Monodisperse micron-sized macroporous poly(styrene-co-divinylbenzene) particles by seeded polymerization

Macroporous poly(styrene-co-divinylbenzene) particles were produced in a micron-size range by two-stage swelling and continuous polymerization. The molecular weight of the polystyrene seed particles was controlled by incorporating a urethane acrylate. It was found that the porosity of the particles produced by the seeded polymerization was dependent on the molecular weight of the seed polymer. As the molecular weight of the polystyrene seed increased, the porous particles produced became macroporous. Interestingly, the high molecular weight of the polystyrene seed had a negligible influence on the change of porosity of the seeded polymerized particles. It is believed that the viscosity of the swollen droplet phase remained pretty high with the change in composition because the polystyrene seed copolymerized with urethane cacrylate had many side chains. Received: 16 December 1999 Accepted: 9 August 2000     

Monodisperse polystyrene particles crosslinked with poly(dimethyl siloxane) diacrylate using dispersion polymerization and their monomer swelling capability

A flexible poly(dimethyl siloxane) diacrylate (PDMSDA) crosslinker was synthesized using different molecular weights of poly(dimethyl siloxane) (PDMS, M _n =550, 1,700, 4,000 g/mol). The monodisperse polystyrene (PS) particles crosslinked with various contents of PDMSDA were prepared by dispersion polymerization, and applied as seed particles in the seeded polymerization. The crosslinking density of the PS particles was determined from the rate of transport of the monomer molecules to the crosslinked seed particles. It was confirmed that the monomer swelling capacity of seed particles and final morphological changes of polymer beads were determined significantly by the crosslinking density of the seed particles. In addition, the morphological change was not observed without the oligomer swelling step in the seeded polymerization due to the hydrophobic property of PDMS. When highly crosslinked seed particles were used in the seeded polymerization, peculiar morphology (doublet structure) of polymer beads appeared.     

Monodisperse glycidyl-functional polymer particles in the micron-size range by seeded polymerization

Polymer particles having glycidyl ether groups were prepared through seeded polymerization in aqueous medium. The polystyrene seed particles were swollen with a mixture of n-butyl methacrylate, glycidyl methacrylate, ethylene glycol dimethacrylate, and benzoyl peroxide initiator. The particles produced after polymerization were characterized regarding the particle morphology and functionality. Optical microscopy and scanning electron microscopy showed that the particles are in the size range of 13–14 μm and are highly monodisperse with heterophase structures. Actually, the high content of glycidyl methacrylate in the second monomer mixture caused the particle phase to be homogeneous. This effect was explained in terms of the surface tension of each polymer phase. Moreover, the cross-linking of the seed particles had a significant effect on the final particle morphology. From the HCl–dioxane back titration method, it was found that about 20–30% of glycidyl ether groups still remained on the final particles. Received: 25 February 2000 Accepted: 10 November 2000     

Synthesis and characterization of sulphonated core-shell latices in the size range between 30 and 80 nm

The objective of the current work was the synthesis of sulphonated core-shell nanolatices and to investigate to which extend it is possible to control the final surface charge of such latices. For this purpose differently sized polystyrene seed latices with average diameters in the size range between 30 and 80 nm were synthesized by emulsion polymerization. To obtain the final latices, a sulphonated comonomer was incorporated in the outer surface shell of the particles by further reaction of the seed latices with styrene and sodium styrene sulphonate (NaSS). In a first test series the seed latex surface was modified with four different amounts of NaSS. In a second test series four different seed latices were reacted with the same amount of NaSS. In the last set of reactions the seed latices were reacted with different amounts of NaSS and in these reactions the ratio of added NaSS to the specific surface area of the seed latex was kept constant to obtain differently sized latices of the same surface charge density. The yield of sulphonic acid groups in the particle shell was found between 57 and 74% after an intensive cleaning step by ion exchange. The results show possibilities for a reproducible synthesis of small sulphonated latex particles with a desired surface charge density.     

Energy-consuming micromechanisms in the fracture of glassy polymers. I. Chain scission in polystyrene

The number of chain scissions per unit area that occur during the fracture of partially annealed latex films from M_n ? 180,000 g/mol polystyrene particles of about 275 Å radius were measured and correlated to annealing times. A curve with four regimes was found. At short annealing times the curve is nearly flat, in what is called the chain pull-out regime. In the second regime, the number of chains broken per unit area increases with a 0.8 power of annealing time as entanglement of the diffusing polymer chains increases in neighboring host particles. This is in good agreement with Wool's theory which predicts a 0.75 power dependence. Then, after reaching a peak, the number of scissions decreases in the third regime, indicating a change in fracture mechanism. The number of chain scissions increases again in the fourth regime, as final healing of the film interface takes place. Fracture surface analysis reveals a rough surface for short annealing times and a smooth surface for longer annealing times. The number of polymer chain scissions per unit area of fracture surface showed no dependence on initial molecular weights for t ? τ_r where t and τ_r are annealing and relaxation times, respectively. The number of chain bridges crossing a unit area of interface was suggested as the basic molecular property. © 1992 John Wiley & Sons, Inc.     

