PVAc Microspheres via Semicontinuous Emulsion Polymerization: Synthesis,Characterization, Kinetic,and Surface Morphology Studies

Poly (vinyl acetate) (PVAc) latexes are economically important products with many desirable features. They are used as adhesives for porous materials in various processing stages of industries. Synthesis parameters have an important role on the physico-chemical properties of PVAc latexes such as: viscosity, average molecular weight, degree of polymerization, and surface morphology. In this work, PVAc was prepared via semicontinous emulsion polymerization (delayed monomer and initiator addition process) in the presence of ammonium persulfate (APS) as conventional anionic initiator, poly (vinyl alcohol) (PVA) as stabilizer, and sodium lauryl sulfate (SLS) as anionic emulsifier. The surface morphology of PVAc microspheres was, examined using a scanning electron microscope (SEM) and atomic force microscope (AFM). It is evident from the SEM photographs that all the particles became microspheres and are uniform in shape. The use of AFM for imaging of polyvinyl acetate confirms a typical sphere polymer. The effect of changes in the different parameters such as concentration of emulsifier, initiator concentration, and presence or absence of buffer on the vinyl acetate (VAc) conversion, the steady state polymerization rate, the viscosity-average molecular weight, and the final latex viscosity of synthesized PVAc were investigated. The effects of anionic emulsifier on the synthesized PVAc are also compared with those obtained by the nonionic emulsifier. The comparison indicated that the VAc monomer conversion and the final latex viscosity of the anionic system were higher than for the nonionic system but the viscosity-average polymer molecular weight of the anionic system was lower than that of the nonionic system. The adhesive strength of the synthesized PVAc latex was examined and the load and deflection data were reported.     

Influence of nonionic emulsifiers on the properties of vinyl acetate/VeoVa10 and vinyl acetate/ethylene emulsions and paints

This paper presents results on the influence of the nonionic surfactant on the properties of vinyl acetate/VeoVa10^® and vinyl acetate/ethylene emulsions and paints made thereof. Emulsions were prepared in which the concentration of the nonionic surfactant and its degree of ethoxylation were varied. An increase of the nonionic emulsifier concentration and of the length of the ethylene oxide chain leads to dispersions with smaller particles and higher viscosities. Using these emulsions as binders in high pigmented paints, it was observed that the pigment binding capacity of the interior paints goes through a maximum which is located at a emulsifier concentration of about 2–3% and at a degree of ethoxylation of 17–28 mol ethylene oxide (EO). In (semi-) gloss paints, the gloss of the paint films improves with an increase of the emulsifier concentration and reaches a constant value at around 4% or a degree of ethoxylation of ca. 17 EO-moieties per molecule. The blocking of the films shows a drastic increase at a concentration above 4% and at a chain length of greater than 17 EO-moieties.     

Photo‐induced emulsion polymerization of vinyl acetate in the presence of poly(oxyethylene) nonyl phenyl ether,a nonionic emulsifier (II)

Synthesis of high molecular weight poly(vinyl acetate) having less branched structure via photo‐induced emulsion polymerization of vinyl acetate in the presence of poly(oxyethylene)₂₀ nonyl phenyl ether, a nonionic emulsifier, was attempted at 0°C or even below 0°C in the presence of methanol. It was found that 100% conversion is always achieved in all runs and poly(vinyl acetate) having the number‐average degree of polymerization of 9000 with less branched structure (degree of branch < 0.5) can be obtained from this photo‐induced emulsion polymerization system. Mechanisms of the polymerization were also discussed on the basis of the kinetic results. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2153–2158, 2002     

Effect of initiators and ethoxylation degree of non‐ionic emulsifiers on vinyl acetate and butyl acrylate emulsion copolymerization in the loop reactor

