Aspects of coagulation during emulsion polymerization of styrene and vinyl acetate

The influence of recipe and process conditions on the coagulation behavior of polystyrene (PS) and polyvinyl acetate (PVAc) latices has been studied. Seeded batch experiments reveal a significant influence of electrolyte concentration on the coagulation behavior of both PS and PVAc latices. Within the experimental error, no dependency of the coagulation behavior on process conditions, in terms of energy dissipation, reactor scale, impeller type, and impeller diameter, has been observed for the reactor scales investigated. These results indicate that intrinsic chemical influences such as electrolyte concentration dominate the coagulation behavior during emulsion polymerization and also in the absence of polymerization over the process conditions. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2409–2421, 1998     

Kinetics of vinyl chloride and vinyl acetate emulsion polymerization

The kinetics of vinyl chloride and vinyl acetate emulsion polymerization are reexamined. The validity of Ugelstad's model for systems with high desorption rate is confirmed by simulating conversion histories for both systems at different initiator concentrations and particle numbers. On the basis of the model, it is shown that at ordinary initiation rates, termination reactions are unimportant with respect to molecular weight development in both systems, and as a consequence, molecular weight development is independent of number and size distribution of polymer particles and of initiator and emulsifier level. Based on this conclusion, it is shown that in accordance with experimental facts, the molecular weight distribution obtained in vinyl chloride emulsion polymerization is the most probable distribution, and it is concluded that the number of long-chain branch points per repetition unit is less than 2 × 10^?4 at high conversions. In vinyl acetate emulsion polymerization, an almost logarithmic normal distribution is obtained. The distribution is strongly broadened by branching reactions with the number of long-chain branch points increasing rapidly with monomer conversion. The increase of M_n with increasing conversion is due to terminal double-bond polymerization, while the increase in M_w is due mainly to transfer to polymer.     

Reaction kinetics of vinyl acetate emulsion polymerization

Transport of free radicals out of latex particles into the aqueous phase plays an important role in the emulsion polymerization of vinyl acetate. This so-called “desorption” process involves chain transfer to monomer which generates a mobile and rather stable monomer-unit free radical followed by the diffusion of this free radical out of the latex particle. A kinetic model is developed based on the reaction mechanisms of such an emulsion system. The experimental data available in the literature are used to test the model under various polymerization conditions. Reasonable agreement between the model predictions and experimental data is observed.     

Kinetics of the emulsion polymerization of vinyl acetate

Recent investigations of the emulsion polymerization of vinyl acetate report a variable behavior. The reaction has been reported to exhibit a half-order rate dependence and no particle number dependence on the initiator level, or a first-order dependence for both the reaction rate and particle number on the initiator concentration, or some behavior between these two extremes. While two recent models have attempted to account for the changes in the reaction rate dependence by postulating either an aqueous phase or a polymer phase termination, no adequate explanation of the particle number behavior has been given, nor has a single model been suggested that agrees with all of the experimental data. This investigation confirms the results of previous investigators and develops an empirical model for the particle number, taking into account the effects of the initiator level, emulsifier level and alkyl chain length, temperature, and ionic strength on the particle number. This particle number model, used with a polymer phase termination reaction model, yields a polymerization rate expression which agrees with all previous data.     

Radiation-induced emulsion polymerization of vinyl acetate in a pilot plant reactor I. Recycle flow reactor

A number of successful radiation polymerization of vinyl acetate in emulsion have been carried out in a modular stainless steel flow pilot plant. In a recycle mode, the system was utilized for extremely accurate kinetic measurements and experimental verification of model restrictions such as plug flow, lack of post irradiation effects and differential reactor behavior. Experimental conditions were explored to minimize contaminant, primarily oxygen, inhibition, and the tendency for this formulation, essentially an adhesive, to build up on the reactor walls. Industrial scaleup of such a prototype system appears attractive.     

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     

Inverse modeling applications in emulsion polymerization of vinyl acetate

The optimization of emulsion polymerization processes can benefit from the application of neural networks (NNs). The aim of this paper is to present yet another important example of how NNs can help with the optimization of emulsion polymerization reactors, and more specifically, with the “inverse” problem, i.e., starting from the polymer's properties and productivity to determine the reactor's operating conditions. The procedure presented in this paper combines a mathematical model with a NN that predicts appropriate operating conditions for the reactor with a maximum error of 5%. The specific example is with the emulsion polymerization of vinyl acetate.     

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.     

