Kinetics and mechanism of emulsifier-free emulsion polymerization. II. Styrene/water soluble comonomer (sodium methallyl sulfonate) system

The emulsifier-free emulsion polymerizations of styrene in the presence of about 1 wt% (related to styrene) of the water soluble comonomer, sodium methallyl sulfonate (NaMS), which has short hydrophobic group and strong hydrophilic ionic group, and of the initiator, potassium persulfate, are carried out. Under constant ionic strength, the number density of polymer particles (N_p) is found to depend on 0.5-power of the initiator concentration and shows a minimum in the comonomer concentration plot. Under constant concentration of monomer, comonomer and initiator, N_p is found to depend on ?1.1-power of the ionic strength. In the earlier period, the presence of styrene oligomer having MW about 1000 and water soluble poly(NaMS) or copolymer with high NaMS content suggests a micellar nucleation mechanism, by which the styrene oligomer behaves as emulsifier and the poly(NaMS) can either stabilize or destabilize the existing particles, depending on its concentration in the aqueous phase. The particle size is rather uniform having an uniformity very close to 1 (ca. 1.001) throughout the entire process. It is much larger than that of the conventional emulsion polymerization or emulsifier-free emulsion polymerization with the other comonomers by about 3 to 4 times in diameter or 27 to 64 times in volume, leading to that the average radical number in the particle could be much greater than 0.5. The (conversion)^2/3 versus time plot is found to be linear from 6 to 50% conversion. During this period, for the conversion from 10 to 40% the polymerization rate increases twice but the particle volume increases four-fold. In addition, MWD shows bimodal (excluding the styrene oligomer peak in the earlier period) during the growth period. But the lower MW peak shifts to higher MW and become larger, while the higher MW peak decreases, and finally the MWD becomes single mode after 58.6% conversion. These results suggest a “gradient polymerization” or “transition stage to core-shell structure” in the earlier stage of particle growth and a “shell part polymerization” in the later stage.     

Functional polymers for colloidal applications. V. Novel behavior of polymeric emulsifiers in emulsion polymerization

The polymeric emulsifier poly(dodecyl acrylate-co-acrylic acid) [i.e., the sodium salt (PDA)] and monomeric emulsifier sodium dodecyl glutarate (SDG) have been synthesized. PDA and SDG are used as emulsifiers in the emulsion polymerization of styrene with both the water-soluble initiator potassium persulfate (K₂S₂O₈) and the oil-soluble initiator 2,2′-azobisisobutyronitrile (AIBN). The PDA/K₂S₂O₈ system showed a bimodel distribution of particle sizes (2 and 0.05 μm). A bimodel particle distribution was also found for the PDA/AIBN system, but the distribution for the large particles was wide (0.1–10 and 0.07 μm). The SDG/K₂S₂O₈ system displayed only one kind of particle size (0.05 μm), but the SDG/AIBN system also showed a bimodel distribution of particle sizes (0.05 and 5 μm). These bimodel distribution results for the PDA/K₂S₂O₈, PDA/AIBN, and SDG/AIBN systems indicate that the polymerization sites are both in oil droplets and in micelles (polymer aggregates). This mechanism is interpreted in terms of the formation of polymer aggregates, which is supported by the results of pyrene solubilization, pyrene fluorescence, surface tension, and pyrene excimer experiments. © 1993 John Wiley & Sons, Inc.     

Synthesis and characterization of secondary‐amine‐functional microparticles

Secondary‐amine‐functional microparticles were prepared in the range of 50–250 μm through the suspension polymerization of styrene, divinylbenzene (DVB), and 2‐(tert‐butylamino)ethyl methacrylate (tBAEMA). This study focused on the effects of the DVB, tBAEMA, initiator, and stabilizer concentrations and shaking rate on the experimental amine content, swelling ratio, average particle size, and particle size distribution. The suspension polymerization experiments were carried out in two different systems. In the first system, an organic phase, including the monomers and initiator, was dispersed in an aqueous medium in the presence of Al₂(SO₄)₃. Al₂(SO₄)₃, in the presence of an amine monomer (pH ～ 10), formed colloidal Al(OH)₃, which built a nonsticky layer on the surface of the polymerizing droplets that prevented them from coalescing and aggregating. Individual and spherical particles within the range of 50–200 μm were obtained by this polymerization method. The second method was similar to the first polymerization protocol, except that a certain amount of sodium dodecyl sulfate was added as a costabilizer in the presence of Al₂(SO₄)₃. In these experiments, individual and spherical particles were obtained within the range of 130–250 μm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem: 3708–3719, 2004     

