Formation of particles in the preparation of carboxylated polystyrene latexes

Carboxylated polystyrene latexes have been prepared by copolymerizing acrylic acid at the appropriate degree of neutralization in the absence or presence of sodium dodecyl sulfate (SDS), and the particle formation process was investigated from the number and uniformity of particles. In the absence of SDS or in a concentration range of SDS lower than 6.41 mmole/l., the formation of particles can predominantly be attributed to the precipitation of growing radicals formed in the aqueous phase; whereas in a concentration range of SDS higher than 6.41 mmole/l., the formation of particles can predominantly be attributed to the initiation of polymerization in the interior of SDS micelles containing solubilized styrene by the collision of growing radicals formed in the aqueous phase. In the former range, the number of particles increases linearly with increasing concentration of SDS below the critical concentration of 1.60 mmole/l., which is sufficient to stabilize particles formed by the precipitation of growing radicals, and remains constant above the critical concentration. The effect of initiator concentration as well as amount of styrene on the formation of particles also supports the particle formation process described above.     

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.     

Preparation and characterization of soap-free carboxylated polystyrene latexes

Soap-free carboxylated polystyrene latexes have been prepared by copolymerizing carboxylic monomers in a wide range of degree of neutralization using a slight amout of soap. In this polymerization system, the formation of particles seems to be explained by the precipitation of growing radicals formed in the aqueous phase. The degree of neutralization of carboxylic monomers has a great effect on the formation of particles, which may be attributed to a change in the hydrophilic nature of growing radicals formed in aqueous phase that governs the number and uniformity of particles. The number of particles increases remarkably with increasing the amount of soap to some extent, which may be attributed to the stabilization of primary particles formed by the precipitation of growing radicals with the adsorption of soap. The localization of carboxyl groups on the surface of particles seems to be governed by the electrostatic repulsion between carboxyl groups. The surface area occupied by a surface carboxyl group, however, is fairly small irrespective of the degree of neutralization of carboxylic monomers or the amount of soap, which indicates that the latexes are sufficiently stabilized with surface carboxyl groups.     

Acid distribution in carboxylated vinyl-acrylic latexes

Distribution of acid groups in carboxylated vinyl-acrylic latexes has been determined by a combination of aqueous conductometric and nonaqueous potentiometric titrations. Titrations analysis of vinyl acrylic latexes, in comparison to earlier reported studies with carboxylated polystyrene and all acrylic latexes, is complicated by the presence of acetic acid which originates from the hydrolysis of polyvinyl acetate. Most of the copolymerized carboxylic acid is located at the latex particle surface with some of it being buried within the particle. No serum phase polymeric carboxylic acid is detected. Polymerization conditions and the choice of the carboxylic monomer affect acid distribution. Effect of acid distribution on some latex properties is also discussed.     

Electrolyte stability of carboxylated latexes prepared by several polymerization processes

Carboxylated isoprene/styrene copolymer or polystyrene latexes have been prepared by several polymerization processes. The density of carboxyl groups chemically bound to the surface of particles (surface carboxyl groups), and the electrolyte stability of these carboxylated latexes was determined to elucidate the relationship between them. The critical coagulation concentration (CCC), which represents the electrolyte stability of latex, decreases considerably with increasing valency of the cation, as expected from theory. The CCC increases remarkably with increase in the density of surface carboxyl groups or increase in the degree of neutralization of surface carboxyl groups. The electrolyte stability of these carboxylated latexes seems to be governed substantially by the density of carboxylate ions on the surface of particles irrespective of the polymerization process or the composition of polymers in the interior of particles.     

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.     

Preparation of small-sized carboxylated latexes by emulsion polymerization using alkali-soluble random copolymer

Alkali-soluble random copolymer (ASR), poly(styrene/α-methylstyrene/acrylic acid) [M_n: 4,300; acid number: 190], was used as a polymeric emulsifier in the emulsion polymerization of styrene and methyl methacrylate, respectively. ASR containing a large number of carboxyl groups could form aggregates like micelles, and the solubilization ability of the aggregates was dependent on the neutralization degree of ASR. The polystyrene latexes prepared using ASR showed the small particle size (ca. 40 nm) and monodispersed particle size distribution. On the other hand, the particle size distribution of poly(methyl methacrylate) latexes became broader as the neutralization of ASR increased. This could be explained by the effects of water solubility of the monomer and the neutralization degree of ASR on particle formation. Thin layer chromatography/flame ionization detector analysis confirmed that the grafting reaction of polystyrene to ASR occurred during emulsion polymerization. The ζ potentials of final latexes showed high values due to ASR that was adsorbed and grafted on the surface of the latex particle. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 543–550, 1998     

