Emulsion polymerizations batch

A typical recipe for batch emulsion polymerization is shown in Table 13. A reaction time of 7—8 h at 30°C is requited for 95—98% conversion. A latex is produced with an average particle diameter of 100—150 nm. Other modifying ingredients may be present, eg, other colloidal protective agents such as gelatin or carboxymethylcellulose, initiator activators such as redox types, chelates, plasticizers, stabilizers, and chain-transfer agents. 

Flexible batch. Both the formula and the processing instructions can change from batch to batch. Emulsion polymerization reactors are a good example of a flexible batch facility. The recipe for each produc t must detail Both the raw materials required and how conditions within the reac tor must be sequenced in order to make the desired product. 

Much has been written on RAFT polymerization under emulsion and miniemulsion conditions. Most work has focused on S polymerization,409-520 521 although polymerizations of BA,461 522 methacrylates382-409 and VAc471-472 have also been reported. The first communication on RAFT polymerization briefly mentioned the successful semi-batch emulsion polymerization of BMA with cumyl dithiobenzoate (175) to provide a polymer with a narrow molecular weight distribution.382 Additional examples and discussion of some of the important factors for successful use of RAFT polymerization in emulsion and miniemulsion were provided in a subsequent paper.409 Much research has shown that the success in RAFT emulsion polymerization depends strongly on the choice of RAFT agent and polymerization conditions.214-409-520027... 

Emulsion Polymerization. Emulsion polymerization uses soaps and anionic surfactants to create two-phase systems that have having long-term stability. The key steps in a batch emulsion polymerization are the following ... 

Batch crystallization, 8 130-134 Batch crystallizers, 23 464 Batch dechlorination, 21 672 Batch desilverizing, 14 751 Batch distillation, in hazardous waste management, 25 813-814 Batch dryer, 9 116 Batch dyeing fixation in, 9 213 machinery for, 9 205-211 Batch emulsion polymerization, of VDC, 25 722-724... 

Chabot et al. at Atofina Chemicals (King of Prussia, PA, USA) used in-line NIR to monitor monomer conversion in real time in a batch emulsion polymerization process. The business value of this monitoring... 

Figures 6, 7 and 8 show experimental verification of Eq.(40) in batch emulsion polymerization of styrene ( 14). The number of polymer particles was measured by electron micrscopy, not at finite but at 1 hour after the start of polymerization. Figure 6 represents the effect of lowering the initial monomer concentration, Mq on the number of polymer particles formed at fixed initial initiator and emulsifier concentrations. The number of polymer particles formed is constant even if M is lowered to the critical value Mc. This is because normal°condition that micelles disappear before the disappearance of monomer droplets is satisfied in the range of monomer concentration above Mc. The value of Mc can be calculated by the following equation obtained by equating XMc, the monomer conversion where micelles disappear, to XMc2, the monomer conversion where monomer droplets disappear.

Figure 5. Conversion representation for a BA/MMA (30/70 by weight) batch emulsion polymerization...

The latexes were prepared using a conventional semi-batch emulsion polymerization system modified for power-feed by the addition of a second monomer tank. Polymerization temperatures ranged from 30-85°C using either redox or thermal initiators. Samples were taken periodically during the polymerization and analyzed to determine residual monomer in order to assure a "starved-feed" condition. As used in this study this is a condition in which monomer feed rate and polymerization rate are identical and residual monomer levels are less than 5%. 

Figure 5. Example data acquisition for the batch emulsion polymerization of MM A at 40°C (initiator (ammonium persulphate) = 0.01 gmol/L H20 emulsifier (SLS) = 0.02 gmol/L H20 wt.ratio monomer /water = 0.43)...

The obtained weight average diameters can reasonably well follow the progress of the reaction as can be seen from Figure 6, where experimentally estimated weight average diameters are plotted with those theoretically predicted by a mathematical model for the batch emulsion polymerization of vinyl acetate.(6)... 

Chain transfer to monomer and to other small molecules leads to lower molecular weight products, but when polymerization occurs in the relative absence of monomer and other transfer agents, such as solvents, chain transfer to polymer becomes more important. As a result, toward the end of batch-suspension or batch-emulsion polymerization reactions, branched polymer chains tend to form. In suspension and emulsion processes where monomer is fed continuously, the products tend to be more branched than when polymerizations are carried out in the presence of a plentiful supply of monomer. 

In a batch emulsion polymerization of St, they found that the number of polymer particles produced increased when the amount of initially charged monomer was decreased below a critical value, M, as shown in Fig. 32, where the solid line shows the values predicted by... 

Fig. 32 Effect of lowering the initial monomer concentration on particle formation in the batch emulsion polymerization of St (Sq (NaLS)=6.25 g/dm -water, Iq (KPS)=1.25 g/dm -water, Mq (St)=variable 50 °C)...

In batch emulsion polymerizations all ingredients are present in the reactor at the start of the reaction and much more monomer is present than can be incorporated into the available micelles. When monomer is being added to an aqueous phase containing a surfactant, the onset of turbidity signals saturation of the micelles. About 99% of the monomer will be located initially in droplets with diameters in the range of 10 cm. There are typically some 10 soap covered droplets per milliliter of water. 

Fig. 3. Conversion and instantaneous heat generation lute for a lyincal isothennal batch emulsion polymerization.

Another mechanism for particle formation involves the scheme shown hi Fig. 7, but it occurs later in some batch polymerizations. This secondary nudeation is caused by free emulsifier which is liberated from the particle surface. Figure 9 shows some data of Gerrens for a batch emulsion polymerization of MMA. These data were successfully modeled by Ray and Min (1976). The population of smaller particles was formed late in the reaction because emulsifier was desorped because of the crowding of radical end groups on the surface and because of particle shrinkage caused by monomer conversion to polymer. 

An example of the use of the population balance method to predict reaction in particulate systems is presented in the work of Min and Ray (M16, M17). The authors developed a computational algorithm for a batch emulsion polymerization reactor. The model combines general balances, individual particle balances, and particle size distribution balances. The individual particle balances were formulated using the population balance... 

Most kinetic studies focus on batch emulsion polymerization. These studies enable estimation of important polymer properties. Only recently, the control of particle size and MWD described by population balance models has been achieved. The differences between emulsion polymerization and copolymerization... 

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