CHAPTER 3. Precise Synthesis of Polyethylene-based Star Polymers: From Anionic Polymerization to Polyhomologation

Low-density polyethylene (LDPE) is indispensable for many applications in our everyday life due to its low cost, excellent physical properties, and easy processability. The rheological behavior that leads to this enhanced processability of LDPE is attributed to the presence of long chain branching (LCB). The linear versions of PE, namely high-density PE (HDPE), and linear low-density PE (LLDPE) both possess superior physical properties but poor processability. Since industrial PEs are not well-defined, model PEs with different branched macromolecular architectures are needed to understand the behavior of the different forms of PE and to improve their properties. Among them, star polymers consisting of several linear chains linked together to a central junction point have attracted the attention of scientists because they constitute the simplest form of branching. In this chapter, the strategies leading to well-defined PE stars from the mature anionic polymerization of butadiene and hydrogenation to the recently discovered polyhomologation (C1 polymerization) of dimethylsulfoxonium methylylide methods are presented. The ring-opening metathesis polymerization (ROMP) of monocyclic alkenes followed by hydrogenation and the Pd-diimine catalyzed “ethylene” polymerization towards PE stars are also briefly reviewed.