Stable Latexes Research Articles

RAFT ab initio emulsion copolymerization of γ-methyl-α-methylene-γ-butyrolactone and styrene

RAFT ab initio emulsion copolymerization of γ-methyl-α-methylene-γ-butyrolactone (MeMBL) and styrene with various monomer ratios was investigated with PAA20-PS5 trithiocarbonate being mediator and surfactant at 70 °C. The polymerization was fully controlled as evidenced by stable latexes, well predicted molecular weights and low PDIs about 1.2 when [MeMBL]:[St] ≤ 1:2. However, in the case of [MeMBL]:[St] = 1:1, the molecular weight became out of control due to gel effect of RAFT reactions. The relatively water-soluble MeMBL was found to dramatically influence the polymerization kinetics and copolymer properties, as evidenced by (1) No inhibition period was observed; (2) The copolymer compositions in the early stage of polymerization were much higher than those predicted by the Mayo-Lewis equation in the case of [MeMBL]:[St] = 1:2, leading to the formation of linear gradient copolymer. (3) Tgs of the copolymers from emulsion copolymerization were higher than those from bulk copolymerization. It was concluded that we could synthesize the gradient copolymer with preset molecular weight and low PDI in RAFT emulsion polymerization, Tg of which should be much higher than 100 °C.

High polymer/surfactant ratio in the seeded semicontinuous heterogeneous polymerization of vinyl acetate

AbstractVinyl acetate (VAc) was polymerized by a seeded semicontinuous heterogeneous process. Stable latexes with a polymer/surfactant weight ratio of 65 were obtained, which is comparable with the highest value reported in the literature for emulsion polymerization but with the advantage of obtaining smaller particles (average diameter, Dp = 53 nm) which are similar to those obtained by microemulsion polymerization. The surfactant (sodium dodecylsulfate, SDS) concentration used in the recipe (0.32 wt%) is much lower than those typically used in microemulsion polymerization. Although molar masses increased during the continuous monomer addition period, they were small at the end of the reaction (Mn = 69 × 103 g·mol–1) and this was attributed to bimolecular termination inside the particles. The values of polymerization rate (Rp) and monomer addition rate (Fm) were nearly the same, indicating that polymerization was performed under monomer starved conditions. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers

Particle nucleation in high solids nitroxide mediated emulsion polymerization of n-butyl acrylate with a difunctional alkoxyamine initiator

In this work, we seek to understand the nature of the relationship between increasing alkoxyamine initiator concentration and increasing particle size for the SG1-mediated, two stage emulsion polymerization of n-butyl acrylate. Using a difunctional alkoxyamine, based upon the commercially available BlocBuilder MA, we studied the impact of various factors on the particle size in the 1st stage (particle nucleation) of the polymerization; these include ionic strength, pH, buffer (type and concentration) and surfactant concentration. The results suggest that superswelling of the particles during nucleation has significant influence on the behaviour of the system. In applying these strategies, we demonstrate that colloidally stable latexes can be created at 45 wt% solids with molecular weight >70 kg mol−1.

Thiol-terminated hydroxy-functional polymer as a transtab toward polymer latex particles

Hydroxy-functional macrodisulfides have been synthesized by atom transfer radical polymerization of 2-hydroxyethyl methacrylate or 2-hydroxypropyl methacrylate in 2-propanol. Mean degrees of polymerization of the polymer chains beside the disulfide were fixed at 30, 60, and 90; since ATRP has reasonably good living character, the molecular weight distribution is relatively narrow. Furthermore, the macrodisulfides were reduced to synthesize corresponding thiol-terminated polymers with relatively narrow molecular weight distributions. 1H nuclear magnetic resonance and gel permeation chromatography were used to characterize the macrodisulfides and thiol-terminated polymers in terms of their chemical structure, molecular weight, and polydispersity, respectively. Dispersion polymerizations of styrene using the thiol-terminated hydroxy-functional polymers as a transtab (chain transfer agent + colloidal stabilizer) in ethanol resulted in colloidally stable submicrometer-sized polystyrene latex particles. Scanning electron microscopy, Fourier transform infrared spectroscopy, and elemental microanalysis were used to characterize the particles in terms of their morphologies, particle sizes and their distributions, and chemical compositions.

