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Effect of Carboxylic Acid Monomer Type on Particle Nucleation and Growth in Emulsifier-free Emulsion Copolymerization of Styrene-Carboxylic Acid Monomer
Abstract and Figures
Carboxylated polystyrene latexes were prepared by emulsifier-free emulsion copolymerization of styrene with various carboxylic acid monomers (AA, MAA and IA). DLS analysis and SEM observations were used to investigate the effect of various carboxylic acid monomers on the particle formation and growth processes. It was found that number of particles per unit volume of aqueous phase (Np) increases with increasing hydrophobicity of carboxylic acid monomers in order of IA < AA < MAA. There was significant difference in polymerization rate per particle (Rp/Np) in all the experiments also. The results revealed that both particle nucleation and growth processes are dependent on the hydrophilic nature of carboxylic acid monomers. SEM studies showed that Np is almost constant in the particle growth stage (conversion above 10%). Through some calculations by data obtained from DLS technique, average diameter of monomer swollen polymer particles (dpswol) of all the carboxylated polystyrene latexes at the same conversion of 0.4 was obtained to be 325.24, 199.30 and 661.02 nm for AA, MAA and IA respectively. Attempt was made to calculate the average number of propagating radicals per particle and to determine its relevance to the kinetics of particle growth by various carboxylic acid monomers.Keywords: Carboxylated Polystyrene Latex, Emulsifier-free Emulsion Polymerization, Particle Nucleation and Growth, Dynamic Light Scattering
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... This has been remarkably successful commercially in many applications including coatings, adhesives and in encapsulation technology [2][3][4]. Although, the nucleation period is typically very short, the formation of particle nuclei throughout the initial stage of the polymerisation plays a fundamental role in determining the final latex particle size and particle size distribution [5][6][7][8][9][10][11][12]. Three major mechanisms for particle nucleation in emulsion polymerization have been proposed to date: Micellar Nucleation Theory, originally proposed by Harkins [5,6,[13][14][15] in 1947 Smith [6,8] and Ewart [10,11,14] and modified by Gardon [5,7,8,[10][11][12]16], states that micelles are the principal loci of particle formation is usually understood to be the main nucleation mechanism for the monomers with relatively low water solubility ([M] aq < 15 mmol dm −3 ) [5][6][7][8]10,[13][14][15][17][18][19]. ...
... Although, the nucleation period is typically very short, the formation of particle nuclei throughout the initial stage of the polymerisation plays a fundamental role in determining the final latex particle size and particle size distribution [5][6][7][8][9][10][11][12]. Three major mechanisms for particle nucleation in emulsion polymerization have been proposed to date: Micellar Nucleation Theory, originally proposed by Harkins [5,6,[13][14][15] in 1947 Smith [6,8] and Ewart [10,11,14] and modified by Gardon [5,7,8,[10][11][12]16], states that micelles are the principal loci of particle formation is usually understood to be the main nucleation mechanism for the monomers with relatively low water solubility ([M] aq < 15 mmol dm −3 ) [5][6][7][8]10,[13][14][15][17][18][19]. Homogeneous nucleation models, proposed by Fitch [13][14][15] and Tsai [5,8,15], Priest [5,8,10,[12][13][14][15] and Roe [8][9][10][11][13][14][15], is considered the primary mechanism for formation of particles in systems with surfactant concertation below the critical micelle concentration CMC, surfactant free polymerisation and formation for the monomers with relatively high water solubility's ([M] aq > 170 mmol dm −3 ) [5][6][7][8][10][11][12][13][14][15][16][17][19][20][21][22]. ...
