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) > 10(4) mol-1 L, k(p)/k(tr) > 10(4), 1/k(t/tr) > 10(4)s (translated to < 10% of chains deactivated at t almost-equal-to 1000 s), which is related to a typical limit of the polymeric chain dimensions (DP almost-equal-to 100) and standard synthetic manipulations (almost-equal-to 15 min). New living cationic systems are discussed in detail with special emphasis on exchange phenomena.