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     

Morphologies of polybutylacrylate/poly(styrene‐co‐methyl methacrylate) latex prepared by starved emulsion polymerization Part I. Thermodynamics equilibrium morphology

Heterogeneous latexes were prepared by a semicontinuous seeded emulsion polymerization process under monomer starved conditions at 80 °C using potassium persulfate as the initiator and sodium dodecyl sulfate as the emulsifier. Poly(butyl acrylate) latexes were used as seeds. The second‐stage polymer was poly(styrene‐co‐methyl methacrylate). By varying the amounts of methyl methacrylate (MMA) in the second‐stage copolymer, the polarity of the copolymer phase could be controlled. Phase separation towards the thermodynamic equilibrium morphology was accelerated either by ageing the composite latex at 80 °C or by adding a chain‐transfer agent during polymerization. The morphologies of the latex particles were examined by transmission electron microscopy (TEM). The morphology distributions of latex particles were described by a statistical method. It was found that the latex particles displayed different equilibrium morphologies depending on the composition of the second‐stage copolymers. This series of equilibrium morphologies of [poly(butyl acrylate)/poly(styrene‐co‐methyl methacrylate)] (PBA/P(St‐co‐MMA)) system provides experimental verification for quantitative simulation. Under limiting conditions, the equilibrium morphologies of PBA/P(St‐co‐MMA) were predicted according to the minimum surface free energy change principle. The particle morphology observed by TEM was in good agreement with the predictions of the thermodynamic model. Therefore, the morphology theory for homopolymer/homopolymer composite systems was extended to homopolymer/copolymer systems. © 2002 Society of Chemical Industry     

Preparation of core-shell emulsion polymer and optimization of shell composition with respect to opacity of paint film

A series of core-shell latexes comprising a poly(n-butyl acrylate-co-methyl methacrylate-co-methacrylic acid) (PBA/MMA/MAA) core and a poly(styrene-co-acrylonitrile) (PS/AN), poly(butyl acrylate-co-methyl methacrylate) (PBA/MMA) shell were prepared at different shell composition ratios. These core-shell binders were used for preparation of decorative coatings. The latexes were synthesized by a semi-continuous sequential emulsion polymerization and characterized by using transmission electron microscopy (TEM), particle size analyser, viscometry and opacity of paint film. The core-shell emulsion with styrene/acrylonitrile ratio 60/40 as shell composition shows the best optical properties.     

Effects of compatibilizing agents in poly(n-butyl acrylate)/poly(methyl methacrylate) composite latexes

Graft copolymers with poly(n-butyl acrylate) (PBA) backbones and poly(methyl methacrylate) (PMMA) macromonomer side chains are used as compatibilizing agents for PBA/PMMA composite latexes. The composite latexes are prepared by seeded emulsion polymerization of methyl methacrylate (MMA) in the presence of PBA particles. Graft copolymers were already incorporated into the PBA particles prior to using these particles as seed via miniemulsion (co)polymerization of n-butyl acrylate (BA) in the presence of the macromonomers. Comparison between size averages of composite and seed particles indicates no secondary nucleation of MMA during seeded emulsion polymerization. Transmission electron microscopy (TEM) observations of composite particles show the dependence of particle morphologies with the amount of macromonomer (i.e., mole ratio of macromonomer to BA and molecular weight of macromonomer) in seed latex. The more uniform coverage with the higher amount of macromonomer suggests that graft copolymers decrease the interfacial tension between core and shell layers in the composite particles. Dynamic mechanical analysis of composite latex films indicates the existence of an interphase region between PBA and PMMA. The dynamic mechanical properties of these films are related to the morphology of the composite particles, the arrangement of phases in the films, and the volume of the interphase polymer. © 1997 John Wiley & Sons, Inc.     

