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     

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 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     

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     

Micron-sized monodispersed polymer particles produced by seeded polymerization for the dispersion of high swelling of polymer particles with a large amount of monomer

 Micron-sized monodispersed polystyrene (PS)/poly(n-butyl methacrylate) composite particles were produced as follows. First, 1.77 μm-sized monodispersed PS seed particles produced by dispersion polymerization were dispersed in ethanol/water (1/2, w/w) medium dissolving poly(vinyl alcohol) as a stabilizer. n-Butyl methacrylate (BMA) monomer dissolving benzoyl peroxide initiator was emulsified in ethanol/water (1/2, w/w) solution of sodium dodecyl sulfate as emulsifier with ultrasonic homogenizer, and the BMA monomer emulsion was mixed with the PS seed emulsion. The PS seed particles absorbed with a large amount of BMA (about 150 times weight of the seed particles) for 2 h to about 10 μm in diameter while keeping good monodispersity and BMA droplets disappeared finally. The seeded polymerization was carried out at 70 °C after a certain amount of water was added to depress the redissolving of BMA from the swollen particles into the medium by raising from room temperature to the polymerzation temperature. Received: 21 February 1996 Accepted: 4 September 1996     

Production of core/shell polystyrene/poly(3,5-xylidine) composite particles by chemical oxidative seeded dispersion polymerization

Micron-sized monodispersed polystyrene (PS)/poly(3,5-xylidine) (PXy) composite particles were produced by chemical oxidative seeded dispersion polymerization of 3,5-xylidine at 20 °C with 1.6-μm-sized monodispersed PS seed particles in HCl aqueous solution, the pH of which was always kept at 2.5 with a pH stat. The composite particles produced consisted of a PS core and a PXy shell. Received: 16 December 1998 Accepted in revised form: 25 March 1999     

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     

Influences of the locations of monomer and initiator in the seeded polymerization systems on the morphologies of micron-sized monodispersed composite polymer particles

Three kinds of micron-sized monodispersed polystyrene (PS)/poly(n-butyl methacrylate) (PBMA) composite particles (PS/BMA=2/1, wt. ratio) were produced by two kinds of seeded polymerizations ofn-butyl methacrylate (BMA) in the presence of about 2 m-sized monodispersed PS particles, and their morphologies were examined. One was produced by a seeded dispersion polymerization where almost monomers and initiators exist in an ethanol/water (1/1, w/w) medium. The others two were produced by seeded polymerizations utilizing the dynamic swelling method, where almost monomers exist in the PS seed particles, with 2,2-azobisisobutyronitrile initiator in the monomer-swollen particles and with 2,2-azobis [2-(2-imidazolin-2-yl)propane] initiator in an ethanol/water (1/5, w/w) medium. In the former polymerization, the produced composite particles had a core-shell structure consisting of a PS-core and a PBMA-shell, whereas in the latter two polymerizations, they had a POO (Polymeric Oil-in-Oil) structure consisting of a PS-matrix and many PBMA-domains, regardless of the location of initiator in the systems. From these results, it is concluded that the location of BMA monomer in the seeded polymerization systems with micron-sized monodispersed PS seed particles greatly affects the morphologies of produced PS/PBMA composite particles.Part CLI of the series Studies on Suspension and Emulsion     

Morphologies of micron-sized monodispersed composite polymer particles having crosslinked structures produced by seeded polymerizations

Three kinds of micron-sized monodispersed polystyrene (PS)/ poly(styrene - divinylbenzene) composite particles were produced by two kinds of seeded copolymerizations of styrene (S) and divinylbenzene (DVB) (PS seed/ (S+DVB)=2/1, wt. ratio; S/DVB=1/1, molar ratio) in the presence of about 2 μm-sized monodispersed PS particles, and their morphologies were examined. One was produced by a seeded dispersion copolymerization where almost monomers and initiators exist in an ethanol/water (12.6/4.0, w/w) medium. The others two were produced by seeded copolymerizations with the dynamic swelling method where almost monomers exist in the monomer-swollen particles using 2, 2'-azobisisobutyronitrile in monomer-swollen PS seed particles or using 4, 4'-azobis (4-cyanopentanoic acid) in an ethanol/water (7/43, w/w) medium. In the former polymerization, the produced composite particles had a high dense crosslinked shell, whereas in the latter two polymerizations, they did the comparatively homogeneous crosslinked structures.     

