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Particle growth in butadiene emulsion polymerization, 4. The promoting effect of mercaptans
Abstract
The observation that butadiene emulsion polymerizations in the presence of fatty acid emulsifiers need minimal amounts of tertiary or n-dodecanethiols to polymerize at a reasonable rate is often referred to as the promoting effect of mercaptans and is evaluated in this paper. Experimental evidence is presented which shows that fatty acid emulsifiers can actively reduce the average number of radicals per particle. In this paper it will be shown that three components are necessary for retardation of the rate of polymerization in the absence of dodecanethiol to occur: (1) Only diene monomer polymerizations show retardation. (2) Only peroxodisulfate-initiated polymerizations show retardation. (3) Retardation of the rate of polymerization only occurs in the presence of fatty acid emulsifiers. These three components are combined for the first time in a reaction scheme which is an extension of a reaction scheme proposed by Kolthoff in 1951. Experimental evidence justifies the suggestion that reaction between a fatty acid radical and butadiene play an important role in the promoting effect.
... Rubbers based on butadiene were also studied quite intensively from the late 1950s to the early 1990s in solution and in emulsions [35,[66][67][68][69][70][71][72]. ...
Ionizing radiation has become the most effective way to modify natural and synthetic polymers through crosslinking, degradation, and graft polymerization. This review will include an in-depth analysis of radiation chemistry mechanisms and the kinetics of the radiation-induced C-centered free radical, anion, and cation polymerization, and grafting. It also presents sections on radiation modifications of synthetic and natural polymers. For decades, low linear energy transfer (LLET) ionizing radiation, such as gamma rays, X-rays, and up to 10 MeV electron beams, has been the primary tool to produce many products through polymerization reactions. Photons and electrons interaction with polymers display various mechanisms. While the interactions of gamma ray and X-ray photons are mainly through the photoelectric effect, Compton scattering, and pair-production, the interactions of the high-energy electrons take place through coulombic interactions. Despite the type of radiation used on materials, photons or high energy electrons, in both cases ions and electrons are produced. The interactions between electrons and monomers takes place within less than a nanosecond. Depending on the dose rate (dose is defined as the absorbed radiation energy per unit mass), the kinetic chain length of the propagation can be controlled, hence allowing for some control over the degree of polymerization. When polymers are submitted to high-energy radiation in the bulk, contrasting behaviors are observed with a dominant effect of cross-linking or chain scission, depending on the chemical nature and physical characteristics of the material. Polymers in solution are subject to indirect effects resulting from the radiolysis of the medium. Likewise, for radiation-induced polymerization, depending on the dose rate, the free radicals generated on polymer chains can undergo various reactions, such as inter/intramolecular combination or inter/intramolecular disproportionation, b-scission. These reactions lead to structural or functional polymer modifications. In the presence of oxygen, playing on irradiation dose-rates, one can favor crosslinking reactions or promotes degradations through oxidations. The competition between the crosslinking reactions of C-centered free radicals and their reactions with oxygen is described through fundamental mechanism formalisms. The fundamentals of polymerization reactions are herein presented to meet industrial needs for various polymer materials produced or degraded by irradiation. Notably, the medical and industrial applications of polymers are endless and thus it is vital to investigate the effects of sterilization dose and dose rate on various polymers and copolymers with different molecular structures and morphologies. The presence or absence of various functional groups, degree of crystallinity, irradiation temperature, etc. all greatly affect the radiation chemistry of the irradiated polymers. Over the past decade, grafting new chemical functionalities on solid polymers by radiation-induced polymerization (also called RIG for Radiation-Induced Grafting) has been widely exploited to develop innovative materials in coherence with actual societal expectations. These novel materials respond not only to health emergencies but also to carbon-free energy needs (e.g., hydrogen fuel cells, piezoelectricity, etc.) and environmental concerns with the development of numerous specific adsorbents of chemical hazards and pollutants. The modification of polymers through RIG is durable as it covalently bonds the functional monomers. As radiation penetration depths can be varied, this technique can be used to modify polymer surface or bulk. The many parameters influencing RIG that control the yield of the grafting process are discussed in this review. These include monomer reactivity, irradiation dose, solvent, presence of inhibitor of homopolymerization, grafting temperature, etc. Today, the general knowledge of RIG can be applied to any solid polymer and may predict, to some extent, the grafting location. A special focus is on how ionizing radiation sources (ion and electron beams, UVs) may be chosen or mixed to combine both solid polymer nanostructuration and RIG. LLET ionizing radiation has also been extensively used to synthesize hydrogel and nanogel for drug delivery systems and other advanced applications. In particular, nanogels can either be produced by radiation-induced polymerization and simultaneous crosslinking of hydrophilic monomers in “nanocompartments”, i.e., within the aqueous phase of inverse micelles, or by intramolecular crosslinking of suitable water-soluble polymers. The radiolytically produced oxidizing species from water, •OH radicals, can easily abstract H-atoms from the backbone of the dissolved polymers (or can add to the unsaturated bonds) leading to the formation of C-centered radicals. These C-centered free radicals can undergo two main competitive reactions; intramolecular and intermolecular crosslinking. When produced by electron beam irradiation, higher temperatures, dose rates within the pulse, and pulse repetition rates favour intramolecular crosslinking over intermolecular crosslinking, thus enabling a better control of particle size and size distribution. For other water-soluble biopolymers such as polysaccharides, proteins, DNA and RNA, the abstraction of H atoms or the addition to the unsaturation by •OH can lead to the direct scission of the backbone, double, or single strand breaks of these polymers.
