Emulsion polymerization of vinyl acetate

Many different combinations of surfactant and protective coUoid are used in emulsion polymerizations of vinyl acetate as stabilizers. The properties of the emulsion and the polymeric film depend to a large extent on the identity and quantity of the stabilizers. The choice of stabilizer affects the mean and distribution of particle size which affects the rheology and film formation. The stabilizer system also impacts the stabiUty of the emulsion to mechanical shear, temperature change, and compounding. Characteristics of the coalesced resin affected by the stabilizer include tack, smoothness, opacity, water resistance, and film strength (41,42). 

Mechanisms. Because of its considerable industrial importance as well as its intrinsic interest, emulsion polymerization of vinyl acetate in the presence of surfactants has been extensively studied (75—77). The Smith-Ewart theory, which describes emulsion polymerization of monomers such as styrene, does not apply to vinyl acetate. Reasons for this are the substantial water solubiUty of vinyl acetate monomer, and the different reactivities of the vinyl acetate and styrene radicals the chain transfer to monomer is much higher for vinyl acetate. The kinetics of the polymerization of vinyl acetate has been studied and mechanisms have been proposed (78—82). 

Emulsion polymerizations of vinyl acetate in the presence of ethylene oxide- or propylene oxide-based surfactants and protective coUoids also are characterized by the formation of graft copolymers of vinyl acetate on these materials. This was also observed in mixed systems of hydroxyethyl cellulose and nonylphenol ethoxylates. The oxyethylene chain groups supply the specific site of transfer (111). The concentration of insoluble (grafted) polymer decreases with increase in surfactant ratio, and (max) is observed at an ethoxylation degree of 8 (112). 

The kinetics of vinyl acetate emulsion polymeriza tion in the presence of alkyl phenyl ethoxylate surfactants of various chain lengths indicate that part of the emulsion polymerization occurs in the aqueous phase and part in the particles (115). A study of the emulsion polymerization of vinyl acetate in the presence of sodium lauryl sulfate reveals that a water-soluble poly(vinyl acetate)—sodium dodecyl sulfate polyelectrolyte complex forms, and that latex stabihty, polymer hydrolysis, and molecular weight are controlled by this phenomenon (116). 

MAIs may also be formed free radically when all azo sites are identical and have, therefore, the same reactivity. In this case the reaction with monomer A will be interrupted prior to the complete decomposition of all azo groups. So, Dicke and Heitz [49] partially decomposed poly(azoester)s in the presence of acrylamide. The reaction time was adjusted to a 37% decomposition of the azo groups. Surface active MAIs (M, > 10 ) consisting of hydrophobic poly(azoester) and hydrophilic poly(acrylamide) blocks were obtained (see Scheme 22) These were used for emulsion polymerization of vinyl acetate—in the polymerization they act simultaneously as emulsifiers (surface activity) and initiators (azo groups). Thus, a ternary block copolymer was synthesized fairly elegantly. 

Litt, M.H. Chang, K.H.S. Symp. on Emulsion Polymerization of Vinyl Acetate, Lehigh University, 1980. 

El-Aasser, M.S. Vanderhofif J.W., 9%, Emulsion Polymerization of Vinyl Acetate, Applied Science Publishers, London. 

Donescu, D., Ciupitoiu, A., Gosa, K. Languri, L, 1993, Water Polymer Interaction During Emulsion Polymerization of Vinyl Acetate, Revue Roumcane de Chimie, 38(12), 1441-1448. 

The final product of emulsion polymerization is an emulsion —a stable, heterogeneous mixture of fine polymer beads in an aqueous solution, sometime called a latex emulsion. Water-based paints, for example, can be formed from the emulsion polymerization of vinyl acetate. In this process, I m of water containing 3% poly(vinyl alcohol) and 1% surfactant are heated to 60°C in a reaction vessel (see Figure 3.27) The temperature rises to around 80°C over a 4 to 5 hour period as monomer and an aqueous persulfate solution are added. The rate at which heat can be removed limits the rate at which monomer can be added. 

Many different combinations of surfactant and protective colloid are used in emulsion polymerizations of vinyl acetate as stabilizers. 

An interesting variation on the use of azo groups-containing polymers is the use of polyacrylamide prepolymers as both initiator and emulsifying agent for the emulsion polymerization of vinyl acetate. The observed reaction kinetics were typical (see Fig. 4.7) for an emulsion polymerization and, in particular, the slope (a = 1) of the plot of lg Rp vs lg CPrep confirms the double function of these prepolymers very clearly. 

Thus these characterization results demonstrate that polymethacrylic acid does not function in the same manner as polyvinyl alcohol in the emulsion polymerization of vinyl acetate and that the adsorbed polymethacrylic acid can be separated from the bulk polymer, thus distinguishing it from grafted polymer. 

The objective of this study was to investigate the feasibility of using a tubular reactor for the seeded emulsion polymerization of vinyl acetate, and to study the effect of process variables on conversion rate and latex properties. 

This study of the continuous, tubular, seeded emulsion polymerization of vinyl acetate has led to the following conclusions ... 

El-Aasser, M. S. Vanderhoff, J. W. "Emulsion Polymerization of Vinyl Acetate", Appl. Sci. Publ., London, 1982. 

The obtained weight average diameters can reasonably well follow the progress of the reaction as can be seen from Figure 6, where experimentally estimated weight average diameters are plotted with those theoretically predicted by a mathematical model for the batch emulsion polymerization of vinyl acetate.(6)... 

Kinetics and Mechanism of the Emulsion Polymerization of Vinyl Acetate... 

The purpose of this paper is first to clarify the detailed characteristics of the emulsion polymerization of vinyl acetate using sodium laiiryl sulfate as emulsifier and potassium persulfate as initiator, and second to propose a new reaction model, based on our theory relating to the role of polymer particles, which enedsle vis to predict the number of polymer pcurticles produced and consequently, the progress of vinyl acetate emulsion polymerization. 

In conclusion, we may say that one of the most Inportant problems which still remain to be solved is to clarify the mechcinism by which polymer particles are formed and to establish a pcirticle nucleation model by which the number of polymer particles produced can be estimated, because the classical theory of Smith md wcu t does not serve for this purpose in the emulsion polymerization of vinyl acetate. In the succeeding section, a new reaction model is... 

In this reaction model e is the most inportant parameter and means the ratio of radical capture by the particle and the micelle. Therefore, the value of e affects directly the rate of particle nucleatlon process. As pointed out in the preceeding section, radicals are very easy to escape from the particles in the emulsion polymerization of vinyl acetate. So, it is quite reasonable to consider that radicals in the emulsifier micelles are also very easy to escape from them and that only part of radicals which entered the micelles are effective for particle nucleation,the others only passing through the micelles without converting them into particles. This phenomenon results in an apparent decrease in the value of k, that is, in an increase in the value of c. 

It is concluded that these equations represent well the characteristics of the emulsion polymerization of vinyl acetate with sodl mi lauryl sulfate as an emulsifier and potassiian persulfate as an initiator. 

The major purpose of this paper is to present experimental results for the emulsion polymerization of vinyl acetate (VA) and methyl methacrylate (MMA) in a single CSTR. Both steady state and transient results will be presented and discussed. Possible causes for prolonged unsteady behavior will be outlined and several techniques for achieving steady operation with a CSTR will be described. 

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