Characterization of polystyrene latexes

Polystyrene latexes were prepared by emulsion polymerization. Styrene was used as monomer, potassium persulfate was the reaction initiator and sodium hydrogen carbonate was used as buffer. Surfactant may or may not be used. Three types of surfactant, ie sodium dodecylbenzene sulfonate (anionic), Triton X‐100 and Vulcastab LW (nonionic), and hexadecyltrimethyl ammonium bromide (cationic), were used. The prepared latexes were characterized according to concentration, density, pH, ionic strength, particle size, particle size distribution and surface charge. For prepared latexes with anionic surfactant, the effects of temperature, initiator concentration, surfactant concentration and amount of monomer on the latex size were investigated. Scanning electron microscopy was used as a tool for latex characterization. The results show that by increasing temperature, initiator and emulsifier concentration, the latex diameter decreases. However, size increases by increasing the amount of monomer. A potentiometric titration technique was employed for determination of surface charge. It was found that for all latexes, surface charge densities are in the same range. © 2000 Society of Chemical Industry     

Preparation of high molecular weight monodisperse polystyrene latexes by concentrated emulsion polymerization

The preparation of high molecular weight monodisperse polystyrene (PS) latexes by the concentrated emulsion polymerization is investigated. The PS latexes thus obtained have diameters in the range of 0.1–0.3 μm. The average size and the dispersity of the latexes are dependent on the concentration of surfactant (SDS), the monomer volume fraction, and the amount of monpolymerizable additive (decane). The ionic strength does not seem to affect the size but affect the dispersity of the latexes. Under proper conditions, monodisperse particles can be prepared with a quite small standard deviation. © 1993 John Wiley & Sons, Inc.     

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 preparation of uniform polystyrene latices by true emulsion polymerization

Conventional emulsion polymerization of styrene produces some polydispersion in particle sizes in the latex. By carrying out a one-stage polymerization of finely emulsified monomer droplets of styrene formed in a mixture of methanol and water, it is possible to prepare stable latices of polystyrene in which the particles are perfectly uniform in size. The polymer has a relatively low molecular weight, but it is more stable to fragmentation by surfactant solutions than polystyrene prepared by conventional emulsion polymerization, the molecular weight of which is greater. The surface charge density of the particles is higher than that of particles produced by emulsion polymerization, and this probably accounts for the stability of the dispersion during polymerization and of the latex.     

无皂乳液聚合法合成单分散性阴离子聚苯乙烯微球

采用无皂乳液聚合法制备了粒径大小可控且均一的聚苯乙烯微球,研究了反应过程中SDS加入量、反应温度、引发剂加入量及反应介质对聚苯乙烯微球粒径大小及分布的影响。利用傅立叶变换红外光谱仪对微球结构进行了表征。     

Anchored block-copolymer surfactants for the synthesis of redispersible polystyrene latexes

Redispersible polystyrene (PS) latexes of particle sizes in the range of 200–220 nm was prepared using low-molecular-weight amphiphilic block copolymer surfactants. Latex powders were obtained by sun drying of the prepared PS latexes and were reintroduced into the solution by simple mechanical agitation/stirring without any additives. DLS and SEM analysis were carried out for pristine/sun-dried latexes to compare the size and shape of the particles. A series of block copolymers with 2-methyl-2-oxazoline and 2-butyl-2-oxazoline or 2-phenyl-2-oxazoline with repeat units 30/20, 60/20, 15/30, and 15/45 were synthesized through cationic ring opening polymerization (CROP) and were used as nonionic surfactants (NIS) in the preparation of poly(styrene) latexes by emulsion polymerization. In this work, we investigated the role of anchoring ability of butyl/phenyl groups of the block copolymer in providing stability and redispersibility of the latex by comparing with simply cetyl and stearyl surfactants that are devoid of such functionality. The ready redispersibility and retainment of size and shape as that of original latexes confirmed the role of anchoring groups. PS latexes prepared by block-copolymer surfactants that are devoid of anchoring units showed lesser stability and no redispersibility compared to anchored surfactants. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48875.     

Method for the determination of surface basic groups in cationic polystyrene latexes

The method for the determination of basic groups chemically bound to the surface of particles (surface basic groups) in cationic polystyrene latexes has been investigated. It is clarified that surface basic groups such as amidino groups resulting from 2,2′-azobis(2-amidinopropane) hydrochloride used as initiator and amino groups resulting from dimethyl aminoethyl methacrylate copolymerized can be determined accurately by the following method. First, latexes are cleaned and surface basic groups are converted into unneutralized from by ion exchange; then, latexes are titrated conductometrically with strong acid. By this method, however, surface amidino groups and surface amino groups cannot be determined separately.     

