Composite Latex Particles Research Articles

Control of particle morphology and film structures of carboxylated poly ( n butylacrylate)/poly (methyl methacrylate) composite latex particles

Particles with a soft (s) core of poly ( n-butyl acrylate)/poly (methyl methacrylate) (PBA/PMMA) copolymer and a hard (h) shell of PMMA were synthesized via a two-stage polymerization process. Two synthesis parameters were investigated: (i) the phase ratio of the core and the shell; and (ii) the compatibility of the two phases. The s/h phase ratio was varied from 100:0 to 0:100. The compatibility between the two phases was changed by (i) using acrylic acid (AA); (ii) by using pure PBA as core material; and (iii) by cross-linking the shell. Particle morphology was characterized by atomic force microscopy (AFM) on freeze-dried and on tempered single particles. The degree of coverage was found to depend on the shell content and the phase compatibility. The results are in good agreement with findings from transmission electron microscopy and solid state NMR given in Acta Polymerica [50 (1999) 347]. The experimental results are compared to predictions from simulation work on the particle morphology based on thermodynamic and kinetic considerations. The second part of the paper focuses on the phase distribution and the film morphology of films formed by the structured particles. Phase distribution at the surfaces, degree of film formation and the phase distribution in the bulk are characterized by AFM, cross-correlated and compared to the findings regarding particle structure in the first part of the paper. This approach is to our knowledge unique regarding its completeness and new in its methodology. The microscopic results concerning the bulk, the single particle and the surface properties are correlated to macroscopic properties like the minimum film forming temperature, pendulum hardness and gloss.

Preparation of polymer/inorganic nanoparticles composites through ultrasonic irradiation

AbstractIn this paper, ultrasonic induced encapsulating emulsion polymerization was first used to prepare the novel polymer/inorganic nanoparticles composites. The behaviors of several inorganic nanoparticles (SiO2, Al2O3, TiO2) under ultrasonic irradiation, such as dispersion, crushing, and activation, were studied. The dispersion stability, morphology, and structure of the ultrasonic irradiated nanoparticles were characterized by means of transmission electron microscopy (TEM), Fourier transform infrared (FTIR), and spectrophotometry, respectively. The results show that the inorganic nanoparticles in the aqueous solution can redisperse more effectively by ultrasonic irradiation than by conventional stirring. This is the basis for preparation of polymer/inorganic nanoparticles composites. By this technique, the long‐term stable latex, which mainly consists of polymer/inorganic nanoparticles composite latex particles, were successfully prepared. TEM, FTIR, thermogravimetric analysis, X‐ray photoelectron spectroscopy, spectrophotometry, and element analysis confirmed that well‐dispersed nanoparticles were encapsulated by the formed polymer, and the thickness of encapsulating polymer layer was in the range of 5–65 nm. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1478–1488, 2001

Synthesis and Physical Properties of the Crosslinking Poly(butyl acrylate)/ Polystyrene Core-Shell Composite Latex

Butyl acrylate and styrene were used as monomers in the first stage and second stage respectively, and potassium persulfate (K 2 S 2 O 8 ), as the initiator to synthesize the polymer/polymer composite latex by two-stage soapless emulsion polymerization. In the first stage, the poly(butyl acrylate) with crosslinking structure (PBA(XL)) was synthesized to be the seed latex. In the second stage, the styrene was polymerized in the presence of PBA(XL) seeds to form the PBA(XL) / PS composite latex. The morphology of the composite latex was observed by transmission electron microscopy (TEM) and showed that composite latex particles were with core-shell structure. The particle size distribution of the composite latex was very uniform. The kinetics of reaction of the second stage polymerization were investigated. The results showed that the reaction rate would be influenced by the degree of crosslinking of the PBA(XL) seeds, initiator concentration and agitation speed. The components of the PBA(XL)/PS composite polymers were measured by thin-layer chromatographic (TLC) analysis. The results showed a thin layer of PBA-graft-PS copolymer between the core (PBA) and shell (PS) region. The morphology of the PBA(XL)/PS composite polymers, processed under heat and pressure, was observed by transmission electron microscope (TEM). The morphology may change gradually with increase of processing time. The mechanical properties and rheological properties of the composite polymers were investigated.

