Formation Of Polymer Particles Research Articles

Preparation of nearly monodisperse pH-responsive microgels by radiation-induced dispersion polymerization

Nearly monodisperse poly(2-(diethylamino) ethyl methacrylate) (PDEA) microgels were prepared directly by radiation-induced dispersion polymerization in water/ethanol media using poly(vinylpyrrolidone) (PVP) as the stabilizer at room temperature under certain circumstance (appropriate ethanol/water ratio and monomer dosage), which afforded novel pH-responsive behavior with range of 600–2500 nm. This method takes the advantages of radiation-induction (no chemical initiator, temperature independent, uniform initiation with a high efficiency and so on) that may result in the formation of uniform polymer particles. PVP acted as not only a physical stabilizer, but also as a macromonomer to form the grafted copolymer, which was confirmed by the Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance ( 1H NMR) and was important for the stabilization of microgels. The characterization (morphology, size and distribution, and swelling/deswelling kinetics) of PDEA microgels were carried out by the scanning electron microscope (SEM), dynamic light scattering (DLS) and turbidity studies.

Preparation of Hollow Polymer Particles with a Single Hole in the Shell by SaPSeP

The influence of sodium dodecyl sulfate (SDS) on the shell formation of hollow polymer particles prepared by the SaPSeP method, which was proposed by the authors for the preparation of micrometer-sized hollow polymer particles, was investigated. A single hole was observed in the shell of the hollow particles prepared by seeded polymerization of micrometer-sized, monodisperse divinylbenzene/p-xylene droplets in aqueous medium in the presence of SDS at concentrations above 43.3 mM, which were prepared by the dynamic swelling method. The fraction of the hollow particles having a single hole in the shell and the area of the hole increased with the SDS concentration.

Monolayer Formation of Cationic Polymer Particles on Hydrophobic Solid Substrates in Aqueous System

Abstract Monodispersed cationic polymer particles bearing quaternary ammonium groups on their surfaces were well self-organized through hydrophobic interaction on hydrophobically modified glass plates in aqueous system. We could fabricate the particle monolayer of close-packed structure with a relatively regular interval by tuning hydrophilic–hydrophobic balance of particles and temperature.

Microemulsion polymerization of styrene in the presence of macroinimer

The kinetics of o/w electrostatically and sterically-stabilized microemulsion polymerization of styrene with and without macromonomeric azoinitiator (macroinimer; MIM) have been investigated. The microemulsion polymerization stabilized by the ionic emulsifier sodium dodecyl sulfate (SDS) or the non-ionic emulsifier Tween 20 (Tw 20) was initiated by ammonium peroxodisulfate (APS)/sodium thiosulfate (STS) redox system. The rate of polymerization vs. conversion curve shows the two non-stationary rate intervals. This behavior is a result of two opposing effects, the continuous particle nucleation and the decrease of monomer concentration at the reaction loci. The addition of MIM favors the additional particle nucleation. The sterically (Tw 20)-stabilized microemulsion polymerization is much faster than that of the electrostatically (SDS)-stabilized microemulsion polymerization. This was attributed to the higher Tw 20 concentration and increased solubilization of MIM and comonomer concentration in the polymer particles. The formation of initial large polymer particles is attributed to the intensive agglomeration polymer particles with monomer droplets. The continuous decrease in the average size is mainly attributed to the additional particle nucleation.

Preparation of monodisperse poly(methyl methacrylate) particles by radiation-induced dispersion polymerization using vinyl terminus polysiloxane macromonomer as a polymerizable stabilizer

Monodisperse poly(methyl methacrylate) particles were prepared directly by radiation-induced dispersion polymerization in hexane–ethanol media using vinyl terminus polysiloxane (PSI) macromonmer as a polymerizable stabilizer at room temperature. This method takes advantage of the specialties of radiation-induction, which may result in the formation of uniform polymer particles. The gel effect is evident from the polymerization kinetics curves. Vinyl terminus PSI macromonomer acted as not only a comonomer, but also as a stabilizer. The characterization of PMMA particles was carried out by the scanning electron microscope (SEM), FT-IR, 1H-NMR and X-ray photoelectron spectroscope (XPS). XPS results show that the graft PSI macromonomers were anchored on the surface of PMMA particles to provide a steric stabilization to the PMMA particles.

Preparation of nonspherical polymer particles by spraying aqueous dispersions of hydrophobic solvent droplets into methanol

Nonspherical polymer particles were prepared by spraying an aqueous dispersion of hydrophobic solvent droplets (containing dissolved polymers) into methanol. Nonspherical particles were prepared for polystyrene and poly(methyl methacrylate), and spherical particles were prepared for poly(ethyl methacrylate) and poly(i-butyl methacrylate). It is concluded that condensation of the polymer molecules at the interface of the droplet is a key factor for the formation of nonspherical polymer particles.

