil in the reaction medium which helps to understand the mechanisms involved and to optimize formulations and operational conditions of polymerizations in the presence of plant oils.Polymerization rate decreases when plants oils are incorporated in PMMA nanoparticles.

Visible-Light-Regulated Controlled/Living Radical Polymerization in Miniemulsion.

The implementation of photopolymerization processes in aqueous dispersed systems has the potential to afford greener approaches to the preparation of polymeric materials and has motivated researchers to perform photopolymerization in emulsion. However, these previous works have employed UV irradiation to induce photodegradation of a photoinitiator in addition to specialized equipment setups, thus limiting widespread use of these approaches. In this work, we aim to remedy these drawbacks via the implementation of photoredox catalysis in the regulation of a controlled/living radical polymerization under visible light. Utilizing the photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) process, we report the miniemulsion polymerization of styrene mediated by a household grade blue LED (λmax = 460 nm, 0.73 mW/cm2). The polymerization rate can be easily manipulated by light intensity and catalyst concentration. Finally, temporal control was demonstrated via ON/OFF experiments, which shows that no significant detriment is caused by prolonged interruptions to the light exposure.

Biocompatible dextran-covered nanoparticles produced by Activator Generated by Electron Transfer Atom Transfer Radical Polymerization in miniemulsion

Abstract Aiming to prepare potentially biocompatible dextran-covered nanoparticles (NPs), the use of a pharmaceutically acceptable oil (Miglyol 810, M810—a medium chain saturated triglyceride) as co-stabilizer and of amphiphilic dextran derivatives (DexPτ) as stabilizers was investigated for Activator Generated by Electron Transfer Atom Transfer Radical Polymerization (AGET ATRP) of methyl methacrylate in miniemulsion. We showed that, as compared to several oils, M810 was the most suitable co-stabilizer. Indeed, it efficiently prevented diffusional degradation and contributed to solubilize ATRP catalytic systems in organic phase (methyl methacrylate + 5 vol% of co-stabilizer). Better control over polymerization and nano-objects size was achieved for polymerization with M810 compared to a standard co-stabilizer (hexadecane). Indeed, with the appropriate formulation conditions, NPs size was very similar to the one of initial emulsion nanodroplets and more than 85% of the initial DexPτ amount was adsorbed at NPs surface. A convenient procedure to eliminate copper from the finals NPs was also experienced.

Shuttling Catalyst for Living Radical Miniemulsion Polymerization: Thermoresponsive Ligand for Efficient Catalysis and Removal.

In this report, we demonstrate the use of a thermoresponsive ligand for the ruthenium-catalyzed living radical polymerization of butyl methacrylate (BMA) in miniemulsion. A phosphine-ligand-functionalized polyethylene glycol chain (PPEG) in conjunction with a Cp*-based ruthenium complex (Cp*: pentamethylcyclopentadienyl) provided thermoresponsive character as well as catalysis for living polymerization: the complex migrated from the water phase to the oil phase for polymerization upon heating and then migrated from the oil to water phase when the temperature was decreased to quench polymerization. Consequently, simple treatment (i.e., water washing or methanol reprecipitation) yielded metal-free polymeric particles containing less than 10 μg/g (by ICP-AES) of ruthenium residue.

First multi-reactive dextran-based inisurf for atom transfer radical polymerization in miniemulsion

A multi-reactive polysaccharide-based inisurf (acting both as initiator and stabilizer) has been designed for the first time from dextran with the aim of preparing dextran-covered nanoparticles with covalent linkage between core and coverage. This inisurf was used for polymerizing butyl acrylate in miniemulsion by AGET–ATRP. Both hydrophobic phenoxy groups and initiator groups (bromoisobutyryl ester) were introduced within hydrophilic dextran chain, conferring it amphiphilic and macroinitiator characters. Amphiphilic properties of dextran inisurfs have been evidenced as well as their ability to stabilize the direct miniemulsion of n-butyl acrylate. After optimization of polymerization conditions with model studies, assays were successfully realized with dextran-based inisurfs. Because of their amphiphilic character, inisurfs migrated at oil/water interface and initiated polymerization from bromoisobutyryl ester groups. Therefore graft copolymers were produced at oil/water interface, due to the multifunctional character of these inisurfs and constituted the particle inner core with covalent links to the dextran coverage.

Nanocomposites based on MWCNT and polystyrene, styrene‐acrylonitrile copolymer, or polymethylmethacrylate, obtained by miniemulsion polymerization

ABSTRACTFree radical miniemulsion polymerization of styrene (St), St/acrylonitrile 3 : 1 mixture or methylmethacrylate in the presence of multiwalled carbon nanotubes (MWCNT) was proven as a convenient way to obtain homogenous hybrids with perspectives in associated applications like foams specialties materials. Miniemulsion polymerization was viable up to 2% wt. MWCNT to monomer, without agglomerations. The grafting on MWCNT during the polymerization occurs without the need for supplementary functionalization and the polymer grafted nanotubes showed stable dispersions in the polymer solvent. Monomer polarity affected the grafting ability during the polymerization process. The nanocomposites obtained after purification and drying were used in foaming process. MWCNT presence in the related nanocomposites decreased the pore sizes in foam‐like materials (for all three different matrices). At 1 wt % MWCNT content, low density (&lt; 0.3 g/cm3), low pore size (&lt; 10 μm) and high cell density (&gt;109 cell/cm3) were achieved. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41148.

Stabilization of Nanoparticles Synthesized by Miniemulsion Polymerization Using “Green” Amino‐Acid Based Surfactants

SummaryIn this study biocompatible amino‐acid based surfactants were used for the stabilization of polystyrene (PS), poly(L‐lactide) (PLLA) and polyphosphate (PP) nanoparticles (NPs). The formation of the nanoparticles was achieved either by radical polymerization in miniemulsion for polystyrene nanoparticles or by using a combination of solvent evaporation and miniemulsion approach for poly(L‐lactide) or polyphosphate nanoparticles. The influence of the three different amino‐acid based surfactants, which were used with different amounts, on the NPs' stability, size, size distribution, zeta potential, morphology and surface tension is discussed. Cell experiments with HeLa cells were performed for the determination of the toxicity. For comparison, sodium dodecyl sulfate (SDS) stabilized NPs were synthesized, and all results obtained from the amino‐acid based surfactant stabilized NPs were compared and discussed with the SDS stabilized NPs.

Activators Regenerated by Electron Transfer Atom Transfer Radical Polymerization in Miniemulsion with 50 ppm of Copper Catalyst.

The design and synthesis of a powerful ligand is reported for use in activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) in miniemulsion. The structure of N',N″-dioctadecyl-N',N″-bis[2-(4-methoxy-3,5-dimethyl)pyridylmethyl]ethane-1,2-diamine (DOD-BPED*) was formulated to produce a tetradentate ligand which was both hydrophobic and highly active. Studies in homogeneous ARGET ATRP with CuBr2/DOD-BPED* demonstrated a high degree of control, similar to those ligands traditionally used. CuBr2/DOD-BPED* also proved itself to be extremely useful in ARGET ATRP miniemulsion systems, at concentrations of catalyst as low as 50 ppm while maintaining control over the polymerization of butyl methacrylate (BMA). Additionally, the catalyst was tested over a range of degrees of polymerization, DP = 2000-10 000, all of which resulted in successful polymerizations. Most notably, high molecular weight polymers with Mn,exp > 700 000 and Mw/Mn < 1.4 were prepared with only 50 ppm of CuBr2/DOD-BPED* catalyst under miniemulsion conditions.