Characterization of composite latex particles by positron annihilation spectroscopy

Characterization of composite latex particles by positron annihilation spectroscopy

A novel positively thermosensitive controlled-release microcapsule with membrane of nano-sized poly(N-isopropylacrylamide) gel dispersed in ethylcellulose matrix

A positively thermosensitive drug-release microcapsule (MC) with diameter around 100 μm was designed and its preparation was carried out by using an air suspension coating technique (the Wurster process). The MC had a core layered with carbazochrome sodium sulfonate (CCSS, a water-soluble model drug) particles and a thermosensitive coat composed of an ethylcellulose matrix containing nano-sized thermosensitive hydrogels. The hydrogel particles consisted of a newly synthesized composite latex with a poly(N-isopropylacrylamide (NIPAAm)) shell that could reversibly change the shell thickness in water with response to an environmental temperature change. This MC demonstrated a positively thermosensitive drug release: the release rate was remarkably enhanced at temperatures above a lower gel collapse point (temperature for complete deswelling) of 32°C, suggesting that the shrinkage of poly(NIPAAm) shells most likely created many voids in the coat and thereby imparted the higher water-permeability to the coat. Thermosensitivity of drug release highly depended on the composite latex particle content in the coat. It became most distinct when its content reached 12.5 and 15 wt%. In addition, it was found that the present MC membrane made it possible to obtain an ‘on-off’ pulsatile release, which could alter the release rate in the order of a minute, in response to stepwise temperature changes between 30 and 50°C.

Particle morphology of carboxylated poly-(n-butyl acrylate)/poly(methyl methacrylate) composite latex particles investigated by TEM and NMR

Particles with a copolymer soft core of poly(n-butyl acrylate)/poly(methyl methacrylate) (PBA/PMMA) and a homopolymer hard shell of PMMA were characterized using transmission electron microscopy and solid-state NMR spectroscopy. Two synthesis parameters were investigated: (1) the phase ratio of the core and the shell and (2) the compatibility of the two phases. A series of core-to-shell ratios from 100/0 to 25/75 were synthesized and characterized. The compatibility between the phases was changed (1) by using acrylic acid in either the core and the shell or in both, (2) by synthesizing a homopolymer or a copolymer core or (3) by introducing crosslinking points in the core. The combination of transmission electron microscopy and solid-state NMR spectroscopy allows quantitative determination of the extent of coverage of the core by the shell polymer and the interphase thickness; both were found to depend on the shell content and the compatibility of the phases.

Morphology and Film Properties of Composite Carboxylated Latexes

In industrial applications, such as paints or adhesives, composite latex particles are very common. Most of the properties which are obtained from composite latexes and their films cannot be achieved by physical blending of different polymer components. Therefore it becomes crucial to examine the morphology of composite latexes formed by a multiple-stage polymerization process. The latexes for this study have been examined by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Various staining methods were used such as ruthenium tetroxide (RuO4), cesium hydroxide (CsOH), and uranyl acetate (UAc) as a negative stain.The poly(n-butyl acrylate/ poly(methylmethacrylate) (PBA/PMMA) composite latex particles consist of a soft core phase and a hard second phase with varying amounts of acrylic acid in the core, the shell and in both core and shell. The latexes were examined before and after cleaning by a centrifugation technique with 100,000 molecular weight filters.

Mechanism and grafting reactions in seeded emulsion polymerization with emulsified monomer feeding

The seeded emulsion polymerization of styrene with emulsified monomer feeding was performed by polyethyl acrylate (PEA) latex as seed emulsion. It was shown that the grafting reactions occurred between two components on the composite latex particles. The loci of seeded polymerization were studied by the kinetics of grafting reaction. The highest grafting efficiency in the initial period of seeded emulsion polymerization supported the fact that the surfaces of PEA particles are the sites of polymerization of styrene. The grafting efficiency decreased with increasing monomer-to-polymer ratio and initiator concentration. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1495–1499, 1999

Study on the synthesis of poly(methyl methacrylate)-poly(methacrylic acid) composite latex and their humidity sensitive properties

