Topological Control of Polymethylene

The lack of polyethylene samples with tailored architectures, controlled molecular weight, low PDI, and absence of branching defects has hmited a systematic study of the relationships between molecular structure and physical properties of polyethylene. Several notable exceptions include cyclic polyethylene that has been synthesized by ring-opening metathesis polymerization (ROMP) (PDI of 2) (Bielawski et al., 2002 Bielawski et al., 2003) and star, comb, H-shape and pom-pom polyethylenes, containing 17—25 ethyl branching defects per 1000 carbons, which were produced by anionic polymerization (Hadjichristidis et al., 2000). 

Postpolymerization modification of PM and the use of structurally novel borane initiators provide control of polymer topology and synthesis of novel PM architectures. Examples including three-arm star polymers, giant tube-like structures and macrocycles are illustrated below. 

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