Synthesis and characterization of fluorine-containing poly-styrene-acrylate latex with core–shell structure using a reactive surfactant

Fluorine-containing poly-styrene-acrylate (PSA) latex with core–shell structure was successfully synthesized by seeded semicontinuous emulsion polymerization using fluorine monomer Actyflon-G₀₄ and reactive emulsifier DNS-86. The chemical composition, morphology of latex, and surface composition of the latex film were characterized by Fourier transform infrared spectra, transmission electron microscopy, and X-ray photoelectron spectroscopy, respectively. The stability properties of latex were tested by Ca²⁺, centrifugal and mechanical stability tests, and the latex film was studied by water contact angle, water absorption ratio, and thermo-gravimetric analysis. The results show that fluorine-containing PSA latex particles with crosslinked core and crosslinked shell structure have excellent stability properties, and the film of latex has excellent water repellency, thermal stability, and chemical resistance properties when the amount of fluorine monomer was only 8.0 wt%.     

Comparison of film properties for crosslinked core–shell latexes

Thermosetting acrylic latexes were synthesized using butyl acrylate (BA), methyl methacrylate (MMA), 2-hydroxyethyl methacrylate (HEMA), and methacrylic acid (MAA) via seeded two-stage process. A 2-level factorial experimental design was employed to investigate the effect of hydroxyl (core phase), carboxylate (shell phase) groups, and type of surfactant (Triton X200, Tergitol XJ) on the mechanical properties of thermosetting latexes. Eight latexes with varying concentration of HEMA, MAA and two types of surfactants were synthesized and crosslinked with three crosslinkers. Latex functionality for crosslinking was located in the core only, the shell only, and both the core–shell with varying concentrations. Melamine-formaldehyde (hexamethoxymethyl melamine) resin was employed to crosslink hydroxyl functionalities in the core. Carboxylic acid groups in the shell were crosslinked with zinc ammonium carbonate. HDI isocyanurate (Desmodur N3300A) were used to crosslink with hydroxyl or carboxyl functional groups in core and shell. The mechanical properties of coatings were evaluated in terms of tensile properties, cross-hatch adhesion, pencil hardness, and impact resistance. Design of experiment (DOE) was utilized to investigate the effect of variables on mechanical properties of crosslinked thermoset films.     

Facile fabrication of polystyrene/halloysite nanotube microspheres with core–shell structure via Pickering suspension polymerization

In this article, a facile method for fabrication of core–shell nanocomposite microspheres with polystyrene (PS) as the core and halloysite nanotubes (HNTs) as the shell via Pickering suspension polymerization was introduced. Stable Pickering emulsions of styrene in water were prepared using HNTs without any modification as a particulate emulsifier. The size of the Pickering emulsions varied from 195.7 to 26.7?μm with the water phase volume fraction increasing from 33.3 to 90.9?%. The resulting Pickering emulsions with the water phase volume fraction of above 66.7?% were easily polymerized in situ at 70?°C without stirring. HNTs played an important role during polymerization and effectively acted as building blocks for creating organic–inorganic nanocomposite microspheres after polymerization. The sizes of PS/HNTs microspheres were roughly in accord with that of the corresponding emulsion droplets before polymerization. The effect of the water phase volume fraction on the stability of Pickering emulsions and the morphologies of nanocomposite microspheres was investigated by optical microscopy, confocal laser scanning microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and so on.     

Crosslinked polyurethane–epoxy hybrid emulsion with core–shell structure

An epoxy resin was used to prepare crosslinked polyurethane hybrid emulsion through the blocked NCO prepolymer mixing process. Due to their hydrophobicity, the amine chain extender, blocked –NCO, and epoxy are located inside the emulsion particles. Thus, the crosslinking reaction occurs mostly in the interior of the particles. In this way, the crosslinking density of the resin is increased without the use of solidifying agents or heating during film formation, and the stability of the emulsions remains uninfluenced. The effects of the type of amine chain extender and the type, dosage, and addition mode of the epoxy resin were studied in terms of mechanical properties and swelling properties in water and toluene of the cast films. Additionally, the stability of the single-pack hybrid emulsion was studied. The results showed that the sample prepared with diethylene triamine had good stability, chemical resistance, and high mechanical strength. The modulus and water resistance of the films increased with the epoxy resin content, which could reach 20 wt%. The type of amine chain extender affected the stability of the emulsions significantly. The molar ratio of NH/NCO at 1:1 led to the best film performance. The optimal temperature of the chain-extension reaction was approximately 80°C. The hybrid emulsions could be stored for at least 6 months without apparent performance changes.     