Vinyl acetate and butyl acrylate copolymers were synthesized in the presence of ammonium persulfate and potassium persulfate initiators, mixture of non‐ionic and anionic emulsifiers, and polyvinyl alcohol as protective colloid in a loop reactor. The monomer ratio was chosen 85:15. The series of non‐ionic emulsifiers, which have 10–40 moles ethoxylated nonyl phenol, were combined with Nansa 66 (sodium dodecyl benzene sulfonate). The effects of the initiators on the physicochemical properties of copolymers were investigated by measuring conversion, viscosity, molecular weight, molecular weight distribution, and surface tension, respectively by using gravimetric method, Brookfield viscometer, gel permeation chromatograpy (GPC), and ring method. The effects of ethoxylation degrees of the non‐ionic emulsifiers to the same properties of copolymers were also investigated. It was determined that the copolymer viscosities showed different tendency for two initiators. They were increased by the increasing ethoxylation degree of the non‐ionic emulsifier for ammonium persulfate. In contrast, latex viscosity was decreased by increasing the ethoxylation degree in presence of potassium persulfate. Similar changes were also found in number average molecular weights of copolymers. On the other hand, weight average molecular weights of copolymers increased by increasing the ethoxylation degree of the non‐ionic emulsifier for both initiators. In the case of potassium persulfate, the surface tension values of copolymers increased by increasing the ethoxylation degree, but generally increasing the ethoxylation degree did not affect the surface tension of copolymer very seriously for two initiators. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 537–543, 2003     

乳液聚合中单体醋酸乙烯酯与保护胶体聚乙烯醇的接枝反应研究

研究了以聚乙烯醇为保护胶体的醋酸乙烯乳液聚合中,聚乙烯醇与单体的接枝反应。探讨了引发剂用量、聚合反应温度、保护胶体聚合度等因素对接枝反应的影响。     

A kinetic study of the emulsion polymerization of vinyl acetate

The emulsion polymerization of vinyl acetate was studied at 50°C. It was found that the rate of polymerization was proportional to the 0.5 power of the initiator concentration and the 0.25 power of the number of particles. The number of particles was proportional to the power 0.5 ± 0.05 of the emulsifier concentration, but independent of the initiator concentration. The limiting viscosity number of the polymers produced was independent of the initiator concentration and number of polymer particles. It is suggested that the mechanism of vinyl acetate emulsion polymerization is similar to that of vinyl chloride. The linearity of the conversion-versus-time curve is explained as being due partly to a decrease in the desorption rate of radicals from the polymer particles and partly to a decrease in the termination rate constant.     

Comparative Study of Effect of Surfactant-Polymer Interactions on Properties of Alkyl Polyglucosides and Alpha Olefin Sulphonate

The properties of Alpha Olefin Sulphonate (AOS) and Alkyl polyglucosides (APG) were studied in the presence and absence of nonionic polymers such as polyethylene glycol, poly vinyl pyrrolidone and methyl cellulose and hydroxy propyl cellulose. Properties like surface tension, foaming, viscosity and emulsification were studied at a constant concentration of polymer (0.1%) and varying concentrations of surfactant. It was found that at low surfactant concentrations there is an association between surfactant and polymer at the liquid/air surface in the case of an anionic surfactant and a nonionic polymer, which is not seen in the case of nonionic surfactants and nonionic polymers. A nonionic polymer reduces the surface tension of AOS by forming a surfactant-polymer complex which in turn increases the foamability, emulsifying property and viscosity of solution. APG does not show any effect on its surface tension in the presence of nonionic polymers but its foamability and emulsifying properties are improved. Reduction in surface tension is not the only reason behind increased foamability in the presence of the polymer. Higher molecular weight polymers give a rich, creamy foam because of increased viscosity in the surfactant solution as compared to lower molecular weight polymers.     

