Synthesis of poly(styrene-co-3-trimethoxysilyl propyl methacrylate) microspheres coated with polysiloxane layer

A procedure has been developed to coat micron-sized poly(styrene-co-3-trimethoxysilyl propyl methacrylate) microspheres with a smooth layer of polysiloxane by the hydrolysis and condensation of methyl trimethoxylsilane (MTMS). Firstly, polystyrene microspheres containing silanol groups were prepared by conventional dispersion polymerization using 3-(trimethoxysilyl) propyl methacrylate (MPS) as a functional comonomer in an ethanol/water medium. Secondly, the synthesis of the polysiloxane shell was carried out using a sol–gel process of MTMS. The thickness of the shells can be easily varied with different copolymer seeds and MTMS feed ratio. When we used copolymer particles with 2.00 μm diameter as seeds, the thickness of the polysiloxane shells can be varied from 0.10 to 0.18 μm. The core/shell structure of the composite microspheres was characterized by transmission electron microscope (TEM).     

Electron microscopic investigations of the structure of crazes in polystyrene

The structures of the deformation zones in polystyrene (PS), the so-called crazes, were investigated in detail by electron microscopy. Compared with the conventional transmission electron microscope (TEM) the usage of a high voltage electron microscope (HVEM) with an accelerating voltage of 1000 kV has several advantages: it renders possible the investigation of relatively thick specimens (thicknesses up to and exceeding 5 m), the performance ofin situ deformation tests, and the application of a special tensile device, producing a defined uniaxial straining state.First, general features of the crazes in PS (pressure-molded samples, solution-cast films) are described, and second, the crazes are precisely characterized by quantitatively measuring the electron micrographs of the crazes. Shape, thickness profile, minimum size, interior structure, and elongation of the crazes are discussed in detail.     

亚微米级聚苯乙烯/聚硅氧烷核壳粒子的制备及其应用

以乳液聚合制备的聚苯乙烯乳液为种子,加入甲基三甲氧基硅烷(MTMS)水解溶液进行缩聚反应,合成亚微米级聚苯乙烯/聚硅氧烷核壳粒子,并以此作为光散射剂添加至聚甲基丙烯酸甲酯(PMMA)树脂中,制备了光散射材料;考察了亚微米级核壳粒子添加在PMMA树脂中的分散性。结果表明:经过双螺杆剪切作用的挤出加工后,可以实现核壳粒子在PMMA树脂中的良好分散。核壳粒子可以大幅度提高PMMA的雾度,当聚苯乙烯/聚硅氧烷核壳粒子(NS82)的含量为1%时,制得的PMMA样片(厚度为2 mm)的雾度为89%,透光率为69%,有效光散射系数为61%。     

Synthesis of large-sized monodisperse polystyrene microspheres by dispersion polymerization with dropwise monomer feeding procedure

Highly monodisperse polystyrene (PS) microspheres in the size range of 3.75–7.09 μm were synthesized by dispersion polymerization with dropwise monomer feeding procedure. The morphology, size, and particle size distribution (PSD) of the PS microspheres obtained by different monomer feeding modes, including batch polymerization and various feeding rates, were investigated. The PSD of particles showed a close dependence on feeding rate. The PS microspheres with low coefficient of variation (CV) values all less than 4.8% obtained by the optimum feeding rates revealed better uniformity than those by batch polymerization (CV values all more than 8.2%). According to the time courses of monomer conversion and particle numbers, the effects of monomer feeding modes on the polymerization reaction of the large-sized PS microspheres were clarified. It is found that the dropwise monomer feeding procedure is promising for the synthesis of large-sized monodisperse PS particles in 3.75–7.09 μm.     

Production of micron-sized, monodisperse composite polymer particles having epoxy groups by seeded dispersion polymerization

 Micron-sized, monodisperse polystyrene (PS)/glycidyl methacrylate–divinylbenzene copolymer core/shell composite particles having epoxy groups in the shells were produced by seeded dispersion copolymerization of glycidyl methacrylate and divinylbenzene in an ethanol/water medium with 1.65-μm-sized, monodisperse PS seed particles. By chemical modifications of epoxy groups with sodium hydrogensulfite and dimethylamine, composite polymer particles having sulfonate and dimethylamino groups, respectively, in the shells were prepared. Received: 13 September 2000 Accepted: 31 January 2001     

Influence of particle diameter on the morphology of micron-sized, monodispersed composite polymer particles produced by seeded polymerization for the dispersion of highly monomer-swollen polymer particles