... Although, the nucleation period is typically very short, the formation of particle nuclei throughout the initial stage of the polymerisation plays a fundamental role in determining the final latex particle size and particle size distribution [5][6][7][8][9][10][11][12]. Three major mechanisms for particle nucleation in emulsion polymerization have been proposed to date: Micellar Nucleation Theory, originally proposed by Harkins [5,6,[13][14][15] in 1947 Smith [6,8] and Ewart [10,11,14] and modified by Gardon [5,7,8,[10][11][12]16], states that micelles are the principal loci of particle formation is usually understood to be the main nucleation mechanism for the monomers with relatively low water solubility ([M] aq < 15 mmol dm −3 ) [5][6][7][8]10,[13][14][15][17][18][19]. Homogeneous nucleation models, proposed by Fitch [13][14][15] and Tsai [5,8,15], Priest [5,8,10,[12][13][14][15] and Roe [8][9][10][11][13][14][15], is considered the primary mechanism for formation of particles in systems with surfactant concertation below the critical micelle concentration CMC, surfactant free polymerisation and formation for the monomers with relatively high water solubility's ([M] aq > 170 mmol dm −3 ) [5][6][7][8][10][11][12][13][14][15][16][17][19][20][21][22]. ...
Statistical copolymers of methacrylic acid and methyl methacrylate were synthesised via free radical catalytic chain transfer polymerisation (CCTP) in emulsion to form a hydrophilic emulsifier/surfactant. The vinyl-terminated oligomers were in turn utilised as chain transfer agents, with no further purification, for the formation of diblock copolymers with butyl and methyl methacrylate which constitutes the emulsifier via sulfur-free reversible addition–fragmentation chain transfer polymerisation (SF-RAFT). In turn these polymers were solubilized with various concentrations of ammonium hydroxide and utilised in the surfactant-free emulsion polymerization of butyl methacrylate using persulfate initiators, which also stabilized the polymer particles with observed no coagulation, with solid contents as high as 40%.
... However, many industrial processes usually use one or more functional monomers with significant water solubilities such as acrylic acid and methacrylic acid. [1,2] These products are called carboxylated latexes, in which carboxylic groups are distributed between aqueous phase, buried inside the polymer particles, or located on the surface of the particles. [3] The most industrially-important rubber latexes of this type are the carboxylated styrene-butadiene rubber latexes. ...
... So it is expected that the type and amount of soluble acidic monomer in continuous phase have an important role in nucleation rate. [1] It is also well known that the type and amount of acidic monomer have a great impact on the stability of carboxylated latexes. [5,[16][17][18] The rate of homogeneous nucleation increases with increasing the amount of acidic monomer and this leads to an increase in the number of particles and polymerization rate. ...
Emulsion polymerization of acrylonitrile-butadiene-carboxylic acid monomers (XNBR latexes) in the absence of emulsifier is associated with thermodynamic and kinetic complexities and is very sensitive to colloidal stability. In this paper, polymerization pressure profiles were utilized for kinetic studies of emulsifier-free emulsion terpolymerization of acrylonitrile, butadiene and two carboxylic acid monomers (i.e., acrylic acid and methacrylic acid). It was found that the type and amount of acidic monomer have a great impact on the nucleation rate as well as particle size distribution and carboxyl group distribution of XNBR latexes. Also, the type of the acidic monomer affects the rates of entry and exit of radicals to and from particles and consequently the average number of radicals per particle, where a higher rate of polymerization was observed for methacrylic acid latexes. The reaction temperature has profound effects on polymerization rate, particle size distribution and colloidal stability of the latex. Partitioning of pressure profiles into four distinct regions in accordance with well-established intervals of Harkins model and analyzing particle size distribution and carboxyl group distribution, established a conceptual framework for kinetic studies in emulsion polymerization of XNBR latexes.
... Therefore, understanding the mechanism of particle formation, the underlying nucleation mechanisms as well as the improvements to and refinements of the synthesis methods have been of increasing interest in achieving better control on the properties of emulsion polymers. 34 In the last two decades, most of literature has dealt with the effect of the type or amount of raw materials, including monomers, [35][36][37][38] surfactants, [39][40][41][42][43][44] and initiators 42-44 on the particle nucleation mechanisms and growth processes. ...
