Desorption of Free Radicals in Emulsion Homopolymerization Systems

1 Desorption of Free Radicals in Emulsion Homopolymerization Systems 

Based on the above-mentioned free radical desorption mechanism, the research groups of Ugelstad [8-10] and Nomura [11, 33, 47] independently derived the following relationship for the desorption rate constant (/Cdes)  

A number of studies endeavored to experimentally determine the values of the desorption rate constant. It is also interesting to note that Lee and Poehlein [46,48,49] modified the approach of Ugelstad et al. [8,9] and applied it to emulsion polymerization carried out in a single continuous stirred tank reactor (CSTR) system. The resultant latex particle size distribution data were then used to determine the value of A des. The k data obtained from other literature are summarized in Table 4.4. Significant variations in the values of k isi for the emulsion polymerizations of styrene at 60 °C are observed. 

Reabsorption of the desorbed free radicals by the latex particles may contribute to the emulsion polymerization kinetics, as proposed by Ugelstad and Hansen [19], According to Gilbert [55], the overall rate of absorption of free radicals by the latex particles (pa) can be written as 

Asua et al. [56-58] also derived a mechanistic model for predicting the desorption rate coefficient, which considers several possible chemical reactions for the desorbed free radicals in the continuous aqueous phase and the competitive free radical desorption and bimolecular termination reaction in the latex particles containing more than one free radical. Some other representative publications related to the free radical desorption process can be found in references 59-61. 

---