PMMA Shell Research Articles

Synthesis and characterization of poly(butyl acrylate)/silica and poly(butyl acrylate)/silica/poly(methyl methacrylate) composite particles

AbstractPoly(butyl acrylate)/poly(methyl methacrylate) (PBA/PMMA) core–shell particles embedded with nanometer‐sized silica particles were prepared by emulsion polymerization of butyl acrylate (BA) in the presence of silica particles preabsorbed with 2,2′‐azobis(2‐amidinopropane)dihydrochloride (AIBA) initiator and subsequent MMA emulsion polymerization in the presence of PBA/silica composite particles. The morphologies of the resulting PBA/silica and PBA/silica/PMMA composite particles were characterized, which showed that AIBA could be absorbed effectively onto silica particles when the pH of the dispersion medium was greater than the isoelectric potential point of silica. The critical amount of AIBA added to have stable dispersion of silica particles increased as the pH of the dispersion medium increased. PBA/silica composite particles prepared by in situ emulsion polymerization using silica preabsorbed with AIBA showed higher silica absorption efficiency than did the PBA/silica composite particles prepared by direct mixing of PBA latex and silica dispersion or by emulsion polymerization in which AIBA was added after the mixing of BA and silica. The PBA/silica composite particles exhibited a raspberrylike morphology, with silica particles “adhered” to the surfaces of the PBA particles, whereas the PBA/silica/PMMA composite latex particles exhibited a sandwich morphology, with silica particles mainly at the interface between the PBA core and the PMMA shell. Subsequently, the PBA/silica/PMMA composite latex obtained had a narrow particle size distribution and good dispersion stability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3425–3432, 2006

Ag nanoparticles-coated silica–PMMA core-shell microspheres and hollow PMMA microspheres with Ag nanoparticles in the interior surfaces

This paper described a simple method of preparing Ag nanoparticles-coated silica–poly(methyl methacrylate) (PMMA) core-shell microspheres by chemical reduction and emulsion polymerization. Ag nanoparticles-coated silica microspheres were fabricated by chemical reduction. After adsorbing a layer of poly(vinylpyrrolidone) (PVP) and growing another layer of silica shell, the composite microspheres were modified by 3-(trimethoxysilyl) propyl methacrylate (MPS). Then using emulsion polymerization method, a layer of PMMA shell was formed on the composite particles. Etching away the silica microspheres by hydrofluoric acid (HF), the hollow PMMA microspheres with Ag nanoparticles in the interior surfaces were fabricated. These composite microspheres were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV–vis spectrophotometer.

SANS Study of Coated Block Copolymer Micelles

AbstractSummary: Multishell particles were prepared by γ‐radiation‐induced polymerization of methyl methacrylate (MMA) in polystyrene‐block‐poly(methacrylic acid) (PS‐b‐PMA) aqueous micellar solution and their structure was studied by small‐angle neutron scattering (SANS). Before polymerization, almost all MMA molecules are distributed in aqueous phase and only 1% of MMA is accumulated inside the micelles. The newly formed polymer (PMMA) is deposited on the surface of PS cores of the original micelles. The effect of the MMA concentration, micelle concentration, absorbed radiation dose, and absorbed dose rate on the characteristics of the resulting particles was examined. The thickness of the PMMA shell (20–218 Å for the presented series of samples) can be easily controlled by variation of monomer and/or micelle concentration. Universal plots of the core volume (PS+PMMA) and SANS curve were presented. These plots facilitate choosing proper monomer and micelle concentrations and detecting possible irregularities in the parameters of the resulting particles. magnified image

Preparation and Characterization of PAni‐PMMA Dispersions

Blends of polyaniline (PAni) and poly(methyl methacrylate) (PMMA) have been produced using core‐shell particle synthesis, which is advantageous because it allows changing surface‐related properties of PMMA with relatively small amounts of PAni and without the use of organic solvents. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements indicated that the deposition of polyaniline seems to alter the regular shape of the primary acrylic latex particles. The coverage of PMMA particles by PAni was confirmed by FTIR measurements, where distinct data were obtained from the transmission and diffuse reflectance modes, since the latter is surface sensitive. The zeta potential, which is also a surface‐related property, increased with the contents of PAni, as the shells probably became protonated with PAni in the emeraldine salt form. Coverage with PAni did not affect the thermal bulk properties of the PMMA shells.

