Semicontinuous emulsion polymerization of vinyl acetate: Effect of ethoxylation degree of nonionic emulsifiers

Poly(vinyl acetate) latices were prepared in the presence of an ammonium persulfate initiator, 10–50 mol of an ethoxylated nonylphenol nonionic emulsifier, and a poly(vinyl alcohol) colloid stabilizer by applying semicontinuous emulsion polymerization (delayed monomer and initiator addition process) in a laboratory scale similar to industrial practice. Two approaches were applied: the molar concentration of the nonionic emulsifier was kept constant and the weight ratios in the polymerization recipe varied or the weight ratios were kept constant. The effects of the change in the ethoxylation degree of the emulsifier to the final latex viscosity, average polymer molecular weight, polymer grafting degree, surface tension of the latex, and the surface free energy of the dried films were investigated. It was determined that the resultant latex viscosity decreases and the viscosity‐average polymer molecular weight increases with increase of the nonionic emulsifier ethoxylation degree. The increase of the ethoxylation degree does not seriously affect the surface tension of the resultant latex or the surface free energy of the dried poly(vinyl acetate) films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 844–851, 2002     

丙烯酸改性聚醋酸乙烯酯乳液聚合的研究

通过丙烯酸与聚乙二醇共聚合成了具有反应活性的丙烯酸聚氧乙烯酯（简称大单体）,将大单体作为表面活性剂对醋酸乙烯酯乳液聚合的动力学进行了研究;同时在性能上与普通的乳液聚合体系进行了比较。实验结果表明聚合速率随亲水链长度、乳化剂浓度、引发剂浓度、温度的增大而增大,pH值的减小而加快,乳液性能也有了很大的改善．     

Surfactant concentration effects on the microemulsion polymerization of vinyl acetate

The polymerization of vinyl acetate in oil-in-water microemulsions stabilized with cetyltrimethylammonium bromide (CTAB) is reported here as a function of surfactant concentration. Reaction rate decreases as the CTAB/water ratio is increased in the parent microemulsions. Polymer particles in the latexes grow with conversion; they also become bigger as the initial surfactant content is increased. Number-average molar masses are smaller than those expected by termination by chain transfer to monomer, but weight-average molar masses increased as the surfactant concentration in the parent microemulsion is raised. However, the latter are much smaller than those obtained by polymerization in an emulsion stabilized with the same surfactant. Possible explanations to this unusual behavior are provided here.     

Emulsion copolymerization of vinyl acetate and 2‐ethyl hexyl acrylate using nonionic emulsifiers in loop reactor

Batch emulsion copolymerization of vinyl acetate and 2‐ethyl hexyl acrylate (VAc/2EHA = 90 : 10) was initiated by the thermal initiators ammonium persulfate and potassium persulfate at 70°C in the presence of nonylphenol ethoxylates with varying chain lengths and poly(vinyl alcohol). VAc–2EHA copolymer latexes were synthesized as two different series in a loop reactor. The first series was initiated by ammonium persulfate, and the second series was initiated by potassium persulfate. The influence of the counterions or initiators and chain lengths of a nonionic emulsifier on the properties of VAc–2EHA copolymer latexes were determined by measuring the viscosities, weight‐average molecular weights, number‐average molecular weights, molecular weight distribution, and surface tension of latexes to air. The results for the copolymer latexes indicated that some of their physicochemical properties increased with increasing chain length of the nonionic emulsifier, but some of them followed a different trend for the two initiators. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1380–1384, 2005     

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     

Miniemulsion and macroemulsion copolymerization of vinyl acetate with vinyl versatate

The miniemulsion and macroemulsion polymerization of vinyl acetate with vinyl versatate in batch and semibatch systems was investigated. Vinyl versatate was added either as an emulsion with the vinyl acetate, or as a neat liquid stream. In the batch runs, there is a poor dispersion of vinyl versatate during the nucleation period for the runs in which the vinyl versatate was added neat at the beginning of the polymerization. This led to smaller particles, lower polymerization rate, and different polymer composition evolution when compared with runs in which the vinyl versatate was emulsified with the vinyl acetate. In seeded semibatch runs, residual surfactant in the seed latex, along with the propensity for homogeneous nucleation in vinyl acetate emulsions, resulted in continuing nucleation during the entire semibatch interval. The polymerization rate was primarily affected by monomer feed rate rather than the feeding mode. The effect of monomer feeding mode on copolymer composition was weak when the semibatch feed rate was low, indicating some level of vinyl versatate mass transfer resistance. In all runs, only one glass transition temperature was observed, indicating effective copolymerization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2219–2229, 2002     

Polymerization of vinyl acetate in microemulsions stabilized with dodecyltrimethylammonium bromide and cetyltrimethylammonium bromide

The polymerization of vinyl acetate in microemulsions stabilized with dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB) or mixture of these surfactants is examined. The polymerization rate diminishes as the surfactant mixture becomes richer in DTAB. Also, particles grow with conversion and become increasingly larger as the DTAB content in the mixture increases. Our results indicate that chain transfer reactions to monomer are more important than chain transfer reactions to polymer even at high conversions with CTAB. However, as the content of DTAB increases, bimolecular termination induced by coagulation, terminal double bond polymerization and chain transfer reactions to polymer become increasingly more important.     