 Micron-sized, monodispersed polystyrene (PS)/poly (n-butyl methacrylate) (PBMA) composite particles, in which the PS domain(s) were dispersed in a PBMA continuous phase, were produced by seeded polymerization for dispersions of n-butyl methacrylate (BMA) swollen PS particles in a wide range of PS/BMA ratios in the presence of NaNO₂ as a water-soluble inhibitor. Moreover, in order to change the diameter of the composite particles at same PS/BMA ratio, PS/PBMA (1/150 w/w) composite particles were produced using five kinds of PS particles in a range of diameters from 0.64 to 3.27 μm as seeds. The percentages of the PS/PBMA composite particles having double and triple and over PS domains, which were thermodynamically unstable morphologies, increased with the increase in the diameter of BMA swollen PS particles. There was a clear influence of the size of the swollen particles on the morphology of the PS/PBMA composite particles produced. Received: 30 September 1999/Accepted: 18 April 2000     

Production of micron-sized, monodispersed, multilayered composite polymer particles by multistep seeded dispersion polymerization

 Micron-sized, monodispersed, poly(methyl methacrylate) (PMMA)/polystyrene (PS)/PMMA/PS multilayered composite particles were successfully produced by three-step seeded dispersion polymerizations in methanol/water media. The first seeded dispersion polymerization was carried out with 2-μm-sized, monodispersed PMMA particles.     

Preparation and application of cross-linked core-shell PBA/PS and PBA/PMMA nanoparticles

This paper reports the preparation of cross-linked core-shell poly(butyl acrylate)/polystyrene (PBA/PS) and poly(butyl acrylate)/poly(methyl methacrylate) (PBA/PMMA) nanoparticles via seeded emulsion polymerization and their application in nylon-based composites. A highly cross-linked structure was formed in both the cores and the shells by using a cross-linking agent, which could prevent the migration of hydrophobic PS shells to the inside of particles. There were covalent bonds on the interfaces between the cores and the shells of both particles. The average particle sizes were 40–50 nm, and the size distributions were narrow. The kinetics of polymerization was investigated. Well-defined core-shell structure and narrow particle size distribution could be achieved under starved conditions of monomer feeding. Furthermore, PBA/PMMA particles were used to fill nylon 6, good dispersion was obtained because of the strong interfacial interaction between the nanoparticles and the nylon 6 matrix and the good deformation ability of nanoparticles, and the toughness and rigidity of the composites were improved evidently. __________ Translated from Acta Polymerica Sinica, 2005, (6) (in Chinese)     

Preparation of micron-sized, monodispersed, anomalous polymer particles by utilizing the solvent-absorbing/releasing method

 About 2-μm-sized polystyrene (PS) particles having uneven surfaces were prepared by a posttreatment in which toluene-swollen PS particles were thrown into a methanol bath to release toluene therefrom rapidly. The posttreatment was named the “solvent-absorbing/releasing method”. The PS particle had large dents at the surface. The size of the dents was changed by the conditions of the posttreatment. Received: 3 August 1999/Accepted: 1 March 2000     

Study of emulsion polymerization stabilized by amphiphilic polymer nanoparticles

Submicron-sized polystyrene (PS) microspheres with a relatively narrow particle size distribution can be easily produced through emulsion polymerization induced by γ-ray at room temperature using a new type of amphiphilic cross-linked poly(stearyl methacrylate-co-acrylamide-co-acrylic acid) particles as stabilizer. The properties of these amphiphilic particles were described, including morphology, size, ζ potential, and contact angles. The effect of the pH value and the content of amphiphilic particles on the formation and stability of emulsions were also investigated. Meanwhile, the obtained PS microspheres were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. In addition, through observing the morphology and size of emulsion droplets at different times under an optical microscope, we found it is interesting that Pickering emulsions formed initially disappeared gradually, which is different from the common Pickering emulsions stabilized by inorganic particles. Thus, the mechanism was further discussed.     

A facile method for the preparation of monodisperse hollow silica spheres with controlled shell thickness

This article presents a facile, effective, mild synthesis process for well‐defined hollow spheres by using cationic polystyrene (PS) submicro‐particles as templates. In this approach, the cationic PS templates can be first prepared via emulsifier‐free polymerization by using the cationic monomer 2‐(methacryloyloxy) ethyltrimethylammonium chloride as comonomer, then, the silica shells from the sol‐gel process of tetraethoxysilane were coated on the surfaces of template particles via electrostatic interaction, finally the PS was dissolved in situ by modification of the reaction conditions in the same medium to form monodisperse hollow silica spheres with controlled shell thickness. Fourier transform‐infrared spectroscopy, thermogravimetric analysis, Brunauer‐Emmett‐Teller, transmission electron microscopy, and scanning electron microscope measurements were used to characterize these hollow silica spheres. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1332–1338, 2010     

