Semi-batch emulsion

Much has been written on RAFT polymerization under emulsion and miniemulsion conditions. Most work has focused on S polymerization,409-520 521 although polymerizations of BA,461 522 methacrylates382-409 and VAc471-472 have also been reported. The first communication on RAFT polymerization briefly mentioned the successful semi-batch emulsion polymerization of BMA with cumyl dithiobenzoate (175) to provide a polymer with a narrow molecular weight distribution.382 Additional examples and discussion of some of the important factors for successful use of RAFT polymerization in emulsion and miniemulsion were provided in a subsequent paper.409 Much research has shown that the success in RAFT emulsion polymerization depends strongly on the choice of RAFT agent and polymerization conditions.214-409-520027... 

O. Elizalde, J.M. Asua and J.R. Leiza, Monitoring of high solids content starved-semi-batch emulsion copolymerization reactions by Fourier transform Raman spectroscopy, Appl. Spectrosc., 59, 1270-1279 (2005). 

The latexes were prepared using a conventional semi-batch emulsion polymerization system modified for power-feed by the addition of a second monomer tank. Polymerization temperatures ranged from 30-85°C using either redox or thermal initiators. Samples were taken periodically during the polymerization and analyzed to determine residual monomer in order to assure a "starved-feed" condition. As used in this study this is a condition in which monomer feed rate and polymerization rate are identical and residual monomer levels are less than 5%. 

Zeaiter, J. Romagnoli, J.A. Gomes, V.G. Gilbert, R.G. Operation of semi-batch emulsion polymerisation reactors modelling, validation, and effect of operating conditions. Chem. Eng. Sci. 2002, 57, 2955-2969. 

Acetate Semi-Batch Emulsion Copolymerization Experimental Design and Preliminary Screening Experiments. 

In order to take full advantage of semi-batch emulsion polymerization, it is necessary to use monomer-starved conditions. The following section is devoted to the reasons why these conditions are so important. Except where indicated otherwise, statements such as addition of monomer and monomer added simply mean... 

Figure 7.3 Semi-batch emulsion polymerizations of styrene carried out at 70 °C using the following formulation styrene, 198 g deionized water, 596 g Aerosol 22 (35% active),...

The study of emulsion copolymerization of vinyl acetate with n-butyl acrylate [1 -3], which was presented in Section 7.3.2.1 with respect to batch reactions, also provides a good example of the use of monomer-starved, semi-batch emulsion... 

Besides properties (which are usually enhanced by adding clay), another crucial factor of PCN materials elaborated through emulsion polymerization is their solid content. Although this point is less frequently addressed, most of the polymer/clay composite latexes reported in literature have solid contents below 20%. However, solid contents between 40% and 60% and sometimes higher are required for industrial applications. Using a seeded semi-batch emulsion polymerization process and a procedure otherwise very similar to that described above for Bentonite,... 

The water dispersions of PVAc were prepared under nitrogen atmosphere using a semi-batch emulsion polymerization technique, in a four-neck kettle equipped with a mechanical stirrer, an inlet for feeding streams and a reflux condenser. The reagent amounts, the reaction conditions and the yields for each preparation are reported in Table 5. Solids content, pH and viscosity were measured and reported in Table 5. 

Lazaridis N, Alexopoulos A.H, Kiparissides C (2001) Semi-batch Emulsion Copol3rmerization of Vinyl Acetate and Butyl Acrylate Using Oligomeric Nonionic Surfactants. Macromol.Chem.Phys. 202 2614-2622. 

The poly(methyl methacrylate) molecules were dispersed in the natural rubber matrix, or vice versa, to form spherical droplets, as observed by optical photographs or scanning electron microscopy. The compatible natural rubber/poly(methyl methacrylate) blends had been made by the addition of the graft copolymer of natural rubber-gr t-poly(methyl methacrylate) as the compatibilizing agent due to its ability to enhance the interfacial adhesion between the two homopolymers. Moreover, Nakasorn and coworkers reported that natural rubber-gr i -poly(methyl methacrylate) could be blended with poly(methyl methacrylate) via a dynamic vulcanization technique with a conventional sulfur vulcanization system. The natural rubber-gra/t-poly(methyl methacrylate) was synthesized by a semi-batch emulsion polymerization technique via different bipolar redox initiation systems, i.e. cumene hydroperoxide and tetraethylene pentamine. ... 