Fabrication of a Highly Transparent Conductive Thin Film from Polypyrrole/Poly(methyl methacrylate) Core/Shell Nanospheres

Polypyrrole (PPy)/poly(methyl methacrylate) (PMMA) core/shell nanospheres with diameters of several tens of nanometers have been synthesized by two-step microemulsion polymerization, and highly transparent conductive thin films have been fabricated using the nanospheres as a filler in a PMMA matrix. The PPy/PMMA core/shell nanoparticles and their composite films have been extensively characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier-transform infrared (FT-IR) and UV-vis spectroscopies, and electrical-conductivity measurements. The fabricated polymer films containing the PPy/PMMA core/shell nanofillers show a much better transparent conductive performance than that of uncoated PPy nanoparticles with similar dimensions or bulk PPy particles with diameters of several hundreds of nanometers. The PMMA shell promotes compatibility of the conductive fillers with the PMMA matrix and enhances dispersion of the PPy/PMMA core/shell nanofillers. In addition, the nanometer-thick PMMA shell has a lower glass-transition temperature (Tg), and can be effectively annealed to form a conductive-filler network with a high electrical conductivity at a relatively low filler content.

Thermal properties of the γ-Fe 2O 3/poly(methyl methacrylate) core/shell nanoparticles

Thermal properties of γ-Fe 2O 3/poly(methyl methacrylate) (PMMA) core/shell particles with an average core size of 4 nm were studied through measurements of thermogravimetry, powder X-ray diffraction and magnetization. The thermal degradation of the PMMA shell in the air was found to occur at temperatures lower by about 60 °C than that of free PMMA. Random scission of the PMMA chains seemed to be catalyzed by the core oxide. The γ-Fe 2O 3 to α-Fe 2O 3 structural transformation took place at different temperatures depending upon the shell material. Namely, α-Fe 2O 3 was the only product for the caprylate-capped γ-Fe 2O 3 nanoparticles treated at 400 °C, whereas γ-Fe 2O 3 still remained for the γ-Fe 2O 3/PMMA composite treated at 500 °C. It is possible that some species containing silicon of the polymerization initiator origin were formed on the surface and prevented interparticle atomic diffusions needed for the γ– α transformation.

Preparation of polystyrene/poly(methyl methacrylate) composite particles having a dent

Nonspherical polystyrene (PS)/poly(methyl methacrylate) (PMMA) composite particles having a dent were prepared by releasing toluene from PS/PMMA/toluene droplets dispersed in a poly(vinyl alcohol) aqueous medium. An ex-centered PS-core/PMMA-shell morphology, in which a part of the PS core contacted with the aqueous medium and toluene partitioned more in the PS core than in the PMMA shell, was formed in the polymers/toluene droplet in the process of phase separation therein with releasing toluene. The volume of the dent became bigger with an increase in the PS content and in the toluene content partitioned in the PS core.

The role of surfactant in controlling particle size and stability in the miniemulsion polymerization of polymeric nanocapsules

The influence of surfactant concentration on particle size and stability of nanocapsules with liquid cores, synthesized by an in situ miniemulsion polymerization process, was investigated. Although the role of surfactant in the synthesis of particles in the nanometer range has frequently been documented, the transition to structured particles, which almost consist of a 1:1 weight ratio of encapsulated liquid hydrophobe to polymeric shell, has not received much attention. Capillary hydrodynamic fractionation (CHDF) analyses were used to evaluate particle size. Results were subsequently used to stoichiometrically calculate the area which is occupied per surfactant molecule on the particle surface. These results were compared with “classical” miniemulsion data, i.e. data generated from the synthesis of polymeric latexes in the presence of a hydrophobe, but at a much lower hydrophobe:monomer ratio as was used here. The surface coverage per surfactant molecule could be related to the surface tension of the latex, thus providing a relationship between particle size and stability. CHDF was furthermore used to investigate particle size after grafting of a secondary PMMA shell. Data obtained from CHDF experiments were in all cases confirmed by TEM analysis of the synthesized particles. To conclude, the synthesis of nanocapsules with liquid cores could be successfully scaled-up, with retention of all the characteristics of the final latex.

