Continuous bulk polymerization

A schematic of a continuous bulk SAN polymerization process is shown in Figure 4 (90). The monomers are continuously fed into a screw reactor where copolymerization is carried out at 150°C to 73% conversion in 55 min. Heat of polymerization is removed through cooling of both the screw and the barrel walls. The polymeric melt is removed and fed to the devolatilizer to remove unreacted monomers under reduced pressure (4 kPa or 30 mm Hg) and high temperature (220°C). The final product is claimed to contain less than 0.7% volatiles. Two devolatilizers in series are found to yield a better quaUty product as well as better operational control (91,92). 

Three bulk polymerization processes are commercially important for the production of methacrylate polymers batch cell casting, continuous casting, and continuous bulk polymerization. Approximately half the worldwide production of bulk polymerized methacrylates is in the form of molding and extmsion compounds, a quarter is in the form of cell cast sheets, and a quarter is in the form of continuous cast sheets. 

Several references to the bulk polymerization of styrene are worth consulting [46-50], Most consider a continuous bulk polymerization apparatus with some using spraying of the monomer through a nozzle. The controlled evaporation of unreacted monomer is one method of removing the heat of reaction. 

For the copolymerization of ethene and vinyl acetate, solution polymerization, suspension polymerization, emulsion polymerization and bulk polymerization may be used, but solution polymerization is preferred (1). A method of either continuous type or batch type may be employed. Methanol is generally used as the solvent. 

A continuous bulk polymerization process with three reaction zones in series has been developed. The degree of polymerization increases from the first reactor to the third reactor. Examples of suitable reactors include continuous stirred tank reactors, stirred tower reactors, axially segregated horizontal reactors, and pipe reactors with static mixers. The continuous stirred tank reactor type is advantageous, because it allows for precise independent control of the residence time in a given reactor by adjusting the level in a given reactor. Thus, the residence time of the polymer mixtures can be independently adjusted and optimized in each of the reactors in series (8). 

Bulk Polymerization. This involves only monomer, initiator, and perhaps chain-transfer agent. It gives the greatest polymer yield per unit of reactor volume and a very pure polymer. However, in large-scale batch form, it must be run slowly or in continuous form with a lot of heat-transfer area per unit of conversion to avoid mnaway. Objects are conveniendy cast to shape using batch bulk polymerization. Poly(methyl methacrylate) glazing sheets are produced by batch bulk polymerization between glass plates. They are also made by continuous bulk polymerization between polished stainless steel... 

In bulk polymerization, no solvents are employed and the monomer acts as the solvent and continuous phase in which the process is carried out. Commercial bulk processes for acrylic polymers are used mainly m the production of sheets, rods and tubes. Rulk processes are also used on a much smaller scale in the preparation of dentures and novelty items and in the preservation of biological specimens. Acrylic castings are produced by pouring monomers or partially polymerized sirups into suitably designed molds and completing the polymerization. Acrylic bulk... 

Polymerization in bulk (or in block) under normal pressure in the temperature range from room temperature to about 15CUC. The batch polymerization of methylmethacrylate to give Lucite" or Plexiglass" and the continuous polymerization of styrene to give the various types of polystyrene can be quoted as examples. 

Today, a large part of the more than one billion lbs/year of impact polystyrene and 500 million lbs/year of ABS produced domestically is made by graft copolymerization. Impact polystyrene may be synthesized by dissolving a diene rubber in styrene monomer, in the presence or absence of another solvent, prepolymerizing the solution, and completing the polymerization in bulk, solution, or suspension. R. B. dejong describes a process wherein he prepolymerizes in emulsion with styrene as the continuous phase and the water as the dispersed phase and completes polymerization in aqueous suspension. 

Henderson, L. S. and Cornejo, R. A. (1989). Temperature control of continuous, bulk styrene polymerization reactors and the influence of viscosity an analytical study. Ind. Eng. Chem. Res., 28, 1644-1653. 

Polystyrene and its Copolymers. Polystyrene (Table 15.7) is made by continuous bulk polymerization, initiated by peroxides and... 

