Mechanism Of Emulsion Polymerization Research Articles

Facile Access to High Solid Content Monodispersed Microspheres via Dual-Component Surfactants Regulation toward High-Performance Colloidal Photonic Crystals.

Monodispersed microspheres play a major role in optical science and engineering, providing ideal building blocks for structural color materials. However, the method toward high solid content (HSC) monodispersed microspheres has remained a key hurdle. Herein, a facile access to harvest monodispersed microspheres based on the emulsion polymerization mechanism is demonstrated, where anionic and nonionic surfactants are employed to achieve the electrostatic and steric dual-stabilization balance in a synergistic manner. Monodispersed poly(styrene-butyl acrylate-methacrylic acid) colloidal latex with 55wt% HSC is achieved, which shows an enhanced self-assembly efficiency of 280% compared with the low solid content (10wt%) latex. In addition, Ag-coated colloidal photonic crystal (Ag@CPC) coating with near-zero refractive index is achieved, presenting the characteristics of metamaterials. And an 11-fold photoluminescence emission enhancement of CdSe@ZnS quantum dots is realized by the Ag@CPC metamaterial coating. Taking advantage of high assembly efficiency, easily large-scale film-forming of the 55wt% HSC microspheres latex, robust Ag@CPC metamaterial coatings could be easily produced for passive cooling. The coating demonstrates excellent thermal insulation performance with theoretical cooling power of 30.4W m-2, providing practical significance for scalable CPC architecture coatings in passive cooling.

Methacrylic acid‐based amphiphilic block‐random copolymer stabilizers for emulsion polymerization

AbstractThe emulsion polymerization of styrene was investigated using polystyrene‐b‐[polystyrene‐r‐poly(methacrylic acid)] amphiphilic block‐random copolymers (BRCs) of different compositions as stabilizers. These stabilizers with molar masses <20,000 g/mol, which possess unique dispersion behaviour (i.e., self‐assembly with low aggregation numbers) when dissolved in aqueous medium at alkaline pH, were prepared by the nitroxide‐mediated bulk polymerization of styrene to achieve a desired molar mass followed by chain extension by batchwise addition of styrene and methacrylic acid monomers to obtain the stabilizing group. Emulsion polymerizations of styrene stabilized by these BRCs yielded stable latexes with particle diameters that range between 30 and 150 nm. When different concentrations of the stabilizer (2–3.5 mM) were utilized for emulsion polymerization of styrene, a similar novel emulsion polymerization mechanism observed previously by our group for the acrylic‐acid based amphiphilic BRCs was also seen, further validating the difference between this class of polymeric surfactants and conventional small molecule surfactants, block copolymers, or alkali soluble resins. The performance of methacrylic‐acid based BRCs was more efficient and yielded higher surface coverage of the polystyrene latexes when compared to the acrylic‐acid based BRCs as a result of the more hydrophobic nature of the former.

Amphiphilic Block-Random Copolymer Stabilizers: A “Seeded-Coagulative” Emulsion Polymerization Mechanism

Amphiphilic Block-Random Copolymer Stabilizers: A “Seeded-Coagulative” Emulsion Polymerization Mechanism

Dispersion Polymerization versus Emulsifier-Free Emulsion Polymerization for Nano-Object Fabrication: A Comprehensive Comparison.

Although the preparation of nano-objects by emulsifier-free controlled/living radical emulsion polymerization has drawn much attention, the morphologies of these formed objects are difficult to predict and to reproduce because of the much more complex nucleation mechanisms of emulsion polymerization compared to only one self-assembling nucleation mechanism of controlled radical dispersion polymerization. The present study compares dispersion polymerization with emulsifier-free emulsion polymerization in terms of nucleation mechanism, polymerization kinetics, and disappearance behavior of the macrochain transfer agent, gel permeation chromatograms curves of the obtained block copolymer as well as the structural and morphological differences between the produced nano-objects on the basis of published data. Moreover, the effects of the inherently heterogeneous nature of emulsion polymerization on the mechanism of reversible addition-fragmentation transfer polymerization and the nano-object morphology are examined, and efficient agitation and adequate solubility of the core-forming monomer in water are identified as the most crucial factors for the fabrication of nonspherical nano-objects.