... Verdurmen et al. investigated some fundamental issues on the kinetics and mechanism of Bu emulsion polymerization [11][12][13]. The value of propagating rate constant, the reason for apparent independency of rate of polymerization per particle on the concentration of persulfate, and the effect of tert-dodecylmercaptane (TDM) as a chain transfer agent on the kinetics of Bu emulsion polymerization, were three matters discussed in their research reports [12][13][14]. The free-emulsifier emulsion polymerization of Bu was led to the synthesis of some completely stable colloidal latexes with high solid content (up to 60%) and small particle diameter (below 300 nm). ...
Emulsion polymerization of the butadiene (Bu) was performed in the presence of disproportionate potassium rosinate (DPR) as anionic emulsifier, potassium hydroxide (KOH), and potassium carbonate (K2CO3) as electrolytes, and three different initiators including potassium persulfate (KPS), 2,2′-azobisisobutyronitrile (AIBN) or 4,4′-azobis(4-cyanovaleric acid) (ACVA, also known as VAZO) at 70 °C. Latexes were prepared with a solid content of about 30 wt%. The particle size and its distribution were measured by dynamic light scattering (DLS) analysis, while the polymerization conversion was determined gravimetrically at different time intervals. Results on the emulsion polymerization of Bu in the presence of KOH and K2CO3 co-electrolytes showed that adding KOH to the reaction media decreases the polymerization rate. Positive effect of co-electrolytes on the control over polybutadiene latex (PBL) particles size and its distribution was also confirmed, where K2CO3 played roles as electrolyte and pH buffer and KOH served double roles as electrolyte and alkaline supplier of the reaction media. Complete solubility of the AIBN in Bu resulted in higher rate of polymerization in the presence of AIBN in comparison to other initiators, i.e., VAZO or KPS. The results showed that initiator type plays a significant role on the formation of PBL nanoparticles and kinetics of the polymerization. The kinetic studies revealed that emulsion polymerization of Bu follows case 1 (i.e., \(\bar{n}\) ≪0.5, where \(\bar{n}\) indicates average number of the propagating chains per particle) of the Smith-Ewart kinetics.
... For increasing the final conversion in emulsion polymerization of isoprene, Cheong et al. added t-DM to the reaction mixture [9]. It is believed that mercaptan enhances entry efficiency in particles through chain transfer from a sulfate (when a persulfate is used as initiator) or oligomeric isoprene radical to the thiol, which may enter micelles/particles directly and/or form an entering species after fewer propagation steps in comparison with those required for oligomeric isoprene radicals [15]. In our case, in spite of using t-DM, final conversion after 24 h reaction was about 35%. ...
Batch polymerization of isoprene was carried out at 25∘C in a normal microemulsion stabilized with sodium dodecyl sulfate and initiated with the redox couple tert-butyl hydroperoxide/tetraethylene-pentamine. Characterization by transmission electronic microscopy showed that polyisoprene nanoparticles with number-average diameter close to 20 nm were obtained. The low molecular weights obtained, as determined by gel permeation chromatography, were probably due to chain scission as inferred from the oxidative ambient at which polymerization was carried out. Microstructure calculated from infrared spectroscopy data indicates that the obtained polyisoprene contains around 80% total 1,4 units, which is in accordance with its glass transition temperature (-60.8∘C) determined by differential scanning calorimetry.
