Reversible star assembly of polyolefins using interconversion between boroxine and boronic acid

Synthetic methods for star-shaped polyolefins have been strongly desired for a long time because they would show large differences in processability and surface properties compared to linear polyolefins. However, present reported synthetic methods are mostly limited to the synthesis of highly branched star polyethylenes and there have been no examples of reversible star assemblies. In this work, we have demonstrated the synthesis of boronic acid end-functionalized polyolefins by a living polymerization system and their reversible star assembly according to a boronic acid–boroxine interconversion. Multiple boron atoms were successfully incorporated onto the chain end of the polymer by the sequential addition of a boronic acid-containing olefin and the other monomer, and the reversible star assembly was confirmed by NMR and GPC measurement. The star poly(norbornene-co-1-octene) prepared by this method showed a highly elastic property, whereas the corresponding linear non-functionalized copolymer was a highly viscous material.