Influences of feeding strategies on AA and MAA carboxylated latexes

Semibatch, power feed, and shot‐addition feeding strategies were employed to synthesize carboxylated latex under acidic conditions, using emulsion polymerization. As a source of carboxyl groups, acrylic (AA) or methacrylic acid (MAA) was used. The distribution of carboxyl groups between feeding strategies were investigated using rheology, potentiometric/conductometric titrations, transmission electron microscopy, and FT‐IR spectroscopy. Upon alkalization, particle swelling was observed using dynamic light scattering. With increasing pH, both the AA‐ and MAA‐based latexes showed significant increase in hydrodynamic diameter as a consequence of the dissociation state of carboxyl groups. However, only MAA‐based latexes exhibit very pronounced increase in viscosity and storage modulus, and were therefore characterized as gels. The effect of feeding strategies was found to be more pronounced with the MAA functionalized latexes. By employing mentioned three procedures, significant differences in the rheological behavior of the neutralized dispersions were detected. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42062.     

Preparation and characterization of carboxylated isoprene/styrene copolymer latexes

Carboxylated isoprene/styrene copolymer latexes were prepared, and the concentration of surface carboxyl groups and the freeze–thaw stability of these latexes were measured. It is clarified that the introduction method of the carboxylic monomer governs the distribution of carboxyl groups in latex particles. Introduction of the carboxylic monomer prior to the initiation of polymerization localizes only 12–13% of total carboxyl groups on the surface of particles, whereas introduction of the carboxylic monomer at the last stage of polymerization localizes more than 60% of total carboxyl groups on the surface of particles, though the percentage is strongly dependent on the conversion when the monomers are shot. These latexes show a remarkable increase in the freeze–thaw stability with the increase in the degree of neutralization of surface carboxyl groups in a fairly narrow range. There exists a linear relationship between the surface area occupied by a surface carboxyl group and the degree of neutralization of surface carboxyl groups at which the remarkable increase in the freeze–thaw stability is observed. The result suggests that the freeze–thaw stability is substantially determined by the density of carboxylate ion on the surface of particles.     

Preparation of cationic polystyrene latexes in the absence of emulsifiers

Preparation of cationic polystyrene latexes has been investigated in the absence of emulsifiers. It is clarified that a stable latex can be obtained by using 2,2′-azobis(2-amidinopropane) hydrochloride as initiator (initiator process). The latex seems to be stabilized with the fragments of the initiator chemically bound to the surface of particles. More stable latexes can be obtained by copolymerizing cationic monomers such as dialkyl aminoethyl methacrylates (copolymerization process). The stability of these latexes may predominantly be attributed to cationic monomers chemically bound to the surface of particles. Stable latexes with high solids content can be obtained by using the two-step polymerization technique in the copolymerization process. The particle formation process in the initiator process and the copolymerization process is discussed.     

Photon transmission technique for studying film formation from polystyrene latexes prepared by dispersion polymerization using various steric stabilizers

A photon-transmission method was used to monitor the evolution of transparency during film formation from various polystyrene (PS) particles which were produced using different steric stabilizers, that is, poly(acrylic acid) (PAA), poly(vinyl alcohol) (PVA), and polyvinylpyrrolidone (PVP). The latex films were prepared from PS particles at room temperature and annealed at elevated temperatures in various time intervals above the glass transition (T_g). To simulate the latex film-formation process, a Monte Carlo technique was performed for photon transmission through a rectangular lattice. The number of transmitted (N_tr) photons were calculated as a function of particle–particle interfaces that disappeared. The increase in the transmitted photon intensity (I_tr) was attributed to the increase in the number of interfaces that disappeared. The Prager–Tirrell (PT) model was employed to interpret the increase in crossing density at the junction surface. The backbone activation energy (ΔE) was measured and found to be around 120 kcal mol⁻¹ for a diffusing polymer chain across the junction surface for all PS latex films. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1257–1267, 1998     

Determination of surface basic groups in cationic polystyrene latexes

Basic groups chemically bound to the surface of particles (surface basic groups) in cationic polystyrene latexes prepared by using 2,2′-azobis(2-amidinopropane) hydrochloride as initiator (initiator process) or by copolymerizing dialky aminoethyl methacrylates (copolymerization process) have been determined. It is clarified that in the initiator process amidino endgroups of polymers are effectively localized on the surface of particles and the latex is sufficiently stabilized with surface amidino groups. In the copolymerization process, the neutralized form of dialkylaminoethyl methacrylates is preferably localized on the surface of particles and the latex is sufficiently stabilized with surface amino groups. A particle formation process in both cases has been proposed.