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．     

Radical entry into particles during emulsion polymerization of vinyl acetate

The entry of free radicals (formed in the aqueous phase) into polymer particles is the subject of the present work. A model has recently been developed based on the postulate that the aqueous-phase growth of the free radicals to a critical size is the rate-determining step for entry. An experimental strategy was devised to study this phenomena. Polystyrene latex with a water-insoluble inhibitor partitioned into the polymer particles was used as seed for secondary polymerization of vinyl acetate. This was done to form and isolate stable oligomers of the critical size. The presence of vinyl acetate oligomers was detected with Fourier transform infrared spectroscopy and thin-layer chromatography. Fast atom bombardment–mass spectroscopy (MS) was used to determine the molecular weights of the oligomers. Though it was not possible to determine the precise size of the vinyl acetate oligomers formed, the MS results show that the number of monomer units in the oligomers has an upper bound of 12–14. The number of units in the oligomer of critical size was estimated to be about 5–6. These experimental results are quite close to model predictions; thus this work helps in corroborating the model. Additional work is necessary to conclusively validate this model. The experimental strategy used in this work has made it possible to determine the approximate size of oligomers formed in the aqueous phase during emulsion polymerization. © 1994 John Wiley & Sons, Inc.     

Some parameters affecting the emulsifier-free emulsion polymerization of vinyl acetate

The kinetics of emulsifier-free emulsion polymerization of vinyl acetate using the redox initiation system of potassium persulfate-potassium metabisulfite was studied. The effect of the reaction conditions on the rate of polymerization was also investigated. The polymerization proceeded smoothly until high conversion and yielded stable emulsions. The apparent activation energy for the polymerization system was calculated and the effect of some inorganic substances on the rate of polymerization was also revealed. © 1997 John Wiley & Sons, Inc.     

Radiation-induced emulsion polymerization of tetrafluoroethylene

The radiation-induced emulsion polymerization of tetrafluoroethylene was carried out with the use of ammonium perfluorooctanoate as an emulsifier at an initial pressure of ca. 30–35 Kg/cm². The polymerization rate was shown to be proportinal to about the 0.8 power of the dose rate in the range of 2 × 10⁴ to 10⁵ R/hr and to be almost independent of emulsifier concentration. The molecular weight of the polymer lies in the range of 10⁴ to 10⁵, increases with reaction time at the initial stage, and decreases with emulsifier concentration, but is independent of the dose rate from 2 × 10⁴ to 6 × 10⁴ R/hr. If the emulsifier is not used, a polymer with a molecular weight as high as 1.8 × 10⁶ to 2 × 10⁷ is obtained. Apparently, the emulsifier and its radiolysis products act as chain transfer agents. Postirradiation polymerization was found to take place with the formation of products with increased molecular weight.     

Grafting and adsorption of poly(vinyl) alcohol in vinyl acetate emulsion polymerization

Poly(vinyl alcohol) is often used in vinyl acetate emulsion polymerization as a protective colloid, but its role is complex and controversial since it partakes in grafting reactions with the monomer, influencing process mechanisms, and affecting the colloidal properties of the latex. Furthermore, in industrial operations, the wide scatter of macromolecular properties of the commercial types of poly(vinyl alcohol) causes process irreproducibilities. In this work different types of polyvinyl alcohol were used to perform a series of polymerizations, and their kinetics were compared. A selective solubilization procedure was applied to separate the three fractions of poly(vinyl alcohol) in the final latex: free in the water phase, physically adsorbed onto the polymer particles and chemically grafted. These results were compared with those obtained from pure adsorption measurements of polyvinyl alcohol onto ‘emulsifier-free’ polyvinyl acetate dispersions. The rheological behavior of the different latexes was also compared, and the results were used to formulate an hypothesis on the interaction mechanisms acting in these systems.     

Effect of electrolyte on the emulsifier-free emulsion polymerization of vinyl acetate

The emulsifier-free emulsion polymerization of vinyl acetate was carried out in the absence or in the presence of some electrolytes such as sodium chloride, calcium chloride, aluminum chloride, sodium sulphate, and ammonium phosphate at 50°C using potassium persulphate—sodium bisulphite as a redox initiation system. The viscosity average molecular weights of the polymers obtained were also determined. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 711–715, 1997     

高固含量聚醋酸乙烯乳液的研究及进展

介绍了有关高固含量醋酸乙烯乳液聚合的制备方法,并阐述制备高固含量PVAc乳液的影响因素。     

Molecular weight distribution in continuous stirred tank vinyl acetate emulsion polymerization

Emulsion polymerization typically produces polymers of high molecular weight with broad distributions of molecular size. Many models have been proposed that use either a Flory type distribution, resulting in a polydispersity of two, or a distribution function to represent the breadth of the distribution. In this work, a model for the distribution of molecular weights is derived as a approximation from a detailed molecular weight model that was previously developed. The model is found to approximate the distribution of molecular weights well for several emulsifier concentrations is continuous stirred tank emulsion polymerization of vinyl acetate. An analysis is also conducted of the transformation of gel permeation chromatography data to weight and number fractional distributions of the molecular sizes.     

Radiation-induced emulsion ploymerization of vinyl acetate in a pilot plant reactor II. Kinetics

The recycle flow reactor pilot plant, described in Part I of this series, has been used to study some kinetic and other features of the emulsion polymerization of vinyl acetate. In particular, the dependence of the rate on the emulsifier concentration was determined and found to be 0.38 ± 0.09. Separate batch experiments were in reasonable agreement as 0.29 ± 0.10. The effects of temperature, dose rate, and agitation rate were also determined and were in agreement with most of the literature values.