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.     

On‐line acoustic attenuation spectroscopy of emulsions stabilized by vinyl alcohol–vinyl acetate copolymers: a model system for the suspension polymerization of vinyl chloride

BACKGROUND: Poly[(vinyl alcohol)‐co‐(vinyl acetate)] (PVA) copolymers obtained by partial hydrolysis of poly(vinyl acetate) are currently used as industrial stabilizers in the suspension polymerization of vinyl chloride monomer (VCM). Their molecular characteristics, mainly the average degree of hydrolysis (DH ) and average degree of polymerization (DPw ), have a major influence on the monomer droplet size and the properties of the final poly(vinyl chloride) resin. RESULTS: The average droplet size and size distribution of chlorobutane/water emulsions, as a model system for VCM/water emulsions, were studied using acoustic attenuation spectroscopy on‐line with an agitated laboratory reactor. The emulsions were stabilized by PVA with DH values between 73 and 88 mol% and DPw values between 450 and 2500. The effects of agitation speed, stirring time and concentration of the PVA copolymers were investigated. An attempt was made to correlate the interfacial tension and the droplet size. CONCLUSION: On‐line acoustic spectroscopy appears to be a suitable technique for the real‐time control of the droplet size of monomer suspensions. The advantages and limitations of the technique are outlined. The validity and the application limits of the commonly cited correlation between the droplet size and the Weber number are established for polymeric surfactant‐stabilized emulsions. Copyright © 2009 Society of Chemical Industry     

Radiation-induced Grafting of Acrylic Acid and Vinyl Acetate Monomers onto Heavy-duty Poly(ethylene–vinyl acetate) Films

The preparation of graft films was carried out by direct radiation-induced graft polymerization of acrylic acid and vinyl acetate comonomer onto heavy-duty poly(ethylene–vinyl acetate) films. The effect of various comonomer compositions on the degree of grafting was investigated. The characterization and some selected properties of the graft copolymers prepared were studied. Thermal stability, mechanical and electrical properties of the films showed great promise for some practical applications. © of SCI.     

有机硅氧烷改性醋酸乙烯酯-丙烯酸酯乳液的合成与性能

采用种子乳液聚合,引入乙烯基三甲氧基硅烷(A-171),以十二烷基苯磺酸钠(DSB)和壬基酚聚氧乙烯(20)醚(OP-10)作复合乳化剂,以过硫酸钾(KPS)为引发剂,在反应温度为78±2℃条件下,合成了A-171改性醋酸乙烯酯(VAc)-丙烯酸酯共聚乳液。实验采用单体滴加工艺,考察了配方中丙烯酸丁酯(BA)、甲基丙烯酸(MAA)和A-171用量对共聚物性能和乳液聚合过程的影响,并用红外光谱仪(FTIR)、粒度仪和差示量热扫描仪(DSC)对共聚物的结构及性能进行了表征。结果表明,引入w(BA)=10%~15%(相对于配方中单体总质量,下同)、w(MAA)=4%、w(A-171)=1%到VAc-丙烯酸酯共聚物乳液中,共聚物乳液涂膜的吸水率<5.0%,耐寒性通过10个循环,60℃加速贮存稳定性>100 d。     

Synthesis and characterization of silicone-modified vinyl acetate–acrylic emulsion copolymers

The triethoxyvinylsilane (TEVS) containing vinyl acetate (VAc)/2-ethylhexylacrylate (2-EHA) copolymers were prepared by emulsion copolymerization. The polymerization was performed with methacrylic acid (MAA) and auxiliary agents at 80 °C in the presence of ammonium peroxodisulfate (APS) as the initiator. Alkyl phenol ether sulfate and Arkupal N-300 were used as anionic and nonionic emulsifiers, respectively. The resulting copolymers were characterized by using Fourier transform infrared spectroscopy (FTIR). Thermal properties of the copolymers were studied by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The morphology of copolymers was also investigated by scanning electron microscopy (SEM) and then the effects of temperature, agitation speed, initiator and silicone concentrations on the properties of the silicone-modified VAc–acrylic emulsion copolymers were discussed. The obtained copolymers have high solid content (53%) and can be used in emulsion paints as a binder. The calculations of monomer conversion versus time histories and monomer conversion indicate that by increasing the TEVS concentration, the polymerization rate and the number of polymer particles decrease, respectively.     

