Physical Transitions of Reaction Mixture During Polymerization

1 Physical Transitions of Reaction Mixture During Polymerization 

In a heterogeneous SPS polymerization at a typical reaction temperature (40-90 °C) with a silica-supported catalyst, the reaction mixture undergoes a series of physical changes as SPS particles precipitate out from the liquid phase. Initially, the total solid content (TSC) in the reaction mixture is very small and it is a clear liquid (Fig. 8.5a). 

The change in the slurry phase volume in SPS polymerization can be calculated using a simple mass balance model. We first consider a mass balance for the entire slurry phase  

At high initial monomer concentrations, the separate liquid phase disappears after about 15%-16% of TSC is reached. It is interesting to observe that even for the vastly different initial monomer concentrations, the liquid phase volume fraction decreases with the increase in the solid phase almost linearly. At lower monomer concentrations, the larger content of inert diluent (e.g., n-heptane) tends to give a slightly larger liquid phase volume fraction than at higher monomer concentration cases. 

It is clearly seen that original silica particles grow with the encapsulation of SPS by the polymerization and that the fuUy grown SPS particles maintain the shape characteristics of the original silica catalyst particles. It is an interesting result because as shown in Rgure 8.7c,d, the SPS particles show a fibrillar 

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