Preparation of hollow silica microspheres with controlled shell thickness in supercritical fluids

This article presents a novel route to prepare hollow silica microspheres with well-defined wall thickness by using cross-linked polystyrene (PS) microspheres as templates with the assistance of supercritical carbon dioxide (SC-CO₂). In this approach, the cross-linked PS templates can be firstly prepared via emulsifier-free polymerization method by using ethylene glycol dimethacrylate or divinylbenzene as cross-linkers. Then, the silica shell from the sol–gel process of tetraethyl orthosilicate (TEOS) which was penetrated into the PS template with the assistance of SC-CO₂ was obtained. Finally, the hollow silica spheres were generated after calcinations at 600 °C for 4 h. The shell thickness of the hollow silica spheres could be finely tuned not only by adjusting the TEOS/PS ratio, which is the most frequently used method, but also by changing the pressure and aging time of the SC-CO₂ treatment. Fourier transform infrared spectroscopy, transmission electron microscopy, and scanning electron microscope were used to characterize these hollow silica spheres.     

Influence of the swelling state of seed polymer particles with monomer on the morphology of micron-sized monodispersed composite polymer particles produced by seeded polymerization utilizing the dynamic swelling method

 Micron-sized mono-dispersed polystyrene (PS)/poly(n-butyl methacrylate) (PBMA) composite particles (PS/PBMA=2/1 by weight) having a heterogeneous structure in which many fine PBMA domains dispersed in a PS matrix near the particle surface were produced by seeded polymerization of n-butyl methacrylate (BMA) of which almost all had been absorbed by 1.8 μm-sized monodispersed PS seed particles utilizing the dynamic swelling method. The morphology was varied by changing the PS/BMA ratio and polymerization temperature. It was concluded that the swelling state of 2 μm-sized BMA-swollen PS particles in the seeded polymerization process is one of the important factors to control the morphology of the composite particles. Received: 27 November 1996 Accepted: 21 March 1997     

Morphology of micron-sized monodispersed composite polymer particles produced by seeded polymerization for the dispersion of highly monomer-swollen polymer particles

 Monodispersed polystyrene (PS)/poly(n-butyl methacrylate) (PBMA) composite particles having 9.4 μm in diameter were produced by seeded polymerization for the dispersion of highly n-butyl methacrylate (BMA)-swollen PS particles, and their morphologies were examined. The highly BMA-swollen PS particles (about 150 times the weight of the PS seed particles) were prepared by mixing monodispersed 1.8 μm-sized PS seed particles and 0.7 μm sized BMA droplets prepared with an ultrasonic homogenizer in ethanol/water (1/2, w/w) medium at room temperature. After NaNO₂ aqueous solution as inhibitor was added in the dispersion, the seeded polymerization was carried out at 70 °C. In an optical microscopic observation, one or two spherical high contrast regions which consisted mainly of PS were observed inside PS/PBMA composite particles. In the PS domain, there were many fine spherical PBMA domains. Such morphologies were based on the phase separation of PS and PBMA within the homogeneous swollen particles during the seeded polymerization. Received: 04 June 1997 Accepted: 27 August 1997     

Fracture surface morphology and phase relationships of polystyrene/poly(methyl methacrylate) systems. I. Low-molecular-weight polystyrene in poly(methyl methacrylate)

Samples of low-molecular-weight polystyrene (PS) in poly(methyl methacrylate) (PMMA) were prepared by first dissolving PS in methyl methacrylate monomer and then polymerizing the monomer. Forty-three specimens of varying number-average molecular weight (2100–49,000) and composition (5–40 wt %) of PS were prepared, and the surface morphology and phase relationships studied by scanning electron microscopy. Four distinct types of phase relationships were observed: (i) a single phase consisting of PS dissolved in PMMA; (ii) PS dispersed in PMMA; (iii) PMMA dispersed in PS; and (iv) regions of PS dispersed in PMMA coexisting with regions of PMMA dispersed in PS. Values of the size and population density of the dispersed particles are reported. Finally, the size and distribution of the dispersed particles and the various types of phase relationships are discussed in terms of the ternary polystyrene/poly(methyl methacrylate)/methyl methacrylate phase diagram.     

