Formation Of Polymer Particles Research Articles

Soapless emulsion polymerization of methyl methacrylate. II. Simulation of polymer particle formation

In this work, a generalized mathematical model was developed to estimate the variation of particle concentration during the entire course of soapless emulsion polymerization of methylmethacrylate (MMA). All of the factors, such as oligomeric radical absorption or desorption by polymer particles, coagulation between polymer particles, and the termination effect on the formation mechanism of polymer particles, were considered and included in this model. When appropriate parameters were selected, this model could be successfully used to interpret the experimental behavior of particle concentration during the entire reaction. Under different conditions, the rate of polymerization, the number of radicals in each particle, the instantaneous average molecular weight of polymers, and the rate constant of termination were also calculated. All of them coincided with the experimental results quite well. © 1996 John Wiley & Sons, Inc.

Characterization of poly(vinyl alcohol) during the emulsion polymerization of vinyl acetate using poly(vinyl alcohol) as emulsifier

During the emulsion polymerization of vinyl acetate (VAc) using poly(vinyl alcohol) (PVA) as stabilizer and potassium persulfate as initiator, the VAc reacts with PVA forming PVA-graft-PVAc. When the grafted polymer reaches a critical size it becomes water-insoluble and precipitates from the aqueous phase contributing to the formation of polymer particles. Since particle formation and therefore the properties of the final latex will depend on the degree of grafting, it is important to quantify and to characterize the grafted PVA. In this work, the quantitative separation and characterization of the grafted water-insoluble PVA was carried out by a two-step selective solubilization of the PVAc latex, first with acetonitrile to separate PVAc homopolymer, followed by water to separate the water-soluble PVA from the remaining acetonitrile-insoluble material. After the separation, the water-soluble and water-insoluble PVA were characterized by Fourier Transform Infrared (FTIR) spectroscopy and 1H and 13C nuclear magnetic resonance (NMR) analyses, from which the details of the PVA-graft-PVAc structure were obtained. © 1996 John Wiley & Sons, Inc.

Mn doping of the Ziegler-Natta PP catalyst support material

Preliminary tests have shown that if MnCl 2 is used as a support material a polypropylene with a low molecular weight is produced. The activity of these catalysts is low. A low molecular fraction increases, however, the gloss of moulded products. As a molecular fraction with short chain length also acts as a lubricant in the polymer this short chain material would be an advantage if it is produced simultaneously with the normal high molecular weight polypropylene. This ability to influence the molecular weight distribution of the product was the reason why MnCl 2 was chosen as a doping salt in the MgCl 2 support material. The effect of Mn doping on the MgCl 2 support material has been investigated. The following conclusions have been drawn from this investigation: (i) Very good morphology is achieved if the MnCl 2 concentration is below 30%. At higher doping concentrations the result is poor morphology. (ii) Large catalyst particles were produced. The particles were of great mechanical strength, leading to the formation of large polymer particles with a very narrow PSD. No fines were produced partly due to agglomerization. This advantage was achieved only if the MnCl 2 concentration was below 30%. (iii) Optimum Mn doping concentration was 10 mol%. Using this doping concentration activity increased 25% (100% if kg PP/g Ti units are used). No loss in isotacticity. At higher Mn concentrations activity decreased linearly. The molecular weight distribution was effected. A broader MWD was achieved. The greatest effect was achieved with a Mn concentration of 10 mol%. The polydispercity increased from the standard value of 3 to 7. At higher Mn concentrations the MWD decreased steadily. Low molecular weight polypropene can be produced by using pure MnCl 2 as support material. (iv) The pore size distribution is effected by the Mn doping. A large portion of pores between 1 and 3 microns are produced. In standard polypropylene the largest fraction is to be found between 10 and 100 microns.

A new technique for preparing monodisperse polymer particles. II. Phase separation mechanisms

AbstractNylon 6 polymer particles with a narrow‐size distribution are made by phase separation of different concentrations of polymer solutions. At concentrations above 0.15 wt %, the diameter of the precipitated particles increases linearly with the increasing of polymer concentration. The experimental results suggest that coagulation plays an important role in particle growth during the propagation stage. A mechanism is proposed for the formation of monodisperse polymer particles during phase separation. The uniformity of the precipitated nylon 6 particles decreases when the cooling process is slowered. The surface morphologies of the nylon 6 particles are controlled by changing the drying conditions. © 1994 John Wiley & Sons, Inc.