Rheological behaviors and structure of hydrophobically associating AM–SMA copolymers synthesized by microemulsion polymerization

A series of hydrophobically associating copolymers of acrylamide and hydrophobic stearyl methacrylate as comonomers were prepared by microemulsion polymerization. The rheological properties of the copolymers in aqueous solution depended on the content of hydrophobic monomer, initiator amount, surfactant concentration, the copolymer concentration and the addition of salt. The hydrophobically associating copolymers showed good temperature, shear, and salt resistance with the critical aggregation concentration around 0.6 g dL^?1. In addition, the apparent viscosities of hydrophobically associating copolymer solutions are increased remarkably by the addition of a small amount of NaCl and CaCl₂, respectively. FTIR and ¹H-NMR spectra indicate the structure of hydrophobically associating copolymers. The shear-thinning behavior of hydrophobically associating copolymer makes it useful in enhanced oil recovery and drilling fluids.     

Synthesis of superhydrophobic core–shell mesoporous silica nanoparticles

Mesoporous silica nanoparticles (MSNPs) have been used in variety of applications due to their morphology and porous structure. This work reports the one-pot synthesis of ultrahydrophobic MSNPs using N-cetyl-n,n,n trimethyl ammonium bromide as a cationic surfactant template and ethanol (EtOH) as a cosolvent to form mesopores in the MSNPs. The effects of EtOH on the size and the pore structure of the MSNPs were studied by scanning electron microscopy and transmission electron microscopy. The results show that an addition of EtOH led to an enlargement of the MSNPs and a change in pore structure from a lamellar structure to a radially oriented structure. Co-condensation with two different types of fluoroalkyl silanes; trimethyl(fluoromethyl)silane, and trichloro(1H,1H,2H,2H-perfluorooctyl)silane provided low surface energy MSNPs with a core–shell structure. An assembly on the surface of these F-MSNPs generated nanostructure surface roughness rendering an improvement in surface wettability with water contact angle of 158.6°, which is a characteristic of oleophobic and ultrahydrophobic material.     

Preparation of core–shell impact modifier particles for PVC with nanometric shell thickness through seeded emulsion polymerization

The improvement in toughness of rigid polymers like poly(vinyl chloride) (PVC) has been of great interest for developing their applications. This could be provided by designing impact modifiers which could be blended with the polymeric matrix. Here, core–shell type impact modifier particles with different glass transition temperatures of the shell and specifically, with nanometric shell thickness were prepared through seeded emulsion polymerization. The core consisted of polybutadiene particles and the shell was made of poly(methylmethacrylate-co-butyl acrylate) that was grafted onto the surface of the seed particles. The polymerization reaction was optimized and the resulting latex particles were well characterized by several techniques such as DSC, DLS, SEM, and TEM. It was found that the core–shell particles have diameters of about 350–360 nm, including the shell with thickness of almost 20–30 nm and glass transition temperatures ranging between 70 and 120 °C. The prepared particles were blended with PVC and the corresponding impact strengths of the moldings were measured by means of Izod impact test. The impact results revealed that by decreasing T _g of the shell in impact modifier particles, the impact resistance of the molded sheets increased remarkably. Also the brittle–ductile transition temperatures (BDTT) of the prepared blends were studied and an increase in BDTT was found with lowering T _g of the shell.     

Synthesis of ambient temperature self-crosslinking VTES-based core–shell polyacrylate emulsion via modified micro-emulsion polymerization process

Modified micro-emulsion polymerization was successfully used to synthesize a kind of ambient temperature self-crosslinking core–shell emulsion, consisting of polyacrylate core and vinyltriethoxysilane (VTES) modified polyacrylate shell, by varying the ratio of soft monomer (BA) and hard monomer (MMA) which is different in the core and shell. The emulsion and its film formed at ambient temperature were characterized by attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Core–shell structure was clearly shown in TEM micrographs, and two distinct glass transition temperatures (T _g) were confirmed by DSC analysis. Lower T _g of core phase analyzed by DSC and self-crosslinking properties of VTES characterized by crosslinking degree cause latex particles form continuous film at ambient temperature. Thermal and mechanical properties and the surface properties of the latex films were also investigated. Results showed that the core–shell latex films containing 5 and 7.5 % VTES exhibited higher thermal stability, better mechanical properties, higher contact angle, and water resistance compared with pure polyacrylate film.     