Study on the Synthesis of Polyester Type Waterborne Polyurethane and Modifying by Nano-Sized Particles

The waterborne polyurethane was prepared by reaction between polyester polyol and isophorone diisocyanat, different nanoparticles were filled into the system for modification. The effect of different ratio of materials, the kinds and mass of nanoparticles on the characters of waterborne polyurethane latex and film were investigated. The results showed that the stable polyurethane latex and polyurethane film with perfect characters could be prepared when the ratio of NNCO/NOH was 2.5~3.0, the DMPA with a mass fraction of 5%~6% was added into reaction as a macromolecule extender after adding small molecule chain extender BPO. Filling nanoparticles into the polyurethane latex could improve the water resistance and mechanical characters of the film. Nano-sized SiO2 was a better modifier than TiO2, and the appropriate mass fraction of SiO2 was 6% of polyurethane raw materials.

Core‐shell latex synthesized by emulsion polymerization using an alkali‐soluble resin as sole surfactant

AbstractA series of alkali‐soluble resins were prepared from esterification reaction of styrene‐maleic anhydride copolymer (SMA) and four fatty alcohols having different alkyl chains. The critical aggregates concentration of the prepared hemiester was lower than SMA, indicating that modification of SMA resin with long alkyl chains could improve their emulsification efficiency. The detailed experiments of emulsion polymerization of methyl methacrylate and butyl acrylate using these hemiesters as sole surfactants showed that SMA‐C12‐75, SMA‐C14‐70, and SMA‐C16‐65 were good surfactants. In the end, we successfully prepared stable latexes using above three good surfactants with relatively low surfactant concentration and high solid content. Characterization of latexes by Zetasizer and transmission electron microscopy revealed that particles of these latexes have core‐shell nanostructure with average particle size below 60 nm. Compared with SMA, the improvement of emulsification efficiency of its hemiesters may come from the better hydrophilic‐lipophilic balance and steric stabilization after incorporation of long alkyl chain. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Studies on the Preparation of Stable PSt Latex in the Presence of Cyclodextrins and a Small Amount of Surfactant

Polystyrene (PSt) latex was successfully prepared via emulsion polymerization using a novel sequential feeding way. In our method, polymerization was conducted in the presence of beta-cyclodextrin (β-CD) and a small amount of surfactant. The concentrations of the surfactant, β-CD and initiator, and the including time of St with β-CD acted as crucial roles in the preparing process. The results showed that the coagulum decreased with increasing of the concentration of the surfactant. The coagulum also decreased greatly when the amount of β-CD was lower than 1%. Furthermore, the coagulum decreased at the early stage and then increased with the increase of the concentration of initiator. Also, the monomer conversion increased by increasing the amount of surfactant and initiator. The morphology of the obtained particle was examined with a transmission electron microscope (TEM). The particle size increased constantly with the increase of the amount of β-CD. Otherwise, it decreased with the increase of the concentration of surfactant and initiator. Comparing with the semicontinuous condition, the sequential feeding way improved the monomer conversion, polymerization rate and the monodispersity.

높은 제타전위를 갖는 단분산의 블루착색 고분자미립자의 제조

2단계 유화중합에 의한 단분산의 블루칼라 착색 poly(styrene-co-acrylic acid) 라텍스를 성공적으로 제조하였다. 0.21 <TEX>${\mu}m$</TEX>의 polystyrene 시드를 이용하여 중합 2단계에서 Blue 606 염료와 acrylic acid의 중합으로 carboxyl 음이온을 갖는 블루칼라 라텍스를 합성하였다. 본 연구에서 제조한 블루칼라 라텍스는 모두 1.01 이하의 우수한 단분산도를 가지며 0.25~0.42 <TEX>${\mu}m$</TEX> 범위의 입자경을 나타내었다. 중합 2단계에서 acrylic acid 부가시간이 늘어남에 따라 입자경은 증가하였고 30 min 이상으로 늘어남에 따라 콜로이드 안정성을 갖는 블루칼라 라텍스가 제조되었다. 20 wt% AA 농도에서 -145 mV의 제타전위와 <TEX>$-9.4{\times}10^{-6}\;cm^2/Vs$</TEX>의 전기영동이동도를 나타내었다. 25 wt% DVB 농도하에서 396.7 K의 높은 유리전이온도를 나타내었다. Monodisperse blue-colored poly(styrene-co-acrylic acid) latices were successfully prepared by seeded emulsion polymerization. Blue-colored latices with carboxyl anionic charge on the surface were synthesized at the second stage with the introduction of Blue 606 dye, acrylic acid, and 0.21 <TEX>${\mu}m$</TEX>-polystyrene seed. All the blue-colored latices synthesized in this study were in the size range of 0.25~0.42 <TEX>${\mu}m$</TEX> and all uniform with less than 1.01 in PSD. The particle size increased with the addition of acrylic acid being delayed and colloidally stable latices were obtained over 30 min after its addition. The blue-colored latex with 20 wt% acrylic acid showed -145 mV of zeta-potential and <TEX>$-9.4{\times}10^{-6}\;cm^2/Vs$</TEX> of electrophoretic mobility, and with 25 wt% of DVB showed high <TEX>$T_g$</TEX> at 396.7 K.

