Controlled/living polymerization definition

All CRP methods rely on a dynamic equihbration between tiny amounts of propagating radicals and various types of dormant species. The essence of the process is a rapid reversible deactivation of growing radicals. Radicals always terminate and therefore CRP is never living in the pure sense of the living polymerization definition. Indeed, lUPAC recommends to avoid using term Uving for the radical polymerization and suggests to use the term controlled reversible deactivation radical polymerization . 

Polymerization of vinyl ethers (VE) has been the subject of a considerable amount of theoretical studies. These monomers can be polymerized through radical initiation but the reaction is very slow and leads only to oligomers. Cationic polymerization initiated by a wide variety of Lewis acids is much more efficient and definitely preferred for homopolymer synthesis. Detailed theoretical aspects, and particularly recent developments concerning the controlled/living cationic polymerization of these monomers, have been discussed as well in previous exhaustive review [1,13,98,99] as in the present book (Chapters 4 and 5), and they will no longer be considered here. 

This review covers mainly the scientific literature that has appeared in relevant journals until early 2001 concerning the metal-catalyzed (or atom-transfer) living radical polymerization. The word living employed here simply refers to polymerizations that provide control over the molecular weights, the molecular weight distributions, and the chain end reactivity as do other living polymerizations. Its definition and use criteria, along with the word controlled , are still under discussion and have recently been discussed elsewhere.39 Thus, the discussion on the difference between these words is not to be treated here. 

In this and many other chapters in this volume as well as in other volumes of this comprehensive, expressions living polymerization and controlled polymerization are used. lUPAC and ACS definitions are given in Section 3.02.11. The expression controlled was not used in its present sense when the first edition of Comprehensive Polymer Science was published. In the past decades, there have been a number of discussions on what kind of a process could bear the corresponding names. 

The first demonstration of living polymerization and the current definition of the process can be attributed to Swarc. Living polymerization mechanisms offer polymers of controlled composition, architecture, and molecular weight distribution. They provide routes to low-dispersity end-functional polymers, to high-purity block copolymers, and to stars and other more complex architectures. Traditional methods of living polymerization are based on ionic, coordination, or group transfer mechanisms. 

More extensive discussion, however, is given in Reference 11, which also describes major criteria for botb living and controlled polymerizations. In addition to the lUPAC definitions, the AGS definitions are quoted bdow. In prindple, there is no difference between the viewpoints of these two groups of experts. 

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