Semicontinuous copolymerization

Maleate Surfmers were found to outperform methacrylic and crotonic compounds in the copolymerization of styrene, butyl acrylate and acrylic acid in seeded and nonseeded semicontinuous processes [17]. The maleate Surfmer achieved high conversion without homopolymerization in the aqueous phase which can result in emulsion instability. The methacrylate Surfmer was too reactive as opposed to the crotonate which was not sufficiently reactive. The reported dependence of the maleate Surfmer conversion on the particle diameter is consistent with a reaction at the particle surface. 

Emulsion polymerization reactors are made of stainless steel and are normally equipped with top-entry stirrers and ports for addition of reactants. Control of the reaction exotherm and particle size distribution of the polymer latex is achieved most readily by semibatch (also called semicontinuous) processes, in which some or all of the reactants are fed into the reactor during the course of the polymerization. Examples are given in Chapter 8. In vinyl acetate copolymerizations, a convenient monomer addition rate is such that keeps the vinyl acetate/water azeotrope retluxing. at about 70°C. 

Pinto, J.C. Dynamic optimization of semicontinu-ous emulsion copolymerization reactions composition and molecular weight distribution. Compos. Chem. Eng. 2001, 25 (4-6), 839-849. 

Semicontinuous addition methods These are very useful for copolymerizations requiring control of homogeneous compositions at the level of the chain and the particle. Variable composition gradient processes permit the introduction of the functional monomer to a suitable conversion, favoring incorporation on the surface or inside the particles. 

Elsynski HA (1987) Batch and Semicontinuous Copolymerization of Vinyl Acetate and Methyl Aery] ate, M.S. Research Report, Lehigh University, Bethlehem... 

The emulsion copolymerization of vinyl acetate and butyl acrylate has received considerable attention. The butyl acrylate confers improved film forming characteristics to the polymer. The disparities in their water solubilities and of their individual polymerization rates may help to explain the variations in reactivity ratios that have been reported [170,171]. The variation in reactivity ratios may also by related to the following observations The reaction method has an effect on the morphology of the polymer particles. In a batch emulsion process, a butyl acrylate—rich core is formed which is surrounded by a vinyl acetate-rich shell, in a process in which the monomers are fed into the reactor in a semicontinuous manner, particles form with a more uniform distribution of the monomers [172]. The kinetics for a batch process indicates that the initially formed polymer is indeed high in butyl acrylate. As this monomer is used up, eventually a copolymer high in vinyl acetate develops. It is this latter polymer which forms the final shell around the particles. 

Al-Bagoury M, Yaacoub E.J (2004) Semicontinuous Emulsion Copolymerization of 3-0-methacryloyl-l,2 5,6-di-0-isopropylidene-a-D-glucofuranose (3-MDG) and Butyl Acrylate (BA) by Pre-emulsion Addition Technique. Europ. Polym. J. 40 2617-2627. 

El-Aasser M.S, Makgawmata T, VanderHoff J.W (1983) Batch and Semicontinuous Emulsion Copolymerization of Vinyl Acetate-Butyl Acrylate, n. Morphological and Mechanical Properties of Copolymer Latex Films. J. Pol)nn. Sci. 21 2383-2395. 

Donescu D, Fusulan L (1994) Semicontinuous Emulsion Polymerization of Vinyl Acetate X. Kinetics of Homopol5rmerizations, Copolymerizations, and Initiator Decomposition in the Presence of Sulfosucdnate-type Surfactants. 15 543-560. 

Roy et fl/.[62] carried out a copolymerization of MMA and nBA in microemulsion through semicontinuous addition of a monomer to the emulsion to obtain a 40 wt% solid content of latex of about 30 nm particle size using 4 wt% Dowfax 2A-1 as surfactant and 0.4 wt% acrylamide as cosurfactant. Xu et hollow-fiber device to feed the monomer continuously into... 

El-Aasser, M.S., Makgawinata, T., Vanderhoff, J.W., and Pichot, C. 1983. Batch and semicontinuous emulsion copolymerization of vinyl acetate-hutyl acrylate. I. Bulk, surface, and colloidal properties of copolymer latexes. J. Polym. Sci. Polym. Chem. Ed. 21 2363-82. 

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