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     

Investigation into the effect of carboxylic acid monomer on particle nucleation and growth in emulsifier-free emulsion copolymerization of styrene-butadiene-acrylic acid

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.     

Effect of itaconic acid on the wet scrub resistance of highly pigmented paints for architectural coatings

This study investigates the influence of carboxylic monomers, such as itaconic acid (IA), on the colloidal properties of the latexes made by semi-continuous emulsion copolymerization of styrene (STy) with n-butyl acrylate (BA). A number of copolymerization runs were carried out with different IA concentrations. The effect of functional monomer on the overall conversion, the colloidal properties of the latexes, and the distribution of the carboxylic groups (buried, particle surface and aqueous phase) were examined. The carboxylic groups present in the latexes were analyzed using conductimetric and potentiometric titrations. The behavior of the IA on the wet scrub resistance of highly pigmented paints for architectural coatings was examined and correlated with the distribution of the carboxylic groups. The results obtained showed that the properties of highly pigmented paints are greatly dependent on the amount and distribution of the carboxylic groups. The carboxylic acid distributed in the aqueous phase has a strong influence on the wet scrub resistance and on the characteristics of the final products.     

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.     

Influence of seed polymer molecular weight on polymerization kinetics and particle morphology of structured styrene–butadiene latexes

Heterogeneous film‐forming latexes were prepared using two‐stage, seeded emulsion polymerization. The polymerization was performed in a calorimetric reactor with a control unit that monitored the reaction rate and controlled the charging rate of the monomers. Three types of styrene seed latexes were prepared at 70°C. The first was an unmodified polystyrene (PS) latex. The second had the molecular weight lowered by the use of carbon tetrachloride (CCl₄) as a chain‐transfer agent, added at the start of the polymerization. For the third one, divinylbenzene (DVB) was used as a comonomer. DVB was added under starved conditions near the end of the polymerization to achieve crosslinked particle shells and to introduce double bonds as possible grafting sites. The second polymerization step was performed at 80°C as a batch operation in a 200‐mL calorimeter reactor. The second‐stage polymer was poly(styrene‐co‐butadiene‐co‐methacrylic acid) (S/B/MAA). A fixed S/B ratio was used together with varying small amounts of MAA. Particle morphology and particle‐size distributions were examined after the second stage using TEM after staining with osmium tetroxide. The particle morphology was found to depend on both the seed composition and the amount of MAA used in the second stage. Molecular weight and crosslinking of the DVB‐containing seed influenced the internal particle viscosity, which gave differences in the polymerization rate and the particle morphology. Crosslinking of the second‐stage polymer decreased the monomer concentration in the particles, which could be detected as a change in the slope the pressure/conversion curve. This phenomenon was used to indicate the critical conversion for crosslinking of the second‐stage polymer. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 297–311, 2000     

Solution and emulsion polymerization with partially neutralized methacrylic acid

Polymerizations of partially neutralized methacrylic acid (MAA) were performed in both solution and emulsion systems. Polymerizations of MAA in solution were performed at an overall degree of neutralization ranging between 0 and 1. The rate of polymerization of the acid is found to decrease as the degree of neutralization increases due to increased electrostatic repulsion of the dissociated acid species (anions). The degree of neutralization of the unreacted monomer increases as the conversion increases. A kinetic model based on a copolymerization mechanism is used to describe the reaction behavior. Partially neutralized methacrylic acid was also polymerized with styrene in a seeded emulsion system. The reaction rates of both the acid and styrene decrease as the overall degree of neutralization increases. A previously developed emulsion copolymerization kinetic model is extended to account for reaction of the anions and used to investigate the overall “terpolymerization” of the acid, anions, and styrene.     

