C1 polymerization: a unique tool towards polyethylene-based complex macromolecular architectures
The recent developments in organoborane initiated C1 polymerization (chain grows by one atom at a time) of ylides open unique horizons towards well-defined/perfectly linear polymethylenes (equivalent to polyethylenes, PE) and PE-based complex macromolecular architectures. The general mechanism of C1 polymerization (polyhomologation) involves the formation of a Lewis complex between methylide (a monomer) and borane (an initiator), followed by migration/insertion of methylene into the initiator and after oxidation/hydrolysis to afford OH-terminated polyethylenes. This review summarizes efforts towards conventional and newly discovered borane-initiators and ylides (monomers), as well as a combination of polyhomologation with other polymerization methods. Initial efforts dealing with C3 polymerization and the synthesis of the first C1/C3 copolymers are also given. Finally, some thoughts for the future of these polymerizations are presented.