Polymerization continued seed latex

Deionized water (720 g), sodium lauryl sulfate (4.3 g), dioctanoyl peroxide (40 g), and acetone (133 g) were emulsified using an ultrasonic probe for 10 minutes. The step 1 polystyrene seed (48.0 g seed, 578 g latex) was added to the emulsion together with lauryl sulfate (0.8 g) and acetone (29.6 g). The mixture was transferred to a flask and left to agitate at approximately 25°C for 48 hours. Acetone was then removed and the solution added to a 5-liter double-walled glass reactor. The temperature was increased to 40°C while styrene (336 g) and divinyl benzene (0.88 g) were added drop-wise over approximately 60 minutes. After 4 hours the mixture was treated with deionized water (1200 g), potassium iodide (1.28 g), and polyvinyl pyrrolidone (18.48 g) with the temperature increased to 70°C. The polymerization continued for 6 hours at 70°C and 1 hour at 90°C. Styrene-based oligomer particles with a diameter of 1.7 pm and with a narrow size distribution were obtained. 

Synthesis. A series of latexes was prepared by semicontinuous emulsion polymerization of methyl methacrylate. A dialkyl ester of sodium sulfosuccinic acid surfactant yielded the narrow particle size distribution required. An ammonium persulfate/sodium metabisulfate/ferrous sulfate initiator system was used. The initiator was fed over the polymerization time, allowing better control of the polymerization rate. For the smaller size latexes (200 to 450 nm), a seed latex was prepared in situ by polymerizing 10% of the monomer in the presence of the ammonium persulfate. Particle size was adjusted by varying the level of surfactant during the heel reaction. As the exotherm of this reaction subsided, the monomer and the sodium metabisulfate/ferrous sulfate feeds were started and continued over approximately one hour. The... 

Polystyrene can be easily prepared by emulsion or suspension techniques. Harkins (1 ), Smith and Ewart(2) and Garden ( ) have described the mechanisms of emulsTon polymerization in batch reactors, and the results have been extended to a series of continuous stirred tank reactors (CSTR)( o Much information on continuous emulsion reactors Ts documented in the patent literature, with such innovations as use of a seed latex (5), use of pulsatile flow to reduce plugging of the tube ( ), and turbulent flow to reduce plugging (7 ). Feldon (8) discusses the tubular polymerization of SBR rubber wTth laminar flow (at Reynolds numbers of 660). There have been recent studies on continuous stirred tank reactors utilizing Smith-Ewart kinetics in a single CSTR ( ) as well as predictions of particle size distribution (10). Continuous tubular reactors have been examined for non-polymeric reactions (1 1 ) and polymeric reactions (12.1 31 The objective of this study was to develop a model for the continuous emulsion polymerization of styrene in a tubular reactor, and to verify the model with experimental data. 

The reaction time is 16 hours for the batch procedure. In the semi-continuous procedure a seed latex is first prepared with 1/10 of the monomer amount during 30 minutes at 80 C. The remaining monomer is then added continuously during 2.5 hours.The polymerization is completed by heating the system for an additional 1 hour. 

Emulsion polymerization leads to a very narrow particle size distribution, which is suitable for use in plastisol applications. Resins having both a monodisperse and bimodal particle size distribution are produced. Blending of latexes is sometimes practiced with the extensive use of seed-latex techniques. A simplified schematic flow sheet for a continuous emulsion polymerization process is given in Figure 7. 

Composite latex particles of poly(n-butyl acrylate) ly(benzyl methacrylate) (PBA/PBM) [67] prepared by semi-continuous seeded onulsion polymerization in the presence of a chain transfer agent (isooctyl mercrptoproprionate) (lOMP) exhibited a hemispherical morphology or else laiger domains of PBM were... 

Other types of IPN s exist, of course. For example, Johnson and Labana (1972) recently synthesized a modified type of latex IPN as follows A crosslinked polymer network I prepared by emulsion polymerization served as a seed latex to linear polymer II. The resulting semi-IPN exhibited the usual core-shell morphology. After suitable coagulation and molding steps, polymer II was selectively crosslinked to form a macroscopic network, resulting in a thermoset material. The topology of this IPN therefore involves microscopic network islands of polymer I embedded in a continuous network of polymer II. 

ABS (acrylonitrile-butadiene-styrene) plastics are actually a type of partially grafted copolymer, similar to HIPS but more oil resistant because of the polar acrylonitrile, and with significantly higher impact resistance. It can be made by several methods, through emulsion polymerization, suspension polymerization, or bulk polymerization, but the most important method utilizes emulsion polymerization. In this case a seed latex of cross-linked polybutadiene is made, which constitutes up the core of the latex. This is followed by the addition of a mix of styrene and acrylonitrile monomers, usually 72/28 or similar in weight, respectively, followed by continued polymerization to form the shell of the latex particle. 

