• For the process of BR, emulsion polymerisation is chosen. Emulsion polymerisation is an extremely important industrial process related to free radicals. With the help of emulsifier and mechanical stirring, the monomer is dispersed in water and then initiator is added to initiate monomer polymerization.
• It has the advantages of high reaction speed and high product molecular weight. Also, water is used as dispersing medium, which is beneficial for heat control. In addition, the system is still stable with a low viscosity while the convertion is high. 【10】The procedures are shown as the figure 6:

                                                         Figure 6.procedures of emulsion polymerization【11】

• The polymerization can either be a batch process or a continuous process. In batch mode, monomer, solvent and catalyst are charged to the reactor, heated to initiate the process, and then allowed to continue to completion. The polymer solution is then transferred to another vessel or process unit to remove the solvent.
• In continuous mode, monomer, solvent and catalyst are continuously fed into the bottom of the first of a series of reactors at a temperature suitable for polymerization. The polymerization progresses as the solution flows through the reactors and polymer solution is taken off at the top of the last reactor without stopping the process.
• The continuous process is the more economical. In both processes, the finished product is usually in the form of bales which weighs from 50 to 75 pounds each. 【12】The flow chart of the total devices are as the figure 7 shows.

                                                                                  Figure 7. device of the whole

Monomer: ButadieneFigure 8.

Emulsifier: The emulsifier is usually a surfactant with a hydrophilic part and hydrophobic (lipophilic) part, which can self-assemble into structures depending on the head to tail volume ratio driven by enthalpic and entropic contributions. It has a positive effect on surface tension reduction, interfacial tension reduction and solubility increases. For this reaction, ‘Soap of Fatty Acid : Soap of Disproportionated rosin acid = 1:1’ is used as emulsifier.

Initiatior: For water-soluble initiator, persulfate, V-50 and redox system are commonly used for initiation and free radical generation.

                                              Figure 9.

Chelating agent: Ethylene Diamine Tetraacetic Acid (EDTA)

                                              Figure 10.

Reaction medium: Since Ca²⁺ and Mg²⁺ can react with the emulsification agent to form insoluble salt leading to a decreasing emlusification process and reaction speed, deionized water is used as reaction medium to avoid raising latex viscosity.

Electrolyte: Sodium phosphate, sodium sulfate and potassium phosphate are added resulting  from the effect of reduced critical micelle concentration and decreasing latex viscosity.

Regulator: Since isopropylxanthic disulfide has a strong chain transfer capability, the molecular weight is markedly decrease when adding this agent. Thus, the molecular weight can be controlled by altering the quantity of molecular regulator.

Termination agent: When the conversion of monomer achieves 60 percent, hydroquinone is added as termination agent to avoid cross-linking reaction and increasing gel content.【13】