Toward an understanding of the role of water‐soluble oligomers in the emulsion polymerization of styrene–butadiene–acrylic acid. Function of carboxylic acid

In a further effort to understand the role of water‐soluble oligomers formed during the emulsion terpolymerization of styrene/butadiene/acrylic acid (St/Bu/AA), the reaction temperature, initiator concentration, and ionic strength were varied and the kinetics and resulting oligomers were characterized as a function of reaction time. The rate of polymerization (R_p) was observed to increase with increasing temperature and initiator concentration; the reasons for this vary. The increase in R_p with increasing initiator concentration is mainly attributed to the increase in the number of oligomeric radicals formed and, subsequently, the resulting number of particles (N_p). Increasing the temperature increases the water solubility of both monomers and polymers, which results in changes in the composition and molecular weight of the oligomeric radicals being formed. The primary reaction locus in the St/Bu/AA system was noted to shift to the aqueous phase after most of the styrene and butadiene had reacted, based on the unreacted AA profile. The role of water‐soluble oligomers (both oligomeric radicals and dead oligomers) during the emulsion polymerization of St/Bu with acrylic acid can be described by three periods: (1) particle generation and (2) before and (3) after the critical surface saturation concentration (CSSC) is reached during the particle growth period. The incorporation of AA monomer into the oligomer chains after the CSSC may cause destabilization of the latexes through a bridging flocculation mechanism. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1988–1999, 2003     

Preparation of micron‐size monodispersed PS/P(St/MAA) microspheres by seeded dispersion polymerization

Uniform polystyrene (PSt) particles with the size of 1.9 μm were first prepared via dispersion polymerization, and then used as the seeds in a second‐stage dispersion copolymerization of styrene (St) and methacrylic acid (MAA) to produce carboxyl‐carrying microspheres. The PSt seed particles were swollen by monomer mixture of St and MAA, including an oil‐soluble initiator 2,2′‐azobisiso‐butyronitrile (AIBN), before polymerization. Finally, uniform PS/P(St/MAA) (polydispersity index, PDI = 1.02) microspheres with the size of 2.2 μm were obtained. The average particle size and size distribution of the final microspheres were investigated. MAA contents between 54 and 97 mg/g were detected from the PS/P(St/MAA) particles produced under different conditions. Dispersion medium has great influence on the kinetics of polymerization, due to its effect on the partitioning of monomers, solvents, and initiator in the particle phase, probably as well as on the conformation of the dispersion agent on the surface of the particles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3586–3591, 2006     

中空聚合物微球的制备——种子及核乳胶粒的制备

为了制得具有中空结构的聚合物微球,首先以十二烷基苯磺酸钠(SDBS)为乳化剂,在其用量低于CMC的条件下,进行甲基丙烯酸甲酯(MMA)、甲基丙烯酸(MAA)和丙烯酸丁酯(BA)的乳液聚合,制备了带羧基的种子乳胶粒.然后采用MMA、MAA和二乙烯基苯为单体进行种子乳液聚合,制备了轻度交联的带羧基的核乳胶粒.该核乳胶粒经过核-壳乳液聚合和适当的碱处理工艺就可成为具有中空结构的聚合物微球.采用粒度仪测定了乳胶粒的直径及其分布,采用TEM对乳胶粒结构形态进行了表征.研究了种子及核乳胶粒制备过程中单体加料方式、乳化剂用量及羧基单体种类等因素对聚合稳定性、乳胶粒直径及其分布以及最终的中空聚合物微球结构形态的影响,确定了制备种子及核乳胶粒的最佳工艺条件.在制备种子阶段,SDBS用量为单体总量的0.5%,采用一次性加入单体的进料工艺;在核乳胶粒制备阶段,以MAA为羧基单体,所有单体采用"饥饿式"加料,半连续补加乳化剂并使乳化剂用量为核单体总量的0.15%时可保持聚合稳定性并保证无新乳胶粒生成.     

Influence of unsaturated acid monomer on the morphology of latex particles in the preparation of hollow latex via the alkali post‐treatment

Multistage hydrophilic core/hydrophobic shell latexes containing carboxyl groups were prepared via multistep seeded emulsion copolymerization, and particles with different morphologies were obtained after alkali post‐treatment. Influences of the type and content of unsaturated acid monomer on the polymerization and the particle morphology were investigated based on conductometric titration and TEM observation. Results showed that the hydrophilic core/hydrophobic shell particles could be easily formed using methacrylic acid (MAA) instead of acrylic acid. When MAA was 12.2 wt % in the core latex preparation, only fine pores existed inside the alkali‐treated particles. With MAA increased from 20.0 to 30.0 wt %, the alkali‐treated particle morphology evolved from porous, hollow to collapse structure. When MAA further increased to 40.0 wt %, it was difficult to prepare uniform multistage particles and distinct morphologies including solid, deficient swelling, hollow and collapse structure were coexistent in the alkali‐treated particles. Moreover, the forming mechanism of different morphologies was proposed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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.     

