Cationic RAFT Polymerization Using ppm Concentrations of Organic Acid

Uchiyama, Mineto; Satoh, Kotaro; Kamigaito, Masami

doi:10.1002/anie.201410858

Cited by 179 publications

(198 citation statements)

References 36 publications

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“…This has been shown for radical polymerizations in the so-called RAFT (reversible addition-fragmentation chain-transfer) process 12 for ring-opening polymerizations in the 'immortal ring-opening polymerization' process 13 in coordinative chain-transfer polymerization 14,15 and, recently, in cationic RAFT polymerization 16 . In principle, any degenerative reversible chain-transfer polymerization requires only catalytic quantities of the propagating species as these are transferred quickly from one polymer chain to the next through a degenerative transfer and so simulate a quasi-simultaneous chain growth.…”

mentioning

confidence: 89%

Catalytic living ring-opening metathesis polymerization

Nagarkar

Kilbinger

2015

Nature Chem

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In living ring-opening metathesis polymerization (ROMP), a transition-metal-carbene complex polymerizes ring-strained olefins with very good control of the molecular weight of the resulting polymers. Because one molecule of the initiator is required for each polymer chain, however, this type of polymerization is expensive for widespread use. We have now designed a chain-transfer agent (CTA) capable of reducing the required amount of metal complex while still maintaining full control over the living polymerization process. This new method introduces a degenerative transfer process to ROMP. We demonstrate that substituted cyclohexene rings are good CTAs, and thereby preserve the 'living' character of the polymerization using catalytic quantities of the metal complex. The resulting polymers show characteristics of a living polymerization, namely narrow molecular-weight distribution, controlled molecular weights and block copolymer formation. This new technique provides access to well-defined polymers for industrial, biomedical and academic use at a fraction of the current costs and significantly reduced levels of residual ruthenium catalyst. In olefin metathesis reactions, olefinic bonds are rearranged with the help of a transition-metal catalyst 1,2 . In the early days following the discovery of this reaction, ill-defined catalysts 3 were used to carry out this transformation. After Herisson and Chauvin 4 had proposed a reaction mechanism, the olefin metathesis reaction was better understood and soon gained much popularity. Typical catalysts used for olefin metathesis reactions include those based on ruthenium (developed mainly by the Grubbs group 5 ), tungsten and molybdenum (developed mainly by the Schrock group 6 ). Owing to the low oxophilicity of ruthenium compared to those of molybdenum and tungsten, the ruthenium metathesis catalysts (commonly known as Grubbs' catalysts) are more tolerant towards many polar functional groups and residual impurities, as well as to water 7 . Therefore, these catalysts are the catalysts of choice in highly functional organic chemistry transformations as well as for the majority of metathesis polymerizations carried out today. Catalysts G1 (first generation) and G3 (third generation) are the most widely used ruthenium initiators for ring-opening metathesis polymerization (ROMP). In comparison to the G1 initiator, the third-generation catalyst G3 exhibits very fast initiation and propagation rates, and thereby gives polymers with very narrow dispersities and an excellent control over their molecular weights. Owing to its superior stability as well as the favourable polymerization kinetics, the third-generation Grubbs' catalyst G3 was used for this work. ROMP is a polymerization technique that uses the metathesis of cyclic olefins to synthesize linear polymers. Depending on the structure of the monomer, such polymerizations can be controlled perfectly to give polymers with a narrow molecular weight distribution and a controlled average molecular weight. Ring-strained monomers, li...

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confidence: 89%

Catalytic living ring-opening metathesis polymerization

Nagarkar

Kilbinger

2015

Nature Chem

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“…It also indicates the high stability of the thioether terminal even during the work-up procedures and MALDI-TOF-MS analysis unlike the thioester terminals obtained by the cationic RAFT polymerization of IBVE. 38 Upon increasing the concentration of TfOH, the acetal terminals originating from the methanol used for quenching the polymerization became visible in both the 1 H NMR and MALDI-TOF-MS spectra ( Figure 2B). A further increase of [TfOH] 0 makes these peaks larger ( Figure 2C).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…3 A relatively large C tr was obtained with 1 (C tr = 5.31, entry 3), which gave the narrowest MWD among the various thioethers examined, whereas it was lower than that with the trithiocarbonate RAFT agent (7; C tr = 7.68, entry 12) previously reported by us. 38,41 A similar oxygen ether or acetal compound (8) that is the adduct of methyl vinyl ether and methanol resulted in a higher molecular weight, a broader MWD (M w /M n ∼ 1.8), and, thus, a low constant (C tr = 1.55, entry 13). Thus, the sulfur atom is necessary for the effective degenerative chain-transfer process via the formation of the sulfonium intermediate.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Thioether-Mediated Degenerative Chain-Transfer Cationic Polymerization: A Simple Metal-Free System for Living Cationic Polymerization

