Emulsifier-free Emulsion Polymerization Of Styrene Research Articles

Synthesis and properties of reactive polymer microspheres by emulsifier-free emulsion polymerization of styrene-butyl acrylate-2-hydroxyethyl acrylate

Reactive polymer microspheres were prepared by emulsifier-free emulsion polymerization of styrene (St), butyl acrylate (BA), and 2-hydroxyethyl acrylate (HEA) by using Potassium persulfate (KPS) as initiator. The effects of different conditions, such as the amount of HEA and KPS, polymerization temperature and cosolvent-methanol, on the polymerization were studied. Increasing the temperature of polymerization and the concentration of HEA and KPS can improve conversion rate and decrease the particle size as well. Moreover, the particle size can be increased by adding methanol to the system. At the same time, the nucleation mechanism was investigated.

Synthesis and characterization of poly(styrene/ α-t -butoxy- ω -vinylbenzyl-polyglycidol) microspheres

Polystyrene microspheres with polyglycidol (polyGL) in a surface layer were synthesized in batch radical emulsifier-free emulsion copolymerizations of styrene and surfmers, α-t-butoxy-ω-vinylbenzyl-polyGL macromonomers (VB-polyGL). Macromonomers with number-average molecular weight M¯ n=950 (VB-polyGL950) and M¯ n=2700 (VB-polyGL2700) were used for these polymerizations. In all syntheses the initial concentrations of styrene and initiator (K2S2O8) were constant. The initial macromonomer-to-styrene ratios were varied from 1.10 × 10−3 to 1.64 × 10−2 mol/mol and from 3.46 × 10−4 to 3.47 × 10−3 mol/mol for VB-polyGL950 and VB-polyGL2700, respectively. The diameters of microspheres obtained were smaller for the syntheses with higher concentrations of macromonomers. Syntheses with VB-polyGL950 yielded microspheres with number-average diameters (D¯ n) from 216 to 900 nm and with a bimodal diameter distribution. The number-average diameters of microspheres obtained with VB-polyGL2700 varied from 220 to 650 nm, depending on the initial concentration of macromonomer. Their diameter distributions were monomodal, with a diameter polydispersity parameter (ratio of weight-average and number-average diameters) in the range 1.007≤D¯ w/D¯ n≤1.022. For each type of microsphere the fraction of polyGL in a surface layer and the surface concentration of sulfate anions were determined. The fraction of polyGL in the surface layer was related to the initial monomer composition in the polymerizing mixture. Adsorption of human serum albumin onto surfaces of some poly(styrene/VB-polyGL) microspheres was up to 10 times lower than for the polystyrene microspheres obtained in a similar emulsifier-free emulsion polymerization of styrene.

Oligomer formation in the emulsifier-free emulsion polymerization of styrene

The formation of oligomers in emulsifier-free emulsion polymerization of styrene was characterized by means of gel permeation chromatography and surface tension measurements. GPC analysis showed incessant oligomer formation throughout the emulsion polymerization process. Oligomers spanned a molecular weight range of 200–1,500, have an Mw of 800–900, an Mn of 600–800 and a polydispersity index of 1.3. On average, the oligomers contain 4 to 6 styrene units. UV detection could not be utilized to acquire the weight ratio of oligomers to polymers without correction. Combination was the major mode of termination of free radicals in the aqueous phase, but disproportionation was not negligible: for every three-combination reactions there was about 1 disproportionation. Surface tension measurements showed that oligomers minimized the surface tension of the latex at about 50 min reaction to only 30 mN/m. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1323–1336, 2000