Continuous conductivity measurements were performed during the batch emulsion polymerization of butadiene along with kinetic and particle size measurements. The critical monomer conversion was obtained around 55% and the rate of polymerization was correlated to the surfactant concentration with an exponent of 0.35 which was not in agreement with the exponent offered by Smith and Ewart. In addition, the evolution of some particle-related quantities such as particle size and number of particles during the three intervals of the emulsion polymerization and their agreements with Smith-Ewart mechanism were investigated. The behavior of conductivity in the emulsion polymerization of butadiene normally containing a buffering agent was found to be completely different from the unbuffered one. Comparison of the conductivity profiles with the kinetic and particle-related quantities represented that the conductivity of the reaction mixture is very sensitive to the changes in the particle size so that any small change in the forms of nucleation, growth, and coagulation is clearly observed in the conductivity profiles. Furthermore, the conductimetric data are capable of determining some important points during the polymerization such as the beginning of the reaction that can be important from the industrial process control point of view. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45262.
This paper presents a mechanistic model for the production of nitrile-butadiene rubber (NBR). The mathematical dynamic model was developed in order to simulate the industrial production of NBR via emulsion copolymerization of acrylonitrile (AN) and butadiene (Bd) in batch, continuous and trains of continuous reactors. For this reason, the model was constructed in a parsimonious manner to avoid complex and time-consuming computations that typically result when modeling details of specific aspects of micro/macro scale emulsion polymerization phenomena (i.e., full molecular weight and particle size distributions, detailed species phase-partitioning, etc.). Thus, the model provides average properties for typical emulsion characteristics, such as monomer conversion, copolymer composition, number- and weight-average molecular weights, tri- and tetra-functional branching frequencies, and the number and average size of polymer latex particles. The proposed model is an extension of a previous model developed by our group, and allows for the dynamic modeling of different reactor types and configurations. Model comparisons are made between limited literature data for batch operation, while representative simulation profiles are shown for a reactor train.
A mathematical model was developed to simulate the emulsion copolymerization of acrylonitrile/butadiene, otherwise known as nitrile rubber. Our goal was to develop a practical tool to predict polymer production rate and product quality on an industrial scale. Model predictions include the polymerization rate, the polymer composition, the number- and weight-average molecular weights, branching averages, and the number and average size of the polymer latex particles. The prediction of conversion was compared to a limited amount of industrial pilot-plant data and was found to be adequate. The model is currently being applied in two ways. The first application involves the testing of nonlinear model-based control schemes for an industrial nitrile rubber reactor. The second application involves using the model as a storehouse of prior knowledge for the implementation of a Bayesian sequential design of emulsion terpolymerization experiments as part of a larger, systematic study of multicomponent polymerization kinetics.
Hybrid thin films containing palladium nanoparticles in different concentrations (0.5% and 1%) with and without nanoparticle stabiliser agent [mercaptopropyl trimethoxysilane, MPTMS] were prepared using a sol–gel process. Pd nanoparticles were found to be highly dispersed on the thin films with particles ranging from 7 to 10 nm. The catalytic properties of the thin films supported Pd nanoparticles were investigated in the Heck reaction of iodobenzene and methyl acrylate. Films containing Pd MNP (with and without MPTMS) gave quantitative conversion and complete selectivity to the targeted product (methyl cinnamate) in a short time of reaction (<15 min) under microwave irradiation. While Pd containing films without MPTMS were highly active and reusable after 3 runs, MPTMS containing films were found to be inactive after the first use. Such phenomenon was correlated to the steric hindrance round the Pd MNP due to the adsorption of species on the surface that render the catalysts inactive.