On the stability and properties of the polyacrylate/Na-MMT nanocomposite obtained by seeded emulsion polymerization

For high performance waterborne coatings usually polymer latexes with low emulsifier content are more preferred. Although polymer/clay nanocomposites offer improved properties, it is difficult to produce clay based nanocomposite latexes containing low emulsifier due to the stabilization problems especially caused by organoclays. Present study deals with the preparation of a tBA/BA/MAA ternary copolymer/clay nanocomposite containing 3wt.% sodium montmorillonite (Na+-MMT) via seeded emulsion polymerization. Experimentally it was observed that even the usage of hydrophilic clay caused stabilization problem and a certain amount of emulsifier (>1wt.%) was necessary to obtain stable latexes. In addition, the usage of a low molecular weight water soluble polymer as steric barrier was found to increase the stability of system. Obtained nanocomposite latex showed fine particle size diameter (127nm) and very narrow size distribution (PDI=0.06). The WAXD and TEM investigations indicated that a mostly exfoliated nanocomposite was obtained. Thermal analyses (DSC, DMTA and TGA) showed that there was no change at Tg of the copolymer while very high improvement was obtained for elastic modulus and a slight increase in thermal stability. According to the rheological measurements, the nanocomposite latex showed a higher low shear viscosity, a stronger shear thinning behavior and an improved physical stability in comparison to the reference latex.

Synthesis and characterization of covalently colored polymer latex based on new polymerizable anthraquinone dyes

Novel polymerizable red and yellow dyes, consisting of anthraquinone chromophore, alkyl spacer, and acryloyl group, were first synthesized and then used as comonomers in the semicontinuous emulsion copolymerization of styrene, butyl acrylate, and methacrylic acid to fabricate polymer latexes. The influences of the dye monomers on the emulsion polymerization process, the latex particle size and its distribution, the molecular weight of the latex polymer, as well as the light fastness of the polymer latex films, were investigated. Results indicated that, despite of the inhibition effect of the polymerizable dyes on polymerization, stable colored polymer latexes could be prepared with high conversion of total monomers, whereas the conversion of the polymerizable dye decreased as increasing the amount of dye. The light fastness of the covalently colored polymer latex films was proved to be much better than that of the noncovalently colored polymer latex films due to the covalent bond of dye and polymer chains.

Preparation of CO2/N2‐Triggered Reversibly Coagulatable and Redispersible Polyacrylate Latexes by Emulsion Polymerization Using a Polymeric Surfactant

We report here a novel approach for making reversibly coagulatable and redispersible polyacrylate latexes by emulsion (co)polymerization of methyl methacrylate (MMA) using a polymeric surfactant, poly(2-(dimethylamino)ethyl methacrylate)(10) -block-poly(methyl methacrylate)(14) . The surfactant was protonated with HCl prior to use. The resulted PMMA latexes were readily coagulated with trace amount of caustic soda. The coagulated latex particles, after washing with deionized water, could be redispersed into fresh water to form stable latexes again by CO(2) bubbling with ultrasonication. The recovered latexes could then be coagulated by N(2) bubbling with gentle heating. These coagulation and redispersion processes were repeatable by the CO(2) /N(2) bubbling.