Oligomer formation in the emulsifier-free emulsion polymerization of styrene

The formation of oligomers in emulsifier-free emulsion polymerization of styrene was characterized by means of gel permeation chromatography and surface tension measurements. GPC analysis showed incessant oligomer formation throughout the emulsion polymerization process. Oligomers spanned a molecular weight range of 200–1,500, have an M̄w of 800–900, an M̄n of 600–800 and a polydispersity index of 1.3. On average, the oligomers contain 4 to 6 styrene units. UV detection could not be utilized to acquire the weight ratio of oligomers to polymers without correction. Combination was the major mode of termination of free radicals in the aqueous phase, but disproportionation was not negligible: for every three-combination reactions there was about 1 disproportionation. Surface tension measurements showed that oligomers minimized the surface tension of the latex at about 50 min reaction to only 30 mN/m. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1323–1336, 2000

NO decomposition by ultrafine noble metals dispersed on the rare earth phosphate hollow particles

Novel fine polymer particles containing ultrafine Pd, Pt or Rh metal dispersed on the core-shell [core, poly(styrene-co-acrylamide) or poly(styrene-co-acrylic acid); shell, LnPO4(Ln = Ce, Nd, Pr, Sm, La)] type microsphere were prepared by the emulsifier-free emulsion polymerization of styrene with acrylamide or acrylic acid followed by the addition of PdCl2, HPtCl6, or RhCl3 and finally by the addition of a mixture of Ln(NO3)3 and NaH2PO4. Pyrolysis of the resulting polymer particles at 700–900°C provides polymer-free hollow particles (diameter 450–550 nm) composed of noble metals and LnPO4. The excellent catalytic reduction of NO gas into N2 and O2 was observed at 500–700°C using the rersulting particles as catalyst.

Hydrogenation of 1-Hexene and Hexadienes by Ultrafine Pd Particles Supported on the Surface of PrPO4 Hollow Particles

Novel fine polymer particles containing ultrafine Pd particles dispersed on the surface of core shell [core, poly(styrene-co-acrylic acid); shell, PrPO4]-type microspheres were prepared by the emulsifier-free emulsion polymerization of styrene with acrylic acid followed by the addition of PdCl2 and a mixture of Pr(NO3)3 and NaH2PO2. Pyrolysis of the resulting polymer particles at 900°C provides organic polymer-free hollow particles (diameter, 473–586 nm) composed of Pd metal and PrPO4. Hydrogenation of 1-hexene, trans-1,3-hexadiene, trans-1,4-hexadiene, and 1,5-hexadiene using the resulting Pd/PrPO4 particles (reactant/Pd = 500 mol/mol) as catalyst revealed very high activity, especially for hydrogenations of 1-hexene and 1,5-hexadiene as compared with conventional Pd particles/Al2O3 and Pd particles on powdered PrPO4.

Preparation and characterization of P(St-co-4VP) particles produced by using emulsifier-free emulsion polymerization

Emulsifier-free emulsion polymerization of styrene (St) and copolymerization of St and 4-vinyl pyridine (4VP) in the presence of ammonium persulfate were studied. A comparison between the two polymerization systems was made. It was found that there were big differences comparing polymerization rate, the number and size of the particles and distribution, and molecular weight. For the St–4VP system, it was found that the additional amount of 4VP influenced the copolymerization of St and 4VP, molecular weight, and particle size. The formation mechanism of the particles was discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1502–1507, 1999

Polymer end groups in persulfate-initiated styrene emulsion polymerization

MALDI-TOF-MS investigations of the polymer inside the particles at the end of a persulfate-initiated emulsifier-free emulsion polymerization of styrene reveal - beside sulfate groups - a variety of different end groups of the polymer molecules almost independent of the buffer concentration employed during the polymerization. The results support at least the existence of the following end group combinations: H-H, H-OH, K +- OO-OH, K +- OO-K +- OO, HO +- OH, K +- OSO 3 -H, K +- OSO 3 -OH, and K +- OSO 3 K +- OSO 3 . These results lead to conclusions concerning particle nucleation and radical entry. As non-micellar particle nucleation is governed by the solubility of waterborne oligomers, chains started with radicals formed by side reactions in the aqueous phase obviously play an important role in particle nucleation. Concerning radical entry, the results suggest that surface activity of the entering radicals is not a prerequisite.

