Suspension polymerization scale formation

Formation of a scale of polymer on the reactor walls is normally less than in corresponding bulk or solution polymerizations. Scale formation is troublesome in PVC suspension polymerizations, however, because the polymer is not soluble in its monomer, and a deposit formed on the wall will not be washed off by fresh monomer. This build-up has to be removed in order to maintain satisfactory heat transfer and prevent inclusion of gelled polymer ( fish eyes ) in the product. Cleanliness of the reactor walls is very important because the productivity of the equipment is enhanced by longer intervals between shutdowns for cleaning. To this end, some phenolic coatings have been designed that inhibit polymer buildup by terminating free-radical reactions on the walls (cf. Section 6.9). 

Suspension polymerization of VDE in water are batch processes in autoclaves designed to limit scale formation (91). Most systems operate from 30 to 100°C and are initiated with monomer-soluble organic free-radical initiators such as diisopropyl peroxydicarbonate (92—96), tert-huty peroxypivalate (97), or / fZ-amyl peroxypivalate (98). Usually water-soluble polymers, eg, cellulose derivatives or poly(vinyl alcohol), are used as suspending agents to reduce coalescence of polymer particles. Organic solvents that may act as a reaction accelerator or chain-transfer agent are often employed. The reactor product is a slurry of suspended polymer particles, usually spheres of 30—100 pm in diameter they are separated from the water phase thoroughly washed and dried. Size and internal stmcture of beads, ie, porosity, and dispersant residues affect how the resin performs in appHcations. 

The fact that alcohols, too, induce the formation of large pores in molded rods is well consistent with the same observation for beaded polymers prepared by suspension polymerization. In general, suspension polymerization is considered to be bulk polymerization on a mini scale. Hence, all dependences that are characteristic of bulk polymerization would have to be valid for both the molded rods and the beads. Indeed, poly(gIycidyl methacrylate-co-ethylene dimethacrylate) obtained under identical conditions in the form of rod or beads have similar surface area and pore volume values. Both polymers can be expected to have more or... 

The main objective of batch suspension polymerization of vinylidene fluoride is to limit the formation of polymer scale on the walls of the reactor, A... 

Redox polymerizations are usually carried out in aqueous solution, suspension, or emulsion rarely in organic solvents. Their special importance lies in the fact that they proceed at relatively low temperatures with high rates and with the formation of high molecular weight polymers. Furthermore, transfer and branching reactions are relatively unimportant. The first large-scale commercial application of redox polymerization was the production of synthetic rubber from butadiene and styrene (SBR1500) at temperatures below 5 °C (see Example 3-44). 

Heterophase polymerization systems can be defined as two-phase systems in which the resulting polymer and/or starting monomer are in the form of a fine dispersion in an immiscible liquid medium defined as the polymerization medium , continuous phase , or outer phase . Even if oil-in-water (o/w) systems are greatly preferred on an industrial scale, water-in-oil (w/o) systems may also be envisaged for specific purposes. Heterogeneous polymerization processes can be classified as suspension, dispersion, precipitation, emulsion, or miniemulsion techniques according to interdependent criteria which are the initial state of the polymerization mixture, the kinetics of polymerization, the mechanism of particle formation and the size and shape of the final polymer particles (Fig. 4.2) [18]. 

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