Zwitterionic Polymerization

Abstract

A zwitterion conducts the polymerization as the key intermediate, which is formed by the reaction between neutral electrophile and nucleophile, or as the monomer itself, which is prepared and isolated before use. The latter case is known in a limited number of articles. On the other hand, a number of examples have been reported for the former case, which is categorized into the following three patterns: (1) Propagation takes place from one site of a zwitterion, accordingly, which is the initiating species to give homopolymer. There is a case that a cyclic polymer is produced by the backbiting. (2) A zwitterion is formed to activate a monomer and reacts with a neutral initiator as well as the same functional group at the polymer terminal for the propagation reaction. In these two patterns, amine, phosphine, or N ‐heterocyclic carbene work as the initiator and the activator, respectively. (3) No catalyst copolymerization takes place by the reactions between zeitterionic intermediates, which are produced by the combination of a nucleophilic monomer with an electrophilic monomer. The monomers that appear in these three patterns involve electron‐deficient and electron‐rich olefinic compounds including qiunone and allene, heterocumulenes such as isocyanate and carbon disulfide, and heterocyclic compounds such as lactone, oxirane, amino acid N ‐carboxyanhydride, cyclic imino ether, cyclic phosphite, and cyclic phophonite.

Experimental and Computational Studies on the Mechanism of Zwitterionic Ring-Opening Polymerization of δ-Valerolactone with N-Heterocyclic Carbenes

“…The intrinsic viscosities of the pVL's generated by NHC 1 relative to an independently prepared linear pVL were lower ([η] cyclic /[η] linear = 0.66), consistent with a cyclic topology. 6 As observed previously for the ZROP of lactide with NHC IMes, 12 the kinetics and evolution of molecular weight with time for the polymerization of VL with carbene 1 are consistent with a chain-growth polymerization that deviates significantly from living behavior. The molecular weights of the cyclic pVL increase with increasing conversion but are higher than predicted and exhibit no obvious correlation to the ratio of [VL] 0 /[NHC] 0 .…”

“…Zwitterionic 5,6 ring-opening polymerization (ZROP) 7 of lactones and other strained cyclic monomers 8,9 with N-heterocyclic carbenes (NHC), 10−13 amidine 14 (DBU = 1,8-diazabicyclo [5.4.0] undecen-7-ene), or pyridines 4,15 such as DMAP (4-dimethylaminopyridine) is a versatile strategy for generating cyclic macromolecules. The ZROP of lactide with the aryl-substituted NHC IMes (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) occurs within minutes at room temperature in tetrahydrofuran (THF) or toluene to generate cyclic poly(lactides).…”

“…Cyclic polymers exhibit intriguing properties − but are challenging synthetic targets due to the entropic constraints of coupling the chain ends of large linear molecules. Zwitterionic , ring-opening polymerization (ZROP) of lactones and other strained cyclic monomers , with N-heterocyclic carbenes (NHC), − amidine (DBU = 1,8-diazabicyclo[5.4.0] undecen-7-ene), or pyridines , such as DMAP (4-dimethylaminopyridine) is a versatile strategy for generating cyclic macromolecules. The ZROP of lactide with the aryl-substituted NHC IMes (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) occurs within minutes at room temperature in tetrahydrofuran (THF) or toluene to generate cyclic poly(lactides). , In contrast, the ring-opening polymerization of ε-caprolactone (CL) or δ-valerolactone (VL) requires the more nucleophilic alkyl-substituted carbenes 1 and 2 .…”

N-Heterocyclic Carbene-Catalyzed Ring Opening Polymerization of ε-Caprolactone with and without Alcohol Initiators: Insights from Theory and Experiment

“…One of the more noteworthy developments in recent years has been the discovery that cyclic polymers may be formed by the exclusion of the alcohol reagent from the reaction in a process known as zwitterionic ring-opening polymerization (ZROP). − Nucleophiles such as TBD, DBU, and NHCs ,− have been used to catalyze the ZROP of lactones, ,, lactides , and other cyclic monomers , to form cyclic polymers. Cyclic polymers are desirable targets since the cyclic architecture may bestow physical properties that are different from their linear analogues. − …”

Synthesis and Topological Trapping of Cyclic Poly(alkylene phosphates)

“…1,2 Nucleophiles can mediate the ring-opening polymerization of lactones or carbosiloxanes by a zwitterionic ring-opening polymerization mechanism to generate cyclic polyesters or cyclic poly-(carbosiloxanes) (Figure 1). 2,6,11 As part of our interest in extending zwitterionic 12,13 ring-opening polymerization with other classes of monomers 11 to generate cyclic polymers, 14−18 we report herein the zwitterionic ring-opening polymerization of cyclic phosphate monomers to macrocyclic poly(alkylene phosphates) and their entrapment in cross-linked hydrogels.…”