Block copolymer synthesis halogen exchange

In Figure 4 it is shown how halogen exchange in block copolymer synthesis influences the resulting molar mass distributions (82). 

For the synthesis of block copolymers, the reactivity of the macroinitiator has to be high enough to ensure fast reinitiation. However, the rate of reinitiation strongly depends on the halogen atom at the end of the macroinitiator. To maintain the controllability, a procedure for the halogen exchange has been developed [46]. The result of the formation of the second block also depends on the choice of the correct catalyst/ligand system. Hence, block formation has to be done in the correct order. For most systems, the catalyst complex as well as the solvent have to be tuned to fit the reactivity of the macroinitiator. 

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