2015

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Cationic degenerative chain-transfer polymerization of vinyl ethers and p-alkoxystyrenes was investigated using a series of thioethers as a reversible chain-transfer agent via the equilibrium between a growing carbocationic species and the resulting sulfonium intermediate in the presence of a small amount of triflic acid (TfOH) as a cationogen. The stable thioether, which was easily prepared from isobutyl vinyl ether (IBVE) and n-butanethiol, efficiently controls the molecular weight of the resulting poly(IBVE) up to M n ∼ 1 × 10 5 with narrow molecular weight distributions (MWDs) (M w /M n ∼ 1.2). Upon increasing the bulkiness of the alkyl substituents in the thiols (R−SH; R: n-Bu < s-Bu < t-Bu) or those in the monomers (CH 2 CHOR′, R′: ethyl < isobutyl < cyclohexyl), the MWDs became broader due to the slower formation of the sulfonium intermediate for the degenerative chain-transfer reaction. For pmethoxystyrene, thioethers derived from bulkier alkylthiols or more electron-rich thiophenols are more effective. A silylprotected difunctional dithioether produced telechelic polymers possessing hydroxyl groups at both chain ends and stable thiol linkers in the middle of the polymer chains. These polymers were subsequently used in chain-extension reactions in conjunction with diisocyanates and diols as chain extenders to be converted into high molecular weight polymers linked via urethane linkages. ■ INTRODUCTIONLiving polymerization is one of the most effective and useful methods for not only controlling the molecular weight of synthetic polymers but also enabling the synthesis of complex polymeric architectures such as block, end-functional, telechelic, and star polymers by design. 1 Recently, there has been great progress in controlled/living polymerization techniques, most of which are based on the transient reversible deactivation of the propagating chain end into a dormant species, and as such, IUPAC recommends the name reversible deactivation polymerization (RDP). 2 This class of polymerization has been most actively studied in radical polymerization systems and can be classified into at least three different mechanisms, 3 i.e., dissociation−combination, 4−7 atom transfer, 8−15 and degenerative chain transfer, 16−23 according to the kinetic treatments.The concept of RDP originates from several living ionic polymerizations 24−27 such as group transfer polymerization (GTP) of methacrylates 28,29 and living cationic polymerization of vinyl ethers and isobutene, 30−35 which were accomplished in the mid-1980s. Most living cationic polymerizations rely on a type of atom transfer mechanism, in which the dormant covalent bonds, such as carbon−halogen and carbon−oxygen ester bonds, are reversibly activated by Lewis acid catalysts into a carbocationic species (Scheme 1B). 30−35 The Lewis acid catalysts are generally metal halides with a few exceptions such as iodine, 34 while the dormant species is derived from a relatively weak protonic acid generating a nucleophilic counteranion that can form a covalent bond via an a...

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“…Kamigaito et al have recently reported another type of "switchable" transfer agent that allowed interconvertible polymerization of acrylates and vinyl ethers by both living cationic or radical polymerization, using a Lewis acid or azo initiator, respectively. 101,102 It is also worth noting that ab initio investigations have suggested the use of fluorine as the stabilizing Z group can afford CTAs that may also be capable of successfully mediating the polymerization of monomers with disparate reactivity. 103,104 However, to date, this possibility has been only rarely explored, perhaps as a result of the rather challenging synthesis required to obtain CTAs with fluorine Z groups.…”

Section: Monomer Class Specificity Of Raft Agentsmentioning

confidence: 99%

Expanding the Scope of RAFT Polymerization: Recent Advances and New Horizons

2015

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Reversible deactivation radical polymerization (RDRP) has revolutionized modern polymer chemistry over the past two decades, thus laying the groundwork for the synthesis of complex macromolecules and enabling the preparation of previously inaccessible materials. Reversible addition-fragmentation chain transfer (RAFT) polymerization has emerged as one of the most promising techniques because of its functional group tolerance, applicability to a wide range of vinyl monomers, and its nondemanding experimental conditions. However, despite the promise and clearly demonstrated utility of RAFT, limitations of the method sometimes still exist, including the occasional need for extended polymerization times, limited access to high molecular weight polymers, low "livingness" due to unavoidable radical termination events, etc. This Perspective focuses on recent advances that have been specifically designed to address many of these perceived limitations to reinforce the promise of RAFT for the synthesis of complex and well-defined polymers under facile conditions.

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Cationic RAFT Polymerization Using ppm Concentrations of Organic Acid

Cited by 179 publications

References 36 publications

Catalytic living ring-opening metathesis polymerization

Catalytic living ring-opening metathesis polymerization

Thioether-Mediated Degenerative Chain-Transfer Cationic Polymerization: A Simple Metal-Free System for Living Cationic Polymerization

Expanding the Scope of RAFT Polymerization: Recent Advances and New Horizons

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