Surface modification of polystyrene latex particles via atom transfer radical polymerization

The atom transfer radical polymerization (ATRP) technique using the copper halide/ N,N′,N′,N″,N″‐pentamethyldiethylenetriamine complex was applied to the graft polymerization of methyl methacrylate and methyl acrylate on the uniform polystyrene (PS) seed particles and formed novel core‐shell particles. The core was submicron crosslinked PS particles that were prepared via emulsifier‐free emulsion polymerization. The crosslinked PS particles obtained were transferred into the organic phase (tetrahydrofuran), and surface modification using the chloromethylation method was performed. Then, the modified seed PS particles were used to initiate ATRP to prepare a controlled poly(methyl methacrylate) (PMMA) and poly(methyl acrylate) (PMA) shell. The final core‐shell particles were characterized using Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy, thermogravimetric analysis, and elementary analysis. The grafting polymerization was conducted successfully on the surface of modified crosslinked PS particles, and the shell thickness and weight ratio (PMMA and PMA) of the particles were calculated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 892–900, 2002; DOI 10.1002/pola.10160     

Understanding and preventing the formation of deformed polymer particles during synthesis by a seeded polymerization method

Uniformly sized porous polymer particles with different polarity namely poly(divinylbenzene), poly(vinyl acetate‐co‐divinylbenzene), poly(ethylene dimethacrylate), and poly (glycidyl methacrylate‐co‐ethylene dimethacrylate) were prepared in the micron‐size range by a seeded polymerization method. Parameters affecting the particle morphologies including monomer mixture content, porogen content, and polystyrene (PS) seed latexes were varied, and the morphologies of the resulting particles were investigated by scanning electron and confocal microscopy. The results obtained indicated that the particle shape depended dominantly on the molecular weight of the PS seed template. Deformed particles, including collapsed spheres and spheres with holes were obtained when high molecular weight PS seeds were used, whereas well‐defined polymer particles were produced easily by using low molecular weight seeds. The use of 1,1‐diphenylethylene as a chain terminator during seed polymerization is proposed in this work as an efficient method to lower molecular weight of PS in seed particles while keeping seed size small. This low molecular weight seed template retained its spherical geometry after swelling and polymerization with different second stage monomers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Surface functionalization of polystyrene latex particles with a liposaccharide monomer

Emulsifier-free latexes with immobilized carbohydrate residues have been prepared by batch or seed (co)polymerization of styrene in the presence of 11-(N-p-vinylbenzyl)amido undecanoyl maltobionamide (LIMA). The critical micelle concentration and the molecular surface area of LIMA were determined by surface tension and fluorescence measurements. Batch polymerization of LIMA with styrene was first performed using potassium persulfate, proving the efficiency of LIMA as emulsifier. Seed copolymerization was then investigated using polystyrene seed particles with varying experimental conditions (especially the LIMA surface coverage). Material balance of LIMA between aqueous phase and particles was obtained by separating both phases by ultracentrifugation and it was found that the surfaceactive monomer is preferentially on or in the particle (nearly 100% in batch and at most 70% in seed copolymerization). The presence of the carbohydrate residues at the particle surface was directly evidenced by ¹H-nuclear magnetic resonance, electron spectroscopy for chemical analysis and electrophoretic mobility.     

核/壳乳液聚合工艺中乳化剂的定量研究

以十二烷基硫酸钠(SDS)为乳化剂,采用多步种子乳液聚合方法制备了核/壳结构乳液,研究了乳化剂加入量以及加料速率对核壳乳液聚合的影响,并推导了核及壳乳液聚合阶段所需乳化剂量的计算公式.研究表明,当种子、核、壳乳液聚合阶段单体量分别为12g、50g和50g,种子乳液聚合阶段加入的乳化剂量为0.44g时,控制核、壳乳液聚合阶段乳化剂的加入量分别在0.64～2.07g及0.04～2.12g之间,且预乳化单体的滴加速度低于2.3g/min时,可以防止二次成核及新乳胶粒子的形成,制得粒径分布窄、核/壳结构明显的乳胶粒子.利用透射电镜(TEM)对所制备的核壳结构乳胶粒子的结构形态进行了验证,试验结果与理论预测结果一致.     

