Polymerization three-stage

Kinetics and Mechanisms. Early researchers misunderstood the fast reaction rates and high molecular weights of emulsion polymerization (11). In 1945 the first recognized quaHtative theory of emulsion polymerization was presented (12). This mechanism for classic emulsion preparation was quantified (13) and the polymerization separated into three stages. 

The diamine and the diacid form a PA salt that is soluble in water at elevated temperatures. The polymerization from the PA salt solution occurs in two or three stages. In the first stage a prepolymer is made. This step is carried out under pressure to prevent the evaporation of the more volatile diamine. In the second stage, a polymer is made in the melt phase at atmospheric or slightly reduced pressure. 

The process of migration of additives or contaminants from polymeric food packaging to food may be separated into three stages diffusion within the polymer, solvation at the polymer food interface, and dispersion into bulk food. 

Fig. 24. Sequential three-stage polymerization of methyl methacrylate (MMA), methacrylo-nitrile (MAN), and MAN in CH2CI2 at rt with the methylaluminum porphyrin (1, X=Me)-methylaluminum bis(2,6-di-tert-butyl-4-methylphenolate) (3e) system. GPC profiles of the polymers formed at I The first stage [MMA]o/[l]o=100, 100% conversion Mn= 13,200, Mw/Mn=1.22, II The second stage [MAN]o/[l]o=50, 100% conversion Mn=17,500, Mw/Mn=1.21, and III The third stage [MAN]o/[l]o=50, 100% conversion Mn=20,700, Mw/Mn=1.29...

Styrene-1,3-butadiene-styrene (SBS) or styrene-isoprene-styrene (SIS) triblock copolymers are manufactured by a three-stage sequential polymerization. One possible way of the synthesis is to start with the polymerization of styrene. Since all polystyrene chains have an active anionic chain end, adding butadiene to this reaction mixture resumes polymerization, leading to the formation of a polybutadiene block. The third block is formed after the addition of styrene again. The polymer thus produced contains glassy (or crystalline) polystyrene domains dispersed in a matrix of rubbery polybutadiene.120,481,486... 

Biosynthesis of bacterial cell wall is remarkable in two respects (1) It entails the synthesis of a regularly cross-linked polymer and (2) Part of the synthesis takes place inside the cell and part outside the cell. The synthesis of cell wall is divided into three stages, which occur at different locations (1) synthesis of UDP-/V-acetylmuramyl-penta-peptide, (2) polymerization of IV-acetylglucosamine and N-acetylmuramyl-pentapeptide to form linear peptidoglycan strands, and (3) cross-linking of the peptidoglycan strands. 

The dependence of the conversion and polymer-composition on the reaction time is shown in Figure 1 for the copolymerization of St with AA at f = 0.4, pH 9.0 and 70°C. The polymerization course was found to consist of three stages At first AA polymerizes preferentially but the preference decreases rapidly with increasing conversion (0 - 1.0 hr) St polymerizes exclusively (1.0 - 1.5 hrs) and again AA polymerizes preferentially (1.5 hrs - end). A similar copolymerization mode was observed in an aqueous copolym-... 

It is clear from Eq. 1 that the monomer concentration in a polymer particle is one of the three key factors that control the particle growth rate, and accordingly, the rate of polymerization. In emulsion polymerization, the course of emulsion polymerization is usually divided into three stages, namely. Intervals I, II and III. In Intervals I and II of emulsion homopolymerization, the monomer concentration in the polymer particles is assumed to be approximately constant. In Interval III, it decreases with reaction time. Two methods are now used to predict the monomer concentration in the polymer particles in emulsion homopolymerization empirical and thermodynamic methods. 

Strictly speaking, the Smith-Ewart model applies only to the batch polymerization of a completely water-insoluble monomer in the presence of micellar soap. (The terms soap, suifactanf, and emulsifier are used interchangeably in this technology.) Its predictions do in fact apply neatly to the case of styrene. Tlie polymerization reaction, after the induction period, can be classified conveniently into three stages, as shown schematically in Fig. 8-2. 

RNA synthesis, like nearly all biological polymerization reactions, takes place in three stages initiation, elongation, and termination. RNA polymerase performs multiple functions in this process ... 

Chain polymerization involves three stages initiation, propagation, and termination. The most important of the chain polymerization methods is free radical polymerization, in which the initiation step occurs by an attack on the monomer molecule by a free radical. A free radical is a reactive molecule possessing an unpaired electron and is usually formed by the decomposition of a relatively unstable molecule referred to as an initiator. In particular, those compounds containing peroxide bonds, (—O— O—), can produce free radicals by thermal decomposition, for example,... 

To ascertain the effect of conversion on polymerization rate, it is useful to determine the ratio Rp / [m] instead of percent conversion as it takes into account the changes in monomer and initiator concentrations with time (or conversion). A plot of Rp / [m] versus conversion (Fig. 6.11) show that three stages can be distinguished in some polymerizations. Stage... 

The three stages in an emulsion polymerization system are depicted in Fig. 6.18. 

Figure 6.18 Schematic conversion-time curve for emulsion polymerization showing three stages.

The value of n in Eq. (6.230) is of critical importance in determining the rate of polymerization in stage II. Three cases — designated 1, 2, 3 — corresponding, respectively, to n < 0.5, n = 0.5, and n > 0.5 can be distinguished based on the work of Smith and Ewart [69] and others [70-74]. The kinetic treatment given above conforms to Case 2 (n = 0.5), which is the predominant behavior for emulsion polymerizations. It occurs when desorption of radicals does not occur or is negligible compared to the... 

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