醋酸乙烯酯与叔碳酸乙烯酯共聚乳液(W乳液)的研制

摘要用叔碳酸乙烯酯(Veova10)单体对醋酸乙烯酯乳液进行改性,采用种子聚合的方法,以过硫酸钾为引发剂,使用阴离子和非离子复配的乳化剂,加入一定量的丙烯酸酯类单体,可制得耐碱性、耐水性、耐候性都非常好的乳液。此共聚乳液特别适合用作内墙和外墙乳胶漆的基料。     

提高聚醋酸乙烯酯乳液性能的实验研究

目的:提高聚醋酸乙烯酯乳液的稳定性和耐水性.方法:采用醋酸乙烯酯为聚合单体、聚乙烯醇为胶体保护剂及乳化剂壬基酚聚氧乙烯醚的聚合反应,制备聚醋酸乙烯酯乳液.再利用单组实验法研究聚乙烯醇、乳化剂、引发剂、加料方式及反应温度等对制备稳定性和耐水性好的聚醋酸乙烯酯乳液的影响规律.结果:制备粘接强度、稳定性和耐水性良好的聚醋酸乙...     

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 polyoxyethylene emulsifier composition on the course of emulsion polymerization of vinyl acetate

Three different emulsifier types from vinyl acetate monomer and methoxypolyoxyethylene (35: 65, 27: 73 and 19: 81wt: wt%) were prepared in the presence of benzoyl peroxide using a macroradical initiator technique. Fourier transform infrared spectroscopy and ¹H nuclear magnetic resonance were carried out to confirm the structure of the copolymers obtained (emulsifiers). The emulsion polymerization of vinyl acetate initiated by sodium persulphate as an initiator in the presence of non-ionic (polyoxyethylene (POE) type) emulsifier has been kinetically investigated. The rate of polymerization was found to be proportional to the 0·33, 0·40 and 0·44 power of the emulsifier concentration and to the 0·71, 0·79 and 0·87 power of the initiator concentration. The apparent activation energy was found to be 135, 56·5 and 38kJmol^-1 for 65wt%, 73wt% and 81wt% POE, respectively. The particle size was observed to increase with increasing initiator concentration and to decrease with increasing emulsifier concentration. The reaction order with respect to the emulsifier concentration (number of particles versus emulsifier concentration) was found to be 0·10, 2·05 and 0·89 for 65wt%, 73wt% and 81wt% POE, respectively. ©1997 SCI     

醋酸乙烯酯乳液与聚乙烯醇接枝反应的研究

研究了以聚乙烯醇为保护胶体的醋酸乙烯乳液聚合中,作为保护胶体的聚乙烯醇与醋酸乙烯的接枝反应。发现聚乙烯醇的接枝主要发生在初期,而醋酸乙烯的接枝链一直增长到胶粒沉析;另外,保护胶体黏度对接枝率也有影响,黏度越大醋酸乙烯的接枝率越低。     

Effects of compatibilizer on the layered silicate/ethylene vinyl acetate nanocomposite

Dispersion behavior of monmorillonite (MMT) is investigated in ethylene vinyl acetate (EVA)/MMT nanocomposite with various vinyl acetate content. Maleic anhydride (MAH) grafted polyethylenes with various MAH contents are used as a compatibilizer to enhance the dispersion of MMT. DMA and XRD studies indicate that an intercalated/exfoliated structure is obtained and vinyl acetate content and the concentration of PEMA play a critical role in EVA/MMT nanocomposite. Higher vinyl acetate content and concentration of grafted maleic anhydride result in better dispersion of MMT. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1057–1061, 2004     

微悬浮聚合法合成聚醋酸乙烯酯的动力学研究

采用微悬浮法合成聚醋酸乙烯酯,对其聚合反应的动力学进行了研究。考察了引发剂浓度、乳化剂浓度、单体浓度以及温度对聚合反应速率的影响。结果表明,聚合反应速率对引发剂浓度、乳化剂浓度和单体浓度的反应级数分别为0．45,0．28,1．90,单体浓度对聚合反应速率的影响最大,反应体系的表观活化能为105．96 kJ/mol。     

Emulsification in batch‐emulsion polymerization of styrene and vinyl acetate: A reaction calorimetric study

Dispersion of liquid–liquid systems is commonly applied in industrial processes such as extraction, suspension, and emulsion polymerization. This article describes the influence of the quality of emulsification on the course and outcome of a batch‐emulsion polymerization of styrene and vinyl acetate. From visualization experiments and polymerizations in combination with reaction calorimetric studies, a critical impeller speed, N*, can accurately be determined for a particular reactor setup and a given recipe. The results show that styrene–water emulsions are more difficult to emulsify than vinyl acetate–water emulsions. In general, a large turbine impeller appears to be more effective in emulsifying monomer–water dispersions than a pitched‐blade impeller. In addition, for vinyl acetate emulsion polymerization, the possibility of premixing the reaction mixture has been investigated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 944–957, 2001