Kinetics of successive seeding of monodisperse polystyrene latexes. I. Initiation via potassium persulfate

The polymerization kinetics of monodisperse polystyrene latexes prepared via successive seeding were studied in the region between Smith-Ewart Case 2 (n? = 1/2) and Case 3 (n? ? 1). Potassium persulfate was used as the initiator. The kinetics were measured in a piston/cylinder dilatometer designed for microgravity experiments. A recipe formulation method was developed by which a constant emulsifier (Aerosol-MA) surface coverage was maintained throughout a sequence, beginning with a 0.19 μm polystyrene seed. Monodisperse latexes up to 1 μm in size were prepared using 0.5 mM K₂S₂O₈ with a 4% emulsifier surface coverage. The polymerizations were commenced in Interval III, the particles being swollen with twice their weight in monomer. The kinetics were characterized by the autoacceleration of the gel effect with the overall polymerization rate decreasing with increasing particle size (decreasing N_p). The Case 2 to Case 3 kinetic transition was experienced in the first seeding step, however, independence of the rate on the number of particles was not evident even at high values of n? (n? > 10). This was attributed to a dependency of the free radical capture efficiency on the particle size (constant solids). Corroborating indirect evidence was supplied through surface charge analysis and detailed examination of the polymerization kinetics.     

Particle Formation in Emulsion Polymerization: Particle Number at Steady State

Abstract

The number of particles formed in batch emulsion polymerization over wide ranges of emulsifier and initiator concentration has been investigated by computer simulation with a mathematical model developed in a previous paper. The influence of particle coagulation is also considered. The results show that, at low emulsifier concentration, the steady-state particle number N _s is governed by homogeneous nucleation so that N _s increases slowly with increasing emulsifier concentration [S]. In this range, N _s increases with increasing monomer polarity. The steep rise in N _s with emulsifier concentration after [S] exceeds a critical value suggests a transition from homogeneous nucleation domination to micelle nucleation. The slope of the N _s vs [S] relationship increases as the particle coagulation rate constant K_f increases. The power x in the empirical relationship N _s ? [S]^x decreases with increasing polarity of monomer in this region. At very high micelle concentration, insufficient radical generation and the increasing tendency for particle coagulation cause N ₂ to be less dependent on emulsifier concentration. These phenomena have been reviewed by Vanderhoff and confirmed by the experimental data presented by Sutterlin. The particle number increases with increasing initiator concentration [I] when [S] is above the CMC. As [I] continues to increase, however, N _s becomes relatively constant. Experimental data for styrene, butyl acrylate, and methyl acrylate from the literature are compared with the model predictions. Agreement between the theoretical predictions and the experimental data is evident over a wide range of emulsifier and initiator concentrations.     

Emulsifier-free emulsion copolymerization of styrene and butyl acrylate. I. Kinetic studies in the absence of surfactant

Soapless emulsion copolymerization of styrene (S) and n-butyl acrylate (BuA) has been investigated using two types of initiator and different comonomer feed mixtures. When using K₂S₂O₈ as initiator, the particle size and size distribution of the final latexes (500 nm and 1.003, respectively) is not significantly affected by the comonomer feed composition, whereas the molecular weight and surface characteristics were found to sharply change at high butyl acrylate content. Based on the most probable particle nucleation mechanism and type of chain termination in the monomer swollen particles, a tentative explanation of these results has been proposed. Replacing persulfate by a carboxylic initiator (4-4′-azobiscyanopentanoic acid) results in the formation of stable particles as α observed with the persulfate, provided the aqueous phase pH is fixed in between 6 and 7. Results on the initiator residue location as a function of the conversion point out that the particle flocculation mechanism is strongly significant in the preparation of such latexes.     