Monodisperse porous polymer particles: Formation of the porous structure

Monodisperse porous styrene-divinylbenzene copolymer particles were prepared via seeded emulsion polymerization using a mixture of linear polymer (polystyrene seed) and non-solvent as inert diluent. Experimental evidence was presented to describe the mechanism of formation of porous polymer particles during the copolymerization and solvent extraction stages, in which porosity was a consequence of phase separation in the presence of diluents. Pore structure formation was investigated by changes in copolymerization kinetics, gel content, crosslinking density, particle morphology, surface area, pore volume, and pore size distribution. The process of copolymerization was presented, based on the concepts of production, agglomeration, and fixation of the interior gel microspheres of polymer particles. A portion of linear polymer used as diluent was found to participate in the network structure while the porous matrix was built-up. The influence of the removal of the linear polymer from the matrix pores during the solvent extraction process on the porous structure was also discussed.     

Chemical bath deposition synthesis of sub-micron ZnS-coated polystyrene

The synthesis of ZnS-coated polystyrene composite colloids by the decomposition of thioacetamide in the presence of polystyrene seed particles and metal salt is presented. The chemical bath deposition technique incorporates poly(vinyl pyrrolidone) to inhibit particle aggregation during the synthesis so that core-shell particles with sizes in the low sub-micron range were achieved. The shell thickness was well controlled through the reaction time and core size. ZnS shells were composed of primary crystallites, approximately 5 nm in diameter, which had the zinc blend crystal structure. The porosity of the shells was between 12 and 19%. Accordingly, the effective refractive index of the particles varied between 1.73 and 1.98 at wavelengths above the optical absorption edge of ZnS. Ordered colloidal crystals were produced by convective assembly of the poly(sodium 4-styrenesulfonate) stabilized core-shell particles. Assemblies of ZnS shell-polystyrene core particles are photonic crystal materials which may have applications in optical computing and communications environments.     

Synthesis of anisotropic nanoparticles by seeded emulsion polymerization

Anisotropic polystyrene nanoparticles of diameters below 0.5 microm were prepared by coating the surface of cross-linked polystyrene latex particles with a thin hydrophilic polymer layer prior to swelling the particles with styrene and then initiating second-stage free-radical polymerization. Conditions were found so that all particles had uniform asymmetry. The effect of surface chemistry on the development of particle anisotropy during seeded emulsion polymerization of sub-0.5 microm diameter particles was studied. The extent and uniformity of the anisotropy of the final particles depended strongly on the presence of the hydrophilic surface coating. Systematic variation of the degree of hydrophilicity of the surface coating provided qualitative insight into the mechanism responsible for anisotropy. Conditions were chosen so that the surface free energy favored the extrusion of a hydrophobic bulge of monomer on the hydrophilic surface of the particle during the swelling phase: the presence of a hydrophilic layer on the particle surface causes this asymmetry to be favored above uniform wetting of the particle surface by the monomer. Kinetic effects, arising from the finite time required for the seed to swell with the monomer, also play a role.     

Synthesis and characterization of monodisperse porous polymer particles

Monodisperse porous polymer particles in the size range of 10 μm in diameter were prepared via seeded emulsion polymerization. Linear polymer (polystyrene seed) or a mixture of linear polymer and solvent or nonsolvent were used as inert diluents. The pore diameters of these porous polymer particles were on the order of 1000 Å with pore volumes up to 0.9 mL/g and specific surface areas up to 200 m²/g. The physical features of the porous polymer particles depended on the diluent type and the crosslinker content, as well as the molecular weight of polymer seed particles. By varying the molecular weight of the linear polymer, monodisperse porous polymer particles with different pore size distribution could be synthesized. Polymer seed with a low degree of crosslinking instead of linear polymer could also be used to prepare monodisperse porous polymer particles with smaller pore volume and pore size.     

Influence of the Sacrificial Polystyrene Removal Pathway on the TiO2 Nanocapsule Structure

This study demonstrates the significant influence of the polystyrene removal pathway on the TiO₂ nanocapsules obtained from PS @TiO₂ core‐shell particles. In a first step, the polystyrene spheres were coated with titanium oxide via hydrolysis and condensation of the titanium precursor to form PS @TiO₂ core‐shell particles. Then, the creation of the empty cavity to form TiO₂ nanocapsules was achieved by removing the polystyrene template by i ) thermal decomposition of the polystyrene or ii ) dissolution of the polystyrene using Soxhlet extractor followed by a thermal procedure. These pathways to remove the polystyrene were investigated by thermogravimetric studies, IR spectroscopy, transmission and scanning electron microscopy and powder X‐ray diffraction. The final TiO₂ nanocapsule structure strongly depends on the sacrificial polystyrene removal pathway. The preservation of the TiO₂ nanocapsules was obtained essentially when the polystyrene was dissolved before the crystallization of the TiO₂.     