Preparation and characterization of imidazole‐functionalized microspheres

The preparation of imidazole‐functionalized latex microspheres by a two‐stage emulsion copolymerization process and their characterization are reported on. Emulsifier‐free emulsion copolymerization of styrene (St) and 1‐vinyl imidazole (VIMZ) exhibited bimodal particle size distributions caused by secondary homogeneous nucleation process. However, secondary nucleation can be avoided by using cetyltrimethylammonium bromide (CTAB) as a stabilizer at a concentration below its cmc (critical micelle concentration). This would result in the formation of monodisperse latex particles. The final particle size diameter depended on the concentration of CTAB as well as the amount of VIMZ. To control the amount of the functional imidazole groups on the latex particle surfaces, independent of the latex diameters, without secondary nucleation of particles, the seeded emulsion copolymerization of styrene and VIMZ was explored as a second‐stage polymerization at different concentrations and ratios of monomers in the presence of the previously prepared monodisperse poly(styrene‐co‐1‐vinyl imidazole) seed latex particles. The concentration of imidazole functional groups on the surface of the latex particles could also be varied through the rearrangement of hydrophilic imidazole groups by varying the second‐stage monomer addition process such as the utilization of monomer‐swollen seed particles or a shot addition of monomers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 120:5753–5762, 2006     

Emulsifier‐minor emulsion copolymerization of BA‐MMA‐St‐MAA (or AA)‐N‐MA

A novel emulsion polymerization technique referred to as emulsifier‐minor emulsion polymerization was achieved by the copolymerization of methyl methacrylate, butyl acrylate, and styrene (MMA‐BA‐St) with a combination of water‐soluble ionic monomers [methacrylic acid (MAA) or acrylic acid (AA)] and nonionic monomers (N‐methylol acrylamide). In the technique, water‐soluble monomers play a crucial role in the stabilization of the latex particles as they can be bound to the particle surface and form a hydrate protective layer, which exhibits steric and/or electrostatic effects to prevent particle coagulation. The minor but over its critical micelle concentration emulsifier sodium alkylated diphenyl ether disulfonate (DSB) results in the nucleation of particles mainly by the micelle nucleation mechanism and thus determines the polymerization rate, the particle size, and the number. The film water resistance of the latices can be improved, and the foaming capacity of can be lowered by using technique instead of conventional emulsion polymerization. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2923–2929, 2004     

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.     

高转化率乳聚丁苯橡胶聚合过程中乳液相对分子质量分布与粒径分布考察

采用中石油吉化分公司乳聚丁苯橡胶高转化率大生产配方,考察了实验室聚合反应釜聚合反应单体转化率随反应时间的变化,采用激光粒度分析仪和凝胶渗透色谱仪测定了聚合反应不同单体转化率的胶乳的粒径分布与分子质量分布,结果表明：胶乳粒径呈正态分布,粒径主要集中分布在0.1μm附近,胶乳的平均粒径随反应时间的延长逐渐增大,但是增加的幅度越来越小;聚合反应时间在11 h前（即转化率小于72%）,胶乳的重均分子质量、Z均分子质量一直增大,而数均分子质量变化无明显规律;而分子质量分布宽度指数随反应的进行变小,表明调整的高转化率配方合成的丁苯橡胶可有效改善聚合生成的胶乳粒径分布。     

A new method to determine monomer concentration in the polymer particles of emulsion polymerization systems by dynamic light scattering

Emulsifier‐free emulsion polymerization of styrene was performed in the presence of small amount of methacrylic and itaconic acids as carboxylic acid monomers and potassium persulfate as an initiator at 70°C to prepare monodisperse polymer particles. Diameter of monomer swollen polymer particles (d_pswol) was measured by dynamic light scattering for samples taken from the reaction mixture during the Intervals II and III of the emulsion polymerization. Graphically treatment of d_pswol versus conversion data allowed us for the first time to directly determine the critical monomer conversion (x_c), from which constant monomer concentration in the polymer particles (C_MP) during the Interval II was then calculated. x_c and C_MP were obtained to be 0.379 and 5.68, respectively. C_MP value is in good agreement with that obtained by centrifugation method and those reported in the literature for the similar system. Attempts were also made to evaluate the average number of growing chain per particle ( ) during the Interval II of emulsion polymerization of styrene. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of functional monomer on the stability and film properties of thermosetting core-shell latexes

