Direct ESR Detection of Free Radicals in the RAFT Polymerization of Styrene

Alberti, Angelo; Benaglia, Massimo; Laus, Michele; Macciantelli, Dante; Sparnacci, Katia

doi:10.1021/ma025713b

Cited by 39 publications

(49 citation statements)

References 23 publications

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“…The intermediates have been observed directly by EPR in RAFT polymerizations of styrene and acrylate esters and in model reactions with dithiobenzoate and dithiophosphonate RAFT agents. [112,[131][132][133][134][135][136] The intermediates 3 or 5 are not detectable during MMA polymerizations or in polymerizations with aliphatic dithioester, trithiocarbonate, xanthate, or dithiocarbamate RAFT agents. This is attributed to the greater rate of fragmentation and the correspondingly shorter lifetime of the adduct in these polymerizations.…”

Section: Evidence In Support Of the Raft Mechanismmentioning

confidence: 99%

Living Radical Polymerization by the RAFT Process

Moad¹,

Rizzardo²,

Thang³

2005

Aust. J. Chem.

2,150

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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Section: Evidence In Support Of the Raft Mechanismmentioning

confidence: 99%

Living Radical Polymerization by the RAFT Process

Moad¹,

Rizzardo²,

Thang³

2005

Aust. J. Chem.

2,150

1,894

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“…[2,3,5] The inclusion of chain-length dependence allows proper description of the initialization processes, but it omits the contribution of the very high intermediate radical concentration that the model predicts for RAFT-mediated reactions, which differs substantially from the experimentally observed values. [6][7][8] The possibility of these radicals being present as reversibly terminated species [9] is potentially a solution to this dilemma, but then the problem is closely related to the perceived flaw of the IRT model in that the concentrations of species that would be expected are such that experimental observation should be possible. In much the same fashion as the SF model, a number of groups have published data and explained their results using the IRT model.…”

Section: Introductionmentioning

confidence: 99%

A Mechanistic Interpretation of Initialization Processes in RAFT‐Mediated Polymerization

McLeary

Tonge

Klumperman

2006

Macromol. Rapid Commun.

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Summary: The presence of strong chain length selectivity behavior during initialization in the RAFT process is an experimental observation. The mechanistic underpinning of the observation is, however, open to interpretation. The rates and concentration profiles for the cyanoisopropyl‐dithiobenzoate‐mediated polymerization of styrene at 70 °C can be relatively well reproduced by either the slow fragmentation or intermediate radical termination models. The use of modeling that provides a fit to the data is an important tool, but should be considered as additional evidence in support of experimental data rather than as experimental evidence in and of itself.Comparison of the time dependencies of the concentrations of AD, AMD, and AM2D by PREDICI modeling for the cyanoisopropyl‐mediated polymerization of styrene at 70 °C generated by the IRT model (lines) versus experimental data.magnified imageComparison of the time dependencies of the concentrations of AD, AMD, and AM2D by PREDICI modeling for the cyanoisopropyl‐mediated polymerization of styrene at 70 °C generated by the IRT model (lines) versus experimental data.

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“…The computed value of conversion (ca. 10%) was lower than the experimental one [12]. Conversely, the optimized model reproduced very well the consumption of BnSC(S)P(O)(OEt) 2 (5; Fig.…”

mentioning

confidence: 62%

“…20%. We also found that the ESR-spectral pattern of the system changed drastically during the first hour, and the reproduction of the spectra at different times by assuming the simultaneous presence of variable amounts of the four radicals 6 -9 (see Scheme 3) allowed the determination of the time profiles of their concentration [12].…”

mentioning

confidence: 74%

“…The spectral parameters of the species contributing to the ESR signals had previously been determined [12] by generating the authentic radicals in benzene solution under steady-state conditions, i.e., 6 (PrSĊ (SBn)P(O)(OEt) 2 ; a P = 2.226 mT, a 2H = 0.250 mT, g = 2.0057 1 ) was obtained by photolyzing 5 and AIBN, 7 (BnSĊ (SBn)P(O)(OEt) 2 ; a P = 2.235 mT, a 4H = 0.168 mT, g = 2.0057 3 ) by heating 5 in the presence of dibenzylmercury, 8 (StSĊ (SBn)P(O)(OEt) 2 ; a P = 2.197 mT, a 2H = 0.229 mT, g = 2.0057 4 ) by photolysis of 5 in the presence of polystyryl bromide (PhCH 2 A C H T U N G T R E N N U N G St 11 A C H T U N G T R E N N U N G Br, PDI = 1.096) and hexabutyldistannane, while 9 (StSĊ (SSt)P(O)(OEt) 2 ; a P = 2.172 mT, g = 2.0058 5 ) was obtained in a similar fashion by replacing 5 with a poly-…”

mentioning

confidence: 99%

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An ESR Approach to the Estimation of the Rate Constants of the Addition and Fragmentation Processes Involved in the RAFT Polymerization of Styrene

Alberti

Benaglia

Fischer

et al. 2006

Helvetica Chimica Acta

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Dedicated to the memory of Emeritus Professor Dr. Hanns FischerThe reversible-addition-fragmentation chain transfer (RAFT) controlled radical polymerization of such vinylic monomers as styrene (= ethenylbenzene) has gained increasing popularity in current years. While there is a general agreement on the mechanism of RAFT polymerization, there is an ongoing debate about the values of the rate constants of its key steps, i.e., the addition of the propagating radicals to the mediator and the fragmentation of the resulting spin adducts. By carrying out an ESR spectroscopic investigation of the AIBN-initiated polymerization of styrene (AIBN = 2,2'-azobis[2-methylpropanenitrile]), mediated by benzyl (diethoxyphosphoryl)dithioformate (5) as RAFT agent, we were able to detect and characterize four different radical species involved in the process. By reproducing their concentration-time profiles through a kinetic model, the addition and fragmentation rate constants at 908 of the propagating radicals to and from the mediator were estimated to be ca.10 , respectively. The validity of the kinetic model was supported by hybrid meta DFT calculations with the BB1K functional that predicted addition-and fragmentation-rate-constant values in good agreement with those estimated from the ESR experiments.

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Direct ESR Detection of Free Radicals in the RAFT Polymerization of Styrene

Cited by 39 publications

References 23 publications

Living Radical Polymerization by the RAFT Process

Living Radical Polymerization by the RAFT Process

A Mechanistic Interpretation of Initialization Processes in RAFT‐Mediated Polymerization

An ESR Approach to the Estimation of the Rate Constants of the Addition and Fragmentation Processes Involved in the RAFT Polymerization of Styrene

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