Emulsifier-free Emulsion Copolymerization Research Articles

Colloidal Polymer Nanoparticles as Smart Inks for Authentication and Indication of Latent Fingerprints and Scratch.

An environmentally friendly smart ink was developed by incorporating fluorescein into functionalized poly(methyl methacrylate) (PMMA) nanoparticles synthesized using an emulsifier-free emulsion copolymerization approach. The functional comonomers of 2-(dimethylamino)ethyl methacrylate (DMAEMA), acrylamide, hydroxyethyl methacrylate, and glycidyl methacrylate in 10 wt % with respect to methyl methacrylate were used to obtain the functionalized colloidal PMMA nanoparticles. Functional groups of the latex nanoparticles were characterized by Fourier-transform infrared spectroscopy. Field emission scanning electron microscopy results showed that all of the latex nanoparticles have nearly spherical morphologies with variations in size and surface smoothness due to the presence of different comonomers. Ultraviolet-visible and fluorescence spectra indicated that the fluorescein-doped latex nanoparticles containing the DMAEMA comonomer had the highest absorbance and fluorescence intensity. In the alkaline media, fluorescein turns to a dianion, showing a red shift and increased absorbance in the UV-vis spectroscopy. In addition, the electron inductive characteristics of the tertiary amine groups result in enhancing the conjugation of fluorescein molecules and increasing the fluorescence intensities. Therefore, the colloidal nanoparticles with amine functional groups were used in the formulation of a smart ink with applications in securing documents and fingerprints, encrypting banknotes and money, detecting latent fingerprints, crafting anticounterfeiting paper, and eventually providing optical detection and indication of surface scratches.

Morphology evolution of functionalized styrene and methyl methacrylate copolymer latex nanoparticles by one-step emulsifier-free emulsion polymerization

Evolution of morphology in the latex nanoparticles synthesized by emulsion polymerization methods has been an interesting challenge. Herein, a fast and facile methodology was developed for the synthesis of functionalized latex nanoparticles based on polystyrene (PS) and poly(methyl methacrylate) (PMMA) by one-step emulsifier-free emulsion copolymerization with functional acrylic comonomers. These functional latex nanoparticles display different particle size in the range of 150–1400 nm and morphologies depending on the surface functional groups. Morphological investigation of the functionalized latex nanoparticles by scanning electron microscopy and transmission electron microscopy display that PMMA and PS latex nanoparticles with amide and hydroxyl functionalities have cauliflower like morphology with a non-smooth surface. The PS latex nanoparticles functionalized with epoxy groups have vesicular morphology in colloidal and red blood cell-like morphology in solid state. The PMMA latex nanoparticles containing epoxy and hydroxyl functionalities on the surface and also the PS latex nanoparticles functionalized with amide groups display highly monodispersed spherical morphologies. The porous surface was observed for the spherical PMMA and PS latex nanoparticles functionalized with carboxylic acid groups by using 4,4′-azobis(4-cyanovaleric acid) as the initiator. Different morphologies observed for the functional PS and PMMA latex nanoparticles prepared by one-step emulsifier-free emulsion polymerization are very interesting and have potential applications in drug-delivery, bioimaging, cell-labeling, and chemosensors.

Unique Oil-in-Brine Pickering Emulsion Using Responsive Antipolyelectrolyte Functionalized Latex: A Versatile Emulsion Stabilizer

A simple and straightforward approach to synthesize oil-in-water (O/W) emulsions under high salinity and temperature using zwitterion functionalized latexes are presented in this work. First, well defined functionalized latexes were synthesized by emulsifier-free emulsion copolymerization in the presence of precursor sulfobetaine comonomer using brine as a continuous phase. The surface-functionalized latex particles were then characterized by DLS, SEM, TEM, XPS, and TGA. The functionalized latex exhibited anti-polyelectrolyte behavior in high salinity brine and at high temperatures. The effects of salinity, temperature, and pH on the long-term stability of the particles were investigated. Further, to evaluate the potential in high salinity brine and high temperature, the saltphilic functionalized latexes were utilized to stabilize the oil/brine (O/W) interface without any other additives. The latex enabled the formation of a stable Pickering emulsion system with low solid content (< 0.02% w/w) in the presence of 50% v/v n-decane. The functionalized latexes were self-assembled at the O/W interface as a spherical colloidosomes in high salinity brine through hydrophobic interactions and irreversible adsorption. The supra-particles were imaged with SEM, providing an insight that the exterior of the emulsion droplets is stabilized by the saltphilic latex particles forming a protective layer at the oil-water interface through electrostatic repulsion. The anti-polyelectrolyte latex can be utilized as a novel emulsion stabilizer, which could provide a versatile alternative for applications in a complex environment such as high salinity, temperature, and low or high pH.

