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1.
M. E. Treviño R. G. López R. D. Peralta F. Becerra E. Mendizábal J. E. Puig 《Polymer Bulletin》1999,42(4):411-417
Summary
Polymerization of vinyl acetate (VA) in three component oil/water (o/w) microemulsions stabilized with a mixture of two cationic
surfactants (DTAB/DDAB in a weight ratio of 3), was carried out at 40, 50 and 60°C using a water soluble initiator, V-50.
In all cases studied, stable latexes containing particles with diameters between 70 and 110 nm were obtained. Particle size
increased with conversion yielding uncommonly large particles for microemulsion polymerization, probably because particle
coagulation. Multimodal molar mass distributions with average molar masses between 1.2 to 2.0×106 g/mol were obtained. Chain transfer to polymer and bimolecular termination reactions play important roles in the microemulsion
polymerization of this monomer.
Received: 5 October 1998/Revised version: 12 February 1999/Accepted: 12 February 1999 相似文献
2.
R. G. López M. E. Treviño L. V. Salazar R. D. Peralta F. Becerra J. E. Puig E. Mendizábal 《Polymer Bulletin》1997,38(4):411-417
The polymerization of vinyl acetate (VA) in three component o/w microemulsions stabilized with the cationic surfactant, CTAB,
is presented. Initiation is achieved thermally with a water soluble initiator (V-50). Stable latex containing small particles
(ca. 35 nm) with molecular weights (Mw) of around 4 × 105 are obtained. Analysis of the molecular weight distribution suggests that chain transfer to monomer (and not to polymer, which is the typical termination mechanism in emulsion polymerization, specially at high conversions) is the
dominant mechanism of termination.
Received: 11. October 1996/Revised: 16 January 1997/Accepted: 21 January 1997 相似文献
3.
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. 相似文献
4.
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. 相似文献
5.
Vinyl pivalate (VPi) and vinyl acetate (VAc) were copolymerized at low temperature using 2,2′-azobis(2,4-dimethylvaleronitrile) as an initiator. Copoly(VPi/VAc) was prepared in a broad range of chemical composition, from 0/10 to 10/0 of VPi/VAc molar feed ratio. A statistical treatment of the 1H NMR peak intensities brought to the determination of the reactivity ratios of the comonomers. A thermodynamic study of the molecular dynamics simulation data led to the estimation of number-average sequence lengths of comonomers and Gibbs free energy change over VPi content. From this result, the retardation of copolymerization rate at about 5/5 composition was also explained. Enthalpies of -VAc-VPi∗, -VPi-VAc∗, and -VPi-VPi∗ formation were calculated as −12.07, −5.57, and −18.33 kcal/mol, respectively. 相似文献
6.
7.
The polymerization of vinyl acetate at 60 °C in microemulsions stabilized with the anionic surfactant, Aerosol OT, with or without cosurfactant (n-butanol) is examined. Partial phase diagrams at 60 °C show that the addition of n-butanol enhances the one-phase microemulsion region. Results indicate that the reaction rate is not affected by the presence of the alcohol. However, average molar masses are smaller although particles are bigger throughout the reaction compared to those values obtained in the absence of n-butanol. An explanation for these results is presented. 相似文献
8.
9.
Influence of nonionic emulsifiers on the properties of vinyl acetate/VeoVa10 and vinyl acetate/ethylene emulsions and paints 总被引:3,自引:0,他引:3
Carsten Heldmann R. Ivan Cabrera Bernhard Momper Rolf Kuropka Klaus Zimmerschied 《Progress in Organic Coatings》1999,35(1-4):69-77
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. 相似文献
10.
丙烯酸改性聚醋酸乙烯酯乳液聚合的研究 总被引:2,自引:0,他引:2
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. 相似文献
11.
The major difficulty in achieving good performance of industrial polymerization reactors lies in the lack of under-standing of their nonlinear dynamics and the lack of wel-developed techniques for the control of nonlinear pro-cesses, which are usually accompanied with bifurcation phenomenon. This work aims at investigating the nonlinear behavior of the parameterized nonlinear system of vinyl acetate polymerization and further modifying the bifurcation characteristics of this process via a washout filter-aid control er, with all the original steady state equilibria preserved. Advantages and possible extensions of the proposed methodology are discussed to provide scientific guide for further controller design and operation improvement. 相似文献
12.
13.
The ethyl eosin/ascorbic acid photosensitized polymerization of vinyl acetate in aqueous methanol using visible radiation has been shown to occur by a mechanism in which polymerization occurs after an induction period during which the dye colour fades completely. During this period the dye is excited by incident radiation and reacts with the reducing agent to form free radical species. These react with dissolved oxygen to produce hydrogen peroxide. It is shown that the polymerization of vinyl acetate is initiated by products of the reaction between ascorbic acid and hydrogen peroxide. 相似文献
14.
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 相似文献
15.