Ambient-curable polysiloxane coatings: structure and mechanical properties

Ambient-curable polysiloxane coatings were prepared by hydrolysis and condensation of 3-methacryloxypropylmethyldimethoxysilane (MPDS) and methyltriethoxysilane (MTES) and subsequently mixing with 3-aminopropyltriethoxysilane (APS). The structures of the as-obtained polysiloxane oligomers as well as the dried polysiloxane coatings on tinplate substrates were analyzed by FTIR and ²⁹Si NMR. The mechanical properties of the coatings were thoroughly examined at both macro-level and micro-level using a pendulum hardness rocker, an impact tester, and a nanoindentation/nanoscratch instrument. Effects of the molar ratio of MPDS/MTES, the dosage of aqueous ammonia solution, and the catalytic condition on the structure of polysiloxane oligomers as well as the structure and mechanical properties of the polysiloxane coatings were investigated. The dried coatings with thickness of 15–26 μm are highly elastic. The hardness (Koenig hardness and microhardness), impact resistance and scratch resistance are mainly dependent on the condensation degree of polysiloxane coatings rather than on the organic component of the coatings. A proper pre-hydrolysis process or more APS is benefit for enhancing the mechanical strength of the polysiloxane coatings. Polysiloxane coatings with high hardness and excellent scratch resistance can be prepared preferentially at low molar ratio of MPDS/MTES.     

High compact melamine-formaldehyde microPCMs containing n-octadecane fabricated by a two-step coacervation method

Microcapsules containing n-octadecane were successfully fabricated by an in-situ polymerization process with melamine-formaldehyde (MF) prepolymer and a hydrolyzed copolymer of styrene and maleic anhydride (SMA) as shell materials. To achieve a long service time of microcapsules containing phase change materials (microPCMs), the compactness of shells was improved by adding the MF prepolymer twice. The mechanism of this method was a two-step coacervation (TSC) under the help of hydrolyzed SMA compared to a one-step coacervation (OSC). To understand the influence of both coacervations, properties of shells were investigated in terms of morphologies, density, thickness, and stability by means of scanning electron microscopy (SEM), transmission electron microscopy, and thermal gravimetric analysis (TGA). The data of shells thickness were achieved from the cross-section SEM images. It shows that the average thickness of shells from two kinds of process are 0.1 μm. The density and stability in water of shells fabricated by TSC are both higher than that of shells by OSC. TGA curves show the expected microPCMs of TSC losing weight from 200 to 400 °C. The release curves, relationship between time and logarithmic residual weight of core, show there are two decrease-linear steps after curve regression. It can be concluded from all these results that the TSC method may be a promising method leading to a compact shell structure for various application.     

Model filled polymers. VIII. Synthesis of crosslinked polymeric beads by seed polymerization

Monodisperse crosslinked polystyrene (PS) and polymethacrylate (PMA) beads of sizes greater than 1 μm in diameter are prepared by particle nucleation onto pre-existing polymer seeds in a multistage emulsion polymerization, in the absence of emulsifier. An adequate seed number concentration, which decreases with increasing seed size, is necessary to achieve monodisperse beads. Monodisperse multicomposition beads are prepared by polymerizing styrene onto PMA seeds, but not by polymerizing methyl methacrylate onto PS seeds. Phase separation in growing seed particles or surface polymerization following free radical capture may lead to the formation of asymmetric shaped particles.     

Preparation of macroporous SAPO-34 microspheres by a spray drying method using polystyrene spheres as hard template

Macroporous microspheres of SAPO-34 (MAMISAPO-34) were fabricated using polystyrene spheres (PS, 2 μm) as hard template. Cubic SAPO-34 (1 μm) synthesized by the conventional hydrothermal method was mixed with kaolin, silica sol, aluminium phosphate sol, template, and deionized water. Spray drying was then performed to prepare 30–50 μm microspheres which were converted to macroporous SAPO-34 by post-hydrothermal and calcination treatments. For comparison, 30–50 μm non-macroporous microspheres (NOMISAPO-34) were also obtained without using PS. XRD, NH₃-TPD, and SEM analyses were used to characterize the macroporous and non-macroporous SAPO-34. The results showed that MAMISAPO-34 was more crystalline and had more strong acid sites than NOMISAPO-34. When used in MTO (methanol to olefins) reactions, MAMISAPO-34 had better catalytic performance than NOMISAPO-34, because of its greater crystallinity.     

Production of electrically conductive, core/shell polystyrene/polyaniline composite particles by chemical oxidative seeded dispersion polymerization

Micron-sized, monodispersed, electrically conductive polystyrene (PS)/polyaniline (PAn) composite particles were produced by chemical oxidative seeded dispersion polymerization of aniline at 0 °C with 1.37-μm-sized, monodispersed PS seed particles in HCl aqueous solution, where the pH value was kept at 2.5 with a pH stat. The composite particles consisted of a PS core and a PAn shell. A pellet of the composite particles had a conductivity of 3.4 × 10⁻³ S/cm. Received: 5 April 2000 Accepted: 10 August 2000