Polymerization continued suspension

Analysis of mixture models, established techniques, 61 Analysis of styrene suspension polymerization continuous models, 210-211 efficiency, 211,212f,213 free volume theory, 215,217 initiator conversion vs. 

Manufacturing Processes. The three manufacturing processes already mentioned (continuous mass polymerization, batch suspension and emulsion polymerization) continued to compete with each other after 1945. Whereas the third one gradually decreased in importance, the other two were given preference in... 

The second large-scale process was the batch mass suspension process. Monsanto did the pioneer work on this (41). In this process, prepolymerization is carried out in bulk and main polymerization in suspension the latter is taken to conversions of over 99%. In contrast to the continuous mass process, peroxide starters are used in order to achieve a high conversion at tolerable reaction times. Figure 3 shows a basic flow diagram of such a plant. A detailed discussion of advantages and disadvantages of the two processes can be found in R. Bishop s monograph published in 1971 (42), and it is continued in a paper by Simon and Chappelear in 1979 (43). It was a decisive factor for the economic success of impact polystyrene that these processes had been completely developed and mastered in theory and practice. 

An inverse suspension polymerization involves an organic solvent as the continuous phase with droplets of a water-soluble monomer (e.g., acrylamide), either neat or dissolved in water. Microsuspension polymerizations are suspension polymerizations in which the size of monomer droplets is about 1 pm. 

Suspension Polymerization. The suspension or pearl polymerization process has been used to prepare polymers for adhesive and coaling applications and for conversion to poly(vinyl alcohol). Suspension polymerization are carried out with monomer-soiubie initiators predominantly, with low levels of stabilizers Continuous tubular polymerization of vinyl acetate in suspension yields stable dispersions of beads with narrow particle size distributions at high yields. 

Superficially, emulsion polymerization resembles suspension polymerization, but there are a number of important differences. Water is used as the continuous phase and heat transfer is very good for both suspension and emulsion polymerization. In contrast to suspension polymerization, the polymer particles produced in emulsion polymerization are on the order of 0.1 xm in diameter.33 Another important difference is the presence of an emulsifying agent or soap. At the beginning of polymerization the soap molecules aggregate together in a group of about 50-100 molecules to form what is called a micelle. Some of the... 

Polymerization in third phase Commercially, the preparation of beads by polymerizing a suspension of a 2-phase emulsion in a third phase appears to be more viable The third phase should ideally be one in which both acrylic esters and allylamine hydrochlorides are insoluble. However, because of the opposite solubility properties of these two monomers, one of them is invariably soluble in a given third phase. It is believed that if one phase is dispersed in the continuous phase, then that should shield the first phase from the third. However, when the two-phase system is added to a third phase, the two-phase emulsion immediately breaks up. In most cases, the two-phase emulsions also disintegrate on heating and so adding the two-phase emulsion to a heated third phase usually proves disastrous. 

Heterogeneous polymerization can be further divided into emulsion polymerization and suspension polymerization. In both types of polymerization, the monomers are dissolved in the dispersed phase. In suspension polymerization, the initiator is dissolved in the dispersed phase as well and nucleation and growth of the beads take place in the droplets. In emulsion polymerization, on the other hand, the initiator is dissolved in the continuous phase, leading to nucleation and bead growth from the continuous phase. 

Styrene is one of the oldest and most studied monomers. It spontaneously generates free radials upon heating above 100 °C and polymerizes yielding amorphous polystyrene (PS). Styrene can also be polymerized by other mechanisms (anionic, cationic, or Zeigler-Natta) with the aid of chemical initiators. Commercially, over twenty billion pounds of PS are produced annually worldwide. All of this polystyrene is produced via free radical (FR) chemistry, and mostly via continuous solution polymerization processes. The commercial preference for the continuous solution process is due mainly to economic factors. Non-solution polymerization processes (suspension and emulsion) have lower reactor efficiency (product/reactor volume) due to reactor volume occupied by the water which adds to the manufacturing cost. 

A number of important commercial resins are manufactured by suspension polymerization, including poly(vinyl chloride) and copolymers, styrene resins [general purpose polystyrene, EPS, high impact polystyrene (HIPS), poly(styrene-acrylonitrile) (SAN), poly(acrylonitrile-butadiene-styrene) (ABS), styrenic ion-exchange resins], poly(methyl methacrylate) and copolymers, and poly(vinyl acetate). However, some of these polymers rather use a mass-suspension process, in which the polymerization starts as a bulk one and, at certain conversion, water and suspending agents are added to the reactor to form a suspension and continue the polymerization in this way up to high conversions. No continuous suspension polymerization process is known to be employed on a... 

Imamura et al. [28] describe a concentric cylinder reactor in which one cylinder is rotated. The axial flow rale and rotational speed are such to generate flows with Taylcn vortices which save to narrow the residence time and particle size distributions. The reactor is also claimed to be useful for continuous suspension polymerization. 

Vinyl chloride is polymerized in bulk, suspension, emulsion, or in the gas phase. The bulk polymerization is a precipitation polymerization. To prevent excessive heat buildup because of the heat of polymerization, it is carried out in two stages. In the gaseous phase polymerization, prepolymerized PVC is loaded with vinyl chloride below the saturated vapour pressure and then further polymerized continuously in a fluidized bed or cascade process. Emulsion polymerizates always contains foreign material, and so, are only used as pastes. 

Water as diluent has obvious advantages and has been developed for many free-radical polymerizations. Thus suspension polymerization involves the dispersion of the non-miscible monomer in water as droplets (0.1-5 mm diameter) by means of agitation and protective colloids or dispersing agents (e.g. polyvinyl alcohol, PVAL), and adding a monomer-soluble initiator. The polymer ends up approximately the same size as the original droplets and the system can be viewed as many small bulk polymerizations. As water is the continuous phase the viscosity remains constant and good heat transfer occurs. This process is used for PVC. 

Suspension polymerization processes are widely used for the production of polymer beads. In typical suspension processes, an organic phase constituted by initiator (or catalyst), comonomers, and the final polymer are suspended in an aqueous phase, which contains additives and residual monomer. Thus, reaction proceeds in a heterogeneous reacting mixture. The main advantages of suspension processes are easy purification of the polymer material, the low viscosity of the reaction medium, and the reduction of the effective heat of reaction, as water absorbs significant amounts of the heat released by the reaction. The main disadvantages are the lower productivities (when compared to bulk processes) and the slicking characteristics of the suspended polymer, which explains why continuous suspension processes have not been used commercially so far. Reactions can follow step or addition mechanisms [102]. 

The term suspension polymerization (also referred to as bead or pearl polymerization) refers to polymerization in an aqueous system with a monomer as a dispersed phase, resulting in a polymer as a dispersed solid phase. The suspension polymerization is carried out by suspending the monomer as droplets (0.001-1 cm in diameter) in water (continuous phase). In a typical suspension polymerization, the initiator is dissolved in the monomer phase. Such initiators are often referred to as oil-soluble initiators. Each monomer droplet in a suspension is considered to be a small bulk polymerization system and the kinetics is the same as that of bulk polymerization. The suspension of a monomer is maintained by agitation and the use of stabilizers. The suspension polymerization method is not used with mono-... 

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