Synthesis of Isotactic Poly(<i>N</i>-isopropylacrylamide) by RAFT Polymerization in the Presence of Lewis Acid

Ray, Biswajit; Isobe, Yutaka; Morioka, Kohei; Habaue, Shigeki; Okamoto, Yoshio; Kamigaito, Masami; Sawamoto, Mitsuo

doi:10.1021/ma0257595

Cited by 192 publications

(147 citation statements)

References 19 publications

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“…The increase in the isotacticity of the polymer is ascribed to the effective complexation of Y(OTf) 3 with the last two pendant amide groups of the propagating radical and the incoming monomer unit which in turn favors the meso-type addition of the Lewis acid-complexed NIPAM monomer. Similar observations have been reported for the polymerization of acrylamides, 15,16,18,19,22 methacrylamides, [16][17][18][19][20][21] and methacrylates 24 in the presence of bulky lanthanide triflate Lewis acids. The increase in the EBIB concentration from 10 mM to 30 mM (entries 3, 5 and 6) while keeping other conditions the same increases the polymer yield, decreases the molecular weight of the polymer, and increases the polydispersities.…”

Section: Effect Of Solventsupporting

confidence: 84%

See 1 more Smart Citation

Novel Initiating System for the Stereocontrolled Radical Polymerization of Acrylamides: Alkyl Bromide/Rare Earth Metal Triflate System

Ray

Isobe

Habaue

et al. 2004

Polym J

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ABSTRACT:A novel radical initiating system -rare-earth metal triflate [Y(OTf) 3 , Yb(OTf) 3 , Lu(OTf) 3 , Sc(OTf) 3 ] and alkyl halide containing -esters (ethyl 2-bromoisobutyrate and ethyl 2-bromopropionate) or -amide (N,N-dimethyl-2-bromo-2-methylpropanamide) was used for the stereocontrolled radical polymerization of N-isopropylacrylamide (NIPAM). The Lewis acids serve a dual role as the promoter of the radical initiation and the controller of the stereospecific polymerization. The effects of the Lewis acid type and concentration, the initiator type and concentration, solvents, and temperature on the polymerization of NIPAM have been reported. The chain-end structure of the resulting polymer was determined by 1 H NMR. We also extended this initiating system for the polymerization of 1 Recent progresses in controlled radical polymerization 2-5 have widened the scope of the radical initiators, one of which should be an initiating system consisting of an alkyl halide and a late transition metal complex of ruthenium, iron, copper, etc.3 In this system, the initiating radical is born from the alkyl halide due to the metal-mediated cleavage of the carbon-halogen bond. The organic halide is thus regarded as an initiator, which generates an initiating radical species, while the metal complex as a catalyst, which mediates the radical formation via the reversible one-electron redox reaction of the metal center. This transitionmetal catalyzed radical polymerization system originates from a similar metal-catalyzed radical addition reaction as already reported. 6 An alternative way for the generation of the radical species from an alkyl halide is to use a free radical initiator like AIBN and Et 3 B/O 2 together for the halogen abstraction.6 This combination is often employed for the organic synthesis of small and sometimes cyclic compounds in atom-transfer free radical addition. 6 Recent progress in this area concerns the addition of a Lewis acid such as metal triflates [M(OTf) n , M ¼ Sc, Yb, etc.] into the addition reaction between an -halo ester, nitrile, or amide and an olefin in the presence of Et 3 B/O 2 , where the added Lewis acid improves the reactivity of the slow atomtransfer reaction. [7][8][9][10][11][12] The improvement stems from the weakening of the C-Br bond due to the coordination of the Lewis acid to the carbonyl or the nitrile group of the -halo ester, nitrile, or amide compounds. 12-14This results in an increase in both the rate of the addition of the -carbonyl radical to the olefin and also the halogen abstraction by the resulting nucleophilic carbon radical.Quite recently, we have found that the metal triflates also dramatically accelerated the radical polymerization of acrylamides and other meth(acrylic) monomers with AIBN. [15][16][17][18][19][20][21][22] The Lewis acids further affected the stereochemistry of the polymers. Especially, for the acrylamides, highly isotactic polymers were obtained with rare-earth metal triflates. The increase in the rate and the stereoregularity is considered to...