Previous attempts to synthesize vinyl acetate monomer (VAM) from synthesis gas involve routes that require a costly recycle of acetic acid through a carbonylation reactor. Two new routes to VAM from synthesis gas that avoid this acetic acid recycle have been investigated. One of these new routes synthesizes VAM from acetic acid via the intermediacy of ketene. Ketene is hydrogenated to acetaldehyde, and the acetaldehyde is reacted directly with ketene to produce VAM. The second route synthesizes VAM from the carbonylation of dimethyl ether to acetic anhydride followed by reaction of the acetic anhydride with acetaldehyde in a reactive distillation column to produce VAM and acetic acid. The co-produced acetic acid is hydrogenated to form the acetaldehyde required in the reactive distillation. 相似文献
16.
17.
Alexander Theis 《Polymer》2006,47(4):999-1010
Living free radical polymerization technology (macromolecular design via the interchange of xanthates (MADIX)) was applied to give accesses to chain length and conversion dependent termination rate coefficients of vinyl acetate (VAc) at 80 °C using the MADIX agent 2-ethoxythiocarbonylsulfanyl-propionic acid methyl ester (EPAME). The kinetic data were verified and probed by simulations using the PREDICI® modelling package. The reversible addition-fragmentation transfer (RAFT) chain length dependent termination (CLD-T) methodology can be applied using a monomer reaction order of unity, since VAc displays significantly lower monomer reaction orders than those observed in acrylate systems (ω(VAc, 80 °C)=1.17±0.05). The observed monomer reaction order for VAc is assigned to chain length dependent termination and a low presence of transfer reactions. The α value for the chain length regime of log(i)=1.25−3.25 (in the often employed expression ) reads 0.09±0.05 at low monomer to polymer conversion (10%) and increases significantly towards larger conversions (α=0.55±0.05 at 80%). Concomitantly with a lesser amount of midchain radicals, the chain length dependence of kt is significantly less pronounced in the VAc system than in the corresponding acrylate systems under identical reaction conditions. The RAFT(MADIX)-CLD-T technique also allows for mapping of kt as a function of conversion at constant chain lengths. Similar to observations made earlier with methyl acrylate, the decrease of kt with conversion is more pronounced at increased chain lengths, with a strong decrease in kt exceeding two logarithmic units from 10 to 80% conversion at chain lengths exceeding 1800. 相似文献
18.
Synthesis of vinyl acetate on Pd-based catalysts 总被引:1,自引:0,他引:1
Vinyl acetate (VA) synthesis over Pd–Au catalysts is an important industrial reaction that has been studied extensively; however, there is no consensus regarding the reaction mechanism, the active site, the key intermediates, and the role of Au. Recent results from our laboratories using a combination of surface science and kinetic methods on technical and model catalytic systems have established that the VA synthesis reaction is structure sensitive, including being dependent on the Pd–Au particle size. The role of Au is to isolate surface Pd atoms into Pd monomeric sites thereby enhancing the VA formation rate and selectivity. This paper reviews the current understanding of this reaction on Pd, Pd–Au, and Pd–Sn catalysts. 相似文献
19.
For application to Li-ion batteries, we studied the electrochemical behavior and thermal stability of the following two combinations of binary electrolyte additives in a triphenylphosphate (TPP)-containing ionic electrolyte: vinyl acetate (VA) plus vinylene carbonate (VC), and vinyl ethylene carbonate (VEC) plus biphenyl (BP). Mesocarbon microbeads (MCMB) and LiCoO2 were used as the anode and cathode materials, respectively. Cyclic voltammetry (CV), differential scanning calorimetry (DSC), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) were used for the analyses. These results confirmed the capability of the VEC + BP electrolyte additive to improve the cell performance and electrolyte thermal stability in TPP-containing solutions in Li-ion batteries. 相似文献
20.
Debashish Roy 《Polymer》2011,52(14):3038-3045
Well-defined homopolymers and block copolymers of vinyl esters were synthesized under microwave irradiation via reversible addition-fragmentation chain transfer (RAFT)/macromolecular design via interchange of xanthates (MADIX) polymerization without the significant inhibition or retardation often observed under conventional heating conditions. Poly(vinyl acetate) (PVAc) with molecular weights of 1000−10 000 g/mol was prepared in less than 15 min under microwave irradiation at an apparent temperature of 70 °C in the presence of the commercially available chain transfer agent ethylxanthogenacetic acid. The polymerizations were well-controlled, leading to polymers with narrow molecular weight distributions and excellent agreement between theoretical and experimental number average molecular weights. Despite the high rates of polymerization, the resulting PVAc homopolymers retained a high degree of thiocarbonylthio end group functionality that allowed the synthesis of block copolymers by chain extension with vinyl benzoate and vinyl pivalate. The rates of polymerization during the addition of the second blocks were also high, and the resulting block copolymers were obtained in good yield with excellent blocking efficiencies. 相似文献