Synthesis of Core-Shell Latex Particles Through One-Step Emulsion Polymerization

Polystyrene/polyacrylate acid (PSt/PAA) core-shell latex particles were obtained through a one-step emulsion polymerization by making use of controlled distribution of the reaction monomer at different temperatures. The polymerization conversion and stability were characterized to find appropriate synthetic conditions. The results show that the mixed solution of certain proportions of St, AA, and distilled water were inhomogeneous at lower temperature, e.g. 25°C, but the mixed solution would become more and more homogeneous with increasing temperature. The mixed solution became completely homogeneous at 75°C. After this, according to the results of uniformity degree change, the pre-emulsion temperature was set at 75°C, and the polymerization temperature was 65°C. α,α-Azobisisobutyronitrile was used as initiator. Stable latex and latex particles, with obvious core-shell structure, were obtained. The composition of the mixed solution was characterized by UV-vis spectrophotometry. The morphology of latex particles was observed using transmission electron microscopy and scanning electron microscopy. The research provides a new method to obtain polymer particles with a core-shell structure.

Preparation of polystyrene-clay nanocomposites via dispersion polymerization using oligomeric styrene-montmorillonite as stabilizer

This study describes the preparation of polystyrene–clay nanocomposite (PS-nanocomposite) colloidal particles via free-radical polymerization in dispersion. Montmorillonite clay (MMT) was pre-modified using different concentrations of cationic styrene oligomeric (‘PS-cationic’), and the subsequent modified PS-MMT was used as stabilizer in the dispersion polymerization of styrene. The main objective of this study was to use the clay platelets as fillers to improve the thermal and mechanical properties of the final PS-nanocomposites and as steric stabilizers in dispersion polymerization after modification with PS-cationic. The correlation between the degree of clay modification and the morphology of the colloidal PS particles was investigated. The clay platelets were found to be encapsulated inside PS latex only when the clay surface was rendered highly hydrophobic, and stable polymer latex was obtained. The morphology of PS-nanocomposite material (after film formation) was found to range from partially exfoliated to intercalated structure depending on the percentage of PS-MMT loading. The impact of the modified clay loading on the monomer conversion, the polymer molecular weight, the thermal stability and the thermomechanical properties of the final PS-nanocomposites was determined. Copyright © 2012 Society of Chemical Industry

Miniemulsification by catastrophic phase inversion

We present an alternative method for the preparation of high solids content, water-borne latex products from a combination of catastrophic phase inversion (CPI) and miniemulsification. Miniemulsions are commonly prepared by the direct emulsification of a monomer in water and subsequent miniemulsification using a high-shear technique. Herein high solid content dispersions of up to 80w/w% solids content monomer-in-water emulsions are prepared by catastrophic phase inversion followed by miniemulsification with a rotor-stator mixer. The subsequent miniemulsification of these monomer-in-water emulsions proves to be almost four times more energy efficient than is possible with direct miniemulsification using the same mixers and recipes. The highly concentrated miniemulsions thus obtained can be successfully diluted to different solid contents for polymerisation, without compromising the droplet size distribution, and used to produce colloidally stable latexes.

Stability Study of Chitosan-g-AM Inverse Emulsion

Graft copolymerization of chitosan and vinyl monomer (such as acryamide and acrylic acid) and application study of the copolymer used as papermaking additive were paid more and more attention in papermaking chemical industry. Chitosan and acrylamide(AM) monomer were graft copolymerizing in inverse emulsion. Several factors such as oil-water proportion, mass ratio of chitosan and AM, emulsifier types and ratio, and initiator concentration that affect the stability of inverse emulsion were elementarily studied. Stable latex can be gained when reaction condition was that the volume ratio of oil phase and water phase was 1:1, the weight ratio of chitosan and AM was 1:8, the initiator concentration was 0.8mmol/L, the dosage of emulsification agent was 8% of the oil phase weight and the weight ratio of 1227 and OP-10 was 1:1.

Stability Study of Chitosan-g-AM Inverse Emulsion

Graft copolymerization of chitosan and vinyl monomer (such as acryamide and acrylic acid) and application study of the copolymer used as papermaking additive were paid more and more attention in papermaking chemical industry. Chitosan and acrylamide(AM) monomer were graft copolymerizing in inverse emulsion. Several factors such as oil-water proportion, mass ratio of chitosan and AM, emulsifier types and ratio, and initiator concentration that affect the stability of inverse emulsion were elementarily studied. Stable latex can be gained when reaction condition was that the volume ratio of oil phase and water phase was 1:1, the weight ratio of chitosan and AM was 1:8, the initiator concentration was 0.8mmol/L, the dosage of emulsification agent was 8% of the oil phase weight and the weight ratio of 1227 and OP-10 was 1:1.