The properties of acrylic-styrene latex (ASL) were investigated using two different nucleation methods by changing the sequence of addition of components, without changing the overall composition of the systems. In the first method, the semi-batch method was used and in the second method, the seeded semi-batch method was used and these were named ASL-1 and ASL-2, respectively. The latexes were characterized by dynamic light scattering, differential scanning calorimetry, tensiometer, gel permeation chromatography, viscometer, scanning electron microscopy, and transmission electron microscopy. The results showed that despite having the constant compositions, the two latexes have significant differences in different parameters studied. Sample ASL-1 showed higher zeta potential, glass transition temperature, surface tension, number average molecular weight and viscosity compared to sample ASL-2, but showed lower particle size. The two synthesized ASLs were also evaluated for their potential for pigment wetting and dispersion, as measured by the color development, by incorporation of three pigment pastes (red, green and blue). The study showed interesting findings that for each color pigment paste, ASL-1 produced deeper color tone than ASL-2. Also, color differences (L, a, b scale), contrast ratios, and gloss of ASL-1 and ASL-2 latexes-based pigment pastes were compared.
... There are three different types of acceptors used: 2cyano acrylonitrile (2CA), cyano acrylic acid (CAA) and 2carboxy acrylic acid (2CAA). N.dimethylphenylendiamino (NDPD) is widely used in hole transport materials due to its donor unit status as an electron donor and charge transfer medium [13][14][15]. ...
The molecular structures and optical properties of six different N.dimethylphenylendiamino dyes were analyzed using a combination of DFT functionals (B3LYP and Cam-B3LYP/6-311+G(p,d)). The six dyes are D1-D6. The various parameters of the solvated phase, such as the polarizabilities, hyperpolarizabilities, peak absorption wavelengths, and HOMO-LUMO energy gaps, were calculated and analyzed. The results of the study are in agreement with the results of the NLO activity order thiophene linker > pyrrole bridge. Compared to the dipyrrole versions, the designed dithiophene-linker dyes exhibit longer absorption wavelengths and smaller HOMO-LUMO gaps. The predicted first hyperpolarisability of dyes D1-D3 are higher than that of D4-D5. This is mainly due to its enhanced electron-withdraw ability and the long p-conjugating action of the thiophene moiety. Highly elevated total hyperpolarisability of the designed dyes, suggests its potential application in organic NLO devices, which is expected to be useful.
... Although there have been a large number of studies examining the preparation of monodisperse polymer microspheres by SFEP, some aspects are not fully understood, including how to control the size of the polymer microspheres, the preparation of small particle size monodisperse functional microspheres, and the role of comonomers in the polymerization process. Therefore, further experimental exploration is still urgently needed [12][13][14][15][16]. ...
Monodisperse polystyrene microspheres with different functional groups have important applications in both the medical and analytical fields. In this study, we prepared monodisperse microspheres with sulfonic acid or carboxyl groups using soap-free emulsion polymerization (SFEP) with potassium persulfate as the initiator. A series of monodisperse polystyrene microspheres with sizes between 100 and 500 nm were successfully prepared by copolymerizing different types of ionic monomers at different concentrations. The microspheres were characterized by using dynamic light scattering (DLS), Zeta potential measurements (ZP), FT-IR spectroscopy, and transmission electron microscopy (TEM). The mechanism of the particle nucleation and growth were studied by combining the changes in particle size and the number of particles. The results showed that the addition of hydrophilic comonomers like sodium p-styrene sulfonate, acrylic acid, and methacrylic acid significantly improved the stability of the polystyrene microspheres and promoted particle nucleation, resulting in less particle aggregation and microspheres with smaller sizes.
Graphical abstract
The leakage of surfactant from waterborne coatings is a matter of concern. Therefore, there is a strong interest in developing surfactant-free polymer dispersion as binders for waterborne coatings. This will accelerate the substitution of solventborne binders by the more environmentally friendly waterborne latexes. However, as the performance of the coating depends on the interaction of the latex with pigments and fillers and this interaction is controlled by the composition of the surface of the polymer particles, it is an open question if the surfactant-free latexes are adequate for coating applications. In this work, surfactant-free latexes synthesized under industrial-like conditions using sodium styrene sulfonate (NaSS) to provide stability to the latex were used to formulate exterior paints and their performance compared with that of a commercial latex binder. It was found that for most of the application properties, the paints based on the NaSS binders present improvements with respect to the surfactant stabilized commercial binder.
