Power feed staged

In Figure 9, the polymer was prepared via a linear power feed profile in which the near tank contained only ethyl acrylate and the far tank contained only styrene. In Figure 10, the polymer was prepared with the tanks reversed the monomer feed began with styrene and ended with ethyl acrylate. In both cases, the transition regions are much broader than those observed with the uniform feed or staged feed examples. 

The "onion skin" growth mechanism is supported by filming experiments in which film formation is greatly effected by the nature of the monomer composition added last in the polymerization. In power feed examples, as well as in staged feeds, hard and hydrophobic compositions hinder film formation while softer and more hydrophilic compositions aid film formation. Curiously, in this respect, it was found that the filming characteristics of all-acrylic latexes responded to non-uniform polymerization techniques much more dramatically than did their styrene-acrylic counterparts. 

Figures 2, 3 and 4 illustrate the differences between conventional mixed feed, staged and power-feed copolymers whose average composition is 50/50 ethyl acrylate/styrene. In the case of the staged polymerization, all the ethyl acrylate was fed first followed by the styrene. The power-feed copolymer was prepared with ethyl acrylate linearly increasing as a function of time, i.e., x = 1.0, = 0.

The differences in the three polymerization processes are immediately apparent in the spectra. For the conventional copolymer, Figure 2, there is a predominance of BAB triads (EA = A). The power-feed copolymer appears to have relatively higher concentrations of mixed (AAB = BAA) and homo (AAA) triads. In the case of the stage polymerization, Figure 3, the carbonyl resonance is essentially identical to that for poly(ethyl acrylate), that is, AAA triads. 

C nuclear magnetic resonance spectroscopy can be employed to study changes in copolymer sequence distribution brought about by differences in monomer feed profiles. Sequence distributions characteristic of conventional, staged, and power-feed copolymers are easily distinguishable in a model system of the type described here. 

A further development of the concept of copolymer composition control has been the invention of power feeds by Bassett and Hoy [64,65]. This takes the starve-fed control of copolymer composition one stage further by providing an easy means of continuously varying the composition of the comonomer mixture being fed into the reaction vessel, and may be considered as a means of achieving controlled composition drift. The simplest power feed Systran employs two monomer feed tanks and is illustrated in Figure 7.4a, whitli shows that tank 2 feeds into tank 1 from which monomer is supplied to the reaction vessel. Consider the mass balance in tank 1 with respect to monomer A ... 

Figure 3, i.e., 50/50-styrene/ethyl acrylate copolymer made by uniform (random), staged, or power feed processes (24). Using the carbonyl carbon of the acrylate ester as a probe of the sequence distributions in a series of random styrene/ethyl acrylate copolymer, assignments were made for the three major resonance regions in terms of triad sequences. Figure 6 illustrates the differences observed. In the... 

Figure 6. Carbon-13 spectra of model 50/50-styrene/ethyl acrylate latexes. A. Uniform monomer feed B. Linear power feed with near tank-STY, far tank-EA C. Two-stage process with stage I-EA, stage II-STY. (Johnston, Bassett, MacRury, Ref. 24)...

Performance The grinding-media diameter should preferably be 10 times that of the feed and should not exceed 100 times the feed diameter. To obtain improved efficiency when reducing size by several orders of magnitude, several stages should be used with different media diameters. As fine grinding proceeds, rheological factors alter the charge ratio, and power requirements may increase. 

The simplest arrangement for a linear accelerator is shown in Fig. 5. Here a single source, either a self-oscillating magnetron or klystron amplifier with appropriate drive stages, feeds power into a single length of accelerator wave-... 

Figure 10 shows in graphic form the utility of molten salt extractions for americium removal in one, two, and three stage extractions for various salt-to-metal extraction feeds. This graph demonstrates the impressive power of molten salt extraction systems for purification of plutonium from americium and related rare earth elements. 

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