Blends containing core–shell impact modifiers. Part 4 – Fatigue crack growth behaviour

Fatigue crack growth measurements have been made on blends of polycarbonate (PC), poly(methyl methacrylate) (PMMA), poly(styrene-acrylonitrile) (PSAN) and poly(vinyl chloride) (PVC) with two impact modifiers. In one modifier, the particles have a polybutadiene core and a PMMA shell; in the other, there is a PMMA core, a poly(butyl acrylate-styrene) inner shell and a PMMA outer shell. The overall pattern of fatigue crack growth is similar in all eight blends, but there are significant quantitative differences in ΔKth, the threshold value of the cyclic range of stress intensity factor, and in the growth rate characteristics above ΔKth. These are related to various features seen on the fracture surfaces under the scanning electron microscope, and hence to the mechanisms of deformation and fracture near the crack tip, which include crazing, particle–matrix debonding, and ductile drawing.

Radiation-induced grafting polymerization of MMA onto polybutadiene rubber latex

The grafting of methyl methacrylate (MMA) onto polybutadiene rubber latex by the direct radiation method was carried out. The effects of monomer concentration, absorbed dose and dose rate of gamma rays on the grafting yield were investigated. The graft copolymers were characterized by transmission electron microscopy (TEM), FTIR spectroscopy, and differential scanning calorimetry. TEM photographs revealed that the core–shell structures of latex particles are formed at low MMA content, and with the increasing of MMA content, the semi-IPN-like structure with core–shell could be developed due to the high gel fraction of polybutadiene (PBD) seed particles. In addition, infrared analysis confirmed that MMA could be grafted onto PBD molecular chains effectively under appropriate irradiation conditions. The interfacial adhesion between PBD rubber (core) and PMMA (shell) phases could be enhanced with the increase of MMA concentration.

Structure-property relationships of in-situ PMMA modified nano-sized antimony trioxide filled poly(vinyl chloride) nanocomposites

Nano-sized antimony trioxide (Sb2O3) particles were modified by in-situ methyl methacrylate (MMA)/Sb2O3 polymerization. Subsequently, these modified nanoparticles were compounded with poly(vinyl chloride) (PVC) to prepare PVC/Sb2O3 nanocomposites. In-situ MMA/Sb2O3 polymerization kinetics shows that nano-Sb2O3 particles do not inhibit polymerization of MMA. PMMA shell covered on the surface of nano-sized Sb2O3 particles have enhanced interactions with PVC matrix, breaking down nano-Sb2O3 particle agglomerates and improving their dispersion in the matrix (average particle size of 60–80 nm) and also increasing the particle-matrix interfacial adhesion. Thus, nano-Sb2O3 particles reinforce and toughen PVC. It was observed that at 2.5 wt% of nano-Sb2O3 particles modified by in-situ PMMA optimal properties were achieved in Young's modulus, tensile yield strength, elongation at break and Charpy notched impact strength. Detailed examinations of micro-failure mechanisms of tensile specimens showed that nano-Sb2O3 particles acted as stress concentrators leading to debonding/voiding and deformation of the matrix material around the nanoparticles. Under impact fracture, the nano-Sb2O3 particles prolonged crack initiation time, and increased energy absorptions for crack initiation and fracture propagation caused by strong interfacial interaction between nanoparticles and PVC matrix. These mechanisms lead to impact toughening of the nanocomposites.

Poly(ethylene‐co‐vinyl acetate)‐graft‐poly(methyl methacrylate) (EVA‐graft‐PMMA) as a modifier of epoxy resins

AbstractConventional approaches to toughen thermosets are: (1) the polymerization‐induced phase separation of a rubber or a thermoplastic, or (2) the use of a dispersion of preformed particles in the initial formulation. In the present study it is shown that it is possible to combine both techniques by using graft copolymers with one of the blocks being initially immiscible and the other that phase separates during polymerization. This is illustrated by the use of poly(ethylene‐co‐vinyl acetate)‐graft‐poly(methyl methacrylate) (EVA‐graft‐PMMA) as modifier of an epoxy resin. EVA is initially immiscible and PMMA phase separates during polymerization. Blends of an epoxy monomer based on diglycidylether of bisphenol A (DGEBA, 100 parts by weight), piperidine (5 parts by weight), and PMMA (5 parts by weight), showed the typical polymerization‐induced phase separation of PMMA‐rich domains before gelation of the epoxy network. Replacing PMMA by EVA‐graft‐PMMA (5 parts by weight), yielded stable dispersions of EVA blocks, favoured by the initial solubility of PMMA blocks. Phase separation of PMMA blocks in the course of polymerization led to a dispersion of in situ generated biphasic particles (plausibly composed of EVA cores surrounded by PMMA shells), with average diameters varying from 0.3 to 0.6 µm with the cure temperature. This procedure may be used to generate stable dispersions of biphasic particles for toughening purposes.© 2002 Society of Chemical Industry