Functionalized core-shell latexes were prepared by copolymerization of butyl acrylate and methyl methacrylate with 2-hydroxyethyl methacrylate (HEMA) or methacrylic acid (MAA), which were added during the first or second stages of polymerization, respectively. The HEMA and MAA concentrations were increased while the equivalent ratio of functional groups remained constant. Colloidal stability, particle size, particle size distribution, film properties and morphology were studied as functions of functional monomer content. The upper limit functionality content was limited by the stability of the system during synthesis. A bimodal particle size distribution was observed for high concentrations of functional monomers. Increase in carboxyl and hydroxyl functionalities improved tensile strength and modulus for un-crosslinked films, and generally higher tensile strength, tensile modulus and storage modulus at high temperature were obtained after the functional latexes were crosslinked with a cycloaliphatic diepoxide.     

Morphology of poly(isoprene-co-styrene-co-methacrylic acid) latex prepared by two-stage seeded emulsion polymerization

Heterogeneous latexes were prepared by a two-stage seeded emulsion polymerization process at 80°C using potassium persulfate as the initiator and sodium dodecyl sulfate as the emulsifier. Poly(styrene-co-methacrylic acid) latexes containing varying amounts of methacrylic acid (MAA) were used as seeds. The second-stage polymer was poly(isoprene-co-styrene-co-methacrylic acid). By using different methods for the addition of the MAA and by varying the amount of MAA, the hydrophilicity of the polymer phases could be controlled. The morphologies and size distributions of the latex particles were examined by transmission electron microscopy. The latexes were in all cases unimodal, and had narrow particle size distributions. The particles displayed different morphologies depending on the polymerization conditions and monomer composition. The hydrophilic properties of the two phases in combination with the internal particle viscosity and crosslinking of the second phase during polymerization were found to be the major factors influencing the particle morphology. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1543–1555, 1997     

Measurements of monomer partitioning in emulsion copolymerization systems

A new apparatus to measure the equilibrium solvent activity in a multiphase system containing a particulated polymer is presented. An experimental procedure to determine the monomer partitioning in typical emulsion copolymerization systems is developed; the method is devised in a way that no phase separation between water and swollen polymer particles is required in order to determine the monomer content in each phase. The analytical technique used is quantitative gas chromatography, either of the vapor or of the liquid phases. Different monomers (styrene, methyl methacrylate, and vinyl acetate) and polymeric matrices (polystyrene and methyl methacrylate–vinyl acetate copolymer) are examined both above and below saturation conditions (corresponding to intervals II and III of an emulsion polymerization process). The experimental results are compared with predictions of a literature model. © 1996 John Wiley & Sons, Inc.     

Modeling and experimental studies of emulsion copolymerization systems. I. Experimental results

A systematic experimental and modeling study of several emulsion copolymerization systems has been performed, and will be reported in a series of papers. Ten binary and three ternary copolymerizations involving styrene, methyl methacrylate, butyl acrylate, butadiene, vinyl acetate, acrylic acid, and ethylene were studied varying polymerization temperature, monomer composition, water to monomer ratio, initiator and emulsifier concentrations. Conversion, particle size, copolymer composition, and gel content were measured at several reaction times. The goal of this series of papers is to assess our quantitative understanding of emulsion copolymerization expressed in the form of a comprehensive mathematical model applied to monomers widely used in industry. In this first paper of the series, a global comparison of the experimental results is made. It is observed that the gel content is higher in systems containing butyl acrylate and butadiene, and smaller in systems containing methyl methacrylate. Larger particle numbers are obtained for lattices containing acrylic acid and butadiene. It is also shown that, for most of the systems, integration of the simple Mayo–Lewis equation is adequate to explain the drift in copolymer composition observed experimentally. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2360–2379, 2001