Acrylo-Styrene Latex. I. Influence of the Emulsifier Amount and Distribution on Product Properties

Emulsifiers play an important part in obtaining emulsion acrylo-styrene resins. They influence the polymer particle formation, the process development rate, and the final system stability in time and toward electrolytes as well. The emulsifiers affect the characteristics of the coating system based on this type of resin due to their indirect influence on resin properties. Finally, they can be found in the formed film. There is an optimum combination of emulsifiers that correspond to every application of mixture of monomers. The present article is of a study of the influence of the emulsifier amount and distribution on an acrylo-styrene resin in paints with good washability, long-term stability, and optimum rheology.

Formulation and Characterization of Immunoreactive Tetanus Toxoid Biodegradable Polymer Particles

Poly lactide-co-glycolide and polylactide polymer particles entrapping immunoreactive tetanus toxoid (TT) were prepared with a view to developing a single shot controlled release vaccine formulation. Denaturation of TT by dichloromethane (DCM) during primary emulsification stage of particle formulation was minimized by incorporation of an optimal amount of rat serum albumin (RSA) in the internal aqueous phase. Incorporation of RSA as a stabilizer during the primary emulsification stage of polymer particle formulation protected the immunoreactivity of TT, enhanced its encapsulation efficiency and also led to uniform polymer particle formation. Use of sonication, both during primary and secondary emulsification processes, resulted in formation of nanoparticles whereas microparticles were formed when the secondary emulsion was carried out by homogenization. Immunoreactive TT particles made from different polymers incorporating stabilizers released antigen continuously for more than four months in vitro. Single injection of both type of particles encapsulating stabilized TT elicited anti-TT antibody titers in rats for more than five months, which was higher than that obtained with TT injected in saline. Anti-TT antibody titers in vivo were in accordance with the in vitro release characteristics of immunoreactive TT from the particles. Immune responses with hydrophobic polymer particles were better than those made using hydrophilic polymers. These results indicate the importance of protecting the immunoreactivity of TT during formation of polymer particles for sustained and improved antibody response.

The Film Formation of Polymer Particles in Drying Thin Films of Aqueous Acrylic LaticesII. Coalescence, Studied with Transmission Spectrophotometry

Abstract The aim of this study is to determine the factors that contribute to the process of film formation of binder particles in drying aqueous dispersion coatings, based on acrylic polymers. It is known that concentrated latices of uniform size show iridescent, colored light patterns. These colors are caused by interparticle interference, and they are only present when the latex particles are ordered in a regular structure. The interparticle interference can be characterized by measuring the transmission as a function of wavelength of the incident light. It appeared that the changes of the interparticle interference of a drying latex film can be related to changes in the interparticle distance and displacement. It was also found that the interparticle distance becomes “negative” upon coalescence of the latex particles. This means that from this point on, the change in interparticle interference is directly related to the indentation or deformation of the latex particles. It became clear that the coalescence process differs from deformation mechanisms accepted in the literature. It seems that the deformation of the particles follows a biaxial mechanism. This means that the particles deform only in one direction, perpendicular to the film surface.

Mathematical modeling of dispersion polymerizations study of the styrene polymerization in ethanol

A mathematical model for prediction of monomer conversion, of particle number and of the evolution of the particle size distribution (PSD) in dispersion polymerization is developed. Despite being completed very early during the polymerization process (monomer conversion <1%), nucleation of new particles is the most important factor affecting the PSD. In order to describe the particle nucleation phenomena, the mechanism of homogeneous coagulative nucleation is considered. According to this mechanism, polymer chain aggregates can either coagulate and grow, to give birth to new polymer particles (particle nucleation), or be captured by existing polymer particles. Two sets of population balance equations are used: one for the aggregates, and a second one for the stable polymer particles. It is shown that the model is able to describe the dispersion polymerization of styrene in ethanol and the formation of micron-size monodisperse polymer particles.

The Film Formation of Polymer Particles in Drying Thin Films of Aqueous Acrylic Latices: II. Coalescence, Studied with Transmission Spectrophotometry

The aim of this study is to determine the factors that contribute to the process of film formation of binder particles in drying aqueous dispersion coatings, based on acrylic polymers. It is known that concentrated latices of uniform size show iridescent, colored light patterns. These colors are caused by interparticle interference, and they are only present when the latex particles are ordered in a regular structure. The interparticle interference can be characterized by measuring the transmission as a function of wavelength of the incident light. It appeared that the changes of the interparticle interference of a drying latex film can be related to changes in the interparticle distance and displacement. It was also found that the interparticle distance becomes “negative” upon coalescence of the latex particles. This means that from this point on, the change in interparticle interference is directly related to the indentation or deformation of the latex particles. It became clear that the coalescence process differs from deformation mechanisms accepted in the literature. It seems that the deformation of the particles follows a biaxial mechanism. This means that the particles deform only in one direction, perpendicular to the film surface.