RESUMO Monômeros carboxílicos são frequentemente empregados em formulações de polímeros obtidos via polimerização em emulsão e miniemulsão visando melhorar ás propriedades de aplicação dos látexes. O objetivo deste trabalho foi avaliar o efeito dos ácidos itacônico IAI), fumárico (AF) e metacrílico (AMA) na copolimerização em emulsão do estireno (STy) com o acrilato de n-butila (ABu), visando a obtenção de látexes carboxilados estáveis e com baixa concentração de poli(ácido carboxílico) na fase aquosa para serem empregados como aditivo na preparação de argamassa cimentícia. Látexes de STy/ABu/AI, STy/ABu/AF e STy/ABu/AMA foram obtidos e caracterizados em relação ao teor de sólidos, diâmetro de partícula, polidispersão, viscosidade, temperatura mínima de formação de filme (TMFF), estabilidade ao gelo-degelo, estabilidade coloidal e distribuição dos grupos carboxílicos. Argamassas cimentícias foram preparadas empregando os látexes produzidos. Os resultados obtidos mostram que o tipo de ácido carboxílico empregado afeta as propriedades físico-químicas dos látexes e a interação com os componentes da argamassa. Dentre os ácidos estudados, o AMA apresentou menor efeito nas propriedades coloidais dos látexes, enquanto que o látex produzido com o AF apresentou baixa estabilidade coloidal, elevada concentração de grupos carboxílicos na fase aquosa e baixa interação com os componentes da argamassa.
We present a systematic study of incorporating carboxyl groups into latex particles to enhance colloidal stability and the physical properties of the latex. Statistical copolymers of methacrylic acid and methyl methacrylate) were synthesized via catalytic chain transfer polymerization (CCTP) in emulsion. The vinyl‐terminated oligomers were in turn successfully utilized as chain transfer agents for the formation of diblock and pseudo triblock copolymers via sulfur‐free reversible addition–fragmentation chain transfer polymerization (SF‐RAFT). These copolymers were characterized using 1H NMR, size exclusion chromatography (SEC), dynamic light scattering (DLS), dynamic mechanical analysis (DMA), contact angle measurements and matrix‐assisted laser desorption/ionization time of flight mass spectroscopy (MALDI‐TOF‐MS) techniques. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 We present a systematic study of incorporating carboxyl groups into latex particles in order to enhance colloidal stability and the physical properties of the latex. Statistical copolymers of methacrylic acid and methyl methacrylate) were synthesised via catalytic chain transfer polymerisation (CCTP) in emulsion. The vinyl‐terminated oligomers were in turn successfully utilised as chain transfer agents for the formation of diblock and pseudo triblock copolymers via sulfur‐free reversible addition‐fragmentation chain transfer polymerisation (SF‐RAFT).
An end-chain extension model for number density of polymer particles is derived in this work. This model shows that the logarithmic value of the number density of polymer particles is proportional to the concentration of acrylic acid in aqueous solution in emulsifier-free emulsion copolymerization of styrene and acrylic acid. The end chains on polymer particles are composed of acrylic acid segments from nucleating oligomers and radicals absorbed by polymer particles. The end chains of hydrophilic segments extend into aqueous solution with surface charge at their terminals. This effect lowers the capture radical ability of polymer particles and increases the number density of polymer particles. The experimental results confirm the extension model with the content of acrylic acid ranging from 1.156 to 5.064 g l−1 at 80°C.
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 radical polymerizations of acrylamide and methacrylamide and of acrylic, methacrylic and fluoroacrylic acids have been studied in various solvents. The nature of the solvent affects the overall rate due to changes in kp and Ep. It has been shown that the effect of solvent also depends on the nature of the monomer. A possible explanation of the observed behaviour is discussed.
