Effect of the carboxylic acid monomer type on the emulsifier‐free emulsion copolymerization of styrene and butadiene

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 monomer‐swollen 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. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effect of carboxylic acid monomer and butadiene on particle growth in the emulsifier-free emulsion copolymerization of styrene-butadiene-carboxylic acid monomer

Carboxylated styrene-butadiene 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 styrene-carboxylic acid monomer.     

Effect of carboxylic monomers on acid distribution in carboxylated polystyrene latices

A study was made of the effect of carboxylic monomers, such as itaconic acid, acrylic acid, and methacrylic acid, on the relative distribution of acid in the aqueous serum phase to that on the latex surface to that buried in the particle of carboxylated polystyrene latices prepared by emulsion polymerization. The relative acid distribution of the carboxylated latices was determined by the conductometric titration method of Hen. Effect of carboxylic monomer levels and latex particle size on acid distribution ratio are given. It is shown that itaconic acid, being the most hydrophilic and having the least solubility in styrene, tends to distribute itself in favor of the aqueous serum phase, while acrylic acid, which has limited solubility in styrene and being sufficiently hydrophilic, tends to prefer the particle surface predominantly. Methacrylic acid, being the most hydrophobic of the three carboxylic monomers studied and having good solubility in styrene, is shown to be concentrated inside the particle core. The observed results are compared with other similar findings in the literature and analyzed in the light of accepted mechanisms for emulsion polymerization of carboxylated styrene systems.     

The effect of carboxylic monomers on surfactant-free emulsion copolymerization

A study was made of the effect of carboxylic monomers on the surfactant-free emulsion polymerization of styrene and styrene–butadiene. Acid monomers, such as acrylic acid, methacrylic acid, and itaconic acid, were shown to play a critical role in particle formation and particle stabilization in such systems. In the emulsion polymerization of styrene, methacrylic acid forms particles more efficiently than acrylic acid. This difference is attributed to the more hydrophobic nature of the methacrylic monomer which allows it to diffuse more rapidly to the particle surface where it acts to prevent agglomeration. The ability of carboxyl groups to orient at the particle–water interface was studied by acid–base and soap titrations of carboxylated styrene–butadiene latices. The polymerization of itaconic acid onto the particle surface of a styrene–butadiene latex produces a surface carboxyl density much higher than is obtainable with classically adsorbed surfactants. This result is used to explain the greater stability of carboxylated versus noncarboxylated emulsion polymers. During the polymerization of styrene–butadiene latices, carboxyl groups dervied from methacrylic acid are shown to be buried more deeply into the particle as compared to carboxyls derived from the more hydrophilic acrylic acid which orient more at the particle–water interface.     

Polymerization behavior and distribution of carboxyl groups in preparation of soap-free carboxylated polystyrene latexes

Soap-free carboxylated polystyrene latexes have been prepared by copolymerizing acrylic acid (AA) in a wide range of the degree of neutralization using a slight amount of soap; and the distribution of carboxyl groups was investigated from the determination of carboxyl groups localized on the surface of particles (surface carboxyl groups). It appears that the degree of neutralization of AA or the amount of AA has a considerable effect on the rate of polymerization as well as the stability of the polymerization system. At a degree of neutralization of approximately 0.80, stable latexes are obtained at a sufficient rate of polymerization. It is also clarified that the distribution of carboxyl groups is governed substantially by the degree of neutralization of AA. At a degree of neutralization of 0.80, approximately 30% of the total carboxyl groups are localized on the surface of particles. The amount of AA or the particle diameter seems to have little effect on the distribution of carboxyl groups.     