The composite latex particles of poly(methyl methacrylate)–poly(methacrylic acid) [poly(MMA–MAA)] were synthesized through either soapless seeded emulsion polymerization or a soapless emulsion copolymerization technique. The reaction kinetics, morphology, and size of latex particles, composition, glass transition temperature (Tg), and molecular weight of polymer products were studied under different experimental conditions. Moreover, this work also focused on the humidity-sensitive properties of the polymer films fabricated by melting under the temperature of 200°C and followed by chemical modification with aqueous solution of NaOH. It is confirmed that there exists both an optimum ratio of hydrophilic to hydrophobic monomers and the initial structure of the latex particle to provide the humidity-sensitive polyelectrolyte film with excellent water resistivity and good sensitivity to humidity. Besides, little hysteresis and quick response were observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 47–57, 1999

Characterization of interphases in core—shell latexes by solid-state NMR

Concepts for the characterization of composite latex particles by advanced solid-state NMR methods are discussed. The techniques are based on 1H spin-diffusion experiments usually applied to detect heterogeneities in polymers and polymer blends. In latexes, they allow one to characterize the morphology, including substructures in the interphase between core and shell. Motional heterogeneities within the phases are also detected. The techniques are used to characterize an extended series of core—shell particles composed of poly(n-butyl acrylate) (PBuA) and poly(methyl methacrylate) (PMMA) synthesized in semicontinuous two-step emulsion polymerization processes. The influence of process parameters such as synthesis temperature, crosslinking density in the core, shell content, particle size, and annealing are investigated.

Morphology, thermal property, and mechanical property of core-shell latex polymers. I. Effect of heating and pressuring on PBA/PS linear composite polymer

In this work, butyl acrylate and styrene were used as monomers in the first stage and second stage of polymerization, respectively, and potassium persulfate (K2S2O8) was used as the initiator to synthesize the poly(butyl acrylate)–polystyrene (PBA/PS) composite latex by the method of two-stage soapless emulsion polymerization. The morphology of the latex particles was observed by transmission electron microscopy (TEM), which showed that the composite latex particles had a core–shell structure. The particle-size distribution of the composite latex was very uniform. A thin layer of a PBA-graft-PS copolymer was formed in between the core (PBA) and shell (PS) regions, which thus increased the compatibility between the PBA and PS phases. The process of heating and pressuring influenced the morphology, mechanical properties, and thermal properties of the PBA/PS composite polymer. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 13–23, 1998

The Morphology of Carboxylated Composite Latex and Latex Film

Abstract Carboxylated latex has become very important in the formation of polymer films. In order to study the film and its properties it is important to know the morphology of the latex that is forming the film. The latex for this study has been examined by transmission electron microscopy(TEM) using positive preferential stains such as ruthenium tetroxide (RuO4) and cesium hydroxide(CsOH); and uranyl acetate(UAc) as a negative stain. The polybutyl acrylate(PBA)/ polymethylmethacrylate(PMMA) composite latex particles consist of a soft core phase and a hard second phase with varying amounts of acrylic acid in the core, the shell and in both core and shell. The latexes were examined before and after cleaning. The cleaning was necessary in order to remove the surfactant and any small particles that might have formed during the emulsion polymerization. Prior to cleaning, the small particles adhered to the surfaces of the particles making it difficult to determine the final morphology of the latex particles.

Effect of amount of emulsifier added in the second stage on morphology of composite latex particles

In this article, PBA/P(MMA–crosslinking agent)-composite particle latexes were prepared by semicontinuous seeded emulsion polymerization. To determine the seed emulsion's saturating capacity of an emulsifier, a mathematical model was built to simulate the changes of the seed PBA emulsion's surface tension with the amount of emulsifier added dropwise. The effects of the emulsifier amount added in the second stage and the addition method on the morphology of the composite particles were studied. The results were shown as follows: If the amount of emulsifier added in one batch to the seed emulsion in the second stage was less than or equal to the saturating capacity of emulsifier of the seed emulsion (Cs), the morphology of the particles was “core–shell”; otherwise, a few particles were of a core–shell structure. However, if shell materials were preemulsified and added dropwise at an appropriate rate, the latex particles were still of a core–shell structure, even when the amount of emulsifier added to the seed emulsion was greater than the Cs. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 969–975, 1998