On the mechanism of acrylamide emulsion polymerization with the participation of its dimers

The role of both dimeric and monomeric forms of acrylamide monomer in the process of polymerization in emulsions initiated by different type of initiators was discussed and the reasons for the reaction order with respect to monomer greater than unity were elucidated for acrylamide free radical polymerization in emulsions. The emulsion polymerization mechanism of acrylamide is discussed separately for the processes initiated by water-soluble initiator and oil-soluble initiator. The main difference in two cases is the distribution of acrylamide and initiator in aqueous and toluene phases. In the case of using water-soluble initiator, the initiator and acrylamide are in the same phase, whereas the molecules of the initiator and acrylamide are distributed between different phases in the case of using oil-soluble initiator. As a result, the participation of the dimers in the process of acrylamide emulsion polymerization is more efficient for the system where water-soluble initiator is used. For that system, it is suggested that both dimers and monomers of acrylamide participate in the propagation reaction at relatively low concentrations of acrylamide, which explains the value of the reaction order with respect to monomer greater than unity.

Time-Resolved Small-Angle X-ray Scattering Studies during Aqueous Emulsion Polymerization.

The persulfate-initiated aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) is studied by time-resolved small-angle X-ray scattering (SAXS) at 60 °C using a stirrable reaction cell. TFEMA was preferred to styrene because it offers much greater X-ray scattering contrast relative to water, which is essential for sufficient temporal resolution. The evolution in particle size is monitored by both in situ SAXS and ex situ DLS in the absence or presence of an anionic surfactant (sodium dodecyl sulfate, SDS). Post-mortem SAXS studies confirmed the formation of well-defined spherical latexes, with volume-average diameters of 353 ± 9 nm and 68 ± 4 nm being obtained for the surfactant-free and SDS formulations, respectively. 1H NMR spectroscopy studies of the equivalent laboratory-scale formulations indicated TFEMA conversions of 99% within 80 min and 93% within 60 min for the surfactant-free and SDS formulations, respectively. Comparable polymerization kinetics are observed for the in situ SAXS experiments and the laboratory-scale syntheses, with nucleation occurring after approximately 6 min in each case. After nucleation, scattering patterns are fitted using a hard sphere scattering model to determine the evolution in particle growth for both formulations. Moreover, in situ SAXS enables identification of the three main intervals (I, II, and III) that are observed during aqueous emulsion polymerization in the presence of surfactant. These intervals are consistent with those indicated by solution conductivity and optical microscopy studies. Significant differences between the surfactant-free and SDS formulations are observed, providing useful insights into the mechanism of emulsion polymerization.

Revisiting the Classical Emulsion Polymerization: An Intriguing Occurrence of Monodispersed Bowl-Shaped Particles

An intriguing phenomenon is found that monodispersed bowl-shaped rather than spherical poly(styrene-co-butyl acrylate) [P(St-co-BA)] particles can be obtained by one pot traditional emulsion polymerization without using any template or redundant process and the cavity size is controllable. The facile implementation method is beneficial to large-scale fabrication of the bowl-shaped particles. Herein, the amphiphilic oligomeric radical with hydrophobic P(St-co-BA) chains and hydrophilic sulfate groups ([−OSO3]−) from water-soluble potassium persulfate could migrate to surface of primary latex particles to act as an emulsifier when amount of the additional emulsifier is so low, which causes an imbalance between inside and outside osmotic pressures of the latex particles to result in bowl-shaped particles for the kinetic stability. This advances the understanding of classical emulsion polymerization mechanism.

Effect of highly hydrophobic plant oil-based monomers on micellization of sodium dodecyl sulfate

The effect of highly hydrophobic olive oil-based (OVM) and high oleic soybean oil-based (HO-SBM) acrylic monomers on micellization of sodium dodecyl sulfate (SDS) was examined at different surfactant and monomer concentrations by determining micellar parameters, size and structure, as well as surface tension measurements. The obtained results indicate SDS ability to solubilize sparingly soluble in water plant oil-based monomer (POBM) molecules and facilitate formation of mixed (SDS/POBM) micelles. Surface activity of a surfactant/monomer mixture varies by adding the POBM and is generally higher than for SDS. Comprehensive trends were observed for micellar aggregation number and number of micelle-bound monomer molecules demonstrating that POBM molecules replace SDS counterparts in the mixed micelles. Based on dynamic light scattering measurements (DLS), we hypothesized that incorporation of POBM into the mixed micelles promotes micellar association and formation of 25–30 nm size structures, also detected using transmission electron microscopy (TEM). Practical importance of these findings is the fact that solubilization of POBM by surfactant molecules can have an impact on reaction kinetics and mechanism of emulsion polymerization, as well as affect latex particles formation and, respectively, resulting particle morphology.

