Reconstruction of morphology of micron-sized,monodisperse composite polymer particles by the solvent-absorbing/releasing method

Micron-sized, monodisperse polystyrene (PS)/poly(n-butyl methacrylate) (PBMA) (2/1 w/w) composite particles having different morphologies were prepared by the solvent-absorbing/releasing method (SARM). There was an obvious influence of the releasing rate of toluene from the toluene-swollen composite particles on the reconstructed morphology by the SARM. In the case of fast release, the reconstructed morphology was a bicontinuous structure that is similar to that formed by spinodal decomposition. On the other hand, in the case of slow release, a hemispherical structure was formed that consisted of PS and PBMA phases.Part CCLIV of the series Studies on Suspension and Emulsion     

Production of micron-sized monodispersed composite polymer particles by seeded polymerization utilizing the dynamic swelling method

 In order to develop the seeded polymerization technique utilizing the dynamic swelling method (DSM) proposed by authors for the production of micron-sized mono-dispersed “composite” polymer particles consisting of two kinds of polymers, the seeded polymerization for the dispersion of ethyl methacry-late (EMA)-swollen PS particles prepared utilizing DSM was carried out. Monodispersed PS/poly(ethyl methacrylate) (PEMA) composite particles having 7 μm in diameter were produced by the addition of NaCl to lower the solubility of EMA in medium and by the addition of CuCl₂ as a water-soluble inhibitor to depress the by-production of submicron-sized PEMA particles. Received: 16 July 1996 Accepted: 10 October 1996     

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     

Preparation of micron-sized monodispersed highly monomer- “adsorbed” polymer particles having snow-man shape by utilizing the dynamic swelling method with tightly cross- linked seed particles

Micron-sized, monodispersed highly styrene-“adsorbed” particles having snow-man shape were prepared by the dynamic swelling method (DSM) with tightly cross-linked polymer seed particles as follows. First, 3.8 μm-sized monodispersed polystyrene (PS)/ poly(divinylbenzene) (PDVB) (PS/PDVB = 1/10 wt. ratio) composite particles produced by seeded polymerization utilizing DSM were dispersed in an ethanol/water (6/4, w/w) solution dissolving styrene monomer, and poly(vinyl alcohol) as a stabilizer. Second, water was subsequently added to the dispersion with a micro-feeder at a rate of 2.88 ml/h at room temperature. The cross-linked seed particles adsorbed a large amount of styrene onto the surfaces and resulted in mono-dispersed highly styrene-“adsorbed” snow-man shape particles having about 10 μm in diameter. Received: 16 April 1998 Accepted: 9 June 1998     

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 of micron-sized, monodispersed, “onion-like” multilayered poly(methyl methacrylate)/polysterene composite particles by reconstruction of morphology with the solvent-absorbing /releasing method

Micron-sized, monodispersed, “onion-like” multilayered poly(methyl methacrylate) (PMMA)/polystyrene (PS) (1/1, w/w) composite particles were prepared by the solvent-absorbing/releasing method (SARM). The viscosity within toluene-swollen composite particles, the release rate of toluene therefrom, the PMMA/PS ratio, and the kind of solvent had great influences on the reconstruction of the morphology of the PMMA/PS composite particles by the SARM. From these results, the conditions for the preparation of the multilayered composite particles by the SARM are clarified. Received: 28 September 2000 Accepted: 27 October 2000     

Production of micron-sized monodispersed core/shell composite polymer particles by seeded dispersion polymerization

 The effect of the weight ratio of seed polymer/monomer on the morphology of the poly(methyl methacrylate) (PMMA)/polystyrene (PS) monodispersed composite particles produced by batch seeded dispersion polymerization of styrene with 1.64-μm-sized monodispersed PMMA seed particles in a methanol/water medium (4/1 w/w) was examined. In the PMMA/PS weight ratios of 3/1 and 2/1, the composite particles had a clear morphology consisting of a PMMA core and a PS shell. In the ratio of 1/1, a lot of small PS domains were observed in the PMMA core though the PS shell was still formed. By stepwise addition of styrene monomer, the formation of the small PS domain was depressed and complete core/shell morphology was formed. Absorption/release treatments of toluene into/from the PMMA/PS (1/1 w/w) composite particles resulted in a drastic morphological change from the core/shell structure to a multi- layered one. Received: 2 February 1999 Accepted in revised form: 7 April     