Effect of the Crosslinking Agent Content on the Emulsion Polymerization Process and Adhesive Properties of Poly(N-Butyl Acrylate-Co-Methacrylic Acid)

A series of poly(n-butyl acrylate-co-methacrylic acid) with different contents of acrylic crosslinking agent (1,4-butanediol dimethacrylate, BDDA) latexes, named as poly(BA-co-MAA-co-BDDA), PBMABD, were synthesized via a two-stage sequential emulsion polymerization. During the polymerization, the particle sizes of the PBMABD latexes and conversions including instantaneous conversion and overall conversion of monomers were monitored online by dynamic light scattering (DLS) technology and gravimetric analysis in half-hour intervals, respectively. The overall conversions at the end of emulsion polymerization with different crosslinking agent contents were high, and the latex particles grew in a spherical shape without secondary particles during the growth process. The adhesive properties, including loop tack force, peel force and shear resistance, were evaluated systematically according to Fédération Internationale des Fabricants et Transformateurs d'Adhésifs et Thermocollants sur Papiers et Autres Supports (FINAT) test methods. When the content of the crosslinking agent was 0.5?wt%, a best equilibrium among the adhesive properties could be achieved. The adhesive properties of the PBMABD polymer were closely related to its viscoelastic behaviour and molecular structure, such as gel content and various molecular weight parameters.     

Morphology of poly(butyl acrylate)/poly(styrene‐co‐methyl methacrylate) latex prepared by starved emulsion polymerization: II. Development of particle morphology

Heterogeneous latexes were prepared by a two‐stage seeded emulsion polymerization process under monomer starved conditions at 80 °C using potassium persulfate as the initiator and sodium dodecyl sulfate as the emulsifier. Poly(butyl acrylate) latexes were used as seeds. The second‐stage polymer was poly(styrene‐co‐methyl methacrylate). By varying the amount of methyl methacrylate (MMA) in the second‐stage copolymer, the polarity of the copolymer phase could be controlled. It was found that the latex particles displayed different morphologies depending on the monomer ratio. The amount of MMA had a significant effect on the evolution of morphology. The morphologies were observed by transmission electron microscopy. In addition, the evolution of the particle morphology was predicted by the mathmatical model for cluster migration. The model gave the same trends as the experimental results. © 2002 Society of Chemical Industry     

Polymer–metal composite particles: Metal particles on poly(St‐co‐MAA) microspheres

Poly(styrene‐co‐methacrylic acid) P(St‐co‐MAA) microspheres with a monodisperse size distribution were prepared by emulsifier‐free emulsion copolymerization of St and MAA. The effects of MAA content on the polymerization rate and the content of MAA in the copolymer were investigated by gravimetrical and IR methods, respectively. The results of XPS measurement indicated the presence of a carboxyl functional group. By chemical metal deposition, nickel or palladium particles were formed and deposited on the surface of P(St‐co‐MAA) microspheres to form P(St‐co‐MAA)Ni or P(St‐co‐MAA)Pd composite particles. XRD measurement and TEM observation confirmed that nickel and palladium metal particles in a small size (20–40 nm) were distributed on surface of the copolymer microspheres. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1693–1698, 2000     

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     

Preparation and properties of poly[styrene‐co‐(butyl acrylate)‐co‐(acrylic acid)]/silica nanocomposite latex prepared using an acidic silica sol

BACKGROUND: Polyacrylate/silica nanocomposite latexes have been fabricated using blending methods with silica nanopowder, in situ polymerization with surface‐functionalized silica nanoparticles or sol–gel processes with silica precursors. But these approaches have the disadvantages of limited silica load, poor emulsion stability or poor film‐forming ability. RESULTS: In this work, poly[styrene‐co‐(butyl acrylate)‐co‐(acrylic acid)] [P(St‐BA‐AA)]/silica nanocomposite latexes and their dried films were prepared by adding an acidic silica sol to the emulsion polymerization stage. Morphological and rheological characterization shows that the silica nanoparticles are not encapsulated within polymer latex particles, but interact partially with polymer latex particles via hydrogen bonds between the silanol groups and the ? COOH groups at the surface of the polymer particles. The dried nanocomposite films have a better UV‐blocking ability than the pure polymer film, and retain their transparency even with a silica content up to 9.1 wt%. More interestingly, the hardness of the nanocomposite films increases markedly with increasing silica content, and the toughness of the films is not reduced at silica contents up to 33.3 wt%. An unexpected improvement of the solvent resistance of the nanocomposite films is also observed. CONCLUSION: Highly stable P(St‐BA‐AA)/silica nanocomposite latexes can be prepared with a wide range of silica content using an acidic silica sol. The dried nanocomposite films of these latexes exhibit simultaneous improvement of hardness and toughness even at high silica load, and enhanced solvent resistance, presumably resulting from hydrogen bond interactions between polymer chains and silica particles as well as silica aggregate/particle networks. Copyright © 2009 Society of Chemical Industry     

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.     