Aqueous heterogeneous radical polymerization of styrene under compressed ethane

Pressurization of emulsions with compressed gases potentially offers a low-energy route for preparation of miniemulsions that can be polymerized to produce polymeric nanoparticles. Conventional approaches typically require high-energy mixing to generate the miniemulsion and this impedes their industrial application. Compressed ethane is employed in this study to generate oil-in-water (mini)emulsions based on styrene/water and the anionic surfactant Dowfax 8390. The initial, turbid emulsion becomes transparent under compressed ethane at 60 °C and 6 MPa. Aqueous heterogeneous radical polymerization of styrene at these conditions yields nanoparticles with diameters of around 60 nm. However, mechanistic investigations reveal that particle formation proceeds via a classical emulsion polymerization mechanism (aqueous micellar nucleation) rather than direct polymerization of monomer droplets (droplet nucleation). The transparency phenomenon is attributed to matching refractive indices in the continuous and dispersed phases. The Lorentz-Lorenz mixing rule is used to estimate both the refractive index and ethane solubility in the dispersed phase at the transparent condition.

Emulsion Polymerization with a Biosurfactant.

Emulsion polymerization of styrene was conducted using a biosurfactant (i.e., sodium surfactin, hereinafter called just "surfactin") having very low critical micelle concentration (CMC, 2.9 × 10-3 mmol/L) and biodegradability characteristics. The nucleation mechanism was investigated by comparing with a conventional surfactant (i.e., sodium dodecyl sulfate) system. Unlike the emulsion polymerization systems using conventional surfactants, nucleation mechanisms changed above CMC in the presence of a biosurfactant. At low concentrations of surfactin (above CMC), the polystyrene (PS) particles are likely generated via a soap-free emulsion polymerization mechanism. In contrast, at high surfactin concentrations, the PS particles would be synthesized by following a micellar nucleation mechanism. However, the slope (0.23) of the log Np versus log Cs plot (Np: number of particles; Cs: concentration of surfactin) did not obey the Smith-Ewart theory (0.6), this probably being produced by the high adsorbability of surfactin.

Preparation of nanoporous carbon microspheres by subcritical water carbonization and electrocapacitive study

In this work, sugar-derived carbon microspheres (CMSs) with diameters in the range of 5–10μm and uniform nanopores were prepared using the subcritical water carbonization method, followed by microwave-assisted KOH activation. The carbonization was conducted at 3MPa and moderate temperatures (150–170°C) in subcritical water, which is a green dehydrating agent. The formation of the CMSs from a sugar solution under subcritical water conditions followed a radical-catalysed emulsion polymerization mechanism. The specific surface area and pore volume of the CMSs were found to increase with increasing the mass ratio of KOH over carbon up to 1:1. Electrocapacitive results showed that a sample prepared at a KOH to carbon ratio of 1:1 and microwave irradiation level of 70% possessed the highest specific capacitance (about 179.2F/g) at a current density of 1A/g and excellent cycling performance over 1000 charging/discharging cycles without significantly loss in capacitance. The specific capacitance and capacitive retention of this electrode are comparable to that of an electrode prepared from commercial YP-80F activated carbon.

