Comb Stars by the Convergent Approach

In a first set of experiments the CEVE polymerization was initiated using HCl/ZnCl2 as catalytic system in toluene at —20 °C and CDVE was added after complete conversion of CEVE. In these conditions the chain-coupling reaction is slow and incomplete, leading both to star-like PCEVE of broad molar mass distribution in admixture with a large amount of linear PCEVE chains (Table 21.5). 

The average number of arms of PCEVE stars calculated from the ratio star/M branch, determined by light scattering, was found to be strongly dependent on the amount and conditions of addition of CDVE and ranged from about 12 to 28 arms. 

In addition, a second star population with a maximum corresponding to objects with about 30-32 branches is also formed. This second set of objects in relatively low proportion can be attributed to core-to-core coupling during the synthesis of the PCEVE stars. These results illustrate the interest of AFM analysis to get a much more precise vision of both single and large population of complex macromolecules. 

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Scheme 21.5 Synthesis of a PS comb star by the convergent approach.

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