Living cationic polymerization

The basic reaction steps are: Living cationic polymerization is characterised by defined and controlled initiation and propagation while minimizing side-reactions termination and chain transfer.

Solution methods require rigorous purification of monomer and solvent although conditions are not as strict as in anionic polymerization.

The active electrophile is then a proton and the counter ion the remaining alkoxide which is stabilized by the Lewis acid.

Electron donors (e.g. nucleophiles, Lewis bases) for example dimethylsulfide and dimethylsulfoxide are believed to stabilize the carbocation.

The method was developed starting in the 1970s and 1980s with contributions from Higashimura on the polymerization of p-methoxystyrene using iodine or acetyl perchlorate,[3] on the polymerization of isobutyl vinyl ether by iodine [4] and with Mitsuo Sawamoto by iodine/HI[5] and on the formation of p-methoxystyrene - isobutyl vinyl ether block copolymers.

[6] Kennedy and Faust studied methylstyrene / boron trichloride polymerization (then called quasi-living) in 1982 [7] and that of isobutylene (system with cumyl acetate, 2,4,4-trimethylpentane-2-acetate and BCl3) in 1984 [8][9] Around same time Kennedy and Mishra discovered very efficient living polymerization of isobutylene (system with Tertiary Alkyl (or Aryl) Methyl Ether and BCl3)[[10] that paved the way for rapid development of macromolecularly engineered polymers.

In Living cationic ring-opening polymerization the monomer is a heterocycle such as an epoxide, THF, an oxazoline or an aziridine such as t-butylaziridine.

Living polymerization is more difficult to achieve because of the ease of termination by nucleophilic attack of a heteroatom in the growing polymer chain.