Morphology and film formation of poly(butyl methacrylate)–polypyrrole core–shell latex particles

 Core–shell latex particles made of a poly(butyl methacrylate) (PBMA) core and a thin polypyrrole (PPy) shell were synthesized by two-stage polymerization. In the first stage, PBMA latex particles were synthesized in a semicontinuous process by free-radical polymerization. PBMA latex particles were labeled either with an energy donor or with an energy acceptor, in two different syntheses. These particles were used in a second stage as seeds for the synthesis of the core–shell particles. The PPy shell was polymerized around the PBMA core latex in an oxidative chemical in situ polymerization. Proofs for the success of the core–shell synthesis were obtained using nonradiative energy transfer (NRET) and atomic force microscopy (AFM). NRET gives access to the rate of polymer chain migration between adjacent particles in a film annealed at a temperature above the glass-transition temperature T _g of the particles. Slower chain migration of the PBMA polymer chains was obtained with the PBMA–PPy core–shell particles compared to rate of the PBMA polymer chain migration found with the pure, uncoated PBMA particles. This result is due to the coating of PBMA by PPy, which hinders the migration of the PBMA polymer chains between adjacent particles in the film. This observation has been confirmed by AFM measurements showing that the flattening of the latex film surface is much slower for the core–shell particles than for the pure PBMA particles. This result can again be explained by the presence of a rigid PPy shell around the PBMA core. Thus, these two complementary methods have given evidence that real core–shell particles were synthesized and that the shell seriously hinders film formation of the particles in spite of the fact that it is very thin (thickness close to 1 nm) compared to the size (750 and 780 nm in diameter) of the PBMA core. Transparency measurements confirm the results obtained by NRET and AFM. When the films are placed at a temperature higher than the T _g of PBMA, the increase in transparency is faster for films made with the uncoated PBMA particles than for films made with the coated PBMA particles. This result indicates again that the presence of the rigid PPy layer around the PBMA core reduces considerably the speed at which the structure of the film is modified when heated above the T _g of PBMA. Received: 02 September 1999 Accepted: 21 December 1999     

Influence of viscosity within polymerizing particle on the morphology of micron-sized,monodisperse composite polymer particles produced by seeded polymerization for the dispersion of highly monomer-swollen polymer particles

Micron-sized, monodisperse polystyrene (PS)/poly( n-butyl methacrylate) (PBMA) composite particles, in which PS domain(s) were dispersed in a PBMA continuous phase, were produced by seeded polymerization for the dispersion of highly n-butyl methacrylate (BMA)-swollen PS particles (PS/BMA=1/150, w/w) using various concentrations of benzoyl peroxide as initiator in the absence/presence of sodium nitrite (NaNO ₂) as a water-soluble inhibitor. The percentages of the composite particles having double, triple and over PS domains, which were thermodynamically unstable morphologies, increased with a rapid increase of viscosity within the polymerizing particle.     

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     

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 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     

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     

Cationic amino-containing N-isopropyl- acrylamide–styrene copolymer latex particles: 1-Particle size and morphology vs. polymerization process