The evaluation of the size and the structure of the interphase in composite particles containing a macromonomer studied by solid-state NMR

The degree of coverage and the structure and thickness of interphases in composite latex particles consisting of a poly(butyl acrylate) (PBA) core incorporated with poly(methyl methacrylate) (PMMA) macromonomer of different molecular wieght and a PMMA shell was analyzed by using solid-state NMR spin-diffusion measurements. By changing the temperature at a given filter strength or by adjusting the filter strength at a given temperature, the spin-diffusion experiment could be performed in such a way that the overall structure could be detected. At filter strengths softer than necessary for the detection of the overall structure, information regarding larger structures can be obtained, whereas for stronger filters detailed information about small structures in the interphase region can be extracted. The data obtained by NMR were related to previous TEM and dynamic mechanical studies on these particles.

Influence of the Addition of Polystyrene-block-poly(methyl methacrylate) Copolymer (PS-b-PMMA) on the Morphologies Generated by Reaction-Induced Phase Separation in PS/PMMA/Epoxy Blends

Homogeneous solutions of polystyrene (PS) and poly(methyl methacrylate) (PMMA) in diglycidylether of bisphenol A, containing about 8 wt.-% total thermoplastic, and with or without 0.5 wt.-% of a PS-b-PMMA block copolymer, were polymerized in two ways (i) in the presence of a tertiary amine (benzyldimethylamine, BDMA), or (ii) using a stoichiometric amount of a diamine (4,4′-diaminodiphenyl sulfone, DDS). A double phase-separation was recorded by light transmission during polymerization. A PS-rich phase was separated at low conversions and a PMMA-rich phase was segregated at more advanced conversions. The addition of the block copolymer produced significant changes in the morphologies generated. For the BDMA-initiated polymerization, the presence of the block copolymer made the small PMMA-rich domains clearly discernible in transmission electron microscopy (TEM) micrographs. For the DDS-cured system, the addition of the block copolymer led to a dispersion of small PS-rich particles encapsulated by PMMA shells. The possibility of generating a stable dispersion of biphasic particles by polymerization-induced phase separation opens a new way to modify thermosetting polymers for toughening purposes.

Blends containing core-shell impact modifiers Part 1. Structure and tensile deformation mechanisms (IUPAC Technical Report)

Two impact modifiers, based respectively on polybutadiene (PB) and poly(butyl acrylate-co-styrene) (PBA), are compared in blends with four glassy polymers: polycarbonate (PC), poly(methyl methacrylate) (PMMA), poly(styrene-co-acrylonitrile) (PSAN), and poly(vinyl chloride) (PVC). Dynamic mechanical tests show glass transitions at about -80 °C in PB and -15 °C in PBA. Both modifiers have grafted PMMA shells, which are seen in the transmission electron microscope (TEM) to be about 10 nm thick. The two-stage PB particles have 200-nm-diameter polybutadiene cores, whereas the three-stage PBA particles have 260-nm-diameter PMMA cores, with 20-nm thick PBA rubber inner shells. Under tension, the PB particles cavitate to form single voids on reaching a critical volume strain, and subsequently offer little resistance to dilatation. By contrast, tensile tests performed in situ in the TEM show that the PBA shells form fibrils that are anchored to the rigid core, and act as constraints on further dilatation: the stresses developed in the PBA fibrils can be sufficient to draw fibrils from both the PMMA core and the PSAN matrix. There is evidence that the PMMA shells can debond from the matrix both in cryogenic fracture and in fatigue at 23 °C. Tensile dilatometry shows that the PB particles cavitate at higher strains than the PBA particles, but that the PB particles then cause a rapid volume increase, leading to a low strain at break. By contrast, the PBA particles produce a more controlled dilatation, and higher strains to break. Later papers in this series treat the mechanical and rheological behavior of these blends in more detail.