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.

Emulsifier-free emulsion copolymerization of styrene with two different amino-containing monomers: II. Surface and colloidal characterization

The colloidal and surface properties of copolymer latex particles prepared by batch emulsifier-free emulsion polymerization of styrene with two different amino-containing monomers (Amino Ethyl Methacrylate Hydrochloride (AEMH) and Vinyl Benzyl Amine Hydrochloride (VBAH)), and 2,2′-azobis(2-amidinopropane) dihydrochloride (V50) as initiator were investigated. The final particle size was found to decrease with increasing the functional monomer concentration. Different titration methods were used to quantify the surface amino (brought by the monomer) and amidino groups (originated from the initiator) on the latex particles. The same behavior was observed on both type of latexes: increasing the functional monomer concentration caused the surface amino groups density to increase from 0 to a plateau value at 8.2 μC/cm2, whereas the surface amidino groups density decreased from 18.5 to 2 μC/cm2. These results were confirmed by electrophoretic measurements and they corroborated those obtained in a previous kinetic study (Part 1) concerning the role of functional monomers as transfer agents. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2331–2342, 1997

Emulsifier‐free emulsion copolymerization of styrene with two different amino‐containing monomers: II. Surface and colloidal characterization

The colloidal and surface properties of copolymer latex particles prepared by batch emulsifier-free emulsion polymerization of styrene with two different amino-containing monomers (Amino Ethyl Methacrylate Hydrochloride (AEMH) and Vinyl Benzyl Amine Hydrochloride (VBAH)), and 2,2′-azobis(2-amidinopropane) dihydrochloride (V50) as initiator were investigated. The final particle size was found to decrease with increasing the functional monomer concentration. Different titration methods were used to quantify the surface amino (brought by the monomer) and amidino groups (originated from the initiator) on the latex particles. The same behavior was observed on both type of latexes: increasing the functional monomer concentration caused the surface amino groups density to increase from 0 to a plateau value at 8.2 μC/cm2, whereas the surface amidino groups density decreased from 18.5 to 2 μC/cm2. These results were confirmed by electrophoretic measurements and they corroborated those obtained in a previous kinetic study (Part 1) concerning the role of functional monomers as transfer agents. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2331–2342, 1997

Nucleation in Emulsion Polymerization: A New Experimental Study. 1. Surfactant-Free Emulsion Polymerization of Styrene

The very early stages of the emulsifier-free emulsion polymerization of styrene were investigated by on-line monitoring of the optical transmission and the conductivity of the reaction mixture. Very careful degassing of the reaction mixture is crucial to achieve high reproducibility. The higher the residual gas concentration the poorer the reproducibility no matter if the gas is air or nitrogen. The results lead to the conclusions that for particle nucleation the rate of initiation in the water phase is very important and that nucleation occurs via cluster formation of water-born oligomers. With the experimental techniques employed, it was possible to investigate the conversion range from 0.47% to 1.8%. However, it was not possible to detect a particle number maximum. Instead of a maximum, a decrease in the particle number was observed followed by a leveling and another increase, indicating another nucleation step.

Practical aspects of the emulsifier-free emulsion polymerization of styrene

The influences of initiator concentration, ionic strength of the aqueous phase and styrene sulfonic acid sodium salt comonomer on the average particle size and particle uniformity of latexes generated via emulsifier-free emulsion polymerization of styrene has been studied. It was found that the average particle size increased with increasing initiator concentration in reactions where the ionic strength was not controlled. The uniformity of the latex particles decreased as the initiator concentration increased. It was also found that at a minimum initiator concentration of 1.5 × 10 −3 M at a temperature of 80°, adequate conversion could not be obtained. This limited the range of particle sizes which could be produced without adding additional surfactants. It was also found that smaller particles, 0.135 μm diameter, could be formed by copolymerizing styrene sulfonic acid sodium salt with styrene. The effects of ionic strength on particle size was also investigated and it was found that the particle size increased with increasing ionic strength. At constant ionic strength, it was found that particle size decreased with increasing initiator concentration as expected theoretically.

