Implementation of emulsion polymerization

In a scenario of increasing international competition, margin reduction and public sensitivity to environmental issues, emulsion polymer producers are forced to achieve an efficient production of high-quality materials in a consistent, safe and environmentally friendly way [83]. Most emulsion polymers are produced in semicontinuous stirred-tank reactors. Therefore, this discussion is focussed on these reactors. 

Emulsion polymers are complex materials whose application properties are determined by many microstructural features. In what follows, methods for controlling some important microstructural features are discussed. 

Substituting Equations 6.60 and 6.61 into Equation 6.59, the monomer ratio needed to obtain the desired copolymer composition F is obtained  

In the presence of CTAs, chain transfer to CTA is the main chain-termination event and the instantaneous MWD has a number-average chain length given by  

Non-linear polymers are frequently characterized by their solubility in a given solvent. The insoluble part, which corresponds to high molecular weight heavily branched polymer and polymer networks, is called gel. In the polymerization of monofunctional monomers that form gel by intermolecular chain transfer to polymer followed by termination by combination (e.g., butyl acrylate), the addition of CTA may reduce the gel content to nil, whereas the sol MWD remains essentially unaffected [89]. 

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Commercial implementation of emulsion polymerization is mostly carried out in stirred-tank reactors operated semicontinuously. Continuous stirred-tank reactors (CSTRs) are used for the production of some high-tonnage emulsion polymers such as SBR. Batch processes are only used to polymerize monomers with similar reactivities and low heat generation rate (e.g., acrylic-fluorinated copolymers for textile apphcations). 

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