Interface, morphology, and the rheological properties of polymethylmethacrylate/impact modifier blends

Impact modifiers with grafted PMMA shell are used to modify polymethylmethacrylate matrix. The composition of the shell is chosen to enhance the interactions at the modifier/matrix interface and to obtain good dispersion of the impact modifier in order to optimize impact strength of the blend. The degree of interactions at the interface is characterized by the interfacial region where the chains of the matrix mix with those of the shell of the modifier. The deviation of the measured viscoelastic behavior of these blends from that predicted by the emulsion models has been attributed to the formation of the network structure due to the association of matrix chains with the shell of the modifier. It is expected that the network structure will decrease with increasing frequency and, as such, the effective volume of the particle is frequency dependent. This study uses the emulsion models to estimate the larger effective volume of the particle and, therefore, the extent of interaction at the interface. In the blends of this study it can be shown that at low modifier levels the solvent swelling of the modifier shell results in stronger interactions with the matrix; this effect is negated by the aggregation of particles at higher modifier loadings. The interaction of core modifier with the PMMA matrix seems to be similar to that of the core-shell modifier. This would not be expected from the calculated interfacial thickness of approximately 4 nm. It is, therefore, proposed that during melt-processing the core modifier surface was altered due to grafting of the matrix PMMA chains during melt-blending to (BA/St) copolymer of the core modifier thus reducing the interfacial tension. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2623–2634, 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

The role of dispersed phase morphology on toughening of epoxies

The use of structural core/shell latex particles as toughening agents provides a model system which allows independent control of several key factors that influence the fracture toughness of modified plastics. This paper focuses on varying the shell composition of poly(butadiene- co-styrene) [P(B-S)] core/poly(methyl methacrylate) (PPMA) shell particles by incorporating acrylonitrile (AN) comonomer into the PMMA shell at various AN/MMA ratios and by crosslinking of the shell at various AN/MMA ratios. It was found that the degree of particle dispersability in the epoxy matrix can be precisely controlled by the AN content in the PMMA shell and by crosslinking the PMMA in the shell. It was also found that the degree of particle dispersability plays a crucial role on the fracture toughness of the modified epoxies. A microclustered morphology provides a much higher toughness than a uniform particle distribution.

Effect of the Composition of Structured Rubber Particles on the Toughness of Poly(methylmethacrylate)

Composite natural rubber (NR) and monodisperse poly(n-butyl-acrylate) (PBuA) based latex particles were tested as possible impact modifiers for a poly(methylmethacrylate) (PMMA) matrix. A continuous extrusion process was used for the incorporation of wet latexes directly into a twin-screw extruder. All latexes had been coated by a PMMA shell. Furthermore, polystyrene (PS) subinclusions were introduced into the NR core. The impact resistance of the prepared PMMA blends can be most effectively improved by NR particles containing a large weight fraction of compatibilising PMMA in the shell. The degree of crosslinking of the shell polymer has to be restricted. PBuA based latex particles of 180 nm in size are ineffective to toughen the PMMA matrix. The degree of grafting of the NR phase in core-shell particles containing PS subinclusions is not crucial. Scanning electron microscopy was used to analyse the failure processes in composite rubber particle toughened PMMA blends at fast (impact conditions) and slow (tensile testing) deformation speeds.

Thermodynamics of solubilization of functional copolymers in the grafted shell of core-shell impact modifiers: 2. Experimental

Certain styrene/maleic anhydride copolymers (SMA) are completely miscible with poly(methyl methacrylate) (PMMA). This paper explores the solubilization of SMA copolymers in the grafted PMMA shell layer of emulsion-made core-shell impact modifiers by examining glass transition behaviour and morphology of SMA/core-shell modifier blends. There appears to be a single, composition-dependent hard phase T g for these blends at all compositions by dynamic mechanical analysis. Transmission electron microscopy reveals that SMA copolymers are evenly distributed around the core-shell particles. Neither approach was able to determine the upper solubilization limit expected from theoretical considerations. A blend of core-shell modifier with polystyrene (PS), which is not miscible with PMMA, was also examined for comparison.