Seeded emulsion polymerization of styrene: influence of acrylic acid on the particle growth process

The seeded batch emulsion copolymerization of styrene and acrylic acid was studied. The polymerization rate was investigated with pH as the main parameter. Some attempts were made to evaluate the average number of growing chains per particle during Stage II of the emulsion polymerization process. The final latex products were characterized by means of conductometric aqueous titration and potentiometric titration in an organic solvent mixture. The distribution of the acid groups over the aqueous phase, the particle surface, and the interior of the particles together with the kinetic results provided insight into important features governing the incorporation of acrylic acid. The results indicate that pH is the dominating parameter for the incorporation process. An optimal incorporation on the surface of the particles is observed for a low value of pH. In that case, all the acid groups are protonated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1186–1196, 2000     

Seeded emulsion polymerization of styrene: Incorporation of acrylic acid in latex products

Seeded batch emulsion polymerization of styrene and acrylic acid was studied. The influence of pH and acrylic acid content on the polymerization rate and the amount of carboxylic acid groups incorporated in the final latex products was investigated. The distribution of the functional groups over the aqueous phase, the latex particle surface, and the interior of the latex particle was determined using aqueous conductometric titration and nonaqueous potentiometric titration at intermediate and complete overall conversions. Combined with kinetic results, the carboxylic acid group distribution history provided valuable information about the process of incorporation of acrylic acid in latex products. Two‐step processes in which a shot of acrylic acid was performed in the last stage of the emulsion polymerization reaction were investigated as a strategy to increase the surface incorporation efficiency. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 875–885, 2000     

Effect of the hydrophilic nature of growing radicals on the formation of particles in the preparation of soap-free carboxylated polystyrene latexes

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.     

Role of itaconic acid in latex particle nucleation

Itaconic acid, a carboxylated water-soluble monomer, was examined in terms of its role in latex particle nucleation when copolymerized with acrylate monomers. From emulsion polymerizations in which the particle number concentrations were followed as a function of monomer conversion, it was found that the greater the amount of itaconic acid present, the larger the final latex particle diameter. This was interpreted as the result of the lower number of primary particles being initially nucleated. The above observations can be explained by the incorporation of the hydrophilic itaconic acid into acrylate oligomeric radicals that initially form. This incorporation increases the water-solubility of the radicals such that a lower proportion of these radicals is likely to precipitate to form primary particles.     

Agglomeration of polybutadiene latex by highly carboxylated functional microspheres

Polybutadiene latex (PBL) was agglomerated by highly carboxylated core-shell agglomerating agents, which contained carboxyl groups in the shell polymer [core monomers (methyl methacrylate, n-butyl acrylate, and ethyl acrylate)/shell monomer (acrylic acid)]. The effects of different parameters upon the particle size of agglomerated PBL were investigated, namely, agglomeration time, amount of agglomerating agent, pH of dispersion medium, amount of acrylic acid and combination of core monomers. The particle growth mechanism was also examined. © 1999 Society of Chemical Industry     

Alkali solubility of carboxylated polymer emulsions

The solubility of carboxylated polymer emulsions in an aqueous alkaline solution was studied. The alkali solubility was shown to depend on the degree of carboxylation, the hydrophilic nature of the noncarboxylic main components, the degree of polymerization, the glass transition temperature, the chain configuration, and the dissolution temperature. Emulsions of the copolymer containing acrylic acid units showed considerably different dissolution behavior from those containing methacrylic acid units, possibly owing to the difference in the distribution state of carboxylic units inside the particle. It is deduced that methacrylic acid units are distributed more homogeneously inside the particle than acrylic acid units.     

An investigation of the emulsion terpolymerization of 2-ethylhexylacrylate–vinyl acetate–acrylic acid

An investigation of the emulsion polymerization of 2-ethylhexylacrylate (EHA)—vinyl acetate (VAc)—acrylic acid (AA) has been done. It was found that the polymerization rate depends on the AA level and that particle nucleation occurs throughout the entire conversion range. At the 5% AA level, there is significant coagulation. The number of particles depends on the balance between nucleation and coagulation. Addition of a small amount of water-soluble comonomer has no significant effect on the course of polymerization, but the viscosity of the latex can increase significantly. The dependence of latex viscosity on pH on neutralization has been studied. The maximum viscosity reached on neutralization depends on the acrylic acid level and the semibatch policy used in the latex synthesis. Addition of salt is a simple and effective way to control viscosity buildup during neutralization.     