Table IX gives the recipe used for these pol3nnerizations. The polybutyl acrylate seed latex was prepared by heating the ingredients for 24 hours at 70° the styrene, water, and potassium persulfate were then added and polymerized for another 8 hours at 70°. Three methods of adding the styrene monomer were used in the second-stage polymerization (i) batch polymerization (ii) equilibrium swelling of the seed latex particles followed by batch pol3nneriza-tion (iii) starved semi-continuous pol3nnerization. The particle growth was essentially stoichiometric, i.e., no new particles were initiated. All three latexes formed transparent continuous films upon drying, whereas a 50 50 mixture of polybutyl acrylate and...

Rgure 7.3. A schematic representation for a continuous emulsion polymerization process, in which the relatively monodisperse particle size distribution of seed latex particles introduced into a continuous stirred tank reactor becomes broader at the exit of the reactor. 

To resolve this instability problem, adopting a feed stream of seed latex particles [62] or installing a continuous tubular reactor, which generates seed particles, upstream of the continuous stirred tank reactor [53] have been proved quite effective (Figure 7.4b). For the latter approach, small latex particles form as a seed latex before the reacting stream enters the continuous stirred tank reactor when the monomer conversion at the exit of the tubular reactor is maintained at an adequate level. As a result, the continuous emulsion polymerization system can be operated at a stable steady state. The work of Nomura and Harada [54] also suggests that a tube-stirred tank reactor series... 

Continuous reactors with seed latex particles in the feed stream could be an interesting polymerization system for morphological studies. The broad residence time distribution of the polymerizing latex particles associated with such a reactor configuration results in a broad particle size distribution of the effluent product. By changing the particle size distribution (monodisperse or polydisperse) of seed latex particles and operation conditions (mean residence time, monomer addition method, etc.) simultaneously, one can essentially obtain a variety of morphological structures of latex particles. 

Figure 16 Two-step SGI-mediated emulsion polymerization initiated with monofunctional (BlocBuilder salt, 72) or difunctional (DIAMA-Na, 73) water-soluble SGI -based alkoxyamines. Synthesis of the living seed latex (a) followed by its chain extension after one shof or continuous addition of...

Preparation of latex Samples. Two-stage latex samples were prepared by emulsion polymerization of the second-stage monomer mix in the presence of the first-stage polymer latex. The first-stage latexes were either in-situ or separately made using an externally prepared polystyrene latex seed. The mode of polymerization was a semi-continuous process for both stages. 

While vinyl acetate is normally polymerized in batch or continuous stirred tank reactors, continuous reactors offer the possibility of better heat transfer and more uniform quality. Tubular reactors have been used to produce polystyrene by a mass process (1, 2), and to produce emulsion polymers from styrene and styrene-butadiene (3 -6). The use of mixed emulsifiers to produce mono-disperse latexes has been applied to polyvinyl toluene (5). Dunn and Taylor have proposed that nucleation in seeded vinyl acetate emulsion is prevented by entrapment of oligomeric radicals by the seed particles (6j. Because of the solubility of vinyl acetate in water, Smith -Ewart kinetics (case 2) does not seem to apply, but the kinetic models developed by Ugelstad (7J and Friis (8 ) seem to be more appropriate. 

Latexes. Latexes were made in a monomer addition recipe described earlier (10). This is a seeded continuous monomer addition recipe using t-butylhydro-peroxide/hydroxylamine hydrochloride redox couple as initiator. Polymerizations were carried out in stirred glass reactors at 50°C. The only variation in the original recipe was in the surfactants. In the present procedvire, < 1/3 of the soap (- 1.5% based on total monomer) was used in the seed and the remainder fed to the reactor during polymerization. The monomer feed contained styrene and butylacrylate in a 40/60 ratio. This composition was selected because it is readily filmforming and is not affected chemically by the electrodeposition process. The polymer remains soluble and... 

The population balance equations are very general and may be applied to batch, semicontinuous, and continuous emulsion polymerizations. Furthermore, both seeded and ab initio polymerizations are comprehended by Eq. (5) in all (or part) of the three commonly considered polymerization intervals. The following sections show how the different possibilities are reflected in different functional forms of the elements of the matrices O and K and of the vector c. It should be remembered, however, that certain conceivable situations are not comprehended by Eq. (5) for example, if the monomer molecules are not freely exchanged between the latex particles so that the monomer concentration inside each latex particle is determined by its growth history. 

Wu and Zhao studied LIPN systems by a two stage emulsion polymerization technique [Wu and Zhao, 1995]. A latex seed (polymer 1) was synthesized first by a semi-continuous emulsion polymerization process, swollen by the second... 

Liu et al. also studied LIPN systems for damping control in coating applications [Liu et al, 1995]. A polystyrene (PS)/polyacrylate (PAcr) latex IPN was synthesized in a two-stage emulsion polymerization. Crosslinked PS was synthesized first as the seed polymer by a semi-continuous process,... 

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