Application To produce a wide range of general purpose polystyrene (GPPS) with excellent high clarity and suitable properties to process PS foam via direct injection extrusion by the continuous bulk polymerization process using Toyo Engineering Corp. (TEC)/Mitsui Chemicals Inc. technology. 

Description The process involves continuous, bulk-phase polymerization of styrene using a combination of thermal and chemical initiation. A typical unit design consists of separate reaction trains for GPPS and HIPS grades, which have been optimized for each resin... 

In evaluating this approach, the question of how and when to introduce the catalyst to the polymerization mixture arose. The simplest method would be to put the catalyst in the styrene monomer being fed to a continuous bulk polymerization system. Then the polymer would be produced with the catalyst molecularly dispersed in it. Priddy et al. evaluated both a sulfonic acid catalyst and also thermally labile acid esters that generate acids during high-temperature devolatilization [38],... 

Another type of initiator that has been evaluated for increasing polystyrene production rates are the multifunctional peroxides. Examples include 2,2-bis [4,4-bis(tert-butylperoxy)cyclohexyl]propane (I) [9], peroxyfumaric acid, 0,0-te/Y-butyl O-butyl ester (II) [10], ter t-butyl peritaconate (III) [11], and poly (monopercarbonates) (IV) (Figure 7.4) [12]. Although all of these initiators indeed show extremely fast production rates of high MW polystyrene, they all suffer from a flaw, i.e. the polystyrene produced is branched and special precautions must be taken to keep the continuous bulk polymerization reactors from fouling [13]. This is likely why none are currently used commercially for polystyrene manufacture. 

Styrene-containing block copolymers are commercially very important materials. Over a billion pounds of these resins are produced annually. They have found many uses, including reinforcement of plastics and asphalt, adhesives, and compatibilizers for polymer blends, and they are directly fabricated into articles. Most styrene-containing block copolymers are manufactured using anionic polymerization chemistry. However, anionic polymerization is one of the more costly polymerization chemistries because of the stringent requirements for monomer and solvent purity. It would be preferred, from an economic cost perspective, to have the capability to utilize free radical chemistry to make block polymers because it is the lowest cost mode of polymerization. The main reasons for the low cost of FR chemistry are that minimal monomer purification is required and it can be carried out in continuous bulk polymerization processes. 

Figure 8.3 TEMs of XII and TIPS made using /ns/ fu-formed S-B by addition of XI to a continuous bulk styrene polymerization...

The commercial manufacture of polystyrene was batch mode through the 1930s and 1940s, with a gradual transition to continuous bulk polymerization beginning in the 1950s. Suspension polymerization was a common early polystyrene production process, where a single reactor produced a polymer slurry that had to be separated from the water and dried. This process was ideal for free radical... 

As a means to improve the rubber utilization, a bulk/suspension process evolved, whereby polybutadiene rubber was dissolved in styrene monomer and polymerized in bulk beyond phase inversion before being dropped into suspension. The HIPS produced this way had two distinct advantages over the compounded version styrene to rubber grafting and discrete rubber spheres or particles uniformly dispersed in a polystyrene matrix. This improved the impact strength dramatically per unit of rubber and gave better processing stability, because the rubber phase was dispersed instead of being co-continuous with the polystyrene. 

Today, HIPS is produced predominantly by the continuous bulk or solution process. Industrial production processes can be subdivided into batch preparation, pre-polymerization, main polymerization and work-up. 

Clearly the benzylic H-atoms attached to the polystyrene backbone are not as labile as in cumene. This is likely due to the steric effect of the coil configuration of the polymer chain which blocks access of the /er/-butoxy radicals. Nonetheless, some backbone H-atom abstraction from the polystyrene backbone does occur during radical polymerization of styrene. The extent of abstraction is proportional to the concentration of peroxide initiator added to the process. Typically, in commercial continuous bulk polymerization processes the concentration of peroxide initiator is kept below 500 ppm. Also a few percent of a solvent having some chain transfer activity (ethylbenzene) is added to the styrene feed. This is done so that the extent of branching is small. If the concentration of initiator is increased to >500 ppm and/or the chain transfer solvent falls below a certain level, the extent of branching can increase to a level where gels began to appear in the product. The mechanism of... 

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