Dispersion polymerization of styrene in aqueous alcohol solution: Effects of reaction parameters on the polymer particle formation

AbstractDispersion polymerization of styrene in an aqueous alcohol solution using poly(2‐ethyl‐2‐oxazoline) as a polymeric stabilizer was performed to prepare micron‐size monodisperse polystyrene particles. As the water content of the solvent increased, the polymerization rate and the molecular weight of the polymer particles increased and the particle size decreased. Effects of concentrations of stabilizer and initiator upon the polymerization and the size of the resulting polystyrene particles have been examined in the solvent containing different water contents.

Superparamagnetism of ferrite particles dispersed in spherical polymeric materials

Superparamagnetic iron oxide particles synthesized in water-in-oil microemulsions have been incorporated into a polymer matrix. The microstructured micellar environment provides a template for polymer synthesis, leading to the formation of interconnected polymer particles with spherical morphologies. The resulting iron oxide-polymer composites reveal superparamagnetic properties and low temperature remanence and susceptibility characteristic of a superparamagnet. The results of temperature and field dependent magnetic characterizations of these composites are described. Ultramicrotomed TEM micrographs show that the iron oxide particles (size <100 /spl Aring/) are uniformly distributed In the polymer microspheres.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Using pressure to improve polymer performance

AbstractPressure has been rediscovered as an additional parameter that can be used in optimizing the performance of traditional polymers. Some interesting advanced applications are under development. This paper reviews some promising research trends in areas such as process optimization, enhanced processing, the formation of polymer particles, polymer gels and plastics recycling.

Reactant partitioning in free‐radical heterophase polymerization: The case of inverse microemulsion polymerization of acrylamide

AbstractConversion curves have been determined at 60°C for the polymerization of acrylamide in percolating inverse microemulsions. Ammonium peroxo‐disulphate (APS) and dibenzoyl peroxide (DBP) were used as initiators of free‐radical polymerization in the presence or absence of potassium nitrosodisulphonate (Fremy's salt, FS). The percolation decreases the rate of polymerization of acrylamide initiated by APS. The polymerization is inhibited by FS. After an inhibition period, retardation of acrylamide polymerization is more pronounced in non‐percolating microemulsions. No inhibition periods were observed for DBP‐initiated polymerization of acrylamide. The percolation shortens the time interval of the ‘slow’ polymerization of acrylamide, but the rates of rapid acrylamide polymerization above 10% conversion are the same for percolating and for non‐percolating inverse microemulsions. The polymer particle diameter is a function of acrylamide/water weight ratio and of [water]/[AOT] (AOT: bis(2‐ethylhexyl)‐sulphosuccinate sodium salt) molar ratio. No effect of the initiator's nature either in the presence or in the absence of FS was found. The results are interpreted on the basis of initiator and/or nitroxide radical partitioning between oil and water phases of the inverse microemulsion, and are discussed with respect to the mechanism of acrylamide polymerization and polymer particle formation proposed for non‐percolating inverse microemulsions.

Turbidity study of the process of film formation of polymer particles in drying thin films of acrylic latices: I. Intrastructure of acrylic latices studied with transmission spectrophotometry

The aim of this study is to determine the factors that define the process of film formation of binder particles in drying aqueous dispersion coatings, based on acrylic polymers. The film formation process is investigated with transmission spectrophotometry. In this paper static measurements are used to relate the turbidity behavior of thin latex films with the physical properties of the latex. This paper focuses on the intrastructure in films of concentrated acrylic dispersions. In concentrated latices the binder particles are arranged in closely packed structures, which cause colored light patterns, due to Bragg diffraction. Light waves traveling in the latex film are scattered at the internal structures of the spheres and the water voids. The pattern of the light transmission as a function of wavelength reveals the internal structure of the latex film. The influence of weight fraction, particle size, film thickness, and particle size distribution on the transmission pattern has been investigated. The results are verified with other particle size measurements and imaging techniques.

Monodisperse porous polymer particles: Formation of the porous structure

AbstractMonodisperse porous styrene‐divinylbenzene copolymer particles were prepared via seeded emulsion polymerization using a mixture of linear polymer (polystyrene seed) and non‐solvent as inert diluent. Experimental evidence was presented to describe the mechanism of formation of porous polymer particles during the copolymerization and solvent extraction stages, in which porosity was a consequence of phase separation in the presence of diluents. Pore structure formation was investigated by changes in copolymerization kinetics, gel content, crosslinking density, particle morphology, surface area, pore volume, and pore size distribution. The process of copolymerization was presented, based on the concepts of production, agglomeration, and fixation of the interior gel microspheres of polymer particles. A portion of linear polymer used as diluent was found to participate in the network structure while the porous matrix was built‐up. The influence of the removal of the linear polymer from the matrix pores during the solvent extraction process on the porous structure was also discussed.