Seeded and ab initio emulsion polymns. of isoprene using redox initiation systems were investigated and suitable reaction conditions detd. to prep. polyisoprene latexes with minimal crosslinking. Polymns. initiated with the potassium persulfate/sodium bisulfite (KPS/SBS) redox couple had a significant inhibition period and low yield. Polymns. initiated with the tert-Bu hydroperoxide/tetraethylenepentamine redox couple showed reasonable yields and no apparent inhibition. It is postulated that the lipophilic nature of the t-Bu group plays a favorable role in the entry of hydroperoxide-initiated oligomeric radicals, while persulfate-initiated radicals are more likely to undergo aq. phase termination before entry. The crosslinking reaction by benzoyl peroxide (BPO) at 70 °C was investigated using this lightly crosslinked polyisoprene latex. 1H NMR and gel permeation chromatog. results were consistent with a reaction mechanism in which the radicals formed by the decompn. of BPO react exclusively with polyisoprene to abstr. a hydrogen atom, and the resulting radicals react by termination to form crosslinks. No loss of double bonds was found, suggesting that radical formation is overwhelmingly achieved by hydrogen abstraction and crosslinking occurs by termination between two radicals. Crosslinking was accompanied by chain scission, which was obsd. only at the beginning of the reaction. At low wt.-fractions of polymer, the rate of crosslinking was dependent on the concns. of BPO and abstractable hydrogens in a manner consistent with the postulated mechanism. [on SciFinder(R)]
This bibliography-base review paper discusses the course and mechanism of emulsion polymerization which involves three phases. In the first phase the particle formation takes place; the end of this phase is not dependent upon the degree of conversion, but on the total amount of polymer formed. With usual recipes, it ends at about 1-5% conversion. Phase II lasts from the end of Phase I until monomer disappears as a separate phase. In this interval, the particle number is usually found to be constant, the particle volume increases proportional to conversion, the monomer concentration in the particles is approximately constant, and therfore the termination is also constant within the particles. Phase III starts when the monomer disappears as a separate phase. The transition from Phase II to III is determined by the degree of conversion and differs for different monomers. All three phases are discussed in theoretical terms with the use of mathematical techniques. The other topics reviewed include - seed polymerization mechanism; the core-and-shell theory; and emulsification of monomer - initiation in monomer droplets. Mathematical equations derived are additionally included in four appendixes.
The emulsion polymerization of vinyl acetate was carried out at 50°C using sodium lauryl sulfate as an emulsifier and potassium persulfate as an initiator, and the role of the polymer particles produced in this system was studied on the basis of a previous theory. The low value of the average number of radicals per particle obtained in this work, i.e. in the range 0.01 - 0.5, is explained by introducing a mechanism of a rapid escape of monomeric radicals produced by the chain-transfer reaction which occurs dominantly in the polymer particles. Semiempirical equations are proposed for the estimation for the average number of radicals per particle over the whole range of monomer conversion.
The rate of emulsion copolymerization of butadiene and styrene, with soap as emulsifier and potassium persulfate as catalyst, is extremely small at 50°C. The presence of very small amounts of high-molecular mercaptans promotes the copolymerization reaction. The promoting effect is at a maximum for primary, secondary, and tertiary dodecyl mercaptans and decreases for mercaptans of either higher or lower molecular weight. The promoting effect is independent within wide limits of the amount of mercaptan added after the minimum quantity has been exceeded. Mercaptans which are poor promoters may be so because they fail to bring about chain initiation or because they aid in chain termination. The low-molecular mercaptans which are poor promoters prevent the high-molecular mercaptans from exerting their good promoting effect when a mixture of both types of mercaptans is used. The mechanism of the promoting effect of mercaptans upon the emulsion copolymerization of butadiene (75 parts) and styrene (25 parts) or upon the polymerization of butadiene alone is not yet clear.
The kinetics of the emulsifier free seeded polymerization of butadiene at 60-degrees-C in Smith-Ewart interval Ill was investigated using sodium peroxodisulfate as initiator. The aim of this work was to measure the propagation rate coefficient (k(p)) of butadiene at 60-degrees-C in emulsion polymerization. Model-independent techniques to measure propagation rate coefficients like spatially intermitted polymerizations1-3 (''rotating sector'' and ''laser flash'' photolysis) have not been used for butadiene so far since network formation prevents acquiring the necessary data from GPC. All experiments were conducted in the presence of tert-dodecylmercaptan, as is usual in industrial practice. The fractional conversion was based on gravimetrically calibrated on-line densitometry and was found to be highly accurate. By analogy with the well-known Ugelstad plots, the product of the propagation rate coefficient (k(p)) and the average number of radicals per particle (nBAR) versus seed latex particle diameter clearly shows Smith-Ewart caseI and case II regimes. From a constancy in values of k(p)nBAR (case II regime) in this plot, a value for k(p) could be calculated that was 3 times larger than the current literature value. It was found that negligible ''thermal background initiation'' is present in the butadiene system. Two linear regions in polymerization rate are observed in interval III. Model calculations are presented in excellent agreement with the experimental data. From these calculations a value of the rate coefficient for transfer to monomer, k(tr) could be estimated.