Particle nucleation in emulsion copolymerization containing multifunctional monomers

Characteristic features of particle nucleation and growth in the emulsion copolymerization of styrene and multifunctional monomers such as ethylene glycol dimethacrylate and divinylbenzene were investigated. It was found that in these emulsion copolymerization systems the rate of polymerization per particle decreased drastically with an increase in the content of the multifunctional monomer in the initial monomer feed, and the number of polymer particles produced, on the other hand, increased corresponding to the decrease in the rate of polymerization per particle. The increase in the number of polymer particles produced was explained on the basis of Smith-Ewart theory, which predicts that the number of polymer particles produced would increase inversely proportional to the 0.4 power of the volumetric growth rate per particle, that is the rate of polymerization per particle during the interval of particle formation (Interval I). It was pointed out that the decrease in the rate of polymerization per particle in Interval I would be due mainly to a decrease in the monomer concentration in the polymer particles which was caused by crosslinking networks of the resultant polymer.     

Particle coagulation at semicontinuous emulsion polymerization. II. Characterization of surface groups

Semicontinuous emulsion polymerization of acrylic monomers with a monomer emulsion feed has been investigated. The amount of coagulum appearing during the polymerization under conditions of insufficient covering of particle surface by emulsifier was studied from the point of view of particle surface charge. Increasing the surface group concentration via copolymerization of butyl acrylate with acrylic acid or sulfoethyl methacrylate caused increased colloid stability of the system and a rapid decrease in coagulum formation. It was established that during the polymerization acid hydrolysis of ester groups took place, which caused an increase in the carboxyl groups concentration at the particle surface. These carboxyl groups contribute to the colloid stability of the polymerizing system.     

Radiation-induced emulsion copolymerization of tetrafluoroethylene with propylene. V. Formation of acid and its effect

In the radiation-induced emulsion copolymerization of tetrafluoroethylene with propylene, it was found that hydrofluoric acid (HF) is formed in the course of polymerization. The amount of HF formed increased linearly with the irradiation time in all cases. The rate of HF formation was maximum at 0.3 wt-% emulsifier and increased linearly with tetrafluoroethylene content in the monomer mixture. On the other hand, the conversion and the molecular weight decreased remarkably by addition of 0.1M HF. The particle diameter of copolymer obtained in the presence of HF was larger than that obtained in the HF-free system. On the contrary, the number of polymer particles was less than that obtained in the HF-free system. The decrease in the conversion and the molecular weight was attributed mainly to the conversion of part of ammonium perfluorooctanoate to perfluorooctanoic acid by formation of acid or addition of acid.     

Styrene miniemulsion polymerization stabilized by carboxylated polyurethane. II. Kinetics

A styrene miniemulsion was prepared using carboxylated polyurethane as the sole costabilizer and sodium dodecyl sulfate as the surfactant. The effects of the amount of carboxylated polyurethane, the amount of the initiator and surfactant, the presence of a water‐phase inhibitor (sodium nitrite), and the reaction temperature on the kinetics of the miniemulsion polymerization were investigated. The evolution of the particle size during the polymerization was measured. The results show that the polymerization rate was proportional to the 0.21 power of the surfactant concentration and the 0.30 power of azobisisobutyronitrile. The droplet nucleation and homogeneous nucleation were found to be coexistent in the polymerization. The hydrophility of the particle surface plays a key role in the nucleation of the particle and, therefore, has an important effect on the kinetics of the polymerization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1941–1947, 2003     

Kinetic studies of the preparation of nanocomposites based on encapsulated Cloisite 30B in poly[styrene‐co‐(butyl acrylate)] via mini‐emulsion polymerization