界面活性剤低濃度下でのスチレン水系析出重合におけるポリマー粒子の生成

Emulsion polymerizations of styrene were carried out in the absence and presence of a surfactant and the number of polymer particles was measured mainly in a range of surfactant concentrations up to the critical micelle concentration with a change in initiator concentration. Experimental results for the number of polymer particles in the absence of the surfactant were compared with predictions from a homogeneous nucleation model which includes the assumption that the rate of radical entrance into the polymer particles is proportional to particle surface area uncovered by ionic end-groups of polymers contained in the polymer particles. The model also takes into account electrostatic effects on radical entrance into the polymer particles and coagulation between polymer particles. The experimental results in the absence of the surfactant compared well with the predictions. The model was extended to the reaction system in the presence of the surfactant, taking into consideration surfactant adsorption to the polymer particles and the adhesion of surfactant molecules to growing radicals. The model predicted well the tendency of the experimental results of the number of particles.

A Novel Approach to Nanoscale Materials Synthesis Using Industrial Laser Processing of Organosilazane Liquid Precursors

ABSTRACTA new approach has been developed for the synthesis of nanoscale ceramic powder materials from liquid organosilazane precursors. This technique, by exploiting fast kinetic chemical and physical reactions, makes it possible to synthesize significant quantities of material in a relatively short time. In the current approach aerosols of a silazane monomer, (CH3SiHNH)n, (n = 3 or 4), of mol. wt. 280–320, are injected into the beam of a cw industrial CO2laser to obtain nanoscale ceramic powders. Injection of the aerosol into the laser-beam results in a high-temperature plume. Rapid condensation of the molecular precursor species emerging from the laser plume results in the formation of preceramic polymer particles, with an average diameter of 62 nm. One attractive feature of this process is that 70 wt.% of the liquid precursor is converted into nanoscale powders. Another feature is that only a further 10 wt.% loss occurs during post thermal treatment to form the end-product.

Formation of monodisperse poly(1-methacryloxybenzotriazole) particles by radiation-induced dispersion polymerization

Radiation-induced dispersion polymerization of 1-methacryloxybenzotriazole (MABt) in ethyl propionate starts as homogeneous mixture and the resulting polymer precipitates as spherical particles. Formation, size, and shape of polymer particles are strongly dependent on the initial monomer concentration. Three regions can be distinguished: formation of deformed particles at concentrations of ≦15 w/v-% MABt; formation of spherical particles at concentrations from 18 to 35 w/v-% MABt; no precipitation of polymer at concentrations of ≧ 40 w/v-% MABt. The spherical particles at 20 w/v-% MABt had a diameter of 0.54 ± 0.31 μm for 3 kGy irradiation and 2.93±0.68 μm for 30 kGy. The number distribution of the microspheres shows that the spherical particles with small sizes formed at low irradiation dose (low conversion) disappears with increasing irradiation dose because of multi-coating by newly produced polymer.

Microscopic Processes in Microemulsion Polymerizations

ABSTRACTThe polymerization of acrylamide inside watcr-swollen micellas of Aerosol OT dispersed in toluene has been investigated. Incorporation of acrylamide enhances the interparticular attractive forces as shown by the intensity curves in small angle neutron scattering. It also induces sharp rises in conductivity which were attributed to a percolative process. The percolation threshold is lowered upon increasing the monomer content, reflecting the enhancement of the attractive interactions. In percolating systems, the structure affects the formation of polymer particles. Microscopy experiments show that particle nucleation occurs continuously throughout the polymerization.

Emulsifier‐free emulsion copolymerization of styrene and butyl acrylate. II. Kinetic studies in the presence of ionogenic comonomers

AbstractBatch emulsifier‐free copolymerizations of styrene (S) and butyl acrylate (BuA) have been performed for a S/BuA weight ratio = 50/50 in the presence of two types of functional comonomers [methacrylic acid (MAA) at different pHs] or potassium sulfopropylmethacrylate (SPM) and two initiators [potassium persulfate or 4–4′azobiscyanopentanoic acid (AZO)]. The use of AZO/MAA system results in the formation of polymer particles with only surface carboxylic end groups. The particle size of the final latexes can be adjusted with the MAA concentration, provided the polymerization is carried out at pH &gt; 6.5. However, the higher the MAA concentration, the sooner the polymerization levels off in conversion. With the K2S2O8/SPM system, particles bearing only sulfate and sulfonate groups are produced and the polymerization is complete. In that case, the particle size of the final latexes is smaller than with the previous system and 30% of the SPM is fixed on the particle surface, instead of 10% with MAA. Using SPM, a too high functional monomer concentration results in the latex destabilization caused by the formation of a large amount of polyelectrolytes. Kinetic studies indicate that most of the functional monomer is incorporated onto the particle surface during the last 30% conversion of the polymerization. A tentative explanation of such a behavior is discussed, based on the existence of two polymerization loci in the latex system.

