Mutual Recipe

The original recipe adopted by the U.S. Government Synthetic Rubber Program was known as the "Mutual Recipe" and is shown iu Table 4. As can be seen, the reaction temperature was set at 50°C, which resulted iu 75% conversion to polymer iu about 12 h. The reaction was then stopped by addition of a "shortstop," such as 0.1 parts hydroquinone, which destroyed any residual catalyst (persulfate), and generated quiuone, which helped inhibit any further polymerisation. 

Second World War [the Mutual recipe consists of (by weight) 26% butadiene, ca. 9% styrene, ca. 63% water, ca. 1.7% soap, 0.17% dedecanethiol (added as a chain-transfer agent) and 0.1% potassium persulfate initiator]. 

Harkins calculated from the solubility of styrene in water (0.00368 mol dm at 50 °C [50]) that there are 4 x 10 molecules dm . In a 3% solution of potassium dodecanoate there are about 1 x 10 micelles dm , but with 61 molecules per micelle with an unswollen radius of 2.1 nm the cross-sectional area of the monomer-swollen micelles exceeds that of the styrene molecules by a factor of at least 12. Hence the micelles are more likely to capture initiator radicals produced in the aqueous phase. Polymerization within the micelles must be much faster than in the water because the concentration of styrene will be much the same as in bulk (8.5 mol dm ). The molar mass of the polystyrene produced is much larger than the molar mass of all the styrene molecules solubilized in a micelle thus, the monomer must be able to diffuse through the aqueous phase from other micelles and monomer droplets to allow the polymer radical to continue to grow until it is finally terminated by the entry of another initiator radical from the aqueous phase. Under the standard conditions of the mutual recipe (Table 4.1) there is 180 g water to 100 g styrene taking the emulsion droplets to have a radius of 1 pm, the ratio of the total cross-sectional areas of droplets to micelles to monomer molecules is about 1 30 2.5. The ratio of total surface areas would be even more heavily biased in favour of micelles. Hence it is probable that many more radicals will be captured from the aqueous phase by the micelles than by the emulsion droplets or than react with the monomer molecules in aqueous solution. 

The commercial preparation of styrene-butadiene rubbers is mainly by continuous emulsion polymerization. The following Mutual Recipe was used in the U.S.A. during the Second World War and is still the basis of current processes ... 

Affinity values have been used to interpret the important practical problem of mutual blocking effects in mixture recipes on nylon [128]. Typical values for some commercially... 

It consists of 15 different programs (most of them written in Turbo Prolog) that call each other mutually and of eight databases containing the data about the considered products and the standard values of the requirements. The user can build up a database containing his own requirements, sequence of operations and recipes. The system is fully flexible. At any time the user can inform himself about all the different topics and he can reset the relevant variables according to his own preferences and needs. The current process can be saved and restarted at any state. 

In emulsion polymerization, the rate of generation of free radicals is about lO Vm-s while the number of monomer-polymer particles for typical recipes, N, is in the range 10 to 10 particles/ml of the aqueous phase. Consequently, if all the initiator radicals are captured by the monomer-qxilymer particles, each particle will acquire, at the most, a radical every 1 to 100 s. It can be shown that if a particle contains two radicals, mutual annihilation of radical activity will occur within a time span of the order... 

Figure 4J Effect of vaiying emulsifier concentration in the mutual (GR-S) recipe (see Table 4.1). The numbers give the emulsifier concentration as percentage on monomer [89]...

Ihble 15.1 Mutual GR-S recipe for production of styrene-butadiene rubber by emulsion polymerization at SOX... 

---