Abstract
Living polymerization discovered by Professor Szwarc is well known to all chemists. Some of the living polymerizations involve dormancy, a process in which there is an equilibrium (or at least exchange) between two types of living polymers, namely active at the given moment and dormant at this moment and becoming active in the process of activation. These processes are at least equally important although less known. This mini review is devoted to these particular living polymerizations, mostly polymerizations by the Ring-Opening Polymerization mechanisms (ROP) compared with some selected close to living vinyl polymerizations (the most spectacular is Atom Transfer Radical Polymerization (ATRP)) involving dormancy. Cationic polymerization of tetrahydrofuran was the first one, based on equilibrium between oxonium ions (active) and covalent (esters) dormant species, i.e., temporarily inactive, and is described in detail. The other systems discussed are polymerization of oxazolines and cyclic esters as well as controlled radical and cationic polymerizations of vinyl monomers.
Highlights
Professor Michael (Michał in Polish) Szwarc’s contributions to the chemical science are related to polymers and to his discovery of living and dormant polymers [1].Dormant polymers, reversibly formed from the active ones, are at the basis of several living/controlled polymerizations described in the present paper.Professor Szwarc is well known for his work on the bond energy and on the electron transfer phenomena [2,3].In 1956, during discussion with Samuel Weissman on the electron transfer in aromatic compounds, Szwarc asked Weissman about styrene “Did you transfer electrons to styrene?” The answer he received was: “No use, it polymerizes” [4]
Even though the cationic polymerization of styrene initiated by perchloric acid (HClO4) does not have the importance of atom transfer radical Polymerization (ATRP), it has to be at least briefly mentioned, as it has triggered several further works involving dormant species
Even though the cationic polymerization of styrene initiated by perchloric acid (HClO4 )
Summary
Professor Michael (Michał in Polish) Szwarc’s contributions to the chemical science are related to polymers and to his discovery of living and (less known) dormant polymers [1]. The concept is based on the Szwarc’s observation that, in the anionic polymerization of styrene in the presence of anthracene, the temporarily active and inactive (dormant) species are formed reversibly [7] It will be shown in the present mini review that dormant polymers play a decisive role in understanding living-controlled processes such as ROP [8] and are a fundamental aspect of the controlled radical polymerizations [9,10,11,12]. Until the discovery of living polymers, steady state reactions (as described by Bodenstein [15]) resulted from an interplay of formation of chain carriers in the initiation reaction and their disappearance in the termination reaction by interaction of two chain carriers This principle is at the bases of the kinetics of the large number of chain reactions, including free radical polymerizations. Definition of these terms has been important from the semantic point of view and to allow researchers to look at their systems in a more careful manner and to elaborate such conditions for the studied processes that would conform them to these definitions, and, to better control of the studied systems
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