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Section: Effect Of Solventsupporting

confidence: 84%

“…[15][16][17][18][19][20][21][22] The Lewis acids further affected the stereochemistry of the polymers. Especially, for the acrylamides, highly isotactic polymers were obtained with rare-earth metal triflates.…”

mentioning

confidence: 99%

Novel Initiating System for the Stereocontrolled Radical Polymerization of Acrylamides: Alkyl Bromide/Rare Earth Metal Triflate System

Ray

Isobe

Habaue

et al. 2004

Polym J

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“…Stereospecific living radical polymerizations of various monomers based on a combination of living and stereospecific radical polymerizations merizations was the RAFT polymerization of N-isopropylacrylamide in the presence of lanthanide triflate, such as Y(OTf) 3 and Yb(OTf) 3 . 34 The obtained poly(NIPAM) had controlled molecular weights and a high isotacticity; the number-average molecular weights (M n ) increased in direct proportion to monomer conversion and agreed well with the calculated values, assuming that one molecule of the RAFT agent generated one polymer chain, while maintaining the high meso contents (m ¼ 80-90%) throughout the polymerizations. This success is most probably due to the robust nature of the RAFT polymerization that can induce a fast interconversion without suffering any decomposition of the thioester group even in the presence of Y(OTf) 3 as well as the effective interaction of the Lewis acid with the polymer terminal and/or the incoming monomer for the isospecific chain growth even in the presence of the RAFT agent.…”

Section: Stereopsecific Living Radical Polymerization Combination Witsupporting

confidence: 77%

Stereospecific living radical polymerization for simultaneous control of molecular weight and tacticity

Kamigaito

Satoh

2006

J. Polym. Sci. A Polym. Chem.

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ABSTRACT:The simultaneous control of the molecular weights and the tacticity was attained even during radical polymerization by the judicious combinations of the living/ controlled radical polymerizations based on the fast interconversion between the dormant and active species, and the stereospecific radical polymerizations mediated by the added Lewis acids or polar solvents via the coordination to the monomer/polymer terminal substituents. This can be useful for various monomers including not only conjugated monomers, such as acrylamides and methacrylates, but also nonconjugated ones such as vinyl acetate and Nvinylpyrrolidone. Stereoblock polymers were easily obtained by the addition of the Lewis acids or by change of the solvents during the living radical polymerizations.

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“…RAFT polymerization can be conducted in the presence of Lewis acids.There are reports of attempted tacticity control of homopolymers [91,[168][169][170] (to enable the synthesis of stereoblock copolymers [171] ) and control of the alternating tendency for copolymerizations [172,173] through the use of Lewis acids as additives. For MMA polymerization, the addition of the Lewis acid scandium triflate, Sc(OTf) 3 , increases the fraction of isotactic triads and enhances the rate of polymerization in conventional radical [174] and RAFT processes.…”

Section: Reaction Conditions (Temperature Pressure Solvent Lewis Amentioning

confidence: 99%

Living Radical Polymerization by the RAFT Process

Moad¹,

Rizzardo²,

Thang³

2005

Aust. J. Chem.

2,146

1,894

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This paper presents a review of living radical polymerization achieved with thiocarbonylthio compounds [ZC( S)SR] by a mechanism of reversible addition-fragmentation chain transfer (RAFT). Since we first introduced the technique in 1998, the number of papers and patents on the RAFT process has increased exponentially as the technique has proved to be one of the most versatile for the provision of polymers of well defined architecture. The factors influencing the effectiveness of RAFT agents and outcome of RAFT polymerization are detailed. With this insight, guidelines are presented on how to conduct RAFT and choose RAFT agents to achieve particular structures. A survey is provided of the current scope and applications of the RAFT process in the synthesis of well defined homo-, gradient, diblock, triblock, and star polymers, as well as more complex architectures including microgels and polymer brushes.

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Synthesis of Isotactic Poly(N-isopropylacrylamide) by RAFT Polymerization in the Presence of Lewis Acid

Cited by 192 publications

References 19 publications

Novel Initiating System for the Stereocontrolled Radical Polymerization of Acrylamides: Alkyl Bromide/Rare Earth Metal Triflate System

Novel Initiating System for the Stereocontrolled Radical Polymerization of Acrylamides: Alkyl Bromide/Rare Earth Metal Triflate System

Stereospecific living radical polymerization for simultaneous control of molecular weight and tacticity

Living Radical Polymerization by the RAFT Process

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