Although microemulsions can be used as an attractive pathway to prepare the ultrafine latex particles, the formulation of microemulsions has been suffering from severe constraints due in large part to the high surfactant level required to not only emulsify the relatively low amount of monomers but also achieve their thermodynamic stability. This fact is in contradiction to the requirement of high solid contents in engineering polymers. That is one important reason that hinders the wide application of microemulsion polymerization in industry. In order to alleviate these limitations involved in the microemulsion polymerization, a monomer-starved semi-batch emulsion polymerization was thereby put... 

In a common semi-batch operation mode (sometimes called semi-continuous mode), some fraction of reactants, i.e. the initial charge, are initially charged into the reactor, and the rest of the formulation is continuously provided to feed over some period of time. In a fully semi-batch emulsion process, the polymerization starts with an aqueous solution only containing a surfactant and an initiator (micellar solution), and then the monomer feed is provided in very small drops with a given rate. 

Crowley TJ, Meadows ES, Kostoulas A, Doyle III FJ. Control of particle size distribution described by a population balance model of semi-batch emulsion polymerisation. J Process Control 2000 10 419-432. 

Vieira, R.A.M., et al., In-Line and in situ Monitoring of Semi-Batch Emulsion Copolymerizations Using Near-Infrared Spectroscopy. J. Appl. Polym. ScL, 2002. 84 2670-2682. 

Fig. 11.13. Schematic representations of the moiar flow rates of monomer in a semi-batch emulsion polymerization. Top graph the feed is optimal it is immediately converted. Middle graph the feed was started too early the...

Vieira RAM, Sayer C, Lima EL, Pinto JC. In-line and in-situ monitoring of semi-batch emulsion copolymerizations nsing near-infrared spectroscopy. J Appl Polym Sci 2002 84 2670-2682. 

Hvalaa N, Aller F, Mitevaa T, Kukanjab D. Modelling, simulation and control of an industrial, semi-batch, emulsion-polymerization reactor. Comp Chem Eng 2011 35 2066-2080. 

Liotta V, Georgakis C, El-Asser MS. Real-time estimation and control of particle size in semi-batch emulsion polymerization. 15th American Control Conference Proceedings 1997 June 4-6 New Mexico, p 1172-1176. 

The ultimate goal of most of the investigations on emulsion copolymerisation is to be able to control the process in such a way as to produce a copolymer product (latex or coagulate) with desired properties. For this purpose the semi-continuous (sometimes called semi-batch) emulsion copolymerisation process is widely used in industry. The main advantages of this process as compared with conventional emulsion batch processes include a convenient control of emulsion polymerisation rate in relation with heat removal and control of chemical composition of the copolymer and particle morphology. These are important features in the preparation of speciality or high performance polymer latexes. 

Figure 4.11 shows simulated data for two-seeded semi-batch emulsion copolymerisations of BA and MMA carried out with feeding times of 3 and 6h, respectively. Figures 4.11(a) and (b) present the cumulative and instantaneous copolymer compositions. The results in the Figures 4.11(a) and (b) clearly demonstrate that the steady state is achieved in both cases. However, for the addition period of 6 h the fraction copolymer with a composition deviating from the desired composition of 0.5 is smaller than for the addition period of 3 h. Furthermore, the cumulative composition is closer to 0.5 for the 6 h addition period than for the 3 h addition. In comparison with the batch process, the composition drift is almost negligible as displayed in Figure 4.11 (d) which shows a very narrow chemical composition distribution (CCD) centred at 0.5. 

Figure 4.11 Simulated data for the starved feed semi-batch emulsion copolymerisation of BA and MMA. Initial molar ratio of BA and MMA is one. Instantaneous and cumulative copolymer composition for (a) 3 h and (b) 6 h monomer addition, respectively (c) polymerisation rates (d) CCD for 3 h addition.

This recipe could be utilized for investigating both batch and semi-batch emulsion polymerization at a range of temperatures. With just these two monomers and one functional monomer, a very wide range of polymers with significant differences in polymer and latex properties can be produced (soft/hard, low/high molecular weight, tacky/non-tacky, stable/unstable, etc.)... 

Fig. 2-11 Influence of number of particles on the instantaneous conversion in a semi-batch emulsion polymerization of styrene-butadiene 45 55 with a feed time of 4.5 h at 85 °C.

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