 Cationic hydrophilic copolymer latexes were synthesized at 70 °C either by batch or two-step emulsifier-free emulsion poly-merization of styrene (St), N-iso-propylacrylamide (NIPAM), and aminoethylmethacrylate hydro-chloride (AEM) using 2,2′-azobis (2-amidinopropane) dihydrochloride as initiator. At first, batch polymerization kinetics were followed by gas chromatography (GC), revealing that NIPAM rapidly homopolymerized, before the polymerization of styrene had started. Particle size analysis by quasi-elastic light scattering (QELS) and transmission electron microscopy (TEM) showed that monodispersed particles were obtained with the formation of a poly[NIPAM] rich shell. Adding a small amount of the cationic monomer caused a strong decrease of the particle size without affecting the size monodispersity. When a shot process was used, a narrow particle size distribution was maintained, provided that the monomer addition was performed at a relatively high conversion of the first batch step. The poly[NIPAM] rich shell layer was larger with the shot process, but increasing the amino-containing monomer in the recipe resulted in a dramatic decrease of the thickness. Combination of transmission, scanning and atomic force microscopy techniques showed that these hydrophilic particles exhibited odd-shaped structures, the unevenness being dependent upon the performed process. Kinetic data and particle morphology information were inferred for discussion of the polymerization mechanism of this system. Received: 21 August 1997 Accepted: 22 October 1997     

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 characterization of multiresponsive polymer composite microspheres with core–shell structure

Fe₃O₄/SiO₂/poly (N-isopropylacrylamide-co-N,N-dimethylaminoethyl methacrylate) [P(NIPAM-co-DMA)] multiresponsive composite microspheres with core–shell structure were synthesized by template precipitation polymerization. First, the magnetite nanoparticles were coated with silica and then modified with 3-(trimethoxysilyl)-propyl methacrylate (MPS). Subsequently, the Fe₃O₄/SiO₂ particles grafted with MPS were used to seed the precipitation copolymerization of NIPAM and DMA. The composite microspheres with core–shell structure were superparamagnetic, pH-sensitive, and thermoresponsive. The swelling ratio (D_{25 °C, pH = 3}/D_{50 °C, pH = 9})³ coupling of pH and temperature increased up to 21.2, which was much higher than that without comonomer DMA.     

Low temperature suspension polymerization of vinyl acetate using 2,2′-azobis(2,4-dimethylvaleronitrile) for the preparation of high molecular weight poly(vinyl alcohol) with high yield

 To obtain high molecular weight (HMW) poly(vinyl acetate) (PVAc) with high conversion and high linearity for a precursor of HMW poly(vinyl alcohol) (PVA), vinyl acetate (VAc) was suspension-poly-merized using a low-temperature initiator, 2,2′-azobis (2,4-dimethyl-valeronitrile) (ADMVN), and the effects of polymerization conditions on the polymerization behavior and molecular structures of PVAc and PVA prepared by saponifying PVAc were investigated. On the whole, the experimental results well corres-ponded to the theoretically predicted tendencies. Suspension polymerization was slightly inferior to bulk polymerization in increasing molecular weight of PVA. In contrast, the former was absolutely superior to the latter in increasing conversion of the polymer, which indicated that the suspension polymerization rate of VAc was faster than the bulk one. These effects could be explained by a kinetic order of ADMVN concentration calculated by initial-rate method and an activation energy difference of polymerization obtained from the Arrhenius plot. Suspension polymerization at 30 °C by adopting ADMVN proved to be successful in obtaining PVA of HMW (number-average degree of polymerization (P _n)): (4200–5800) and of high yield (ultimate conversion of VAc into PVAc: 85–95%) with diminishing heat generated during polymerization. In the case of bulk polymerization of VAc at the same conditions, maximum P _n and conversion of 5200–6200 and 20–30% was obtained, respectively. The P _n, lightness, and syndiotacticity were higher with PVA prepared from PVAc polymerized at lower temperatures. Received: 10 February 1998 Accepted: 15 April 1998     

Production of soft core/hard shell composite polymer particles by the stepwise heterocoagulation method with heat treatment

Soft core/hard shell composite polymer particle was prepared by the stepwise heterocoagulation, which was proposed by authors in 1990, of many cationic hard small polymer particles (SPs) onto an anionic soft large polymer particle (LP). The powder was obtained by freeze-drying at 0 ^°C which was higher than glass transition temperature of LP (−7 ^°C) and lower than that of SP (90 ^°C). Received: 9 December 1997 Accepted: 12 May 1998