Preparation of polystyrene/poly(vinyl acetate) nanocomposites with a core–shell structure via emulsifier‐free emulsion polymerization

Polystyrene/poly(vinyl acetate) latex nanoparticles with a core–shell morphology in an emulsifier‐free emulsion polymerization system were prepared with purified styrene and vinyl acetate (VAc) as monomers and 2,2′‐azo bis(2‐amino propane) dihydrochloride (ABA,2HCl) as the initiator and emulsifier. The optimized conditions of polymerization of VAc, on top of the already‐formed polystyrene as a core polymer, with a core–shell morphology were obtained using various parameters such as volume ratio of the first and second stages, type of process, and reaction time. The morphologic structure of the nanoparticles was studied by scanning electron microscopy and transmission electron microscopy. The latex nanoparticles and polymers were characterized by differential scanning calorimetry. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2409–2414, 2006     

Preparation of poly(vinyl acetate) latex with ultrasonic and redox initiation

The high water solubility of vinyl acetate (VAc) monomer increases the need for a good initiator system to speed up the polymerization and remove unreacted monomers. Ultrasonic energy can be used to initiate VAc redox emulsion polymerization in the absence of an inert gas and with sodium dodecyl sulfate as a surfactant. Combining ultrasonic energy and a redox initiator at the ambient temperature leads to a higher conversion and higher rate of polymer production in comparison with just using a redox initiator. Ultrasonic energy plays an important role in synthesizing and controlling the polymer structure. The particle size distribution is an important variable in the formulation of latex paint. Ultrasonic energy has an effect on the particle size distribution and average molecular weight of VAc polymer. The particle size increases with an increase in the monomer conversion for ultrasonic polymerization, whereas the particle size stays constant with the monomer conversion for redox polymerization. An ultrasonic polymer has a broader particle size distribution than a redox polymer. The average molecular weight of poly(vinyl acetate) falls with an increase in the sonication time, whereas it increases with time for a redox polymer. Ultrasonic energy also produces a stable, milky white, opaque latex. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 812–817, 2005     

高固含量改性聚醋酸乙烯酯乳液的制备

通过半种子连续乳液聚合工艺,以过硫酸铵为引发剂,以非离子和阴离子乳化剂为复合乳化剂,加入一定量的保护胶体,利用叔碳酸乙烯酯（Veova10）和丙烯酸异辛酯（2-EHA）为改性单体,合成了高固含量的改性聚醋酸乙烯酯乳液。研究了乳化剂用量,阴／非离子乳化剂质量比,叔碳酸乙烯酯、丙烯酸异辛酯和保护胶体用量对合成乳液的稳定性、黏度及吸水性的影响。研究结果表明,乳化剂质量分数为3．0％,阴／非离子乳化剂质量比为1：2,叔碳酸乙烯酯质量分数为20％,丙烯酸异辛酯质量分数为10％,保护胶体质量分数为0．25％时,乳液具有较好的稳定性、耐水性和成膜性。     

Synthesis of latices with hydrophobic cores and poly(vinyl acetate) shells. 2. Use of poly(vinyl acetate) seeds

A strategy is explored for synthesizing latex particles with polystyrene cores and poly(vinyl acetate) shells. The seed particles are poly(vinyl acetate), which theory indicates should be immune to secondary particle formation when a second-stage seeded emulsion polymerization with styrene is carried out. The objective is to form a single hydrophobic core by inversion of the second and first stages. While this morphology is favoured thermodynamically, conditions need to be optimized so that it is kinetically achievable: many attempts to implement this using straightforward synthetic procedures result in either no core (acorn morphology) or multiple polystyrene cores. A series of experiments enables this goal to be implemented by ensuring sufficiently fast diffusion of the first-stage hydrophilic polymer (using chain-transfer agent to reduce the molecular weight and, more importantly, the degree of branching of the parent poly(vinyl acetate) seed polymer), an initiator which minimized grafting between the first- and second-stage polymers, and modifying the seed poly(vinyl acetate) to increase its hydrophilicity.     