Limiting conversion for systems of emulsifier-free emulsion polymerization of styrene

Factors that might affect the behavior of limiting conversion are studied including particle size, solvent addition, reaaction temperature, T g , surface charge density and addition of hydrophilic comonomers. Accordingly, limiting conversion can be attributed to the consequence of a shell-region polymerization characteristic of large emulsion particles and a monomer-diffusion-controlled polymerization reaction within the particles during the high-conversion period

Preparation and co-catalytic properties of functionalized latices

Stable cationic latices were prepared by emulsifier-free emulsion polymerization of styrene with 1-methyl-4-vinylpyridinium bromide or 1-methyl-4-vinylpyridinium iodide as comonomers using azobis(isobutyramidine hydrochloride) as initiator. Comonomers were prepared by a new and simple synthetic procedure. Addition of methanol and especially comonomer increased the surface charge density of cleaned latices and enhanced the polymerization rate. In the presence of iodide, the polymerization rate was lowered. The co-catalytic properties of silica-cleaned latices on the oxidative coupling of 2-mercaptoethanol were tested after cobalt(II)phthalocyanine-tetrasodiumsulphonate (CoTSPc) immobilization onto the functionalized latex particles. A significant increase in oxidation rate was found as compared with the polymer-free CoTSPc system.

Kinetics of Emulsifier-Free Emulsion Polymerization of Styrene in the Presence of Chain-Transfer Agents

Abstract The influence of chain-transfer agent on the kinetic behavior of emulsifier-free emulsion polymerization of styrene using potassium persulfate as initiator has been investigated. the presence of a small amount of a chain-transfer agent such as carbon tetrabromide or a mercaptan in the system increased the reaction rate. This rate increase is believed to be caused by a large number of precursor particles which exist in dynamic equilibrium with the mature latex particles in the reacting system. These precursor particles, although colloidally unstable and unable to be detected with an electron microscope, are believed to be an important locus for polymerization. the size of the monomer-swollen polymer particles obtained when CBr4 or ethyl mercaptan (ESH) are used is sensitive to agitation conditions. Large monodisperse polymer particles can be obtained in the presence of CBr4 or ESH under some agitation conditions.

Particle formation in emulsifier-free aqueous-phase polymerization of styrene

Particle nucleation in emulsifier-free emulsion polymerization of styrene using potassium persulfate as initiator is thought to involve an in situ micellization mechanism. The particle nucleation period can be divided into two stages. Stage 1 is short (less than 10 min) and large amounts of oligomer micellar particle nuclei is produced during this stage, which consist mainly of oligomers of molecular weight ca. 1000 and are stable due to surface charge generated by the initiator end groups. As these particle nuclei capture free radicals from the aqueous phase and produce internal high molecular weight polymers, the surface charge density decreases dramatically. The particle nuclei then lose their stability and begin to undergo coagulation, which marks the beginning of Stage 2. The critical chain length for in situ micellization, n∗, decreases during Stage 1 due to the increase of oligomer concentration through significant aqueous-phase termination of radicals. Particle size increases during Stage 2 through coagulation and polymerization. Radical capture by particles begins to be more significant than the aqueous-phase termination during Stage 2. The concentration of oligomer stops increasing and n∗ becomes constant. Particle number decreases toward a constant value with time in Stage 2 because of coagulation. A model has been developed and used to simulate particle nucleation during the transient period (both Stage 1 and Stage 2) described above. The criterion used to identify the beginning of Stage 2 was arbitrarily selected as that point when the ratio of the rate of radical capture by the particles to the rate of aqueous-phase termination becomes 2.