Emulsifier-Free Emulsion Copolymerization of Methyl Methacrylate As a Method of Obtaining Cationic Particles for Diagnostics of Tick-Borne Encephalitis Virus

Cross-linked cationic particles 150–300 nm in diameter have been synthesized via single-stage emulsifier-free copolymerization of methyl methacrylate and 2-aminoethyl methacrylate hydrochloride in the presence of cross-linking agents (ethylene glycol dimethacrylate and N,N'-methylenebisacrylamide). Factors that enable one to control the morphology and polydispersity of the resulting particles have been determined. It has been shown that the dispersions of the particles are aggregatively stable in physiological solutions and after the sorption of biologically active molecules. The synthesized particles can be used for efficient revealing tick-borne encephalitis virus via latex agglutination reaction, with the analysis time being no longer than 10 min.

Research on factors of influencing the preparation of 2D/3D poly(methyl methacrylate) (PMMA) colloidal crystal films at the air/water interface

In this study, PMMA microspheres were synthesized by emulsifier-free emulsion copolymerization of methyl methacrylate with sodium persulfate for the fabrication of colloidal crystal films. A rapid and facile approach to fabricate 2D or 3D PMMA colloidal crystal films at the air/water interface was developed without any complex devices. During this process, the hydrophobic PMMA microspheres were dispersed into various alcohol and self-assemble at the air/water interface to form a 2D colloidal crystal film which could further be transferred onto a solid substrate layer by layer to fabricate a 3D colloidal crystal film. The orderliness of the colloidal crystal film could be influenced by types of dispersant, the ratio of the dispersant to the PMMA microspheres emulsion and the pH of colloidal suspension. In addition, the zeta potential (ζ) of PMMA microspheres could be changed with the pH of colloidal suspension. As a result, when the ratio of n-propanol to the PMMA microspheres emulsion was 1:3 and the pH was between 4 and 5, PMMA colloidal crystal films with close-packed and high-ordered structure could be easily obtained. The morphologies and microstructures of PMMA colloidal crystal films were identified by Atomic Force microscopy (AFM) and scanning electron microscope (SEM). Their transmission spectra were measured by UV-visible spectrophotometer (UV). The results also showed that the positions of Bragg diffraction peaks were shifted to a longer wavelength with the increase of the sizes of PMMA microspheres and in good agreement with particle diameters which were theoretically calculated.

Synthesis of highly-energetic nanoparticles based on monodisperse hollow mesoporous nanospheres

Abstract Highly-energetic monodisperse nanospheres were prepared based on surface-modified, hollow mesoporous silica nanospheres. The monodisperse, cationic polymer nanospheres were prepared by the emulsifier-free emulsion copolymerization and used as a template to obtain copolymer/silica core-shell nanospheres and monodisperse, hollow mesoporous silica (HMS) nanospheres. The surface of the HMS nanospheres was treated with (3-aminopropyl) trimethoxysilane to obtain (3-aminopropyl)trimethoxysilane-grafted HMS nanospheres, which facilitated the adsorption of cyclomethylene trinitramine within the inorganic framework. The uptake of RDX within the dried, final nanospheres was measured by thermogravimetric analysis.

Light-Induced Aggregation and Disaggregation of Stimuli-Responsive Latex Particles Depending on Spiropyran Concentration: Kinetics of Photochromism and Investigation of Reversible Photopatterning.