Soap-free carboxylated polystyrene latexes have been prepared by copolymerizing acrylic acid (AA) in a wide range of degree of neutralization using a slight amount of soap, and the particle formation process was investigated from the number and uniformity of particles. It was found that the degree of neutralization of AA as well as the amount of AA have a great effect on the formation of particles. On the basis of the calculation results of the composition of the growing radical formed in the aqueous phase at the initial stage of the polymerization, the results can reasonable be explained by a change in the hydrophilic nature of growing radicals formed in the aqueous phase at the initial stage of the polymerization, the results can reasonably be explained by a change in the hydrophilic nature of growing radicals which are formed in the aqueous phase and precipitate out to form particles. It was also established that the introduction of α-methylstyrene or methyl methacrylate has a great effect on the formation of particles, which is consistent with the above-described considerations.
The kinetics of the seeded emulsion polymerization of styrene, with the swollen radii of the seed ranging from 44 to 79 nm, have been measured dilatometrically. The conversion against time curves displayed an increase in the instantaneous rate of polymerization, followed by an apparent steady state domain. These measurements permitted for the first time the direct evaluation of the kinetic parameters that govern both the entry of free radicals into the latex particles and the first-order loss of free radicals from the particles. The latter rate coefficient was found to vary with the inverse square of the swollen particle radius, as expected for the diffusion controlled exit of free radicals from the particles. The magnitudes of the observed entry rate coefficients, when coupled with their dependence upon the initiator concentration, suggest that free radical capture by the seed particles was relatively inefficient. The capture efficiency increased significantly, however, with decreasing initiator concentration if the number of seed latex particles was held constant. The results obtained show clearly that the average number of free radicals per particle can be < 1/2 for styrene emulsion polymerizations under suitable conditions (e.g., low initiator concentrations and/or small particle sizes). Thus styrene can follow Smith—Ewart case 1 kinetics.
Latexes of carboxylated styrene–butadiene rubber were prepared via batch emulsion copolymerization with different amounts of acrylic acid in the absence of emulsifier. The effect of acid monomer was investigated in the particle formation and growth. It was observed that the amount of acrylic acid strongly affected the particle formation. The number of particles and thus polymerization rate increased with increasing of the acid content. There was no significant difference in the polymerization rate per particle in all experiments. The results show that in this case particle growth process is less dependent on the acrylic acid amount in comparison with its influence on nucleation stage and then particle number. Several parameters such as polymerization rate and number of latex particle per unit volume of the aqueous phase were calculated. Attempt was made to evaluate the average number of growing chain per particle. Also average particle diameter of the above carboxylated SBR latexes was obtained through some calculations from the direct measurement of average particle diameter in the swollen state by light scattering technique for the first time.
As a basis for understanding emulsion polymerization, the kinetics of free radical reactions in isolated loci is discussed subject to the condition that the free radicals are supplied to the loci from an external source. Three cases of interest are considered: that in which the average number of free radicals per locus is small compared with unity, that in which this number approximates one-half, and that in which the number is large. Of these three possibilities, the second, in which the free radicals per locus approximate one-half, is by far the most interesting as it explains in a satisfactory manner the characteristic features of styrene emulsion polymerization. For this case the average rate of reaction per locus is independent of the size of the locus, since this rate is simply one-half the rate of polymerization of a single free radical. Thus the rate of emulsion polymerization, the concentration of monomer in the loci, and the number of loci present provide the information needed for calculating the chain propagation constant for the monomer.
A simplified treatment is given for approximating the number of reaction loci (polymer particles) produced in emulsion polymerization when the rate of polymerization per locus is constant (see case 2 above). The law obtained indicates that the number of particles should increase with the soap concentration (3/5ths power) and with the rate of formation of free radicals (2/5ths power), but should decrease with increasing rate of growth of the free radicals (−2/5ths power).
The mechanism of catalytic copolymerization of two monomers A and B is treated with the the aid of steady state approximation. Two initiation and two termination rates are assumed, one for each monomer. Four propagation rates are considered, corresponding to the four possibilities of addition, namely, addition of monomer A to a chain ending in A* or to a chain ending in B* and addition of monomer B to a chain ending in A* or to a chain ending in B*. Over‐all rate and number average molecular weight are calculated. The composition of the polymer and the number distribution curves of groups of submolecules a and of submolecules b are calculated as functions of the monomer composition and two rate constant ratios. These last results are of general character and independent of the nature of the initiation and termination processes provided that the average degree of polymerization is ``high.''