Effect of amount of emulsifier added in the second stage on morphology of composite latex particles

In this article, PBA/P(MMA–crosslinking agent)-composite particle latexes were prepared by semicontinuous seeded emulsion polymerization. To determine the seed emulsion's saturating capacity of an emulsifier, a mathematical model was built to simulate the changes of the seed PBA emulsion's surface tension with the amount of emulsifier added dropwise. The effects of the emulsifier amount added in the second stage and the addition method on the morphology of the composite particles were studied. The results were shown as follows: If the amount of emulsifier added in one batch to the seed emulsion in the second stage was less than or equal to the saturating capacity of emulsifier of the seed emulsion (Cs), the morphology of the particles was “core–shell”; otherwise, a few particles were of a core–shell structure. However, if shell materials were preemulsified and added dropwise at an appropriate rate, the latex particles were still of a core–shell structure, even when the amount of emulsifier added to the seed emulsion was greater than the Cs. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 969–975, 1998

Effect of the core/shell latex particle interphase on the mechanical behavior of rubber‐toughened poly(methyl methacrylate)

Two- and three-layer composite latex particles were used to prepare rubber-toughened poly(methyl methacrylate) (RT-PMMA). The interfacial thicknesses of the multi-layered particles were varied by using different emulsion polymerization synthesis techniques. The resulting interphases were previously characterized by 13C nuclear magnetic resonance techniques. The poly(divinyl benzene)/poly(butyl acrylate) (PDVB/PBA) interphase thickness was found to be in the range of 5–7 nm. It was also found that the PBA/PMMA interphase thickness could be varied from 5 to 7 nm (batch addition of MMA) to 15 to 17 nm (interphase compatibilized with PMMA macromonomer). The interphase thickness was expected to play an important role in the mechanical behavior of PMMA. The effect of the interphase of two- and three-layer particles on the tensile and fracture behavior of PMMA composites was evaluated. The fracture surfaces were examined by scanning electron microscopy. The two-layer PBA/PMMA particles with a thicker interphase (15–17 nm) exhibited higher KIC values with the PMMA composites compared with PBA/PMMA particles with a thinner interphase (5–7 nm). The three-layer particles were found to be more effective in toughening PMMA compared with the two-layer particles. The differences in toughening behavior are speculated to arise from the morphological effects caused by a thicker interphase, which in turn results in better coverage by the PMMA shell and a more uniform distribution of the toughening particles in the PMMA matrix. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:581–593, 1997

Grafting behavior of n‐butyl acrylate onto poly(butadiene‐co‐styrene) latexes

The radical-induced grafting of n-butyl acrylate (BA) onto poly(butadiene-co-styrene) [(P(Bd-S)] latexes during seeded emulsion polymerization was studied. This P(Bd-S)/PBA rubber/rubber core/shell latex system exhibited unique grafting behavior as compared to other extensively studied rubber/glass core/shell latex systems, such as poly(butadiene-co-styrene)/poly(methyl methacrylate) [P(Bd-S)/PMMA], poly(butadiene-co-styrene)/polystyrene [P(Bd-S)/PS] and poly(butadiene-co-styrene)/poly(acrylonitrile)[P(Bd-S)/PAN]. These composite latexes were characterized by the formation of a highly grafted/crosslinked P(Bd-S)/PBA interphase zone generated during the seeded emulsion polymerization process. Although both of the individual core and shell polymers studied were “soft” themselves, the resulting P(Bd-S)/PBA composite latex particles were found to be rather “hard.” The formation of the interphase zone was studied by using techniques such as solvent extraction, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:511–523, 1997

Preparation and morphological characterization of two- and three-component natural rubber-based latex particles