Synthesis and characterization of thermosensitive core–shell polymeric nanoparticles

Thermosensitive core–shell nanoparticles were synthesized by semicontinuous heterophase polymerization of styrene, followed by a seeded polymerization for forming a shell of poly(N-isopropyl acrylamide) (PNIPAM). Nanoparticles characterization by scanning transmission electronic microscopy showed core–shell morphology with average particle diameters around 40 nm. An inverse dependence of the particle size with temperature in the range 20–55 °C was identified by quasielastic light scattering measurements. As was expected for core–shell particles with PNIPAM as the shell, a volume phase transition near 32 °C was detected. In spite of thermosensitive properties of core–shell nanoparticles synthesized here, the volume percentage loss values were not so high, probably due to their relatively low content of PNIPAM.     

Synthesis and dynamic mechanical study of core–shell structure epoxy/polyacrylate composite particle

A material with high damping property and based on epoxy/polyacrylate (EP/PA) composite particles was synthesized by two-stage emulsion polymerization. Transmission electron microscopy (TEM) showed that the composite particles have a spherical morphology, a core–shell structure and a diameter of 100 nm–130 nm. Fourier transform infrared spectra (FTIR) indicated the cross-linking between EP groups in the core layer and carboxyl groups in the shell layer of the composite particles during film formation. The cross-linking reaction improved the dynamic mechanical property by the interaction of core and shell polymers. The effects of the cross-linking agent and ratio of the two polymers on the damping capacity were studied by dynamic mechanical analysis (DMA). DMA results revealed that a certain amount of acrylic acid could markedly enhance the loss factor (tan δ) and slightly widen the damping temperature range. When the EP/PA ratio was 1:7, peak values for tan δ of the composite materials could reach 2.10, exceeding the value for most damping materials. The result implies that the EP/PA composites have great potential application in damping steel surface coatings.     

Preparation of water soluble Am–AA–SSS copolymers by inverse microemulsion polymerization

Inverse microemulsion copolymerization of acrylamide (Am), acrylic acid (AA), and sodium 4-styrenesulfonate (SSS) initiated by redox initiators composed of ammonium peroxodisulphate (APS) and sodium bisulfite, and stabilized by the mixed emulsifier system sorbitan monooleate (Span-80) and polyoxyethylene sorbitan monooleate (Tween 80) were examined as a function of the combination of hydrophilic (Tween 80) and hydrophobic (Span 80) emulsifiers, reaction temperature, AM/AA mass ratio, SSS concentration, and initiator concentration. The physicochemical and thermal properties and the structure of this copolymer were also determined and discussed. The reaction rates for all runs of the experiments exhibited two intervals, which were typical of microemulsion polymerization. The copolymer had only one glass transition temperature of 115.5 °C, indicating a random structure.     

Preparation and characterization of novel polyethylene/carbon nanotubes nanocomposites with core–shell structure

Preparation of novel polyethylene/carbon nanotubes (CNTs) nanocomposites with core–shell structure was presented. The method involved in situ ethylene polymerization in which nanotube surface was treated with Grignard Agent, followed by reacting with active transition metal compound, TiCl₄. The multiwalled carbon nanotubes (MWCNTs) supported catalysts polymerize ethylene to form polymer nanocomposite. MWCNTs were homogeneously dispersed within polymer matrix, and as expected, the resultant nanocomposites featured core–shell structure which was confirmed by HRTEM. For the nanocomposite, the microscopic examination of the cryogenically fractured surface not only ensured a good distribution of carbon nano-particles in the PE matrix but also revealed the ductile-like fracture. The Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed for the study of covalent sidewall functionalization and chemical bonding environment of MWCNTs, also indicated effective immobilization of titanium catalyst on the MWCNTs surface. The crystalline properties, dielectric property and thermal stability of the nanocomposites were determined by WAXD, impedance analyzer and TGA. The dielectric result showed a slight decline of the dielectric constant of the nanocomposites with increase of the polymerization time, and lower dielectric loss was also observed.     