Light-controlling the physical and chemical properties of smart polymers by using photochromic compounds has been an interesting research subject. Incorporation of spiropyran (SP) on the surface of particles can induce photoswitchable aggregation/disaggregation to stimuli-responsive colloids. Herein, we developed a novel class of stimuli-responsive latex particles bearing SP with different contents (0, 0.5, 1, 3, and 5 wt %) by semicontinuous emulsifier-free emulsion copolymerization, which is able to change the particle size by light-induced aggregation/disaggregation in response to ultraviolet (UV) irradiation and visible light. The scanning electron microscopy images revealed the spherical morphology of the latex particles, with the size in the range of 400-900 nm. Light-induced aggregation and disaggregation of stimuli-responsive latex particles were investigated by dynamic light scattering and also confirmed by variation of transmittance during UV illumination time using ultraviolet-visible spectroscopy. The range of the light-induced shift in the particle size is about 200-600 nm (depending on the concentration of SP), where the reduction of transmittance upon UV irradiation (and conversely upon visible light) confirms the ability of latex particles for displaying reversible photoswitchable aggregation/disaggregation and also light-controlling the particle size. The kinetics of SP to merocyanine (MC) and MC to SP isomerizations were experimentally investigated and fitted by exponential equations. The photochromic latexes displayed remarkable photoswitchability and photofatigue resistant properties under alternating UV and visible light irradiation cycles. Additionally, these stimuli-responsive latexes displayed potential applications such as anticounterfeiting inks in erasable and rewritable writings on cellulosic papers for increasing safety in security documents.

Design and Concept of Polyzwitterionic Copolymer Microgel Drug Delivery Systems In Situ Loaded with Non-steroidal Anti-inflammatory Ibuprofen.

Nowadays, the modern pharmaceutical investigations are directed toward obtaining of new polymer micro- and nano-sized drug delivery carriers. In this respect, the use of hydrogel carriers based on polyzwitterions (PZIs) is an opportunity in the preparation of polymer drug delivery systems with desired characteristics. This paper describes the synthesis and characterization of micro-structured p(VA-co-DMAPS) systems with different compositions in situ loaded with Ibuprofen by emulsifier-free emulsion copolymerization (EEC) in water. The mean size of the prepared microparticles was measured by SEM and particles have been visualized by AFM. The inclusion of Ibuprofen in the polyzwitterionic copolymer microgel systems was established by using DSC. In vitro drug release experiments were carried out in order to estimate the ability of the obtained microgels to modify the release of water-insoluble Ibuprofen.

Cationic styrene-butyl acrylate-quaternary ammonium copolymer nanospheres for surface modification of cotton fibers

Cationic copolymer nanospheres are important functional materials, for example, for fiber modification. Here, emulsifier-free ternary emulsion copolymerizations of styrene (St) and butyl acrylate (BA) with two different quaternary ammonium cationic monomers (QACMs), methacryloxyethyl trimethyl ammonium chloride (DMC) and trimethyl (vinylbenzyl) ammonium chloride (VBT), and 2,2’-azobis[2-methylpropionamidine] dihydrochloride (AIBA) as an initiator were conducted at 80 ×C, under agitation at 300 rpm. The differences between the two cationic comonomers strongly influenced the monomer conversion, diameter, morphology, and surface charge density of the nanospheres. In particular, a higher cationic comonomer content is found to produce more oligomer radicals and thus more primary particles in the polymerization process, which leads to higher monomer conversion, smaller particle diameter, and increased surface charge density. The cationic nanospheres could be adsorbed in either a monolayer or in multiple layers on the oppositely charged cotton fiber because of their fierce electrostatic attraction. Compared with poly(St-BA-VBT) nanospheres, the distribution of poly(St-BA-DMC) nanospheres was more nonuniform on fiber surfaces accompanied by agglomerates.