A model, together with a comparison with previously published experimental data, is presented for initiator efficiency in seeded styrene emulsion polymerization systems in the absence of secondary particle formation. The data had shown that a number of previous models are inapplicable, viz., those assuming that the rate-determining step for free-radical entry into a particle is either diffusional capture, surfactant displacement, or colloidal entry. The data support the supposition that the rate-determining step for free-radical capture by latex particles is aqueous-phase propagation to a critical degree of polymerization, whereupon capture (irreversible adsorption) of the resulting oligomeric free radical by a particle is essentially instantaneous. Mutual aqueous-phase termination of smaller species also occurs. When account is taken of the fact that the rate coefficients for (a) the first aqueous-phase propagation step and (b) aqueous-phase termination are both in the diffusion limit, this model is in qualitative accord with the experimental dependences of the entry rate coefficient on the concentrations of initiator, of surfactant, of aqueous-phase monomer, and of latex particles as well as on particle size and on ionic strength. For styrene emulsion polymerization initiated by persulfate, the critical oligomer size for entry was found to be dimeric.
Mercaptans containing 8 to 12 carbon atoms solubilized in solutions of saturated fatty acid soaps are oxidized by persulfate to disulfide. Evidence is given that the first step in the persulfate oxidation of solubilized mercaptans is a reaction of persulfate with the soap forming carboxylate free radicals which oxidize the solubilized mercaptan to mercaptyl free radicals which combine to form disulfide. In the absence of mercaptan persulfate reacts with saturated fatty acid soaps removing the carboxylate group. The disappearance of persulfate in soap solutions is first order and the reaction rate is the same in the presence as in the absence of mercaptan and is independent of the soap concentration over a wide range of concentrations. The oxidation of solubilized normal mercaptans by persulfate is zero order with regard to mercaptan concentration over a wide range of concentrations. Solubilized n-octyl and n-dodecyl mercaptans are oxidized by persulfate at the same rate.
Evidence is given that potassium persulfate decomposes thermally in aqueous solutions by two reactions, (a) a symmetrical rupture of the O-O bond to form two sulfate free-radicals which disappear by reaction with water to liberate oxygen, and (b) an acid-catalyzed reaction involving the unsymmetrical rupture of the O-O bond of the HS2O3- ion to form sulfur tetroxide and bisulfate. In dilute acid solutions sulfur tetroxide decomposes rapidly to form oxygen and sulfuric acid while in solutions 2 to 5 M in perchloric or sulfuric acid sulfur tetroxide hydrolyzes rapidly to Caro's acid (H2SO5). The kinetics of the thermal decomposition of the persulfate ion are described by the equation -dS2O3-/dt = k1[S2O8-] + k2[H+][S2O8-]. The values of k1 and k2, respectively, are 6.0× 10-5 min.-1 and 3.5× 10-3 (min.-1)(m./l.)-1 at an ionic strength of 0.4 at 50°. The activation energy for the uncatalyzed reaction is 33.5 kcal, and for the acid-catalyzed reaction 26.0 kcal. The rate of the uncatalyzed reaction is independent of ionic strength but the rate of the acid-catalyzed reaction decreases with increasing ionic strength. The oxygen liberated by the uncatalyzed reaction comes from the water while the oxygen liberated by the acid-catalyzed reaction comes from the persulfate ion.
Latices produced by the polymerization of vinyl acetate in water have been examined by means of electron-microscopic observations. Particles produced in the absence of surfactants are large, of the order 0.1-1.0 micron in diameter The size distribution of these particles is quite narrow. A mechanism for particle-size development by interparticle combination during polymerization has been proposed, based on measurements of relative size and size distribution. Factors influencing particle size and growth have been investigated. Conclusions pertaining to the stabilization of latices of the vinyl acetate type are presented based on these data. Less detailed examination of the latices from other slightly water-soluble monomers polymerized in "self-stabilized" systems indicates that the mechanism given for growth of particles of vinyl acetate latices is general.
With the use of persulfate containing radioactive sulfur it is shown that the termination reaction of the polymerization of styrene is a coupling of the free radical chains. In the presence of m-dinitrobenzene as a retarder evidence has been presented that the termination reaction is a disproportionation and not a combination of two free radical chains. Mercaptan in the emulsion polymerization of styrene acts solely as a chain transfer agent. Any chemical reaction between persulfate and mercaptan does not contribute to the initiation. In the presence of detergent the rate of initiation of the polymerization of styrene is equal to the rate of thermal dissociation of persulfate:
Thus, any reaction between persulfate with monomer and detergent does not contribute to the initiation. The much smaller rate of initiation in the absence of detergent is attributed to the slight solubility of styrene, the concentration of the monomer being so small that it cannot capture all the free radicals. The effect of the detergent is a physical one, by its solubilizing action it increases the solubility of the monomer in the water layer to such an extent that the “activator” now becomes 100% efficient.
