Composition drift in emulsion co- and terpolymerisation

A special aspect of (emulsion) copolymerisation compared to (emulsion) homopolymerisation is the occurrence of composition drift. In combination with the instantaneous heterogeneity (statistical broadening around the average chemical composition), this phenomenon is responsible for the chemical heterogeneity of the copolymers formed. Composition drift is a consequence of the difference between instantaneous copolymer composition and overall monomer feed composition. This difference is determined by (a) the reactivity ratios of the monomers (kinetics) and (b) the monomer ratio in the main loci of polymerisation (viz., latex particles) that can differ from the overall monomer ratio of the feed (as added according to the recipe), which in turn is caused by monomer 

In order to be able to describe and control an emulsion copolymerisation, both the reactivity ratios and monomer partitioning have to be known. 

Ternary emulsion copolymerisation. In the fundamental investigations described in literature dealing with emulsion copolymerisation most attention has been given to binary copolymerisation, that is, polymerisation of two monomers. Far less attention has been paid to ternary emulsion copolymerisation (three monomers), that is, terpolymerisation. Emulsion terpolymerisation investigations, mostly dealing with properties and applications, have been published mainly in the patent literature. 

It is obvious that the typical aspects that distinguish emulsion copolymerisation from homopolymerisation, for example, monomer partitioning, dependence of kinetics on the local monomer concentration ratio etc., become much more complex when three monomers are involved, not to mention the complications in terpolymer analysis. 

However, since it can easilybe understood that using three monomers gives the possibility to obtain an even larger variety and refinement of copolymer properties, there is considerable research on emulsion terpolymerisation, although it is to be expected that there will be little or no fundamental mechanistic differences between binary and ternary emulsion copolymerisation systems. 

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