Synthesis of zinc oxide-encapsulated poly(methyl methacrylate)–chitosan core–shell hybrid particles and their electrochemical property

The synthesis of hybrid materials possessing zinc oxide nanoparticles encapsulated in core–shell polymer particles having poly(methyl methacrylate) core and chitosan shell (PMMA–CS/ZnO) was carried out via an emulsifier-free emulsion polymerization. The ZnO nanoparticles modified by 3-(trimethoxysilyl)propyl methacrylate (TPMZnO) were first prepared before being charged to the polymerization system. The effects of polymerization time (from 2h to 6h) and the amount of TPMZnO added (0.018g, 0.020g, and 0.030g) were studied. It was found that the polymerization time of 5h yielded colloidally stable hybrid latex with% MMA conversion up to 90%. Moreover, the increase in the amount of TPMZnO resulted in a decrease in% MMA conversion from 90% to 80%. It was also found from TGA analysis that the amount of TPMZnO added affected the percentage of TPMZnO encapsulation. PMMA–CS/ZnO particles with the size ranging from 173 to 245nm were observed by TEM. In addition, the PMMA–CS/ZnO hybrid latexes possessed high positive charges in the range of 40–51mV. The electrochemical property of the electrodes fabricated from PMMA–CS/ZnO nanoparticles was illustrated by cyclic voltammetry.

Imidazoline derivatives as promising cationic emulsifiers for styrene heterophase polymerization

The colloidochemical properties of new cationic surfactants synthesized from fatty acids of palm oil and diethylenetriamine are first studied. It is found that, at solution pH below 6.0, the examined surfactants exist mainly as salts formed from protonated surfactant molecules and residues of strong acids, e.g., hydrochloric acid. In the pH range above 7.0, the protonated and nonprotonated forms of the surfactants are at equilibrium, which shifts to the nonprotonated form with an increase in pH. The analysis of interfacial tension isotherms shows that the minimum values of the interfacial tension are achieved at pH 7.0 when the concentrations of the protonated and nonprotonated forms of surfactant molecules are equal. New cationic surfactants are used as emulsifiers in emulsion polymerization of styrene. It is found that stable polystyrene latexes with narrow particle size distributions and high positive ζ potentials (as high as +68.4 mV) can be obtained at styrene concentration in an initial emulsion of 25 vol % and surfactant concentration in an aqueous phase of 2 wt %. A hydrogen peroxide-iron(II) salt redox system is used as an initiator of polymerization at component concentrations equal to 5 and 0.05 wt % of the monomer, respectively.

Mg(OH)2/polystyrene Hybrid Nanocomposite Particles Prepared by Emulsion Polymerization

Core-shell type Mg(OH)2/polystyrene nanocomposite particles were prepared by the emulsion polymerization of styrene in the presence of surface-functionalized Mg(OH)2 particles. Platelet-like, 80 nm Mg(OH)2 particles were previously functionalized with 3-(trimethoxysilyl)propyl methacrylate and used for the polymerization to produce stable hybrid composite latexes. Polyencapsulation of the Mg(OH)2 particles in polystyrene matrix took place when the reaction was conducted with 10 to 30% w/w of Mg(OH)2 with respect to the monomer. With 40% loading of Mg(OH)2, an unstable latex having aggregated particles was produced. Transmission electron microscopic images revealed the hybrid composites to be multi-core/shell type encapsulated particles, while thermogravimetric analysis showed that a difference in the decomposition onset temperature of polystyrene was not apparent in the range of 0 to 40% content of nano-Mg(OH)2.

High Ionic Strength Promotes the Formation of Spherical Copolymer Particles

AbstractA comprehensive experimental study of thermally initiated styrene‐styrene sulfonate emulsion copolymerization in the presence of 15 different low‐molecular‐weight electrolytes clarifies the enormous influence of both the concentration and nature of the added salt on the outcome of the polymerization. The ionic strength (IS) has a direct influence on the styrene sulfonate content in the final copolymer and determines whether the physical state of the final reaction product is a solution or dispersion. Stable latexes have been obtained for IS as high as 18 M. Electron microscopy images show irregularly shaped clusters at low and spherical particles at high IS. The properties of the copolymer molecules and dispersion can be additionally modified by the chemical properties of the counter‐ and coions introduced with the salt.magnified image