Preparation of temperature‐ and pH‐sensitive,stimuli‐responsive poly(N‐isopropylacrylamide‐co‐methacrylic acid) nanoparticles

The effects of the monomer ratio, surfactant, and crosslinker contents on the particle size and phase‐transition behavior of the copolymer poly(N‐isopropylacrylamide‐co‐methacrylic acid) (PNIPAAm–MAA) were investigated with Fourier transform infrared, differential scanning calorimetry, and dynamic laser scattering techniques. In addition to the thermoresponsive property of poly(N‐isopropylacrylamide), ionized methacrylic acid groups brought pH sensitivity to the PNIPAAm–MAA copolymer particles. The polymer particle size varied with the amounts of the monomer ratio, surfactant, and crosslinker. As the monomer ratio and crosslinker content increased and the amount of the surfactants decreased, the particle size increased. The influence of the crosslinker content on the particle size was less significant than the effect of the monomer ratio and surfactants. When the temperature increased, the particles tended to shrink and decreased in size to near or below 100 nm. Particle sizes at 20°C decreased to less than 100 nm with increased surfactant content. The control of the particle size within the 100‐nm range makes PNIPAAm–MAA copolymer particles useful for biomedical and heavy‐metal‐ion adsorption applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of porous poly(methacrylic acid‐co‐triethylene glycol dimethacrylate) by seed emulsion polymerization

Porous poly(methacrylic acid‐co‐triethylene glycol dimethacrylate) (poly MAA‐co‐3G) particles in the size range of 10–40 μm were prepared via seed emulsion polymerization. Mixtures of linear polymer, solvent, and/or nonsolvent were used as inert diluents. The prepared porous polymer was converted using hydroxylamine hydrochloride and sodium methoxide into the corresponding poly(hydroxamic acid). The surface area of the porous copolymer particles was determined colorimetrically. The effect of the diluent type and concentration on the surface area of the prepared porous polymer was examined. The metal ion absorption capacity of the resin toward the different metal ions was examined using an atomic absorption spectrophotometer. The thermal stability of the polymers was examined by thermal gravimetric analysis. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1209–1215, 2000     

Preparation and characterization of titanium dioxide core and polymer shell hybrid composite particles prepared by two-step dispersion polymerization

Titanium dioxide core and polymer shell composite poly (styrene-co-divinylbenzene)-methacrylic acid [P (St-co-DVB)-MAA]] particles were prepared by two-step dispersion polymerization. Fourier transform IR spectroscopy and elemental analysis were used to measure the content of methacrylic acid in composites particles. X-ray measurement photoelectron spectroscopy (XPS) measurements indicated the presence of an MAA unit on the surface of the composite particles. The combined results of the elemental analysis and the XPS measurements showed that the copolymer on the surface of poly (St-co-DVB)-MAA composite particles was rich in MAA compared with that in the interior of the composite particles. Field-emission scanning electron microscopy (FE-SEM) was used to study the morphology characterization. The composite particles produced showing good spectral reflectance compare with bare TiO₂. TGA results indicated that the encapsulation efficiency and estimated density of composite particles. Encapsulation of TiO₂ was up to 87.4% and the density was ranged from 1.78 to 2.06 g/cm³. Estimated density of the composite particles is suitable to 1.73 g/cm³, due to density matching with suspending fluid.     

