Batch polymerization, latex

Band broadening HDC, 259-260 sedimentation FFF, 223 Batch polymerization, latex, 266-267 Bentonite suspensions dynamic light-scattering... 

Hou et al. [42] studied the effect of AA in pressure-sensitive adhesives composed of a terpolymer of 2-ethylhexyl acrylate, VAc and AA. Like Gajria et al. they noticed a dependence of latex swelling with polymerization procedure. Hou et al. noted that batch polymerized latexes produced greater viscosity responses with pH adjustments. They demonstrated that addition of sodium chloride effectively reduced the pH-thickening response curve. Hnally, Kries and Sheiman [43] studied the influence of polymerizing various fimctional monomers on the wet adhesion of VAc/B A latexes. A number of monomer types were studied, such as polymoizable monomers containing amines, amides and acetoacetates, alone and in combination with each other. The ureido functional monomras exhibited supoior wet adhesion. 

The results showed that all batch polymerizations gave a two-peaked copolymer compositional distribution, a butyl acrylate-rich fraction, which varied according to the monomer ratio, and polyvinyl acetate. All starved semi-continuous polymerizations gave a single-peaked copolymer compositional distribution which corresponded to the monomer ratio. The latex particle sizes and type and concentration of surface groups were correlated with the conditions of polymerization. The stability of the latex to added electrolyte showed that particles were stabilized by both electrostatic and steric stabilization with the steric stabilization groups provided by surface hydrolysis of vinyl acetate units in the polymer chain. The extent of this surface hydrolysis was greater for the starved semi-continuous sample than for the batch sample. 

Figure 5. Distribution of carboxyl groups in MMA-MAA copolymer latexes as weight percent based on the MAA content used in the polymerization (1) carboxyl groups in the serum (2) surface carboxyl groups (3) carboxyl groups next to the surface (4) carboxyl groups buried deeply (5) unneutralized carboxyl groups (A) batch-type latexes (B) semicontinuous-type latexes...

Quality Control of Latex Polymerization Using Hydrodynamic Chromatography. Latex polymers are most commonly manufactured in a large vessel with all the product being removed at the end of the polymerization reaction. This so-called batch polymerization process... 

In a more fundamental approach, i.e. by using systems of lower solid content, we examined the batch polymerization of styrene and BMA, to establish a correlation between the polyester content and the final latex particle size. 

Analytic solutions for Eq. (5) provide the most direct path of the prediction of PSD evolution. For batch polymerizations in Interval II, however, analytic solutions have only been achieved for the so-called zero-one system (Lichti et al., 1981). These are systems wherein negligibly few particles contain two or more free radicals because of the rapidity of the bimolecular termination reaction (e.g., in styrene emulsion polymerizations with small latex particles). In this case, Eq. (5) may be written as follows ... 

Semicontinuous emulsion polymerizations are characterized by the continued addition of monomer to the reaction vessel. This permits the production of latexes with high weight percentage solids while allowing the initial burst of nucleation to be achieved in substantially aqueous surroundings. The theory for semicontinuous systems is substantially that set forth for Interval III of batch polymerizations, except that the materials balance equations [Eq. (17)] must be modified to include the flow of new material into the reactor. The effect of the monomer input is twofold first, the mass of material present in the system is increased and seccmd, the concentration of other reagents may be reduced. 

In the semicontinuous process, the reactor is initially charged with a fraction of the formulation (monomers, emulsifiers, initiator and water). The initial charge is polymerized in batch for some time and then the rest of the formulation is added over a certain period of time (typically 3—4 h). The monomers can be fed either as an aqueous pre-emulsion sta-bihzed with some emulsifier or as neat monomers. Monomers contain inhibitors to allow safe storage and they are used without purification. The initiator is fed in a separate stream. The goal of the batch polymerization of the initial charge is to nucleate the desired number of polymer particles. Because particle nucleation is prone to suffer run-to-run irreprodu-cibility, seeded semicontinuous emulsion polymerization is often used to overcome this problem. In this process, the initial charge contains a previously synthesized latex (seed) and eventually a fraction of the formulation (monomers, emulsifiers, initiator and water). Therefore, nucleation of new particles is minimized leading to better reproducibility. 

In addition to the use of NIPAM as the main monomer, few works have been dedicated to the use of NIPMAM monomer. Poly(A-isopropylmethacrylamide) (PNIPMAM)-based microgel latexes have been prepared at 80 C using methylene-bisacrylamide (MBA) as the cross-linking agent and potassium persulfate (KPS) as the initiator [5]. The polymerization kinetic was found to be rapid and complete but with high water-soluble polymer formation compared to NIPAM batch polymerization [4]. 

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...

Most commercicil continuous systems for emulsion polymerization consist of a series of CSTR s in which all the recipe ingredients enter the first reactor and the product latex is removed from the last reactor. The individual reactors in the train are generally quite similar to the reactors employed for batch and semi-batch polymerizations. In fact some of the early continuous processes were constructed by installing piping between batch reactors. 

The acylation of alcohol-containing monomers, such as hydroxyethyl acrylates and methacrylates or vinylbenzyl alcohol, with maleic, or succinic, or sulfosuccinic anhydride, allows easy preparation of bifunctional polymerizable surfactants [64]. Some among these compounds, listed in Table 5, have been engaged in batch polymerization of styrene as well as in core-shell copolymerization of styrene and butyl acrylate. Stable latexes have been obtained in both cases, with only low floe production. A high conversion of the surfmers was most often reached, with little burying. However, these latexes do not show a noticeable resistance to the addition of electrolytes and cannot withstand freezing tests these features are not so surprising because their stabilization is only electrostatic and in no way steric. It can be noted, however, that their water rebound is somewhat limited, unless their water... 

Taking latex particle size distribution as an example, nucleation of latex particles in the early stage of an ideal batch emulsion polymerization is normally very fast. Therefore, the total particle surface area generated is large enough to capture the free surfactant molecules and particle nucleation ceases quite early in the polymerization ( 2-10% monomer conversion). Latex particles thus formed would have approximately identical ages at the end of an ideal batch polymerization (Figure 7.5a). The particle size distribution of these... 

After the mbber latex is produced, it is subjected to further polymerization in the presence of styrene (CgHg) and acrylonitrile (C H N) monomers to produce the ABS latex. This can be done in batch, semibatch, or continuous reactors. The other ingredients required for this polymerization are similar to those required for the mbber latex reaction. 

A typical recipe for batch emulsion polymerization is shown in Table 13. A reaction time of 7—8 h at 30°C is requited for 95—98% conversion. A latex is produced with an average particle diameter of 100—150 nm. Other modifying ingredients may be present, eg, other colloidal protective agents such as gelatin or carboxymethylcellulose, initiator activators such as redox types, chelates, plasticizers, stabilizers, and chain-transfer agents. 

The aqueous emulsion polymerization can be conducted by a batch, semibatch, or continuous process (Fig. 5). In a simple batch process, all the ingredients are charged to the reactor, the temperature is raised, and the polymerization is mn to completion. In a semibatch process, all ingredients are charged except the monomers. The monomers are then added continuously to maintain a constant pressure. Once the desired soflds level of the latex is reached (typically 20—40% soflds) the monomer stream is halted, excess monomer is recovered and the latex is isolated. In a continuous process (37), feeding of the ingredients and removal of the polymer latex is continuous through a pressure control or rehef valve. 

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