Preparation of Syndiotacticity-Rich High Molecular Weight Polyvinyl Alcohol by Low Temperature Emulsifier-Free Emulsion Copolymerization of Vinyl Acetate and Vinyl Pivalate

Low temperature emulsifier-free emulsion copolymerization of vinyl acetate (VAc) and vinyl pivalate (VPi) was carried out using a redox initiation system to prepare syndiotacticity-rich high-molecular weight (HMW) polyvinyl alcohol (PVA) with high yield. The effects of the polymerization conditions on the conversion, the molecular weight, the structure of poly (vinyl acetate-co-vinyl pivalate) (P (VAc-VPi)) and syndiotacticity of PVA were investigated. With the increases of the initiator concentration, the VPi molar ratio in monomer and polymerization temperature, the degree of polymerization (DP) of PVA decreases distinctly, but VPi contents in copolymer and syndiotactic diad (S-diad) contents of PVA increase obviously. PVA with the maximum DP of 11030 can be prepared by complete saponification of P(VAc-VPi) obtained under condition that the molar ratio of KPS to monomer is 1/2000, the molar ratio of VAc to VPi is 7:3 and reaction temperature is 12°C. The highest S-diad content in PVA can be up to 59.31% while the DP of PVA decreases to 5180 under the condition that the feed ratio of VPi is 70 mol%, which means the syndiotacticity-rich HMW PVA can be prepared successfully. And the conversions of all reactions are above 80%. Syndiotacticity-rich HMW PVA is effectively prepared in this study, which is useful for the preparation of high-strength and high-modulus PVA fiber.

Cross-linked poly(methyl methacrylate) particles with surface amino groups

Positively charged monodisperse particles have been synthesized via emulsifier-free emulsion copolymerization of methyl methacrylate with vinylformamide and ethylene glycol dimethacrylate. The effect of the cross-linking agent on the conversion of the monomers, as well as on the shape, size distribution, and surface characteristics of the obtained particles, has been determined. Addition of the cross-linking agent (5 wt %) to the reaction system has been shown to result in the formation of particles, which, after hydrolysis, have positive ζ potentials at pH 2–10.

Facile two-step preparation of polystyrene/anatase TiO2 core/shell colloidal particles and their potential use as an oxidation photocatalyst

Titania and materials containing titania have received considerable attention due to their technological importance in many areas. In this study, anatase crystalline titania (TiO2) coated polystyrene (PS) colloidal particles were successfully prepared in two easy steps. First, a one pot synthesis of the colloidal particles was produced via an emulsifier-free emulsion copolymerization of styrene (S) and 2-(dimethylamino)ethyl methacrylate (DMA) at pH 4.0. In the second step, the synthesized particles were coated by titania using a sol–gel process in-situ hydrolysis and a condensation reaction of titanium(IV) isopropoxide in an acidic aqueous solution. In this way, anatase crystalline titania, rather than the usual amorphous form, was obtained as a shell on the PS colloidal particles. Both the PS colloidal particles and the polystyrene/anatase titania (PS/TiO2) core/shell colloidal particles had monodisperse morphology and were characterized using SEM, Zetasizer, FTIR, XRD and TGA techniques or measurements. In addition, the photocatalytic activity of the PS/TiO2 core/shell particles was tested for the first time in an oxidation reaction, in the oxidation of 4-methoxybenzyl alcohol (MBA) with O2 in water. Much higher selectivities of the target product, p-anisaldehyde (AA), were obtained with the PS/TiO2 core/shell particles than with a commercial anatase crystalline TiO2.

Polyzwitterionic copolymer nanoparticles loaded in situ with metoprolol tartrate: synthesis, morphology and drug release properties

Polyzwitterions belong to the “smart” polymers’ group because of their specific swelling properties which depend on pH and ionic strength of the aqueous media. Novel polyzwitterionic copolymer nanoparticles of vinyl acetate (VA) and 3-dimethyl(methacryloyloxyethyl)ammonium propane sulfonate (DMAPS) (p(VA-co-DMAPS)) with loaded in situ metoprolol tartrate were synthesized by emulsifier-free emulsion copolymerization in water. The influence of in situ addition of metoprolol tartrate on the emulsifier-free emulsion copolymerization mechanism was studied. It was suggested that the interactions between metoprolol tartrate and the copolymer nanoparticles are responsible for the creation of “bridge” connections between them and these bonds led to the formation of coagulum. To validate possible mechanisms of interaction between metoprolol tartrate and copolymer nanoparticles Differential Scanning Calorimetry was employed. Scanning Electron Microscopy, Atomic Force Microscopy, Dynamic Light Scattering and ζ-potential measurements were used to determine the average diameter, size distribution and ζ-potential of the copolymer nanoparticles. It was shown that the copolymer composition was an effective parameter for control of the release kinetics of in situ loaded metoprolol tartrate in copolymer nanoparticles.