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     

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     

Synthesis of temperature-sensitive micron-sized monodispersed composite polymer particles and its application as a carrier for biomolecules

 Temperature-sensitive micron-sized monodispersed composite polymer particles were prepared by seeded copolymerization of dimethylaminoethyl methacrylate and ethylene glycol dimethacrylate with 1.77 μm-sized monodispersed polystyrene seed particles. The change in surface property at temperature above and below 35 °C was examined by differential scanning calorimetry, trypsin activity and the adsorption/ desorption behaviors of low molecular weight cationic emulsifier as well as biomolecules. Received: 6 August 1997 Accepted: 16 January 1998     

Formation mechanism of micron-sized monodispersed polymer particles having a hollow structure

 Recently, the authors reported that micron-sized monodispersed cross-linked polymer particles having a single hollow in the inside were produced by seeded polymerization for the dispersion of (toluene/divinylbenzene)-swollen polystyrene (PS) particles prepared utilizing the dynamic swelling method which the authors had proposed. In this article, the particles at various conversions of the seeded polymerization were observed with an optical microscope in detail. From the obtained results, the formation mechanism of the hollow structure is suggested as follows. As seeded polymerization proceeds, poly-divinylbenzene (PDVB) molecules precipitated in the swollen particle are trapped near the interface and gradually pile at the inner surface, which results in a cross-linked PDVB shell. PS which dissolves in the swollen particles is repelled gradually to the inside. After the completion of the polymerization, toluene in the hollow evaporates by drying, and PS clings to the inner wall of the shell uniformly. Received: 14 February 1997 Accepted: 16 April 1997     

Preparation of micron-sized, monodispersed, monomer-adsorbed polymer particles utilizing the dynamic swelling method with loosely cross-linked seed particles

Influence of the water-addition rate (R _w ) (ml/h) on the monodispersity of monomer-adsorbed polymer particles prepared by utilizing the dynamic swelling method (DSM) with 1.9-μm-sized, monodispersed, loosely cross-linked polystyrene/styrene-divinylbenzene copolymer [1/(47.5–2.5), w/w] composite particles was examined theoretically and experimentally. The thermodynamic simulation under a kinetic control state indicates that, at the R _w values below 4, the cross-linked composite particles adsorb all styrenes separated from ethanol/water media. The experimental result at the R _w value of 2.66 supported it. At the R _w values above 5.32 and below 1.33, polydispersed styrene-adsorbed particles were prepared. The former depended on the formation of some pure styrene droplets not containing the composite particle. The latter depended on coalescence among the adsorbed particles by DSM. Received: 5 April 2000 Accepted: 5 October 2000     

Adsorption of styrene on micron-sized, monodisperse, cross-linked polymer particles in a snowman-shaped state by utilizing the dynamic swelling method

Polystyrene/styrene–divinylbenzene copolymer composite particles with different cross-linking densities were produced by seeded copolymerization for (styrene/divinylbenzene)-swollen polystyrene particles prepared by utilizing the dynamic swelling method (DSM) which was proposed by the authors in 1991. Using the cross-linked, composite particles as seeds, styrene-adsorbed (swollen) composite particles having snowman shapes were prepared by the DSM. With a decrease in the cross-linking density in the composite particles, the volume of the composite particle which was embedded in a spherical styrene phase in the snowman-shaped, styrene-adsorbed particle increased and the contact angle of the styrene phase on the composite particle decreased. In the DSM process, the absorption stage of styrene in the composite particles and the adsorption stage thereon were clearly observed. This suggests that the cross-linking density of the composite particles greatly affects the morphology of the snowman-shaped particles. Received: 13 December 2000 Accepted: 14 March 2001     

Production of micron-sized monodispersed polymer particles by seeded polymerization for the dispersion of highly monomer-swollen particles prepared with submicron-sized polymer seed particles utilizing the dynamic swelling method

