Influence of acid-base equilibrium in emulsifier-free styrene polymerization with carboxyl-containing initiator on colloidal characteristics of the disperse system (original) (raw)
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Polymer journal, 2007
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 (N p ) increases with increasing hydrophobicity of carboxylic acid monomers in order of IA < AA < MAA. There was significant difference in polymerization rate per particle (R p =N p ) 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 N p 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 (d pswol ) 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. [
Polymer, 2004
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. q
Journal of applied …, 2007
Carboxylated styrene-butadiene rubber latexes were prepared through the emulsifier-free emulsion copolymerization of styrene and butadiene with various carboxylic acid monomers. The effects of various carboxylic acid monomers on the particle formation process were investigated. The type of carboxylic acid monomer strongly affected the particle nucleation. The number of particles and thus the polymerization rate increased with the increasing hydrophobicity of the carboxylic acid monomers. There was a significant difference in the polymerization rate per particle. The results showed that particle nucleation and growth were dependent on the hydrophilic nature of the carboxylic acid monomers. The average particle diameter of the carboxylated styrene-butadiene rubber latexes in the dry state was obtained through some calculations using direct measurements of the average particle diameter in the monomerswollen state by a dynamic light scattering technique. Several parameters, such as the polymerization rate, number of latex particles per unit of volume of the aqueous phase, and polymerization rate per particle, were calculated.
Reactive and Functional Polymers, 2006
Carboxylated styrene-butadiene latexes with 30% solid content were prepared by emulsion copolymerization technique with initial charge and shot-addition methods. The distribution of carboxylic groups in different locations of latex system i.e. interior and surface of particles and aqueous phase during polymerization reaction was studied by conductometric back titration method (Hen method). The obtained results from shot process show that addition of acrylic acid with some water in interval III of emulsion polymerization will decrease the amount of surface bound carboxylic acids relative to initial charge method. So the process of shot-addition was modified by addition of styrene, emulsifier and initiator accompanied with acrylic acid and water in conversions above 80% in the second stage. The analysis of the obtained latex shows that the amount of surface bound acid was raised from 58% for initial charge method to 72% for this modified technique. 9 th Iranian Chemical Engineering Congress
Polymer, 2007
Carboxylated styreneebutadiene rubber (XSBR) latexes were prepared by emulsifier-free batch emulsion copolymerization of styrene and butadiene with different types of carboxylic acid monomers (AA, MAA, IA). It was found that the particle growth is dependent on the hydrophilic nature of carboxylic acid monomers. SEM studies showed that N p 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 of all the XSBR latexes at the same conversion of 0.4 was obtained to be 368.91, 174.17 and 437.15 nm for AA, MAA and IA, respectively. Several kinetic parameters related to the particle growth stage such as the average number of growing chain per particle were calculated to be 0.474, 0.370 and 1.685 for AA, MAA and IA, respectively. It was observed that these kinetic parameters increase with increasing average diameter of monomer swollen polymer particles, which is consistent with the emulsion polymerization kinetics. Moreover, results indicated that the polymerization rate per particle or equivalently the average number of the growing chain per particle (particle growth stage) decreases by replacing a part of styrene with butadiene in the emulsion copolymerization recipe of styreneecarboxylic acid monomer.
Colloid and Polymer Science, 2014
This work is an extension of previous research results reported by our team (Colloid Polym Sci 291:2385-2389, where monodisperse, large-scale, and highsolid-content latexes of poly(n-butyl acrylate) were obtained with the particle coagulation method induced by the electrolyte. However, large-scale polystyrene latex particle is difficult to synthesize with this approach; moreover, demulsification phenomena easily take place especially in high solid content. In this article, a new approach to prepare large-scale polystyrene latex particle was proposed. Methanol was added to aqueous phases to decrease the interfacial tension between the polymer particle surface and continual phases, further decreasing interfacial free energy. Consequently, the surfactant molecules would loosely pack on the polymer particle surface, which is favored by particle coagulation. Experimental investigations showed that the final polystyrene particle scale only reaches to 93.5 nm when the methanol/ water ratio is equal to 0:100, but the particle size attains 270 nm when the methanol/water ratio is equal to 30:70. These results indicated that polystyrene particle coagulation can be induced by methanol by varying the surfactant molecule adsorption on the particle surface. This investigation also provided a new simple approach to prepare large-scale, stable latex particles.
The effects of electrolyte concentration in the emulsion polymerization of styrene
Polymer, 1982
Using concentrations below that required to coagulate the latex, the effects of the addition of potassium chloride on the emulsion polymerization of styrene have been investigated. When potassium decanoate (an emulsifier with a high critical micelle concentration (c.m.c.)) is used the increase in the concentration of micellar emulsifier and the decrease in the area occupied by an emulsifier molecule at the polymer/water interface are significant. When this is taken into account Gardon's equation for latex particle size reproduces the trend of the experimental results at the lower electrolyte concentrations. The agreement can be made quantitative by choosing alternative values for the propagation rate constant of styrene and the rate of radical formation from persulphate. With potassium octadecanoate (which has a low c.m.c.) and with potassium decanoate at the higher electrolyte concentrations these factors cannot account for the results observed.
Monatshefte für Chemie - Chemical Monthly, 2007
Suspensions of polymer nanoparticles in water (latices) with average particle diameters between 20 and 80 nm were synthesized by batch emulsion polymerization of styrene using sodium dodecyl sulphate (SDS) as surfactant and potassium persulphate (KPS) as initiator. The influence of surfactant concentration, initiator concentration, monomer concentration, and reaction temperature on the final average particle diameters and size distributions of the latices were studied. The number of particles generated was proportional to the 0.56 power of the emulsifier concentration and to the 0.37 power of the initiator concentration in the whole concentration range which was observed. Furthermore, the final number of particles was dependant on the reaction temperature to the 2.06 power. With these correlations the average particle number as well as the average particle size could be estimated, and the results were in good agreement (AE6%) with the experimental values. A reduction of the monomer=water ratio from 1:5 to 1:20 yielded smaller particle diameters, while leaving the particle number unaffected. The lower particle size limits for monomer ratios of 1:10 and 1:15 were estimated with diameters of about 18 and 16 nm.