Method changes cross-coupling

Terminal ring functionalization has been explored as a route to block copolymer synthesis. The Stille coupling approach affords Br and RsSn termini on an isolable product. Iraqi and Barker isolated a low-A/ fraction (DP 14) then homo-cross-coupled to increase Af (DP ra 28), thus demonstrating telechelic utility [43]. The nature of the nickel-initiated cross-coupling polymerization (GRIM method) allows chain extension from the quasi-living end until the reaction is terminated. Controlled blocks of HT-PHT with HT-PDDT were prepared by changing the monomer [63]. 

Br > OTf Cl. Thus, sequential cross-coupling of halotriflates provides unsymmetrical terphenyls when two leaving groups with different reactivity are selected. An alternative method is a stepwise, double crosscoupling of halophenol derivatives (Eq. 40). However, care must be taken because the phosphine ligand changes the order of reactivity... 

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