The kinetics of continuous emulsion polymerization of styrene were studied theoretically on the basis of the authors' batch reaction model, and a new reaction model was proposed for continuous operation. The validity of the model was tested by experiments conducted with stirred tank reactors in series. The characteristics of the first reactor used to generate polymer particles were studied in particular detail. It was found that there was an optimum residence time for the first reactor, the value of which was quantitatively predictable from the operating variables. The most suitable combinations of several types of reactors for continuous emulsion polymerization are also discussed.
The kinetis of the emulsion polymerization of butadiene at 60°C in Smith-Ewart interval III were investigated using peroxodisulfate as initiator. The aim of this work was to obtain insight in the radical adsorption and desorption rate coefficients through monitoring non-steady state kinetics. The acquired data shows an initiator concentration dependence of the desorption rate coefficients. This dependence explains the independences of the rate of butadiene emulsion polymerization of the peroxodisulfate concentration in the presence of tertiary dodecylthiols.
The role of thiols of low water solubility, commonly used in the emulsion polymerization of butadiene, has been considered. The following effects have become apparent: (1) dodecanethiols act as efficient chain transfer agents in limiting the formation of heavily cross-linked polymer networks; (2) the monomer concentration within the particles is not influenced by such thiols; (3) C12-thiol radicals do not desorb because of their extremely low water solubility. The ‘promoting effect’ of thiols in emulsion polymerizations of diene-hydrocarbons is still poorly understood, but it appears to be related to impurities present in the emulsifier, as it was found completely absent in emulsifier-free polymerizations.
The kinetics of the seeded emulsion polymerization of butadiene in combination with variable Fremy salt (potassium nitrosodisulfonate) concentrations was investigated in order to monitor non-steady state kinetics necessary for obtaining information on entry and exit of radicals from latex particles. Fremy salt is used because it is an entirely water-soluble stable radical that in principle can scavenge water-soluble radicals produced by a water-soluble initiator like peroxodisulfate, but allegedly will not interfere with radicals within latex particles. Adequate buffering of the pH is a prerequisite for stable Fremy salt concentrations in time. Emulsion polymerizations in the presence of Fremy salt showed that not all radicals in the aqueous phase of a swollen polybutadiene latex are scavenged. The use of Fremy salt to monitor non-steady state kinetics in the seeded emulsion polymerization of butadiene in the presence of tertiary dodecyl mercaptan yields no satisfying results. The use of Fremy salt seems to be restricted to systems where the rate of polymerization is strongly influenced by variation in initiator concentration, i.e. the styrene system or the butadiene system in the absence of tertiary dodecyl mercaptan.
The kinetics of the emulsion polymerization of butadiene was investigated using Dresinate 214 as emulsifier and three dissociative initiators, viz. potassium peroxodisulfate, 4,4′-azobis-(4-cyanopentanoic acid) and 2,2′-azoisobutyronitrile. All experiments were conducted in the presence of a thiol as chain transfer agent, as usual in diene-polymerizations. The polymerization rate in interval II, Rpol, was found to be highly insensitive to changes in the initiator concentration (Rpol ∝ [I]0,08). Primary radicals are generated in large abundance in interval I as compared with the final particle number, indicating that the initiator efficiency with regard to particle nucleation is very low. The development of particle number as a function of conversion at several emulsifier concentrations shows that limited coagulation is occurring in the present system. Rpol depends on the emulsifier concentration with an exponent of 0,61, while the final particle number after cessation of coagulation depends on the emulsifier concentration to the 1,6th power. As a consequence the average number of radicals per particle must be a function of particle size, because the monomer concentration in the latex particles is approximately constant in interval II. A certain analogy in behaviour between the emulsion polymerization of various polar monomers, kinetically dominated by radical desorption, and the emulsion polymerization of butadiene, suggests that similar events determine the kinetic course in the present system.
Thesis (Ph. D.)--Technische Universiteit Eindhoven, The Netherlands, 1990. Includes bibliographical references.
Thesis (doctoral)--Technische Universiteit Eindhoven, 1993.
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