Dormant Polymers and Their Role in Living and Controlled Polymerizations; Influence on Polymer Chemistry, Particularly on the Ring Opening Polymerization

Abstract

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.

Activated Monomer Mechanism (AMM) in Cationic Ring-Opening Polymerization. The Origin of the AMM and Further Development in Polymerization of Cyclic Esters

“…4 Nevertheless, the term "immortal" is still used in CROP by some authors, not mentioning the IUPAC terminology. 26 According to the IUPAC definition, the reversible chain deactivation, as the original source of the "immortal" process, provides temporarily dormant polymers, e.g., −CH 2 X shown below, and preserves the ability to grow and therefore the livingness 27 (eq 1). The term activated monomer was defined by IUPAC as: 4 reactive species generated reversibly from a monomer.…”

Living Cationic Ring-Opening Homo- and Copolymerization of Cyclohexene Oxide by “Dormant” Species Generation Using Cyclic Ethers as Lewis Basic Additives

“…After the initial development of living anionic polymerization of styrene by Szwarc in 1956, living polymerization of various monomers has been achieved. Living polymerization mediated by inherently stable propagating species, such as a carbanion derived from styrene and an oxonium ion derived from tetrahydrofuran (THF), − was achieved through the efficient generation of initiating species and rigorous removal of impurities such as adventitious water because side reactions such as chain transfer and spontaneous termination are negligible at the stable propagating ends. However, in the cationic and radical polymerization of vinyl monomers, side reactions originating from the active, unstable propagating species need to be suppressed to achieve living polymerization.…”

“…They are mainly classified into three categories: a dissociation-combination mechanism, atom transfer mechanism, and degenerative chain transfer mechanism, which correspond to nitroxide-mediated polymerization, atom transfer radical polymerization, and reversible addition-fragmentation chain transfer polymerization, respectively, in radical polymerization. In cationic polymerization, living polymerization of vinyl monomers such as vinyl ethers, isobutene, and styrene derivatives has become feasible by using appropriate counteranions and additives. ,− …”

“…For example, polyethylene oxide, which is obtained by the ring-opening polymerization of ethylene oxide, is used in a very wide range of products, such as pharmaceuticals, cosmetics, skincare products, detergents, tablets, and food additives, , due to its amphiphilicity and biocompatibility. In the ring-opening polymerization of oxiranes, living polymerization occurs mainly by anionic or coordination mechanisms. ,− Various strategies have been devised to enable living polymerization of oxiranes. ,− In contrast, in the cationic polymerization of oxiranes, side reactions such as backbiting reactions frequently occur, which results in low-MW oligomers, − and living polymerization is usually difficult. The controlled polymerization of oxiranes by the activated monomer mechanism was developed; − however, problems remain, such as minimizing the monomer concentration and a very long polymerization time.…”

Synthesis of Bottlebrush Copolymers Using a Polypseudorotaxane Intermediate

“…Accordingly, the complexation could include other known host–guest pseudorotaxanes, for example, cyclodextrin-admantyl (and other hydrophobic guests), ,,,,, pillararene-aliphatic chains, aromatics, − and so on; note that these would produce systems without ionic charges. Finally, the brushes could be constructed using other approaches, for example, atom transfer radical polymerization, ,,,,,− reversible addition-fragmentation chain transfer polymerization (RAFT), ,,,− ring-opening polymerization (ROP), including ring-opening metathesis polymerization ,,,− and so on. Therefore, we believe that this approach represents a new, useful, and flexible paradigm for the synthesis of bottlebrush polymers.…”