无乳化剂乳液聚合法合成单分散大粒径高分子微球的研究

无乳化剂乳液聚合法合成单分散大粒径高分子微球的研究朱世雄杜金环金熹高陈柳生（中国科学院化学研究所北京１０００８０）关键词无乳化剂乳液聚合，单分散，均相成核，低聚物胶束微米级大粒径单分散高分子微球在标准计量、情报信息、分析化学等许多领域都有广泛的...     

Synthesis of biocompatible and biodegradable polymer particles in supercritical carbon dioxide

The free radical copolymerization of N-vinyl-2-pyrrolidone and 2-methylene-1,3-dioxepane was carried out in supercritical carbon dioxide (scCO₂) using three kinds of dispersants and 2,2′-azobisisobutyronitrile as the initiator. Polymerization was performed with fluorinated polymeric dispersants synthesized in scCO₂ using the solution polymerization method and commercially available siloxane-based surfactant. Spherical biocompatible and biodegradable polymeric particles were prepared within the sub-micron size range. The effect of various ratios of the comonomer, reaction temperature, and concentration of initiator, in addition to the types and concentrations of the dispersants, on the particle size and morphology was investigated. The particle size and particle size distribution of copolymer particles were controlled using the above mentioned experimental parameters. Glass transition temperatures of copolymers were varied according to the comonomer ratios used.     

Kinetics of successive seeding of monodisperse polystyrene latexes. II. Azo initiators with and without inhibitors

Oil soluble azo initiators in combination with water soluble inhibitors were used to extend the particle size limit in studies of the kinetics of successive seeding of monodisperse polystyrene latexes. Monodisperse latexes were prepared up to 2.5 μm in diam using 4.0 mM AMBN and 14.5 mM hydroquinone with a constant 15% emulsifier (Aerosol–MA) surface coverage throughout the seven step sequence. The polymerization kinetics were measured in a piston/cylinder dilatometer designed for microgravity experiments. The Interval III kinetics were dominated by the gel effect although these were affected by the nature of the inhibitor. In general, the overall polymerization rate decreased with increasing particle size (decreasing N_p) up to a size of about 1 μm. Thereafter, the kinetics were independent of these variables, exhibiting Smith-Ewart Case 3 (bulk) kinetics. The initiator efficiencies were found to be of the order of 10%, considerably lower than reported for bulk polymerizations.     

An emulsifier‐free core–shell polyacrylate/diacetone acrylamide emulsion with nano‐SiO2 for room temperature curable waterborne coatings

An emulsifier‐free core–shell polyacrylate emulsion, containing nano‐SiO₂ nanoparticles in the core and diacetone acrylamide (DAAM) in the shell, has been successfully prepared by emulsifier‐free seeded emulsion polymerization. The effects of reaction temperature, dropping time, nano‐SiO₂ and initiator contents, and variation of the composition of core monomers on the amount of coagulum, particle size, and monomer conversion have been investigated. The particle morphology and the distribution of emulsion particles have been measured by transmission electron microscopy (TEM) and dynamic light scattering. The keto‐carbonyl groups on the surface of the polyacrylate emulsion nanoparticles reacted with adipic dihydrazide (ADH) to form a film with a cross‐linked network structure at room temperature. Therefore, the emulsifier‐free core–shell emulsion could be used as a two‐component room temperature curable waterborne coating. It was also found that the properties of the coating were clearly superior after using the cross‐linker. Copyright © 2009 John Wiley & Sons, Ltd.     