Improvement on solvent resistance of photonic crystals by surface modification

In this study polystyrene (PS) spheres were synthesized by emulsifier-free emulsion copolymerization of styrene with methacrylic acid for the fabrication of photonic crystals. A facile method to significantly improve the solvent resistance of photonic crystals was developed through surface modification of PS spheres by poly(vinyl pyrrolidone) (PVP). We used an ethanol soaking test to evaluate the solvent resistance of photonic crystals prepared by pristine, thermal-treatment, and PVP-modification methods. The crystal structure and the absorption band of the photonic crystals before and after the soaking test were investigated. Experimental results revealed that the photonic crystals prepared from the unmodified PS spheres have a very weak resistance to ethanol, resulting in impossibility of carrying out inverse opal photonic crystals. The improvement on solvent resistance by the thermal-treatment method was limited due to the weak bonding or the mergence of PS spheres. We found the photonic crystal prepared from the PVP-modification PS spheres maintains its integrity very well in the ethanol solution after 5-h soaking. Moreover, the photonic crystal and the corresponding inverse opal photonic crystal revealed excellent structure and optical properties.

Preparation of PS Colloids with DMA and MMA Comonomers and Suitability of P(S/DMA) for Colloidal Silica Deposition

There is a lack of investigation on the effects of hydrophilic comonomer and pH on the particle size of functionalized polystyrene colloids. In this study, polystyrene (PS) colloids were prepared via emulsifier-free emulsion copolymerization of styrene (S) with 2-(dimethylamino)ethyl methacrylate (DMA) and methyl methacrylate (MMA) at pH 3.0 and 7.0. The sizes of the colloidal particles greatly depended on the comonomer type and pH. The hydrodynamic diameters of the particles ranged from 95 nm to 265 nm and their polydispersity index (PDI) values were less than 0.1. The particles containing comonomer moieties had spherical morphology and good stabilities. P(S/DMA) particles, especially showed excellent colloidal stability and had positive zeta potential values at the acidic pH range as a result of protonation of tertiary amine group of the DMA moiety. In addition, DMA functionalized PS colloids enabled to easy way for the preparation of PS/SiO2 composites. By physically deposition of silica nanoparticles onto the P(S/DMA) at acidic medium, PS/SiO2 core/shell composite particles were obtained. Both preparations of PS colloids and PS/SiO2 composites were easy and one-pot syntheses.

Superparamagnetic Temperature-Responsive Ionic-Cross-Linked Polymeric Hybrid Nanocapsules via Self-Templating Approach

A facile strategy was developed for the preparation of the superparamagnetic temperature-responsive ionic-cross-linked polymeric hybrid nanocapsules via the “self-templating” approach based on the terpolymer (poly(tert-butyl acrylate-co-N-isopropylacrylamide-co-acrylic acid, (poly(t-BA-co-NIPAm-co-AA))) latex particles prepared by the emulsifier-free emulsion copolymerization as the self-templates. The multifunctional polymeric nanocapsules with a particle size of about 150 nm were obtained by etching the terpolymer self-templates with acetone after their surface carboxyl groups were ionic-cross-linked with the glycine-modified ferroferric oxide nanoparticles (Fe3O4-glycine). They exhibited the temperature-responsive charateristics with the lower critical solution temperature (LCST) of about 25 °C and the superparamagnetic properties, validated by the dynamic light scattering (DLS) and vibrating sample magnetometer (VSM) analysis. Their controlled release of a drug molecule (a model hydrophobic drug, dipyridamole (DIP)) was also investigated. The multifunctional polymeric nanocapsules could be used as a promising smart drug delivery system with magnetic-targeted function.