Mini‐emulsion polymerization of poly[styrene‐co‐(butyl acrylate)] encapsulating various contents of Cloisite 30B was performed. The kinetic behaviours of mini‐emulsions were investigated using the gravimetric method and the effect of nanoclay content on the polymerization rate was investigated. The average number of radicals per particle was estimated by calculating the number of particles. The results showed that by increasing the nanoclay content, the average diameter of polymer particles increased. Studies of the polymerization rate indicated that the increase in particle size provided a greater average number of reactive radicals per polymer particle, which increased from 0.0520 for the neat copolymer to 0.2462 for the nanocomposite containing 5.3 wt% encapsulated nanoclay. This study also confirmed our previous claim about the role of sodium dodecylsulfate (SDS) molecules in the exfoliation of nanoclay platelets. On increasing the clay content, fewer SDS molecules will be available on particle surfaces resulting in larger particles at the end of the reaction. Copyright © 2011 Society of Chemical Industry     

Particle number and size of polystyrene‐dependent micellar crosslinking polymerization of acrylic acid

The effect of the number and size of polystyrene particles and the concentration of ammonium persulfate used as the initiator on the micellar crosslinking polymerization of acrylic acid was studied by real‐time monitoring of the storage modulus (G ′), the damping factor (tanδ), and the ratio of the complex modulus (G*) to the maximum G* (G*_max) during 1 h of polymerization. The molar ratio (5.83 × 10^?4) of N,N′‐methylenebis‐acrylamide to acrylic acid was fixed. Polystyrene particles were prepared by emulsifier‐free emulsion polymerization. The diameter of the particles ranged from 233 to 696 nm. The results show that crosslinking polymerization was most effective when 1.31 × 10¹² particles were incorporated into the system, while crosslinking polymerization was less effective in the particle‐filled system than in the unfilled polymerization system if the particle number was 50% lower or higher. Crosslinking was also more effective with the use of uncrosslinked firmer and larger particles at the fixed particle number, except for the anomalous behavior observed with 696 nm polystyrene particles. Increasing the feed concentration of the initiator resulted in more efficient crosslinking up to a limiting concentration of 0.765 mg mL^?1 (the molar ratio of initiator to monomer was 8.52 × 10^?4). When this initiator concentration was doubled, the rate of increase of G ′ in the deceleration phase was slower after the network was formed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42851.     

Effect of carboxyl on vulcanization and mechanical properties of carboxylated acrylic rubber prepared by 60Co‐γ‐ray‐induced polymerization

Acrylic acid carboxylated acrylic rubber (ACM) and itaconic acid carboxylated acrylic rubber were prepared by ⁶⁰Co‐γ‐ray‐induced emulsion copolymerization. The polymers were characterized using FTIR and ¹³C NMR spectroscopies. The acid value was determined with nonaqueous titration method. The molecular weight and the polydispersity index of the polymers were measured using gel permeation chromatography. The influence of the cure‐site (carboxyl) on the vulcanization and mechanical properties of the ACM was researched by means of rheometric study, gel fraction analysis, mechanical property tests, and dynamic mechanical thermal analysis. The results show that the crosslink density of polymers increases with amounts of the carboxyl cure‐site. The itaconic acid carboxylated ACM has better cure characteristics and mechanical properties than the acrylic acid carboxylated ACM has. In addition, the comparison of ACM prepared by ⁶⁰Co‐γ‐ray‐induced polymerization with ACM prepared by chemical‐initiator‐induced polymerization has been investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5587–5594, 2006     

Kinetics of emulsion copolymerization with acrylic acids

A kinetic model is presented that describes the reaction behavior of emulsion copolymerization systems where significant polymerization occurs in both the particle and aqueous phases. Equations for predicting aqueous-phase free-radical concentrations and aqueous-phase and particle-phase reaction rates are developed. A method for estimating the radical entry rate coefficient is also presented. The model is applied to two seeded carboxylated emulsion copolymerization systems, acrylic acid-styrene and methacrylic acid-styrene. Both experimental and predicted results reveal that the reaction behavior is greatly affected by the type of acid monomer, partition of monomer between the various phases, and locus of polymerization. The mechanism for the acrylic acid-styrene system is more complicated than that for the methacrylic acid-styrene system. Evidence suggests that the primary reaction locus in the acrylic acid-styrene system shifts from the particles to the aqueous phase after the hydrophobic monomer, styrene, has been consumed.