Preparation and Properties of Anionic Polymer Emulsion in the Presence of a Reactive Surfactant

Stable polymer emulsion derived from Butyl Methacrylate (BMA), 4-vinyl pyridine (4-VP), vinylidene chloride (VDC) and divinylbenzene (DVB) with different size and distribution were prepared through soapless emulsion polymerization by using a reactive surfactant and a redox initiator. The influences of the quality ratio of the reactive surfactant to the monomers and the dosages of the cross-linking agent on the stability and thermal properties of the emulsion were studied. The obtained polymer nano-particles have higher ξ potential, and the particle sizes have narrow distribution. This polymerization system can give some further understanding on the mechanism of emulsion polymerization .The solid content of the emulsion could be as high as 40% and the particle sizes could be adjusted in the range of 40-300nm. Otherwise, using infrared spectroscopy, size and ξ analyzer, gravitational thermal analysis and differential scanning calorimeter, properties of the emulsion latex were tested. This kind of latex may have applications in the development of water-developable thermal-sensitive material system.

Aqueous Emulsion Polymerization of Substituted Acetylenes: Effects of Organic Solvent and Analysis of Blue Shifts and Emulsion Polymerization Mechanism

A series of optically active nanoparticles composed of helical substituted polyacetylene is prepared via emulsion polymerization. A specific organic solvent is required for solid substituted acetylene monomers to undergo emulsion polymerization. The effects of this organic solvent are investigated. Its amount is found to be decisive for obtaining stable polymer emulsions. The helical conformations of the substituted polyacetylenes in nanoparticle state are identified with the help of CD and UV-vis spectra. A blue shift occurs in CD and UV-vis spectra of some of the polyacetylene emulsions. The underlying driving force for the blue shift is discussed, and an emulsion polymerization mechanism is proposed.

Preaparation of cationic latexes of poly(styrene-CO-butyl acrylate) and their properties evolution in latex dilution

Cationic latexes were prepared through emulsion copolymerization of styrene (St) and butyl acrylate (BA) with a cationic surfactant, cetyl trimethyl ammonium bromide (CTAB). Latex properties, including particle size, size distribution, potential, surface tension and monomer conversion, were determined for latexes prepared with different CTAB amounts. Evolution of these properties during emulsion polymerization was followed in order to understand the mechanism of the particles formation. Results showed that both particle size and potential were function of polymerization time and latex solids. Parallel emulsion polymerizations with cationic, anionic charged initiator and charge-free initiators were also carried out, the latex properties were determined at different polymerization time. All these results were attentively interpreted based on the mechanisms of emulsion polymerization, surfactant adsorption and latex particle stabilization.

Polymerization Model for Hydrogen Peroxide Initiated Synthesis of Polypyrrole Nanoparticles

A very simple, environmentally friendly, one-step oxidative polymerization route to fabricate polypyrrole (Ppy) nanoparticles of fixed size and morphology was developed and investigated. The herein proposed method is based on the application of sodium dodecyl sulfate and hydrogen peroxide, both easily degradable and cheap materials. The polymerization reaction is performed on 24 h time scale under standard conditions. We monitored a polaronic peak at 465 nm and estimated nanoparticle concentration during various stages of the reaction. Using this data we proposed a mechanism for Ppy nanoparticle formation in accordance with earlier emulsion polymerization mechanisms. Rates of various steps in the polymerization mechanism were accounted for and the resulting particles identified using atomic force microscopy. Application of Ppy nanoparticles prepared by the route presented here seems very promising for biomedical applications where biocompatibility is paramount. In addition, this kind of synthesis could be suitable for the development of solar cells, where very pure and low-cost conducting polymers are required.

Waterborne RAFT polymers

A recently invented novel family of RAFT ( Reversible Addition- Fragmentation chain Transfer) agents having a common formula Z–C( S)–S–CR 2COOR 1 where Z = –SR, –NR 2, or –OR, and R 1 represents H or a variety of functional groups allows for tailoring their hydrophilicity–hydrophobicity balance. A limited hydrophilicity of the RAFT agents can be achieved which is sufficient for their diffusion through water, yet the agents are hydrophobic enough to phase-separate out of water. Thus, the limited hydrophilicity of otherwise hydrophobic agents allows them to be at the loci of polymerization making them suitable for the emulsion polymerization mechanism. With several RAFT agents, good control over molecular weight was demonstrated for a broad variety of ab initio acrylic emulsion polymers. For methyl methacrylate, a portion of RAFT did not engage, resulting in less than the theoretical number of polymer chains. It was found, however, that as little as ∼10 wt% of an acrylic monomer slowed down polymerization enough to engage all RAFT agent molecules and yield predicted molecular weights. A broad variety of colorless and odorless telechelic acrylic and methacrylic emulsion polymers were synthesized. Microemulsion and solution-dispersion techniques produced clean colloidally stable RAFT dispersions. These two techniques did not require RAFT agents with tailored hydrophilicity–hydrophobicity. The UV spectra and photooxidative stability of the RAFT polymers were studied. The RAFT fragment in polymers appeared to have no impact on their photooxidative stability.