Unseeded semibatch emulsion polymerization of butyl acrylate: Bimodal particle size distribution

Unseeded semibatch emulsion polymerization of butyl acrylate (BA) using sodium lauryl sulfate as emulsifier and potassium persulfate as initiator was carried out at the conditions where secondary nucleation was probable. This was achieved by using no emulsifier in the initial reactor charge. The effects of changes in monomer emulsion feed rate, initiator concentration and distribution, emulsifier concentration in the feed, and temperature on the evolution of particle size averages and distribution were investigated. Bimodal particle size distributions (PSD) were obtained for most of the latexes. Inhibition effects were found to be important in the development of PSD. Primary particle formation occurred through micellar nucleation, whereas secondary nucleation probably occurred through homogenous nucleation. The polydispersity index (PDI) of the latexes increased with the decreasing monomer emulsion feed rate. The application of a larger amount of initiator to the reactor charge or using a higher temperature, reduced the formation of secondary particles and resulted in a formation of an unimodal PSD. The overall steady‐state rate of polymerization was found to approach the rate of monomer addition (R_p ≈ R_a ), if the emulsifier concentration in the aqueous phase was appreciable. This is different from the correlation 1/R_p = 1/K + 1/R_a obtained for the BA semibatch process with neat monomer feed. This suggests that different rate expressions can be used for BA semibatch emulsion polymerization at different conditions. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 528–545, 2000     

Polymeric Fluorosurfactant‐Mediated Perfluorocarbon Emulsions

Polymeric fluorosurfactants, using poly(N,N‐dimethylacrylamide) (PDMA) or PDMA copolymers containing acrylic acid (AA) or 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) comonomers were synthesized by copolymerization of DMA, DMA/AA, or DMA/AMPS and methacrylates composed of 1,1‐dihydroperfluorodecanoyl groups separated from the methacrylate by polyethylene glycol (PEG) groups with molecular weights ranging from 1 to 6 kD. The stability of aqueous perfluorocarbon (PFC) emulsions mediated by these polymeric fluorosurfactants was found to be affected by polymer concentration, ionic comonomer content, perfluoroalkyl (R_F) comonomer content, and PEG spacer length. Thus, emulsion stability characterized by average particle size and morphology was improved by increased AA or AMPS content (up to 30 weight percent), increased PEG chain length and R_F comonomer content, and greater polymer concentration.     

反相乳液共聚合制备两性丙烯酰胺共聚物的研究

采用Span80-Tween80复合乳化剂和AIBA引发剂,进行丙烯酸钠(NaAA)/丙烯酰胺(AM)/丙烯酰氧基乙基三甲基氯化铵(DAC)反相乳液共聚合.研究了聚合温度、引发剂用量、单体浓度、共聚单体中DAC和AM含量、乳化剂用量及其HLB值、水/油比和水相pH值等聚合反应工艺条件或参数对聚合反应单体转化率和聚合物特性粘度的影响,聚合物特性粘度随引发剂用量和单体浓度的增大而增大的实验结果证实了该两性丙烯酰胺共聚物反相乳液制备过程中凝胶效应的存在.傅立叶红外光谱组成分析表明了两性丙烯酰胺共聚物的成功合成,扫描电镜观测乳胶粒粒径范围在0.6~8.0μm.     

沉淀聚合法制备窄分散聚(甲基丙烯酸缩水甘油酯-co-乙二醇二甲基丙烯酸酯)功能聚合物微球

以偶氮二异丁腈(AIBN)为引发剂,甲基丙烯酸缩水甘油酯(GMA)和乙二醇二甲基丙烯酸酯(EGDMA)为共聚单体,采用沉淀聚合法制备了不同交联度的窄分散聚合物微球,考察了共聚单体对聚合物微球粒度、分散性以及产率的影响,并用扫描电镜(SEM)和红外光谱对微球进行了表征,SEM结果显示当EGDMA的比例在40mol%～70mol%之间时,可得到单分散的poly-(GMA-co-EGDMA)微球.     