One-step synthesis of pH-sensitive poly(Acrylamide-co-Sodium Acrylate) beads with core–shell structure

This work describes a novel one-step method to prepare poly(AMm-co-AAcNa) pH-sensitive hydrogel beads with core–shell structure induced by a spontaneous phase separation process during polymerization. In virtue of the phase separation process, polymers with high molecular weight separate to the core phase whereas monomers are left in the shell. This redistribution inside the droplets enables the polymerization environment change sharply to endow the beads with different network structure in core and shell. FTIR spectrum and EDS show that core and shell share identical composition; yet GPC exhibits a bimodal molecular weight distribution which lead to a conventional network in core but a rich-in-branch network in shell. This difference in structure results in mainly three discrepancies in performance. The level of volume change that the beads exhibit at about pH = 4 is much more intense for shell than for core; the swelling/shrinking kinetics of the core and shell indicates that shell responses about 30 times faster than core does; fitting of the absorbency capacity exhibited that the ones of the core and shell are about 67 g/g and 2126 g/g, respectively. A microfluidic device with co-axial channel structure is introduced in this fabrication. The hydrogel beads exhibited narrow size distribution and the diameter of core and shell could be freely controlled by the high controllability of microfluidic technology and by manipulating the phase separation process. In sum, this method impart us an easy and fast-running way to obtain hydrogel beads with core–shell structure, which has potential in various applications like optical material, lenses and sensors.     

Ionic liquid mediated synthesis of silica/polystyrene core–shell composite nanospheres by radical dispersion polymerization

This report describes the novel preparation of silica/polystyrene (SiO₂/PS) core–shell composite nanospheres by in situ radical dispersion polymerization in an ionic liquid (IL). Silica nanoparticles were first surface modified by the silane coupling agent methacryloxypropyltrimethoxysilane (MPTMS), which is capable of copolymerizing with styrene and provided a reactive CC bond. Transmission electron microscopy (TEM) revealed core–shell morphology with smooth surfaces. X-ray photoelectron spectroscopy (XPS) analysis demonstrated that almost all of the SiO₂ nanoparticles were encapsulated by the polymer. The composite particles were also analyzed by FT-IR spectroscopy and thermogravimetric analysis (TGA). In principle, this simple and environmentally-friendly synthetic procedure can be employed to prepare other inorganic oxide-containing polymer composites.     

Thermoresponsive core–shell nanoparticles with cross-linked π-conjugate core based on amphiphilic block copolymers by RAFT polymerization and palladium-catalyzed coupling reactions

Well-defined amphiphilic block copolymers composed of S-vinyl sulfides and N-isopropyl acrylamide (NIPAM) were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. Thermoresponsive core–shell nanoparticles with cross-linked π-conjugate cores were obtained by in situ cross-linking reactions between 4-bromophenyl moieties in the block copolymers and diboronic acids or a diamine compound in the presence of a palladium catalyst following micelle formation in ethanol/H₂O or ethanol. We initially investigated RAFT polymerization of two S-vinyl sulfide derivatives, namely phenyl vinyl sulfide (PVS) and 4-bromophenyl vinyl sulfide (BPVS), using a dithiocarbamate-type chain transfer agent (CTA). Then, RAFT polymerization of NIPAM using poly(S-vinyl sulfide) macro-CTAs was conducted to synthesize the amphiphilic block copolymers. Suzuki and Buchwald-Hartwig coupling reactions were found to be effective in the preparation of core–shell nanoparticles with thermoresponsive shells and cross-linked optoelectronic cores. The resulting nanoparticles showed characteristic thermoresponsive properties, as confirmed by turbidity and dynamic light scattering measurements. Stable and uniform core cross-linked nanoparticles were successfully prepared by the in situ palladium-catalyzed coupling reactions, and the optoelectronic and thermoresponsive properties of the nanoparticles could be tuned depending on the nature of the difunctional coupling agents, reaction conditions, and comonomer composition of the block copolymers.     

Synthesis of silane monomer-modified styrene–acrylate microemulsion coatings by photopolymerization

A relatively concentrated silane monomer-modified styrene–acrylate microemulsion coating with high monomer to surfactant ratio of 7.5:1 has been prepared by microemulsion photopolymerization. The properties and the structure of the microemulsion coatings were investigated using TEM, FTIR and UV–vis measurements. The microemulsions are transparent with high transmittance in the visible range. The particle sizes of the produced latexes are in the range of 34–52 nm with the number average diameter of 40.9 nm and D_w/D_n of 1.16. FTIR spectrum indicates the possible structure of the silane monomer-modified styrene–acrylate copolymer, and confirms the hydrolysis and condensation resulting in siloxane bonds between polymer particles. The microemulsion coatings show enhanced acid, base and water resistance with decrease of surfactant content and increase of silane coupling agent.     

