Suspension polymerization description

The authors considered their description of a series of bulk and suspension polymerizations of vinyl chloride with various initiators as very satisfactory [17] with Q St 15. In spite of that, their approach has been criticized by Ugelstad who considers termination of growing radicals exclusively by mutual collisions to be very improbable [19], A large number of primary particles are formed in a short time interval, and many of these are then easily absorbed by the already solid flakes. Desorption of sorbed radicals has also to be considered. Radical distribution among the two phases should be controlled by these processes, especially at low conversion. 

Description of suspension polymerizations fits most appropriately in Chapter 10, where polymer reaction engineering is the topic. This chapter focuses on dispersion and emulsion polymerizations. 

When water-soluble initiators and surface-active agents are used, relatively stable latices are formed from which the polymer cannot be separated by filtration. In the case of vinyl acetate, the distinctions are more blurred. Our description of Procedure 3-3 above represents a transitional situation between a solution and a suspension process since the product separated from the reaction medium. Between the true suspension and the true emulsion polymerization, we find, according to Bartl [4], the processes for formation of reasonably stable dispersion of fine particles of poly(vinyl acetate) using reagents which are normally associated with suspension polymerization. The product is described as creme-like. The well-known white, poly(vinyl acetate), household adhesives may very well be examples of these creamy dispersions. The true latices are characterized by low viscosities and particles of 0.005-1 /im diameter. The creme-like dispersions exhibit higher viscosities and particle diameters of 0.5-15 fim. 

If some particles remain in the continuous phase, it is not feasible for the coverage theory to provide a description for every case of suspension polymerization in which an inorganic solid is used as a stabilizer. Wang and Brooks suggested a... 

Alvarez J, Alvarez J, Hernandez M. A population balance approach for the description of particle size distribution in suspension polymerization reactors. Chem Eng Sci 1994 49 99-113. 

Another heterogeneous process of wide technological importance is emulsion polymerization. It differs from suspension polymerization in that the droplet size is much smaller, typically 0.05 to 5pm in diameter and the initiator is soluble in the aqueous phase rather than the monomer. The droplet particles are held in a stable colloidal suspension with the aid of surface-active agents (emulsifiers) and rapid agitation of the system produces a true emulsion. The mechanism of polymerization is thought to be quite complex and even now is not completely understood. However, the description of emulsion polymerization that is given below is consistent with the widely held views of the probable mechanism. 

Gaylord et al. have reported the suspension polymerization of vinyl chloride using the redox system, such as t-butyl peroxyoctoate-SnClz [23,194] and t-butyl peroxyoctoate-stannous carboxylate [192,193]. The polymerization of VCM in the presence of the redox system has several unusual characteristics which can be explained on the basis of the description already made above. 

There are two problems in the manufacture of PS removal of the heat of polymeriza tion (ca 700 kj /kg (300 Btu/lb)) of styrene polymerized and the simultaneous handling of a partially converted polymer symp with a viscosity of ca 10 mPa(=cP). The latter problem strongly aggravates the former. A wide variety of solutions to these problems have been reported for the four mechanisms described earlier, ie, free radical, anionic, cationic, and Ziegler, several processes can be used. Table 6 summarizes the processes which have been used to implement each mechanism for Hquid-phase systems. Free-radical polymerization of styrenic systems, primarily in solution, is of principal commercial interest. Details of suspension processes, which are declining in importance, are available (208,209), as are descriptions of emulsion processes (210) and summaries of the historical development of styrene polymerization processes (208,211,212). 

Access to Practice. Publications and patents on the batch mass process are limited. Bishop s book CD contains the most detailed description of the polymerization press and mass-suspension processes for PS and HIPS. Fong (16) presents an economic analysis of the press process based on Bishop s description. Patent references are few for the batch-mass process the 1939 Bakelite patent on transfer of prepoly syrup to chambers or containers is of historical interest (17). 

For the discrete bubble model described in Section V.C, future work will be focused on implementation of closure equations in the force balance, like empirical relations for bubble-rise velocities and the interaction between bubbles. Clearly, a more refined model for the bubble-bubble interaction, including coalescence and breakup, is required along with a more realistic description of the rheology of fluidized suspensions. Finally, the adapted model should be augmented with a thermal energy balance, and associated closures for the thermophysical properties, to study heat transport in large-scale fluidized beds, such as FCC-regenerators and PE and PP gas-phase polymerization reactors. 

Description The BP/Lummus styrene polymerization technology for the manufacture of regular and flame-retardant grades of EPS is a one-step batch suspension reaction followed by continuous dewatering, drying and size classification. 