Microemulsion Polymerization of Butyl Acrylate in the Presence of Polymeric Hydrophobes

Microemulsion polymerization of butyl acrylate initiated by a water-soluble ammonium peroxodisulfate initiator in the presence of polymeric hydrophobe was investigated. The polymerization rate (without polymer) vs. conversion curve shows two nonconstant rate intervals. The addition of polymeric hydrophobe promotes increase of maximum rate of polymerization, appearance of a rate shoulder at ca. 50—70% conversion and formation of polymer particles with bimodal size distribution. The maximum rate of polymerization increases with initiator concentration, particularly so with predissolved polymer. The enhanced polymerization rate with predissolved polymer is attributed to preservation of monomer droplets and larger number of latex particles. This is observed in runs with a higher weight ratio of monomer to emulsifier. The synergetic effect of predissolved polymer is also attributed to the incompatibility of polymer with (co)emusifier (BA and undissociated emulsifier), which may increase the fraction of micellar emulsifier. The non-stationary rate of polymerization is discussed in terms of continuous particle nucleation, decrease of monomer at the reaction loci, increase in weight ratio emulsifier/monomer or chain transfer to emulsifier and preservation of monomer droplets.

Polymer synthesis and processing using supercritical carbon dioxide

Carbon dioxide is a clean and versatile solvent for the synthesis and processing of a range of materials. This review focuses on recent advances in polymer synthesis and processing using liquid and supercritical CO2. The synthetic techniques discussed include homogeneous solution polymerisation, precipitation polymerisation, dispersion and emulsion polymerisation, and bulk polycondensation. The formation of porous polymers and polymer blends is also considered, and the specific advantages of CO2 in these processes are evaluated in each case. The use of CO2 as a solvent for polymer processing is reviewed from a materials perspective, with particular attention being given to the formation of polymers with well defined morphologies. The variable solvent strength associated with supercritical fluids has been utilised in areas such as polymer fractionation and polymer extraction. Plasticisation phenomena have been exploited for the impregnation and heterogeneous chemical modification of polymeric materials. The formation of microcellular polymer foams by pressure induced phase separation is considered, as is the use of CO2 for polymer particle formation, spray coating, and microlithography. The aim of the review is to highlight the wide range of opportunities available to the materials chemist through the use of carbon dioxide as an alternative solvent.

Online observation of emulsion polymerization by fluorescence technique

An online observation of local polarity via fluorescence spectroscopy was used to study the formation and growth of polymer particles during an emulsifier-free heterogeneous polymerization. The reaction mixture consisted of styrene dispersed in water and the polymerization was initiated by a macro-initiator (hydrolyzed propene-maleic acid copolymer with t-butyl perester groups). Pyrenyl probes were attached to the backbone of the initiator to analyze the heterogeneous reaction. The experimental results allow a clear distinction of different time regions during the heterogeneous polymerization. Information about the heating period, the latex formation, the particle growth and the final stage of the polymerization process (gel point) were obtained.

Kinetics of Particle Formation at the Graft Polymerization of Methylacrylate onto Hydroxyethyl Cellulose

The kinetics of polymer particle formation and distribution of monomers between a solution and a dispersed phase at the graft polymerization of methylacrylate onto hydroxyethyl cellulose has been studied. The particle number increases at the first stage of polymerization, then it is constant. The concentration of adsorbed monomer decreases during the polymerization process. The monomer concentration in the dispersed phase is greater than in the solution. A mathematical model of particle formation and monomer adsorption in the polymerization process has been suggested. Some values of rate constant ratios have been calculated.

Inverse micro-emulsion polymerization of acrylamide in the presence of a mixture of oleophilic/hydrophilic surfactants

The effect of sodium dodecyl sulphate (SDS) on the formation of inverse micro-emulsion toluene/sodium bis(2-ethylhexyl)sulphosuccinate (AOT)/water/acrylamide (AAm)/SDS and on polymerization of acrylamide initiated by oil soluble dibenzoyl peroxide was studied. The presence of SDS shifts the value of the volume fraction of aqueous phase (Φaw) at which a two-phase Winsor II system forms, to higher values. It was shown that an increase of the mass ratio of SDS/water led to a decrease of acrylamide polymerization rate, of polyacrylamide particle size and of polyacrylamide molecular mass distribution. It was also found that in the presence of SDS, a nearly constant value for acrylamide polymerization rate in inverse micro-emulsion in the range of Φaw values between 5% and 50% can be obtained. The polymerization kinetics and polymer particle formation were explained as consequences of the initiation of acrylamide polymerization in two reaction loci—in inverse micelles and in the oil macrophase of the inverse micro-emulsion. © 1998 SCI.