Synthesis and characterization of polychloromethylstyrene nanoparticles of narrow size distribution by emulsion and miniemulsion polymerization processes

Polychloromethylstyrene nanoparticles of sizes from 12.0 ± 2.3 to 229.6 ± 65 nm were prepared by the emulsion and miniemulsion polymerization of chloromethylstyrene in an aqueous continuous phase in the presence of potassium persulfate as initiator, sodium octylbenzenesulfonate as surfactant, and hexadecane as costabilizer for the miniemulsion polymerization process only. The influence of various polymerization parameters (e.g., concentration of the monomer, initiator, the crosslinker monomer, and the surfactant) on the properties of the particles (e.g., size, size distribution, and yield) has been elucidated. The polychloromethylstyrene nanoparticles formed via the emulsion polymerization mechanism possess smaller diameter and size distribution than those formed under similar conditions via the miniemulsion polymerization mechanism. Other differences between these two polymerization mechanisms have also been elucidated. For future study, we wish to use these nanoparticles for the covalent immobilization of bioactive reagents such as proteins to the surface of these nanoparticles for various biomedical applications.

Kinetics of suspended emulsion copolymerization of acrylonitrile with itaconic acid

AbstractAcrylonitrile(AN) was successfully used to copolymerize with itaconic acid (IA) by suspension emulsion polymerization at 70 ˚C under N2 atmosphere for the first time. Porous AN/IA copolymers were prepared by using potassium peroxydisulphate (KPS) as initiator, poly(vinyl alcohol) (PVA) as dispersant and Span60 as emulsifier. Kinetics of suspension emulsion copolymerization of AN with IA were studied. Effects of various mass ratios of water/monomer, initiator concentrations, emulsifier concentrations and dispersant concentrations on AN/IA copolymerization rate and changes of particle size and size distribution with the extension of polymerization time were investigated. It was found that the copolymerization rate increased with water/monomer mass ratio and KPS concentration. Span60 concentration and PVA concentration had no obvious effect on the polymerization rate. Finally, a suspension emulsion polymerization mechanism for AN and IA was proposed.

Towards a consistent mechanism of emulsion polymerization—new experimental details

The application of atypical experimental methods such as conductivity measurements, optical microscopy, and nonstirred polymerizations to investigations of the ‘classical’ batch ab initio emulsion polymerization of styrene revealed astonishing facts. The most important result is the discovery of spontaneous emulsification leading to monomer droplets even in the quiescent styrene in water system. These monomer droplets with a size between a few and some hundreds of nanometers, which are formed by spontaneous emulsification as soon as styrene and water are brought into contact, have a strong influence on the particle nucleation, the particle morphology, and the swelling of the particles. Experimental results confirm that micelles of low-molecular-weight surfactants are not a major locus of particle nucleation. Brownian dynamics simulations show that the capture of matter by the particles strongly depends on the polymer volume fraction and the size of the captured species (primary free radicals, oligomers, single monomer molecules, or clusters).

Adaption of the Mechanism of Emulsion Polymerization to New Experimental Results

AbstractSummary: New experimental investigations of the 'classical' batch ab‐initio emulsion polymerization of styrene reveal the important role of monomer droplets for the whole process. Monomer droplets with a size between a few and some hundreds of nanometers, which are formed by spontaneous emulsification as soon as styrene and water are brought into contact, have a strong influence on the particle nucleation, the particle morphology, and the swelling of the particles. Experimental results confirm that micelles of low molecular weight surfactants are not a major locus of particle nucleation. Brownian dynamics simulations show that the capture of matter by the particles (monomer or radicals) strongly depends on the polymer volume fraction and the size of the captured species (primary free radicals, oligomers, single monomer molecules, or clusters).