Production of micron-sized polystyrene particles containing PEG near the particles surface

Polystyrene (PS) particles in the size range of 1-7 µm, containing poly(ethylene glycol) or PEG on the particles surface, were prepared by multi-step seeded polymerizations. Micron-sized PS particles were first prepared by dispersion polymerization using 2,2'-azobisisobutyronitrile as initiator and polyvinyl pyrrolidone as stabilizer. Conventional swelling method was then used to increase the size of the PS particles with a large amount of styrene in presence of oil soluble initiator, benzoyl peroxide. In the final step, the PS particles have been used to carry out seeded polymerization with small amount of styrene in presence of poly(ethylene glycol)-azo or PEGA initiator with average molecular weights of the PEG chains of 200 and 3000 g mol^-1 , respectively. The average size, size distribution, and surface morphology indicate that seeded polymerization in the final step with small amount of styrene in presence of PEGA is the best way to produce monodisperse polystyrene particles containing PEG near the particles surface.     

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     

Anionic dispersion polymerization of styrene. I. Investigation of parameters for preparation of uniform micron-size polystyrene particles with narrow molecular weight distribution

Anionic dispersion polymerization in a hexane medium has been applied to the synthesis of monodisperse polystyrene particles in the size range of 1.41–6.16 μm, and having narrow molecular weight distributions M_w/M_n of 1.02–1.28. sec-Butyllithium was used as the initiator. Polystyrene-block-polybutadiene diblock copolymer containing 23% polystyrene block, (i.e., Stereon 730A) with a molecular weight of 147,000 g/mol and a polydispersity of 1.05, was found to be a suitable steric stabilizer for the preparation of micron-size polystyrene particles with narrow size distribution. Tetrahydrofuran (THF) was used as a promoter for obtaining narrow molecular weight distributions. However, this study revealed that the addition of small amounts of THF as promoter broadened the particle size distribution. High solids content polystyrene dispersions were also prepared without using any promoter by both batch and/or multi-addition monomer processes. © 1996 John Wiley & Sons, Inc.     

Synthesis and characterization of micrometer‐sized particles of narrow size distribution with chloromethyl functionality on the basis of single‐step swelling of uniform polystyrene template microspheres

Polystyrene template microspheres of 1.4 ± 0.1 μm were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2‐methoxy ethanol. These template particles were then swelled at room temperature in a single step with emulsion that was prepared in sodium dodecyl sulfate aqueous solution from a swelling solvent (dibutyl phthalate) containing the initiator (benzoyl peroxide) and monomer(s) (chlormethylstyrene, divinylbenzene, or ethylene dimethacrylate). Composite uniform particles composed of the template polystyrene and noncrosslinked or crosslinked polychloromethylstyrene were prepared by polymerizing the monomer(s) within the swelled particles at 73 °C. Crosslinked uniform polychloromethylstyrene particles of higher surface area were formed by dissolving the template polystyrene polymer of the composite particles. The influence of various reaction parameters, such as dibuthyl phthalate concentration, chloromethylstyrene concentration, crosslinker type and concentration, and so forth on the molecular weight, size, size distribution, shape, morphology, surface area, and decomposition temperature of the particles was investigated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1342–1352, 2002     

一种室温下制备多孔锐钛矿型TiO2薄膜的方法

 采用具有锐钛矿晶粒的TiO2溶胶与聚苯乙烯球形粒子混合制得涂膜液,通过浸渍提拉法制备薄膜,然后在超声波振荡条件下,以甲苯为溶剂,将薄膜中的聚苯乙烯球选择性地溶解去除,在室温下获得了锐钛矿型多孔TiO2薄膜. 与致密的TiO2薄膜相比,该多孔TiO2薄膜具有较高的光催化活性. 该方法有以下两方面的优点: 一是实现了多孔TiO2薄膜的室温制备,增大了薄膜基材的选择范围; 二是可以通过添加不同粒径的聚苯乙烯球,较为方便地实现了对薄膜孔径的调节.     

Preparation of novel and unique nonspherical particles with almond-shell-like shape via dual-seeded dispersion polymerization in the presence of saturated hydrocarbon droplets

In this study, the preparation of micron-sized polymer particles having a novel and unique nonspherical shape which we called almond-shell-like by dual-seeded dispersion polymerization (DSDP) of 2-ethylhexyl methacrylate (EHMA) with polystyrene (PS) and poly(methyl methacrylate) (PMMA) seed particles in the presence of decane droplets and evaporation of decane after the polymerization was discussed. The experimental results showed that mushroom-like morphology which is a precursor of the almond-shell-like shape was obtained from DSDP of EHMA. It was found that with changing the PS/PMMA seed particles' weight ratio, the size of the dents on the surface of the particles can be controlled. Furthermore, it was observed that various nonspherical particles can be produced using different methacrylic seed particles and initiators.