Emulsion polymerization apparatus

Fig. 8-1. Laboratory emulsion polymerization apparatus. I, reactor 2, stirrer 3, motor 4, reflux condenser 5, pump 6, monomer feed 7, magnetic stirrer 8, water bath.

Fig. 6. Apparatus for continuous-addition emulsion polymerization of a VDC-acrylate mixture (153).

Emulsion Polymerization The polymerization apparatus was a dilatometer which was similar to though smaller than the one used before.(10) A graduated 10 ml column (adapted from a 10 ml pipette) was connected to a 50 ml volumetric flask with three indentations in it set at 120°. Latex volume changes were read by taking the emulsion to a reference point in the column and reading the height on a precision bore side tube. 

Polyfvinyl acetate) (PVAc) latexes produced by batch and continuous emulsion polymerization were used in this study. Details for the apparatus and the polymerization procedure can be found in Penlidis et al. (6,12,K3). Samples taken during the reaction were subsequently analyzed to follow conversion- and particle growth-time histories. The batch experimental runs were designed to yield similar conversion-time histories but different particle sizes. Conversion was measured both off-line, by gravimetric analysis, and on-line using an on-line densitometer (a U-tube DPR-YWE model with a Y-mode oscillator with a PTE-98 excitation cell and a DPR-2000 electronic board by Anton Paar, Austria). A number of runs were repeated to check for reproducibility of the results. Four batch runs are described in Table I below and their conversion histories are plotted in Figure 1. 

Figure 8-1 is a schematic of a typical laboratory apparatus for emulsion polymerization. Industrial reactors are usually large-scale versions of this basic... 

Emulsion polymerization of methyl methacrylate under the action of pulsed microwave irradiation was studied by Zhu et al. [11], The reactions were conducted in a self-designed single-mode microwave reaction apparatus with a frequency of 1250 MHz and a pulse width of 1.5 or 3.5 ps. The output peak pulse power, duty cycles, and mean output power were continuously adjustable within the ranges 20-350 kW, 0.1-0.2%, and 2-350 W, respectively. Temperature during microwave experiments was maintained by immersing the reaction flask in a thermostatted jacket with a thermostatic medium with little microwave absorption (for example tetrachloroethylene). In a typical experiment, 8.0 mL methyl methacrylate, 20 mL deionized water, and 0.2 g sodium dodecylsulfonate were transferred to a 100-mL reaction flask which was placed in the microwave cavity. When the temperature reached a preset temperature, 10 mL of an aqueous solution of the initiator (potassium persulfate) was added and the flask was exposed to microwave irradiation. 

In a complex apparatus, Gimesch and Schneider [30, 119] studied the suspension polymerization of vinyl acetate. Their procedure involved equipment which automatically added tempered water to the reacting system as heat was evolved as a result of the polymerization process. Thus they maintained isothermal reaction conditions. The rate of reaction could be followed by recording the water uptake of the equipment with time. The heat of polymerization was also determined (found to be 23 kcal/mole which was considered a satisfactory check of the literature value which is scattered around 21.4 kcal/mole). From this work, a somewhat different mechanism of the suspension polymerization process emerges than the widely accepted concept of the water-cooled bulk polymerization of small particles. It was noted that with an increase in the initiator concentration, there was the expected increase in polymerization rate. With increasing stirring rate, the rate of polymerization decreased. Along with the suspension polymerization, there was always a certain amoimt of imdesirable emulsion polymerization. It was postulated that in the process, free radicals, formed in a monomer drop may be extracted into the aqueous phase where they may act on dissolved vinyl acetate by kinetic processes unique to this system and different from the conventional mechanism of suspension polymerization. 

It should be noted again that in the procedure attributed to Wilson [123], as in many other suspension polymerization procedures mentioned above and in many procedures for emulsion polymerizations to be described later, reaction temperatures are given which are above the boiling point of the monomer (72.7°C at 760 mm Hg), not to mention, above the boiling point of the vinyl acetate-water azeotrope (66°C) (composition, 92.7% vinyl acetate, 7.3% water, cf. Table I). For reactions carried out in sealed ampoules or closed bottles, this reaction temperature is readily explained. How such reaction temperatures are reached in a reflux apparatus open to the atmosphere is in question. It is hardly likely that the rate of polymerization is so rapid that no free monomer exists when it is added with conventional initiators to hot water. We presume that most of the polymerizations reported to proceed at about 66 C in an aqueous medium are simply run at reflux. At such a temperature, initiation by dibenzoyl peroxide is rather slow. If the suspension polymerization is to be forced at higher temperatures, provisions will have to be made to force the monomer into the... 

Fig. 2-1 Typical laboratory apparatus for emulsion polymerization at atmospheric pressure (photograph courtesy BASF Corporation).

Monomer (and hydrophobe - in miniemulsion cases) was mixed with surfactant and AIBN, and the whole mixture was stirred at room temperature for 1 h. The amount of SDBS in emulsion polymerization without SWNTs is 6mM (5 cmc). After 1 hour of stirring, the flask was sonicated for 60 s and, immediately after sonication, the mixed solution was stirred at 65°C for 14 h. Water was evaporated and the solid polymer remaining was extracted with isopropanol using a Soxhlet apparatus to remove hexadecane and surfactant. The resulting product was then dried to remove isopropanol. The oil/water phase mass ratio is 10/90 in both types of reactions. In... 

The purification procedures to be applied depend on the monomer, on the expected impurities, and especially on the purpose for which the monomer is to be employed, e.g., whether it is to be used for radical polymerization in aqueous emulsion or for ionic polymerization initiated with sodium naphthalene. It is not possible to devise a general purification scheme instead the most suitable method must be chosen in each case from those given below. A prerequisite for successful purification is extreme cleanliness of all apparatus (if necessary, treating with hot nitrating acid and repeatedly thorough washing with distilled water). 

When the appropriate precautions are taken the method appears particularly suited for measuring very low tensions 10 mN m sometimes even as low as 10 mN m ). Such ultralow tensions are for example encountered in micro-emulsion systems and in just phase-separated polymeric or micellar solutions. For phase-separated colloid-polymer systems de Hoog and Lekkerkerker ) even reported values down to a few pN m , reproducibly being obtained after implementing a number of methodical improvements. (Alternatives for low tensions are the sessile and pending (micro-) drop but these do not usually go below 10 mN m ) Commercial apparatus are nowadays available. A variant proposed by Than et al. J employs a thin rod in the axis of the cylinder, to reduce spin-up time and suppress drift. Another variant, proposed by Kokov, analyses the centrifugal field required to squeeze liquid out of an orifice" ). 

The dilatometer was so immersed in a thermostat, that the onionlike vessel with its stirring fish exactly matched an underwater stirrer magnet in the thermostat. The whole apparatus was reproducibly fixed in the irradiation chamber. To avoid creaming, the emulsion was stirred throughout the polymerization reaction. 

The major limitations to the use of ESR other than for fundamental studies of the radical and other trapped species formed during reactive processing are the experimental requirements of the apparatus. There has been success in using ESR to monitor the concentration of the propagating free radicals during the emulsion batch polymerization of methyl methacrylate (Parker et al, 1996) by using a time-sweep method for data acquisition and... 

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