Enhanced toughness for polyamide 6 with a core-shell structured polyacrylic modifier

Polyamide 6 (PA 6) is an important thermoplastic with excellent strength, stiffness, and good chemical resistance. The notch sensitivity and low notch impact toughness of PA 6, however, limit its application. A core-shell structured polyacrylic modifier, poly(n-butyl acrylate)/poly(methyl methacrylate-co-methacrylic acid) modifier (PBM-co-MAA), was used to toughen PA 6. To study the effect of PBM-co-MAA particles on the toughness of PA 6, various contents of poly(BA) in PBM-co-MAA latexes of 300 nm were synthesized by seed emulsion polymerization. The results showed that polymerization had an instantaneous conversion higher than 95 wt% and an overall conversion higher than 97 wt%. The PBM-co-MAA particles had a clear core–shell structure confirmed by transmission electron microscope (TEM). The mechanical properties of PA 6/PBM-co-MAA blends showed that the notch impact strength of PA 6/PBM-co-MAA blends with 85 wt% poly(BA) and 0.5 wt% MAA in PBM-co-MAA was nearly six times greater than that of pure PA 6, being consistent with the scanning electron microscope (SEM) observations on the fractured surfaces. The notch impact strengths of PA 6/PBM-co-MAA blends were also better than that of PA 6/PBM blend, which did not contain MAA functional group in the modifier. Dynamic mechanical analysis (DMA) results showed improved compatibility between PA 6 matrix and core-shell toughening modifier, which should contain a functional group in the shell layer and a suitable core rubbery content to toughen PA 6 effectively.     

Preparation and characterization of titanium dioxide core/polymer shell hybrid composite particles prepared by emulsion polymerization

Titanium dioxide inorganic core and polymer shell composite poly(methyl methacrylate‐co‐butylacrylate‐co‐methacrylic acid) [P(MMA‐co‐BA)‐MAA] particles were prepared by emulsion copolymerization. Fourier transform IR (FTIR) spectroscopy was used to measure the content of MAA composite particles. Dynamic light scattering (DLS) characterized the composite particle size and size distribution. The field emission SEM (FE‐SEM) results of the composite particles showed regular spherical shape and no bare TiO₂ was detected on the whole surface of the samples. The composite particles were produced, showing good spectral reflectance compared with bare TiO₂. TGA results indicated the encapsulation efficiency and estimated density of composite particles. Encapsulation efficiency was up to 78.9% and the density ranged from 1.76 to 1.94 g/cm³. Estimated density of the composite particles is suitable to 1.73 g/cm³, due to density matching with suspending media. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2970–2975, 2004     

Morphological studies in thermally initiated emulsion (co)polymerization without conventional initiators

Poly(methyl methacrylate‐co‐styrene) composite latices were prepared by thermally initiated seed emulsion (co)polymerization of styrene (ST), methyl methacrylate (MMA), or ST and MMA employing a PST or PMMA seed in the absence of conventional initiators. The changes of particle morphology, observed by transmission electron microscopy (TEM), were investigated by varying seed particle component, the weight ratio of monomer to seed polymer, monomer composition, and employing preswelling of the seed particles. The size distribution of polymer particles obtained from thermally initiated emulsion (co)polymerization was improved by employing the seed process. Hemisphere‐like, sandwich‐like, core‐shell, and inverted core‐shell particle morphologies were observed depending upon the polymerization conditions. The preswelling of seed particles did not affect the morphology of final particles. The particle morphologies, obtained from the thermal process, were compared with those obtained from conventional seed emulsion polymerization. The incorporation of an initiator fragment SO to polymer chain ends seemed to allow the PST chains to gain some hydrophilicity. From the observation of particle morphology, the hydrophilicity of involved polymers were in the following order: PMMA with ionic (? SO) chain ends > PMMA with no ionic ends > PST with ionic ends > 60% MMA P(MMA‐co‐ST) with no polar ends > 40% MMA P(MMA‐co‐ST) with no polar ends > PST with no polar ends. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1737–1748, 2002; DOI 10.1002/app.10581     

Viscoelastic properties and film morphology of heterogeneous styrene–butadiene latexes