Synthesis of Sub-100 nm Nanoparticles by Emulsifier-free Emulsion Polymerization of α-Methylstyrene, Methyl Methacrylate and Acrylic Acid

The emulsifier-free emulsion copolymerization of α-methylstyrene (AMS) and methyl methacrylate (MMA) in the presence of functional monomer acrylic acid (AA) was carried out in batch process, giving birth to sub-100 nm nanoparticles. The kinetics of polymerization was investigated. The morphology and size of particles were monitored by TEM. The influences of the functional monomer AA concentration, initiator ammonium persulfate (APS) concentration, and polymerization temperature were studied. It was found that AMS caused a drastic decrease in both the rate of polymerization and the average degree of polymerization. The activation energy calculated from Arrhenius plot turned out to be 83.6 kJ/mol.

Preparation and optical properties of novel bioactive photonic crystals obtained from core-shell poly(styrene/α-tert-butoxy-ω-vinylbenzyl-polyglycidol) microspheres

Optical properties of polymer microspheres with polystyrene cores and polyglycidol-enriched shells poly(styrene/α-tert-butoxy-ω-vinylbenzyl-polyglycidol) (P(S/PGL) particles with number average diameters D n determined by scanning electron microscopy equal 237 and 271 nm), were studied before and after immobilization of ovalbumin. The particles were synthesized by emulsifier-free emulsion copolymerization of styrene and polyglycidol macromonomer (poly(styrene/α-tert-butoxy-ω-vinylbenzyl-polyglycidol)) initiated with potassium persulfate. Molar fraction of polyglycidol units in the interfacial layer of the microspheres determined by XPS was equal 42.6 and 34.0%, for the particles with D n equal 137 and 271 nm, respectively. Colloidal crystals from the aforementioned particles were prepared by deposition of particle suspensions on the glass slides and subsequent evaporation of water. It was found that optical properties of colloidal crystals from the P(S/PGL) microspheres strongly depend on modification of their interfacial layer by covalent immobilization of ovalbumin. The coating of particles with ovalbumin resulted in decreasing their refractive index from 1.58 to 1.52.

Studies on the Preparation of Stable and High Solid Content Emulsifier-Free Poly(MMA/BA/HEA) Latex with the Addition of AMPS and Characterization of the Obtained Copolymers

The 2-acrylamido -2-methylpropane sulfonic acid (AMPS) was used as a reactive comonomer for the methyl methacrylate (MMA), n-butyl acrylate (BA) and 2-hydroxyethyl acrylate (HEA) emulsifier-free emulsion copolymerization system to obtain latices of stable and high-solid content (50 wt%).The polymerization and storage process is very stable, and the emulsion could store at room temperature for more than six months with the addition of AMPS. Properties of the latices, such as stability, flow behavior, particles diameter and morphology were studied. In addition, physical properties of the obtained copolymers, such as water resistance, glass transition temperature (Tg) were also investigated. The final size of the latex particles is 200∼300 nm in diameter. Compared with the copolymers that were prepared by surfactant emulsion polymerization water resistance is greatly improved.

Bioligand carriers based on methyl methacrylate copolymers with N-vinylformamide or glycidyl methacrylate

Emulsifier-free emulsion copolymerization of methyl methacrylate with N-vinylformamide and glycidyl methacrylate initiated by a cationic or anionic azoinitiator in the presence of dextran is used to produce monodisperse polymer particles with a developed multifunctional surface. As a result, monodisperse particles are obtained with a diameter of 350–660 nm, the surface layer of which contains, in addition to carboxyl groups, amino or epoxy groups. The conditions are determined for the formation of multifunctional hydrophilic particle surface via the hydrolysis of comonomer units and residual groups of initiators. The limiting values of bovine serum albumin chemisorption (2.4 and 1.0 mg/m2 on the particles of methyl methacrylate copolymers with glycidyl methacrylate or N-vinyl formamide, respectively) indicate that the obtained particles have sufficient sorption capacity to be applied as carriers for immunoreagents.