Assisted Devolatilization

An effective way to get below equilibrium is to replace the styrene in the vapor phase with something else [6]. Generally, it is preferred that the material in the 

Another technique to expedite the transport of the volatile components from the molten polymer is to increase the number and rate of bubbles formed [14], Techniques that have been used to increase the number of bubbles and their rate of formation (nucleation) are the addition of chemical nucleating agents [15] and ultrasound [16]. Nucleation of bubbles in the molten polymer can help expedite the achievement of equilibrium in conventional falling strand devolatilizers. However, this facilitation mechanism cannot get below equilibrium and thus has minimal value. 

Another situation effecting residual levels existing during PS devolatilization is polymer decomposition or unzipping, which limits the devolatilization temperature to 260 °C. If one tries to go to higher temperature to achieve a more favorable vapor-polymer equilibrium concentration, polymer decomposition begins to dominate. The rate of polymer decomposition can be affected by stabilizing the polymer by the addition of phenolic antioxidants, e.g. 2,6-di-tert-butyl-4-methylphenol [17]. Several Asahi patents indicate the superior 

4-Di -tert -amy l-6-[ 1 -(3,5-di -tert -amy 1-2-hydroxypheny l)ethy l]pheny 1 acrylate 

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Many techniques have also been developed to improve devolatilization efficiency, including steam stripping [114], second fluid-assisted devolatilization [115], supercritical fluid devolatilization [116], and a variety of specially designed... 

One of the key benefits of anionic PS is that it contains much lower levels of residual styrene monomer than free-radical PS (222). This is becanse free-radical polymerization processes only operate at 60-80% styrene conversion, while anionic processes operate at >99% styrene conversion. Removal of unreacted styrene monomer from free-radical PS is accomplished nsing continuous devolatilization at high temperature (220-260°C) and vacnnm. This process leaves about 200-800 ppm of styrene monomer in the product. Taking the styrene to a lower level requires special assisted devolatilization processes such as steam stripping (223). 

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