Polymerization bulk processes

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. 

The Hquid monomers are suitable for bulk polymerization processes. The reaction can be conducted in a mold (casting, reaction injection mol ding), continuously on a conveyor (block and panel foam production), or in an extmder (thermoplastic polyurethane elastomers and engineering thermoplastics). Also, spraying of the monomers onto the surface of suitable substrates provides insulation barriers or cross-linked coatings. 

Describe the bulk polymerization process for the manufacture of polystyrene. What limitations exist with this method ... 

Polymerization of vinyl chloride occurs through a radical chain addition mechanism, which can be achieved through bulk, suspension, or emulsion polymerization processes. Radical initiators used in vinyl chloride polymerization fall into two classes water-soluble or monomer-soluble. The water-soluble initiators, such as hydrogen peroxide and alkali metal persulfates, are used in emulsion polymerization processes where polymerization begins in the aqueous phase. Monomer-soluble initiators include peroxides, such as dilauryl and benzoyl peroxide, and azo species, such as 1,1 -azobisisobutyrate, which are shown in Fig. 22.2. These initiators are used in emulsion and bulk polymerization processes. 

The bulk polymerization process needs monomers that can dissolve their own polymers. (There s no solvent or water in the reactor to keep the polymer floating around.) Styrene and some of the more commonly used comonomers have this property, and so its generally cheaper to use bulk polymerization. 

A bnlk polymerization reactor can be as simple as a tube into which the reactants are fed and from which the polymer mixture emerges at the end it can be more of a traditional, continnons stirred-tank reactor (CSTR), or even a high-pressure autoclave-type reactor (see Figure 3.21). A bulk polymerization process need not be continuous, but it should not be confnsed with a batch reaction. There can be batch bnlk polymerizations jnst as there are continnons bulk polymerizations processes. 

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). 

The already low cost of converting VCM to PVC probably precludes any revolutionary new process replacing the current suspension and emulsion processes. The Pechiney-St. Gobain bulk polymerization process is being tested thoroughly within the next year it will be evident if the process offers advantages, either in product quality or conversion cost. 

There have also been some prominent studies of IPNs based on chitin [92, 93], alginate [94], etc. For example, the microscopic incorporation of chitin with methacrylate polymers such as poly(glycidyl methacrylate) [92] and poly(2-hydroxyethyl methacrylate) [93] was achieved by the combination of solution coagulation and bulk polymerization processes (Sect. 3.1.3). From... 

Bulk polymerization processes described so far are performed without the use of substantial amounts of solvents. Only small amounts of solvents (< 2 wt. %, and > 98 wt. % monomer) are required for preparation and addition of the catalyst solutions. 

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. 

Commercial polystyrene manufacturing techniques are based either on a suspension process if the material is to be foamed or on a bulk polymerization process for GPPS and IPS. ABS-type polymers can also be produced via emulsion polymerization. Figure 2.5 shows the differences in emulsion and mass polymerization processes and the resulting morphology. Typically,... 

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. 

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... 

Considering the process constraints in Table I, the design of a melt-bulk polymerization process (8) must take four factors into account ... 

PVC is insoluble in VCM. The precipitated polymer tends to coagulate in the conversion range of 1-8%. As the conversion continues, the precipitated polymer absorbs more and more monomer, and at a 15-20% conversion, the reactor contains solid polymer swollen with monomer in a monomer atmosphere. The horizontal autoclave prevents the formation of large polymer blocks by breaking them up. Advantages claimed for this process are the higher bulk density, improved particle size distribution, and more rapid plasticizer absorption. Talamini and coworkers (J ) have demonstrated that the bulk polymerization process is kinetically equivalent to suspension polymerization. 

NMR has also been used to study the degree of syndiotacticity in PVC as, for example, that prepared by the bulk polymerization process at temperatures ranging from -78 to 120 C. By the analytical techniques used, an atactic polymer would have a fraction of syndiotactic diads, 8 equal to a, the fraction of isotactic diads, or equal to 0.5. Polymer prepared at or near commercial temperatures had a syndiotactic diad fraction 8, equal to 0.51 to... 

Toyo Engineering Corp. (TOYO)/Mitsui Chemcials Inc. Polystyrene, high-impact (HIPS) Styrene monomer Continuous bulk polymerization process produces a wide range of HIPS with well-balanced mechanical properties and processability. Swing production feature also capable of producing GPPS 6 NA... 

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