Styrene suspension polymerization, using

Santos et al. [55, 148] studied the styrene suspension polymerization using NIRS. A dispersive NIR instrument equipped with a transflectance probe was used to monitor the reaction course and very good PLS calibration models were developed for the final average particle sizes. Calibration models were then used as references for the implementation of an in-line procedure for control of average... 

FIGURE 6.12 Proposed scheme for control of average particle sizes in free-radical snspension polymerizations. This material is reproduced with permission of John Wiley Sons, Inc. from Santos AF, Lima EL, Pinto JC. Control and design of average particle size in styrene suspension polymerization using NIRS. J Appl Polym Sci 2000 77 453 62. 2000 John Wiley Sons, Inc. 

Santos AF, Lima EL, Pinto JC. In-line evaluation of average particle size in styrene suspension polymerizations using near-infrared spectroscopy. J Appl Polym Sci 1998 70 1737-1745. 

One can view th e monoliths as a single big porous particle. Thus, some of the preparation procedures use similar ingredients as the procedures used to make tnacroporous particles by suspension polymerization. Consequently, the structures of the monoliths are similar to the pore structure of macroporous particles, as can easily be seen by electron microscopy. Also similar chemistries are available, including styrene- ivinylbenzene and methacrylates, which have been proven to form sufBciently rigid structures to be useful in HPLC. But the tedmology of the formation of the monoliths is less constrained than the suspension polymerization used to form particles, and thus a broader range of chemistries is available. The classic monoliths were based on polyurethanes (20). Recently, silica-based monoliths were formed in a capillary (24). 

To form a dispersion, the monomer must be quite insoluble in the suspension system. To decrease the solubility and to sometimes also increase the particle size of the resultant polymer bead, partially polymerized monomers or prepolymers may be used. Optimum results are obtained with initiators that are soluble in the monomer. Often, no differences in rates are observed between polymerization in bulk and suspension. Kinetic studies of styrene suspension polymerization have shown that all the reaction steps, initiation, propagation, and termination, occur inside the particles. ... 

Pickering stabilizers, commonly used in styrene suspension polymerization, are inorganic solids, insoluble in the aqueous phase. Their main advantage is that they can be removed easily from the final particulate product (e.g., by dilute acid), which improves the clarity and transparency of the polymer. Also, the amount of polymer deposited on the wall and on other parts of the reactor decreases, which considerably improves the heat transfer rate from the reaction medium to the coolant. Finally, it should be mentioned that inorganic powders are usually cheaper [5]. 

Commercial styrene-acrylonitrile copolymers (SAN) generally contain 20-30% acrylonitrile. They are random amorphous copolymers and are produced by bulk or suspension polymerization using techniques similar to those described previously for the homopolymer (section 3.2.3). 

Styrene-based polymer supports are produced by o/w suspension polymerization of styrene and divinylbenzene. Suspension polymerization is usually carried out by using a monomer-soluble initiator such as benzoperoxide (BPO) or 2,2-azo-bis-isobutylnitrile (AIBN) at a temperature of 55-85°C (19). A relatively high initiator concentration of 1-5% (w/w) based on the monomer is used. The time required for complete monomer conversion must be determined by preliminary experiments and is usually between 5 and 20 h, depending on the initiator concentration, the temperature, and the exact composition of the monomer mixture (11-18). 

Because most widely used methods used to prepare classical styrene/divinylben-zene copolymers have always been based on suspension polymerization, it seemed logical that a series of porous PDVB gels using similar methodologies could be developed. In suspension polymerization, divinylbenzene is suspended as a dispersion of small droplets in a continuous phase of water and polymerized by classical free radical initiation. This process produces the spherical beads... 

When the polymer was prepared by the suspension polymerization technique, the product was crosslinked beads of unusually uniform size (see Fig. 16 for SEM picture of the beads) with hydrophobic surface characteristics. This shows that cardanyl acrylate/methacry-late can be used as comonomers-cum-cross-linking agents in vinyl polymerizations. This further gives rise to more opportunities to prepare polymer supports for synthesis particularly for experiments in solid-state peptide synthesis. Polymer supports based on activated acrylates have recently been reported to be useful in supported organic reactions, metal ion separation, etc. [198,199]. Copolymers are expected to give better performance and, hence, coplymers of CA and CM A with methyl methacrylate (MMA), styrene (St), and acrylonitrile (AN) were prepared and characterized [196,197]. 

The key to the successful production of polystyrene is the reaction. The ratio of materials to be used is a compromise of the literature values, as was discussed in the section on the scope. All the authors discussing suspension polymerization say the reaction should be allowed to go to completion. (Removing and recycling the unreacted styrene would be more expensive.) It will be assumed that this means 99.8% of the styrene is reacted, and that this can be accomplished by using an average of the temperatures and cycle times given in Table 2E-2. 

The Instantaneous values for the initiator efficiencies and the rate constants associated with the suspension polymerization of styrene using benzoyl peroxide have been determined from explicit equations based on the instantaneous polymer properties. The explicit equations for the rate parameters have been derived based on accepted reaction schemes and the standard kinetic assumptions (SSH and LCA). The instantaneous polymer properties have been obtained from the cummulative experimental values by proposing empirical models for the instantaneous properties and then fitting them to the cummulative experimental values. This has circumvented some of the problems associated with differenciating experimental data. The results obtained show that ... 

The most widely used type of resin is a copolymer of styrene and divinyl benzene produced in bead form by suspension polymerization in an aqueous medium. 

Figure 5.18 Styryl-functionalized chiral salen ligands used in the crosslinking radical suspension polymerization with styrene to generate Mn epoxidation catalysts [71].

The most important commercial processes for polyacrylonitrile (XLIII) are solution and suspension polymerizations. Almost all the products containing acrylonitrile are copolymers. Styrene-acrylonitrile (SAN) copolymers are useful as plastics (Sec. 6-8a). 

In suspension polymerization water is used as a diluent and as a heat transfer aid. Suspending agents such as starch and melhylcellulose are used to keep the styrene monomer particles in suspension. The more efficient heat transfer of this process also allows for a narrower molecular weight distribution. 

Uses. The azobisnitriles have been used for bulk, solution, emulsion, and suspension polymerization of all of the common vinyl monomers, including ethylene, styrene vinyl chloride, vinyl acetate, acylonitrile, and methyl methacrylate. The polymerizations of unsaturated polyesters and copolymerizations of vinyl compounds also have been initiated by these compounds. 

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