Heterogeneous carboxylated styrene–butadiene (S/Bu) latexes were prepared by a twostage emulsion polymerization process, using three PS seeds with different molecular weights. The second-stage polymer was a copolymer with a fixed S/Bu ratio of 1 : 1 and a methacrylic acid (MAA) content of either 1 or 10 wt %. Morphological studies by transmission electron microscopy (TEM) as well as studies of the viscoelastic properties by mechanical spectroscopy have been performed on films prepared from the latexes. The studies showed that the glass transition temperature, T_g, of the second-stage polymer was considerably affected by copolymerization with MAA. An increase in the MAA content in the second-stage polymer increased the T_g of this phase significantly. Addition of DVB as a crosslinking agent in the preparation of the PS seed phase substantially increased the rubbery moduli of the films, whereas the glass transition temperature of the second-stage polymer was unaffected. On the other hand, the presence of a chain transfer agent reduced the glass transition of the second-stage copolymer containing 1 wt % MAA dramatically, whereas the rubbery modulus was unaffected. When the MAA content was increased to 10 wt % the influence of the MAA monomer had a dominating effect on T_g. Latexes containing 10 wt % MAA had T_g values close to each other, regardless of chain transfer agent present in the second-stage polymerization. It was found that the morphology of the latex particles influenced the rubbery modulus of the films. The presence of irregularly shaped seed particles in samples prepared from a crosslinked PS seed had a considerable reinforcing effect on the films, whereas spherical seed particles originating from core–shell particles had a less reinforcing effect. © 1996 John Wiley & Sons, Inc.     

Adsorption of Cu2+ ions with poly(N‐isopropylacrylamide‐co‐methacrylic acid) micro/nanoparticles

Chelation efficiency of stimuli‐responsive poly(N‐iospropylacrylamide‐co‐methyacrylic acid) (PNIPAAm‐MAA) nanoparticles with Cu²⁺ ions from CuSO₄·5H₂O solution and from wood treated with copper‐based preservatives was studied. It was shown that particle size played a very important role in the adsorption process. The nano‐scale particles showed much improved Cu ion adsorption efficiency, compared with the micro hydrogels. The amount of Cu ion adsorption increased with increase of MAA ratio in copolymers and adsorption efficiency decreased with increased particle size. Furthermore, the adsorption amount varied with adsorption temperature at temperatures both below and above the corresponding low critical solution temperature (LCST). The high adsorption efficiency of Cu ions by PNIPAAm‐MAA polymer particles provides an effective technique for recovering metal ions (e.g., Cu²⁺) from wood treated with metal‐based preservatives. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Dispersion polymerization of uniform cross‐linked polystyrene microspheres in butan‐1‐ol

Butan‐1‐ol can be used as the solvent in the synthesis of poly(styrene‐co‐divinylbenzene‐co‐acrylic acid) microspheres by dispersion polymerization of a mixture of styrene, divinylbenzene (DVB), and acrylic acid (AA). Varying the proportion of the crosslinker DVB affects the size distribution and particle morphology profoundly, with 0.5–1.0% w/w producing spherical particles, whereas 2.0% w/w DVB produces irregular, concave morphologies. Varying the amount of AA from 5–7% w/w increases the average diameter of the spherical particles, whereas 9% w/w AA results in ovoid particles with dimpled surface morphology. In an optimized synthesis using 1.0% w/w DVB and 5% AA, uniform polymer microspheres with an average diameter of 0.8 µm and a coefficient of variation (CV) of diameter of 8.2% are produced. The use of a medium‐polarity solvent, such as butan‐1‐ol, as the solvent for dispersion polymerization will facilitate the incorporation of non‐polar moieties, such as organically‐passivated quantum dots, into the polymer during synthesis. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43103.     

Synthesis of monodisperse crosslinked poly(styrene‐co‐divinylbenzene) microspheres by precipitation polymerization in acetic acid

Poly(styrene‐co‐divinylbenzene) microspheres with size ranging from 1.6 to 1.8 μm were prepared in acetic acid by precipitation polymerization. The particle size and particle size distribution were determined by laser diffraction particle size analyzer, and the morphology of the particles was observed with scanning electron microscope. Besides, effects of various polymerization parameters such as initiator and total monomer concentration, divinylbenzene (DVB) content, polymerization time and polymerization temperature on the morphology and particle size were investigated in this article. In addition, the yield of microspheres increased with the increasing total monomer concentration, initiator loading, DVB concentration and polymerization time. In addition, the optimum polymerization conditions for synthesis of monodisperse crosslinked poly(styrene‐co‐divinylbenzene) microspheres by precipitation polymerization in acetic acid were obtained. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012