Description PVC is produced by batch polymerization of VCM dispersed in water, using reactors of up to 140 m3. The stirred reactor is charged with water (1), additives (2) and VCM (3) and heated to reaction temperature. The reaction is controlled at a conversion up to 94% to produce the properties for a particular grade. The heat of reaction is removed by cooling water through the reactor jacket and reflux condenser. Chilled water is not needed for reactor cooling, thus capital and operating costs are reduced. At reaction completion, the PVC and water suspension (4) are run down to a blowdown vessel where a proportion of unreacted VCM is flashed off (5) and recovered. 

Investigations of water-in-oil polymerizations employing new monomers or emulsifiers for which kinetic or colloidal characterization is incomplete, require careful nomenclature designation. Under such circumstances a general description such as Water-in-Oil Polymerization or Heterophase Polymerization is recommended until the physical and chemical nature of the polymerizations can be identified. The designations inverse-suspension, inverse-emulsion and inverse-microemulsion should be reserved for processes for which a relatively advanced level of understanding exists. 

Process description The INNOVENE S process utilizes a proprietary vertical slurry-loop reactor, as shown in the flow diagram. Two reactors are used for bimodal capability. Isobutane is normally used as the hydrocarbon diluent in the process, although hexane may be used as an alternative. The diluent is used as a catalyst carrier and as the polymerization reactor suspension and heat transfer medium. Hexene-1 and/or butene-1 can be used as a comonomer. Hydrogen is used for molecular weight control when using the Zieglerg catalyst platform. Titanium-based and chromium-based catalysts are both used. 

The preparation of micron-sized polymer particles has been achieved through the use of a variety of polymerization techniques, including emulsion, suspension, dispersion, and precipitation polymerization. Although the focus of this review is on dispersion and precipitation polymerization, a brief description of emulsion and suspension is included below to be able to compare the different mechanisms. 

Electrokinetics is essentially the consequence of a coupling between electrostatics and hydrodynamics. Newtonian hydrodynamics is widely assumed for the classic description of electrokinetics. However, practical applications of electrokinetics frequently deal with biofluids (such as solutions of DNA, blood, and protein, polymeric solutions, and colloid suspensions) which all are complex fluids and therefore demonstrate non-Newtonian behaviors. Recently intensive efforts on electrokinetics of non-Newtonian fluids have been made after Das and Chakraborty [1] who pioneered a theoretical analysis of electroosmosis of non-Newtonian fluids. Here in this entry the example of electroosmosis of non-Newtonian fluids in microchannels is used to demonstrate the fundamental formulation of non-Newtonian electrokinetics. 

This chapter, will begin with a brief description of polymeric surfactants and their solution properties, followed by a description of the fundamental principles of using polymeric surfactants for stabilization of emulsions (as well as suspensions), starting with a section on the adsorption and conformation of these molecules at the interface. This is followed by a section on stabilization of dispersions by polymeric surfactants. Particular... 

There are other important polymerization processes such as those of the suspension or emulsion type. Examples of these two types are given in Figs. 4.55 and 4.56. For an excellent description of the synthesis and kinetics of polymerization methods and processes the reader is referred to more detailed texts focusing on polymer science, eg. Painter and Coleman, (1994) and Billmeyer, (1984). 

This chapter will start with a short account of the general classification and description of polymeric surfactants. This is followed by a summary on then-solutions properties. The adsorption and conformation of polymeric surfactants at the solid-liquid interface will be discussed at a fundamental level and some experimental results will be presented to illustrate the prediction of the theories. The interaction energies between particles or droplets containing adsorbed polymeric surfactants will be briefly described. The final section will give some applications of polymeric surfactants in suspensions, emulsions, and multiple emulsions. 

On the basis of the results obtained so far using the three methods mentioned above, a relevant conclusion can be drawn the accurate temperature control (S 170 ° C) permits to mn polymerizations of CL in quasi-isothermal conditions and very efficiently contribute to the minimization of side reactions, the other relevant factor in this respect being the use of very fast activator/initiator pairs. Only the simultaneous effect of both factors, that is, temperature control and very fast catalytic systems, allows to reach both optimum process conditions and excellent polymer properties. The use of slow activators, such as N-acetyl-CL, on the contrary, strongly limits possible advantages of the method. Moreover, it should be taken into account that in general, solution polymerizations (methods 1 and 3) ate characterized by lower reaction rates as compared to suspension processes (method 2). On the other hand, these latter methods have to face more difficult and expensive purification procedures of the polyamide from the reaction mixture. The only other lactam-based polyamide synthesized in powder form in laboratory by a suspension process is poly(2-pyrrolidone). A description of its synthesis is given in Section 4.14.11.1. 

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