RADICAL DESORPTION IN EMULSION POLYMERIZATION OF VINYL ACETATE

In the present paper a model equation for calculating the radical desorption rate constant,k_0,in the emulsion polymerization of vinyl acetate was suggested and the various parameters forevaluating k_0 were determined.Effects of reaction temperature,emulsifier concentration,initiator con-centration,monomer conversion and phase ratio on k_0 were studied.It indicates that the desorptionof radicals from latex particles to aqueous phase must be taken into account in the modelling ofemulsion polymerization for the monomers with higher hydrophilicity such as vinyl acetate.     

Anionic ring-opening polymerization of octamethylcyclotetrasiloxane in emulsion above critical micelle concentration

Batch anionic ring-opening polymerization of octamethylcyclotetrasiloxane in emulsion using nonionic and cationic emulsifiers was studied. The concentration of emulsifiers was set above their critical micelle concentration. Effects of emulsifier concentration, nonionic/cationic emulsifier ratio and cationic emulsifier/initiator (KOH) ratio on the kinetics, average particle size and distribution and on the average molecular weight and distribution were investigated and discussed. At the beginning of the polymerization, empty micelles, active micelles (polymer particles) and monomer droplets co-exist in emulsion. The transport of monomer from monomer droplets toward empty micelles was confirmed by monomer droplets and empty micelles disappearance and by formation of smaller particles. The transport of monomer from monomer droplets toward polymer particles was not confirmed, since the average polymer particle size did not increase during polymerization. It was proposed, that at lower conversions, monomer diffuses from polymer particle interior to particle surface, while at higher conversions, the monomer diffuses from larger to smaller polymer particles. Emulsifier concentration, nonionic/cationic emulsifier ratio and cationic emulsifier/KOH ratio have an evident effect on the kinetics and on the average molecular weight, thus demonstrating that cationic emulsifier participates to the initiation reaction.     

Continuous emulsion polymerization of vinyl acetate. Part I: Experimental studies

An interesting feature of commercial continuous emulsion polymerization reactors is the important phenomenon of sustained oscillations. Laboratory investigations of emulsion polymerization in a continuous stirred tank reactor (CSTR) have shown that the conversion, number of polymer particles and other related properties often oscillate widely with time. These oscillations can lead to emulsifier levels too small to adequately cover polymer particles resulting in excessive agglomeration and reactor fouling. Herein is reported an extensive experimental study of vinyl acetate emulsion polymerization in a CSTR. The effects of initiator and emulsifier concentrations, mean residence time and rate of agitation on the production rate and size distribution of polyvinyl acetate latices were investigated. Domains of reactor operation which give rise to sustained oscillations and massive agglomeration of the latex are mapped which give rise to sustained oscillations and massive agglomeration of the latex are mapped out. The effect of different start-up policies on reactor transients were also investigated.     

丙烯酸甲酯与聚醋酸乙烯酯的核／壳乳液聚合反应

本文研究了丙烯酸甲酯在聚醋酸乙烯酯种子胶粒上的核/壳复合高分子乳液聚合反应。讨论了接枝聚合反应中引发剂的浓度、单体与聚合物的比例、乳化剂用量等工艺参数对该类接枝聚合反应的影响,提出了核/壳乳液聚合反应的一些反应规律。     

Die Emulgierung oxidierter Polyäthylen-Wachse mit ionisch-nichtionischen Emulgator-Systemen

Emulsification of Oxidized Polyethylene Waxes with Ionic-Nonionic Emulsifier Systems The author reports on the emulsification of oxidized polyethylene waxes with varying acid values and molecular weight distributions. The emulsifier system comprised of predominantly a nonionic ethoxylated surfactant based on alkyl phenol in combination with a small amount of alkali hydroxide to which the water for emulsification was added. Emulsion properties, such as viscosity, pH-value, particle size (light transmission), and glaze of the dry films on plane surface, were used to formulate the optimum emulsifier systems. Thus, the optimum ratio of the components and the degree of ethoxylation of the nonionic surfactant were determined. Similarly, the method of emulsifying was optimized and the differences among the various existing polyethylene waxes were determined.     