Carbon nanotube-gelatin-hydroxyapatite nanohybrids with multilayer core–shell structure for mimicking natural bone

We attempted to mimic collagen fibrils bearing apatite crystals in natural bone, using gelatin, carboxylic acid functionalized carbon nanotubes (f-CNTs), and hydroxyapatite (HA). Gelatin molecules were covalently grafted on the surface of f-CNTs by the formation of amide linkages. HA crystals were then assembled onto the gelatin-grafted f-CNTs in a highly concentrated CaP solution, resulting a multilayered core–shell structure, consisting of a f-CNT core and gelatin-HA shells (as a fibrous multilayered f-CNT/Gel/HA nanohybrid), and in a similar formation to the collagen fibers of natural bone. The tensile strength, elastic modulus, and elongation rate of the new hybrid material were significantly improved compared to both pure (f-CNT free) gelatin and a mixture of f-CNT and gelatin, by 4.6–8.8, 9–10, and 28–42 times, respectively. Cell viability studies of the f-CNT/Gel/HA nanohybrid also suggest a higher degree of biocompatibility compared to pure gelatin.     

Inorganic microencapsulated core/shell structure of Al–Si alloy micro-particles with silane coupling agent

Al–Si eutectic alloy is a kind of ideal high temperature phase change materials (PCMs) because of its high latent heat and good heat transfer performance. However, it is difficult for Al–Si alloy to be safely applied because of its causticity and incompatibility. In this paper, an inorganic Al–Si/Al₂O₃ micro-particles core/shell structure was prepared by the sol–gel process with the modification of silane coupling agent. The direct evidence for the forming of the dense and stable α-Al₂O₃ shell layer, whose thickness is about 3–5 μm, is presented by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). In terms of the analyses of Fourier transform infrared (FT-IR) and thermogravimetry (TG), it is apparent that the silane coupling agent is successfully grafted on the surface of Al–Si alloy micro-particles, which promotes the condensation between boehmite sols and silanol groups. The latent heat of the encapsulated Al–Si alloy was 307.21 kJ/kg and decreased during the process of microencapsulation. The reasons for the reduction of the latent heat are the excess alumina sols and the depletion of Al–Si alloy.     

Synthesis of core–shell-type styrene acrylic latexes with low NMA content and their application in pigment printing pastes

In this paper, novel core–shell polymers comprising styrene (St) and butyl acrylate (BA) in both core and shell layers of the polymer particles have been synthesized and employed in pigment printing pastes which were applied on 100% cotton and 65% cotton/35% polyester (PET) fabrics. The aim was to reduce the NMA content and the formation of free formaldehyde from pigment printing pastes by employing newly synthesized core-/shell-type polymers. After five washing cycles, the synthesized core-/shell-type polymer including 1% NMA in the core and 1% NMA in the shell with T _g values +30°C and ?20°C, respectively, with lowest total NMA content (1.03%) yielded the best result and showed closest ΔE values to the commercially available polymer including 4% NMA. Dry and wet rubbing fastness results showed no significant changes in the absence of NMA when compared with NMA containing samples. The penetration degree of the pigment pastes of the corresponding polymers was relatively higher on 100% cotton fabric for both red- and blue-colored pigments. A negligible decrease in color strength has been observed for all polymers when colored in red.     

Synthesis of multifunctional core–shell toughening agent with light stability and its application in polycarbonate

A light stabilizer compound of 2-(2′-propionyloxy-5′-methylphenyl) benzotriazole (AMB) was synthesized by the esterification of the 2-(2′-hydroxy-5′-methylphenyl) benzotriazole with acryloyl chloride (AC), and the AMB was then copolymerized with the methyl methacrylate (MMA), butyl acrylate (BA), and silicone monomers (D4) to prepare the silicone light toughener of poly(D4-MMA-BA-AMB). Effects of the AMB monomer on the conversion and polymerization stability and the toughening and photostabilizing effects of the poly(D4-MMA-BA-AMB) on the polycarbonate (PC) were studied. The prepared multifunctional toughening agent was characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, thermogravimetric analyzer, transmission electron microscopy, dynamic light scattering analyzer, and ultraviolet absorption spectroscopy. Results show that the prepared poly(D4-MMA-BA-AMB) toughening agent possessed core–shell structure and could effectively absorb the ultraviolet rays. Although the addition of the poly(D4-MMA-BA-AMB) toughening agent had a negative effect on the tensile strength of the PC, it could greatly improve the low-temperature notched impact strength, toughness performance, and yellowness performance of PC products after UV irradiation. Compared with the silicone toughening agent, the toughening agent of the poly(D4-MMA-BA-AMB) had better anti-ultraviolet property for the PC/poly(D4-MMA-BA-AMB) composite. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48747.