Different emulsion polymerization processes allowed variation in the microstructure of composite natural rubber (NR)-based latex particles. A prevulcanized and a not-crosslinked natural rubber latex were coated with a shell of crosslinked poly(methyl methacrylate) (PMMA) or polystyrene (PS). The bipolar redox initiating system tert-butyl hydroperoxide/tetraethylene pentamine promoted a core–shell arrangement. Furthermore, PS subinclusions were introduced into the NR core. The initiators used for the subinclusion synthesis were azobisisobutyronitrile at high temperature and a redox initiation system consisting of tert-butyl hydroperoxide/dimethylaniline at low temperature. The morphology of the resulting latex interpenetrating networks (IPN) was characterized by transmission electron micros-copy (TEM) and scanning electron microscopy (SEM). Different staining methods allowed us to increase the contrast between the NR phase and the secondary polymers in the composite latex particles. A semicontinuous feeding process decreased the PS subinclusions size by a factor of 6 in comparison with a batch reaction. Depending on the NR/styrene swelling ratio, the crosslinking degree, and the polymerization temperature used, distinct differences of the phase arrangement of polymers in the latex particles were revealed. © 1996 John Wiley & Sons, Inc.

Preparation and morphological characterization of two‐ and three‐component natural rubber‐based latex particles

Different emulsion polymerization processes allowed variation in the microstructure of composite natural rubber (NR)-based latex particles. A prevulcanized and a not-crosslinked natural rubber latex were coated with a shell of crosslinked poly(methyl methacrylate) (PMMA) or polystyrene (PS). The bipolar redox initiating system tert-butyl hydroperoxide/tetraethylene pentamine promoted a core–shell arrangement. Furthermore, PS subinclusions were introduced into the NR core. The initiators used for the subinclusion synthesis were azobisisobutyronitrile at high temperature and a redox initiation system consisting of tert-butyl hydroperoxide/dimethylaniline at low temperature. The morphology of the resulting latex interpenetrating networks (IPN) was characterized by transmission electron micros-copy (TEM) and scanning electron microscopy (SEM). Different staining methods allowed us to increase the contrast between the NR phase and the secondary polymers in the composite latex particles. A semicontinuous feeding process decreased the PS subinclusions size by a factor of 6 in comparison with a batch reaction. Depending on the NR/styrene swelling ratio, the crosslinking degree, and the polymerization temperature used, distinct differences of the phase arrangement of polymers in the latex particles were revealed. © 1996 John Wiley & Sons, Inc.

Preparation of composite latex particles by engulfment

It can be predicted that, provided the interfacial energies are well chosen for two individual particles, then it is possible to engulf one particle into the other. This has now been achieved experimentally using poly-[butylmethacrylate] particles as the host material and poly-[styrene] particles for engulfment. Initially, anionic poly-[styrene] particles were heterocoagulated onto electrosterically stabilised cationic particles of poly-[butylmethacrylate]. Then on heating the heterocoagulated units above the glass transition temperature of the latter engulfment occurred.

The Role of the Morphology of Natural Rubber and Polybutylacrylate‐based Composite Latex Particles on the Toughness of Polycarbonate\Brittle Polymer Blends

The dependence of the toughness of polycarbonate (PC)/poly(styrene-co-acrylonitrile) (PSAN) and PC/polystyrene (PS) blends on the architectural structure of incorporated natural rubber (NR) or poly(n-butylacrylate) (PBuA)-based latex particles is presented. By means of a twin screw extruder PC was melt blended with PSAN or PS blends containing different composite latex particles. Those materials that consisted of 70% PC could be effectively toughened by only 6–8% of the prepared toughening particles. Fractographic analysis by scanning electron microscopy has been used to analyze the failure mechanisms of the reinforced ternary PC blends. The principal feature of fracture surfaces of PC/PSAN blends containing pure NR particles was multiple rubber particle cavitation. A hard polymethylmethacrylate shell deteriorated the effectiveness of NR-based latex particles. Rigid PS subinclusions considerably increased the performance of the NR-based core—shell particles. They shifted the failure mechanism at impact from a brittle mode to a ductile tearing mode and much more energy could be absorbed. Good impact properties were also achieved in PC/PS blends reinforced by NR-based core—shell particles containing rigid subinclusions. The morphological structure of smaller-sized PBuA-based latex particles was less crucial.