聚合工艺条件对含氟涂膜表面性能的影响

运用种子乳液聚合法制备了较高性价比的含氟乳液。FTIR光谱和DSC测试表明,含氟单体参与了聚合反应。运用KrussK12型动态表面能分析仪,测定聚合工艺中以不同用量的乳化剂、引发剂、含氟单体、N 羟甲基丙烯酰胺(N MA)在不同的单体滴加速度下合成的乳液涂膜对水和十六烷的接触角,结果表明,w(乳化剂)=3 5%、w(引发剂)=0 45%、w(N MA)=4%、聚合物中x(F)=14%时,乳液涂膜对水和十六烷的接触角较佳,对水的接触角达115°,涂膜表现出良好的表面性能。     

醋-丙共聚乳液胶粘剂的制备

采用预乳化半连续种子乳液聚合工艺对改性醋酸乙烯酯-丙烯酸丁酯共聚乳液胶粘剂的制备工艺进行了研究。实验中具体考察了聚合方式、单体配比、功能单体、乳化剂、引发剂、聚合温度、保护胶体等因素对乳液胶粘剂制备及性能的影响,确定了最佳工艺条件,并对所合成乳液胶粘剂的性能进行了测试与表征。当醋酸乙烯酯和丙烯酸丁酯的比例为1∶1时,共聚乳液具有最佳的粘接性能。功能性单体丙烯酸的加入可显著提高乳液的内聚力。聚合反应的最佳工艺条件是乳化剂的用量3%~5%,引发剂用量1%~3%,温度80℃。该工艺得到的改性醋-丙共聚乳液粒径分布均匀,机械稳定性好,并具有良好的纸塑粘接性能。     

Complexation of poly(dimethylsiloxane)/poly(methyl methacrylate‐co‐butyl acrylate‐co‐methacrylic acid) latex with poly(dimethylsiloxane)/poly(vinyl acetate‐co‐butyl acrylate) latex

Two latices—the poly(dimethylsiloxane) (PDMS)/poly(methyl methacrylate‐co‐butyl acrylate‐co‐methacrylic acid) system (PA latex) and the PDMS/poly(vinyl acetate‐co‐butyl acrylate) system (PB latex)—were prepared by seeded emulsion polymerization, and PA/PB complex latices were obtained through the interparticle complexation of the PA latex with the PB latex. In addition, for the further study of the interparticle complexation of the PA latex with the PB latex, copolymer latices [PDMS/methyl methacrylate‐co‐butyl acrylate‐co‐vinyl acetate‐co‐methacrylic acid) (PC)] were prepared according to the monomer recipe of the complex latices and the polymerization process of the component latices. The properties of the obtained polymer latices and complex latices were investigated with surface‐tension, contact‐angle, and viscosity measurements. The mechanical properties of the coatings obtained from the latices were investigated with tensile‐strength measurements. The results showed that, in comparison with the two component latices (PA latex and PB latex) and the corresponding copolymer latices (PC latices), the PA/PB complex latices had lower surface tension, lower viscosities, and better wettability to different substrates. The tensile strengths of the coatings obtained from the complex latices were higher than the tensile strengths of the coatings from the two component latices and copolymer latices. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2522–2527, 2004     

醋丙乳液型纸塑覆膜胶的研制

以醋酸乙烯(VAc)为硬单体,丙烯酸丁酯(BA)、丙烯酸异辛酯(EHA)为软单体,丙烯酸(AA)、叔碳酸乙烯酯(VV-10)、丙烯酸羟丙酯(HPA)为功能单体,采用乳液聚合方法制备醋丙共聚乳液覆膜胶。讨论了玻璃化温度、功能单体、乳化剂以及引发剂的用量等因素对乳液性能的影响。实验结果表明,当玻璃化温度为23.14℃、w(功能单体)=10%、w(乳化剂)=2%、w(引发剂)=0.4%时,乳液的各项性能良好。