Influence of crosslinker and ionic comonomer concentration on glass transition and demixing/mixing transition of copolymers poly(N-isopropylacrylamide) and poly(sodium acrylate) hydrogels

Hydrogels based on N-isopropylacrylamide and sodium acrylate as ionic comonomer were synthesized by free radical polymerization in water using N,N′-methylenebisacrylamide as crosslinker and ammonium persulfate as initiator. The glass transition of dried copolymers poly(N-isopropylacrylamide) (PNIPA) and poly(sodium acrylate) (SA) gels and demixing/mixing transition of PNIPA-SA hydrogels swollen with increasing amounts of water were studied using conventional differential scanning calorimetry. In the crosslinked polymers, the glass transition linearly increases, and the transition range becomes broader, with increasing crosslinker content. Increasing content of ionic comonomer also produces an increase of glass transition temperature, which moves to higher temperatures with higher sodium acrylate fraction. The influence of chemical structure of PNIPA-SA hydrogels on the lower critical solution temperature (LCST) of PNIPA-SA/water mixtures during heating and cooling was quantified as function of the content of the crosslinker and the ionic comonomer, as well as water content of the hydrogel in the range from 95 to 70 wt%. At parity of water content, the LCST occurs at higher temperatures for gels containing higher amounts of sodium acrylate. Similarly, the introduction of N,N′-methylenebisacrylamide causes an increase of the LCST, which grows with increasing of crosslinking degree of the hydrogel.     

Emulsion copolymerization of vinylidene chloride and methyl methacrylate. I. Effects of operating variables on the kinetic behavior

The effects of operating variables on the kinetic behavior of the emulsion copolymerization of vinylidene chloride (VDC) and methyl methacrylate (MMA) were examined at 50 °C with sodium lauryl sulfate as an emulsifier and potassium persulfate as an initiator, respectively. The number of polymer particles produced increased in proportion to the 1.0 power of the initial emulsifier concentration and to the 0.3 power of the initial initiator concentration and decreased with an increasing content of MMA in the initial monomer charge. The rate of copolymerization was proportional to the 0.4 power of the initial emulsifier concentration and to the 0.5 power of the initial initiator concentration and increased with an increasing content of MMA in the initial monomer charge. The molecular weight of copolymer produced decreased drastically with an increasing content of VDC in the initial monomer charge. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1275–1284, 2002     

Particle nucleation in emulsion polymerization. IV. Nucleation in monomer droplets

Nucleation in finely dispersed monomer emulsions in competition with homogeneous and micellar mechanism was studied. The emulsions were prepared with a high-pressure homogenizer under varying homogenizing conditions and made stable by the addition of hexadecane to the monomer. Sodium dodecyl sulfate was used as emulsifer. The number of particles in latexes polymerized with potassium persulfate and benzoyl peroxide initiators was measured and plotted as a function of the free emulsifier concentrations. With persulfate initiator the particle number achieved a minimum in the transition region between droplet and water phase–micellar nucleation mechanisms. With very fine emulsions Smith–Ewart case II kinetics with n = 0.5 applied. The reaction rate, which differed from conventional emulsion polymerizations, decreased with time up to the point at which n began to increase. In these runs the particle size distribution became nearly monodisperse.     

Preparation and Stabilization of Emulsifier‐free Macromolecule Nanoparticle Latex Particles

By using acetone‐water as the medium and potassium persulfate (KFS) as the initiator, emulsifier‐free emulsion co‐polymerization of styrene with co‐monomers: MMA, BMA, EA and BDA under microwave irradiation has been investigated. The influence of the each co‐monomer content and hydrophilicity on the hydrodynamic radius R_h of the synthesized copolymer nanoparticles is discussed in detail. The results show mat the increase in ratio of hydrophilic copolymer causes an increase in consumption of the initiator in the initiation reaction, so an increase in the concentration of the surface ? OSO₃ groups which cause the increase in the stability of the latex and gives rise to the formation of smaller micelles. The nano‐particle radius will increase again when the co‐monomer content increases to a certain degree. The curve of the particle hydrodynamic radius vs the co‐monomer content has a minimum point.     

Polystyrene microspheres with narrow particle size distribution

Crosslinked polystyrene microspheres of a diameter of the order of more than 2 μm and a narrow particle diameter distribution were synthesized by emulsifier-free emulsion polymerization. The dependence of various parameters such as an electrolyte (NaCl), an initiator (K₂S₂O₈), the phase volume ratio, the reaction temperature and time on the diameter and the particle size distribution has been discussed.     

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.