Dispersion copolymerization of poly(oxyethylene) macromonomers and styrene

The kinetics of dispersion copolymerization of methacryloyl-terminated poly(oxyethylene) (PEO-MA) and p-vinylbenzyl-terminated (PEO-St) polyoxyethylene macromonomers and styrene (St), initiated by a water- and/or oil-soluble initiator, was investigated using conventional gravimetric and NMR methods at 60°C. The batch copolymerizations in the water/ethanol continuous phase were conducted to high conversion. The rate of polymerization was described by the curve with a maximum at very low conversion. The initial rate of polymerization and the number-average molecular weight were found to decrease with increasing [PEO-MA], and the decrease was more pronounced in the range of a high macromonomer concentration. The rate per particle (at ca. 20% conversion) was found to be proportional to the −1.55th, the particle size to the −0.92nd, and the number of particles (at final conversion) to the 3.2nd power of [PEO-MA], respectively. At the beginning of polymerization the continuous phase is the main reaction locus. As the polymerization advances, the reaction locus is shifted from the continuous phase to the polymer particles. The transform of the reaction loci from the continuous phase to the polymer particles increases the rate of polymerization and the polymer molecular weights. The increase of the weight ratio PEO-MA/St favors the formation of monodisperse polymer particles, the colloidal stability of dispersion, and the formation of a larger number of polymer particles. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3131–3139, 1997

Dispersion copolymerization of poly(oxyethylene) macromonomers and styrene

The kinetics of dispersion copolymerization of methacryloyl-terminated poly(oxyethylene) (PEO-MA) and p-vinylbenzyl-terminated (PEO-St) polyoxyethylene macromonomers and styrene (St), initiated by a water- and/or oil-soluble initiator, was investigated using conventional gravimetric and NMR methods at 60°C. The batch copolymerizations in the water/ethanol continuous phase were conducted to high conversion. The rate of polymerization was described by the curve with a maximum at very low conversion. The initial rate of polymerization and the number-average molecular weight were found to decrease with increasing [PEO-MA], and the decrease was more pronounced in the range of a high macromonomer concentration. The rate per particle (at ca. 20% conversion) was found to be proportional to the −1.55th, the particle size to the −0.92nd, and the number of particles (at final conversion) to the 3.2nd power of [PEO-MA], respectively. At the beginning of polymerization the continuous phase is the main reaction locus. As the polymerization advances, the reaction locus is shifted from the continuous phase to the polymer particles. The transform of the reaction loci from the continuous phase to the polymer particles increases the rate of polymerization and the polymer molecular weights. The increase of the weight ratio PEO-MA/St favors the formation of monodisperse polymer particles, the colloidal stability of dispersion, and the formation of a larger number of polymer particles. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3131–3139, 1997

5631561 Arrangement for measuring and controlling the basic field of an NMR tomography apparatus

Monodisperse poly(methyl methacrylate) particles were prepared directly by radiation-induced dispersion polymerization in hexane–ethanol media using vinyl terminus polysiloxane (PSI) macromonmer as a polymerizable stabilizer at room temperature. This method takes advantage of the specialties of radiation-induction, which may result in the formation of uniform polymer particles. The gel effect is evident from the polymerization kinetics curves. Vinyl terminus PSI macromonomer acted as not only a comonomer, but also as a stabilizer. The characterization of PMMA particles was carried out by the scanning electron microscope (SEM), FT-IR, 1H-NMR and X-ray photoelectron spectroscope (XPS). XPS results show that the graft PSI macromonomers were anchored on the surface of PMMA particles to provide a steric stabilization to the PMMA particles.

Reactive surfactants in heterophase polymerization

The mechanism for the formation of polymer particles in the dispersion polymerization of methyl methacrylate and styrene in alcohol-water mixtures has been investigated. Methacrylic based poly(ethylene oxide) macromonomers and poly(vinyl-pyrrolidone) have been used as steric stabilizers. Dynamic light scattering as well as transmission electron microscopy have been applied to determine the evolution of the average particle size at the beginning of the polymerization. Stable nuclei from 80 to 400 nm in diameter size were detected. The nucleation process was quite rapid and completed within less thanca. 0.1% monomer conversion. The experimental results are compared with those predicted by the multibin kinetics model for coalescence developed by Paine [(1990) Macromolecules 23: 3109].