For the purpose of extending the size range of polymer seed particles used in “dynamic swelling method” (DSM), first it was verified theoretically that the submicron-sized polymer particles produced by emulsion polymerization can also absorb a large amount of monomer by DSM in both equilibrium and kinetic control states. Next, on the basis of the theoretical results, experimentally about 2.6 μm-sized styrene-swollen polystyrene (PS) particles were prepared utilizing DSM in the presence of 0.64 μm-sized monodispersed PS seed particles produced by emulsifier-free emulsion polymerization. Moreover, 2.5 μm-sized monodispersed PS particles were produced by the addition of cupric chloride as a water-soluble inhibitor to depress the by-production of submicron-sized PS particles in the seeded polymerization at 30°C with 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) initiator. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2513–2519, 1998     

Production of micron-sized monodispersed core/shell polymethyl methacrylate/polystyrene particles by seeded dispersion polymerization

 Micron-sized monodispersed polymethyl methacrylate (PMMA)/polystyrene (PS) (PMMA/PS=2/1, wt ratio) composite particles consisting of PMMA-core and PS-shell were successfully produced by seeded dispersion polymerization of styrene in a methanol/water medium in the presence of about 2 μm-sized monodispersed PMMA particles. From the view point of thermodynamic equilibrium, such a morphology is difficult to form by usual seeded polymerization in a polar medium such as water. It is concluded that seeded dispersion polymerization in which almost all monomers and initiators exist in the medium has an advantage to produce core/shell polymer particles in which polymer layers accumulate in their order of the production regardless of the hydrophobicity of polymers, because of high viscosity in polymerizing particles. Received: 9 December 1996 Accepted: 26 February 1997     

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     

Production of micron-sized, monodispersed, multihollow polystyrene/poly(3,5-xylidine) composite particles by chemical oxidative seeded polymerization

 Micron-sized, monodispersed polystyrene/poly(3,5-xylidine) composite polymer particles were produced by chemical oxidative seeded polymerization of 3,5-xylidine with 1.37-μm-sized, monodispersed polystyrene seed particles. The chemical oxidative seeded polymerization was conducted in an aqueous medium at 25 °C in the presence of poly(vinyl alcohol) as a stabilizer using ammonium persulfate as an oxidant. The composite particles had a multihollow structure. Received: 30 June 1999/Accepted in revised form: 21 October 1999     

Preparation of monodispersed plate-like particles of tungstic acid

 To understand the properties of colloidal dispersions it is often vital to prepare model materials with particles that have a small polydispersity in order to make experimental tests of theories or models. However few preparations have been developed that yield anisotropic particles with a narrow size distribution and precise shape. In this paper the preparation of a dispersion of charge stabilized, tungstic acid particles is described. The particles are rectangular and have a length of 7.0 μm, a width of 2.8 μm and a thickness of 0.2 μm. The polydispersity is 8% in length and 10% in width, making it one of the most monodisperse dispersions of anisotropic particles. Each particle is monocrystalline and the crystal orientation is fixed with respect to the particle morphology. Some interesting behavior is observed: these particles aggregate perpendicular and parallel to each other to give flat, ordered flocs when the stability is reduced. Received: 22 January 1998 Accepted: 4 February 1998     

Effect of molecular weight on the production of multi-hollow polymer particles by the alkali/cooling method

 The effects of molecular weight, particle diameter and cooling condition on the formation of multi-hollow structure formed within submicron-sized styrene-methacrylic acid copolymer particles by the “alkali/cooling method” proposed by the authors were examined and the formation mechanism was proposed. The original particles were produced by emulsion copolymerization in the presence of n-octyl mercaptan as a chain transfer agent. Received: 29 March 1996 Accepted: 19 June 1996     

Production of multi-hollow polymer particles by the stepwise acid/alkali method

 Recently, we reported that multi-hollow polymer particles can be prepared from carboxylated polymer particles by the stepwise alkali/acid method. In this article, an attempt was made to prepare similar particles from acid-swellable polymer particles by the stepwise treatment with acid and alkali, which was named the stepwise acid/alkali method. The acid-swellable particles were produced by emulsion terpolymerization of styrene, butyl acrylate, and dimethyl 2-amino ethyl methacrylate. The effects of initial pH value, temperature, and time in the acid and alkali treatment processes on the multi-hollow structure were examined. Received: 18 December 1996 Accepted: 11 March 1997