Criteria for living systems with a special emphasis on living cationic polymerization of alkenes

A number of new living systems have been reported in recent years. Classic anionic polymerization of nonpolar monomers allows the synthesis of well-defined high molecular weight polymers (DP > 1000), block copolymers, chains with perfect terminal functionalities and behaves as a true living system. Some new systems abuse the term “living polymerization.” A relatively modest criterion for living systems is proposed “3 X 10,000,” i.e., k_p/k_t > 10⁴ mol^-1 L, k_p/k_tr > 10⁴, 1/k_t/tr > 10⁴ s (translated to < 10% of chains deactivated at t ≈ 1000 s), which is related to a typical limit of the polymeric chain dimensions (DP ≈ 100) and standard synthetic manipulations (≈ 15 min). New living cationic systems are discussed in detail with special emphasis on exchange phenomena. © 1993 John Wiley & Sons, Inc.