Liposome-polymer systems. Introduction of liposomes into a polymer gel and preparation of the polymer gel inside a liposome

The evolution of liposomes after their introduction into a model polymer gel based on acrylamide is studied. Liposomes containing the polymerizable monomer in the internal aqueous phase are obtained. This monomer has been polymerized with formation of microsphere polymer particles coated with a phospholipid double layer. Both types of liposomal polymer preparations obtained can be useful for the creation of new systems of controlled drug release and new types of immunological aids.

Electron microscopic study of particles of polypropylene prepared on applied catalysts

1. Replication of the shape and morphological features of the structure of the carrier by the polymer particles formed takes place during polymerization of propylene in the presence of an applied catalyst based on a porous carrier with spherical particles of a globular structure. 2. The growth of the particles of the polymer and its structural elements (globular formations and pores) was followed in time. Based on the features studied, the scheme of the formation and growth of polymer particles was examined. The size of the particles of the polymer and its most characteristic structural elements was determined in the polymerization time interval studied.

On loci of acrylonitrile polymerization with bisulfite‐persulfate initiators under the conditions of low water/monomer ratio

AbstractIn the preparation of acrylonitrile–vinylacetate copolymer (93:7 in weight) by continuous polymerization in aqueous medium using the complete mixing type reactor, the author and co‐workers studied the effects of the water/monomer ratio on polymer properties and polymerization. They reported that the structure of a polymer particle becomes more compact with decreasing water/monomer ratio. This was noted in studying the physical properties of the polymer and the formation of polymer particles in this system. 1,2 Here the author has performed kinetic studies based on the results of polymerization to determine the loci of the polymerization in the range of water/monomer ratio roughly from 1.75 to 4.0. Most of the primary radicals from the initiators attack the monomers in the aqueous phase to form monomer radicals attached to initiator fragments, and most of the monomer radicals grow to form polymer radicals until termination occurs in the aqueous phase. Hence, the loci of polymerization in this system are not the surfaces and inner parts of the polymer particles, the diameters of which are roughly from 20 to 60 μm observed by a microscope, but the aqueous phase excluding these particles.

Polymerization of styrene miniemulsions

AbstractPolymerization of styrene miniemulsions, prepared using a mixed emulsifier system comprising sodium lauryl sulfate and cetyl alcohol, was carried out using both water‐soluble (potassium persulfate) and oil‐soluble [2,2′‐azobis‐(2‐methyl butyronitrile)] initiators. The effects of variation of initiator concentration, polymerization temperature, and added inhibitor on the kinetics and particle‐size distributions were investigated to obtain more quantitative evidence concerning the locus of polymerization in miniemulsion systems. Experimental results for the kinetics and particle‐size distributions clearly showed that monomer droplets became the main source of polymer particle formation. This was attributed to the fact that stable emulsions with droplet diameters in the range of 0.05 to 0.15 μm were produced using this mixed‐emulsifier system. In this size range, droplet initiation could effectively compete with other mechanisms due to their large surface area. Their size was indeed similar to the corresponding latex particle size obtained after polymerization.

Kinetics and mechanism of emulsifier‐free emulsion polymerization: Styrene/surface active ionic comonomer system

AbstractThe emulsifier‐free emulsion polymerizations of styrene in the presence of the surface active comonomer, undecylenic isethionate sodium salt (at concentration below its critical micelle concentration), and of the initiator, potassium persulfate, indicate that the number of polymer particles and the rate of polymerization at steady state is dependent on 1‐power of the comonomer concentration and 1/2‐power of the initiator concentration. This result suggests a homogeneous nucleation mechanism by which particles are formed from coiled‐up oligomeric radical chains originally dissolved in the aqueous phase. Size distribution of the particles is rather narrow and has a uniformity very close to one (ca. 1.02) after 30% conversion. Addition of salt such as sodium sulfate to increase the ionic strength in the aqueous phase results in a formation of micelles (which can grow to become polymer particles) in addition to the formation of polymer particles through the homogeneous nucleation mechanism. Variation of the ionic strength leads to a variation in the number of polymer particles due to a competition between these two nucleation mechanisms and gives a minimum of the number of polymer particles and a maximum of the average particle diameter.