New aspects of chain-length dependent termination

Olaj, Oskar Friedrich; Kornherr, Andreas; Vana, Philipp; Zoder, Monika; Zifferer, Gerhard

doi:10.1002/1521-3900(200206)182:1<15::aid-masy15>3.0.co;2-o

Cited by 24 publications

(38 citation statements)

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“…For STY the situation is largely the same, although admittedly the short-chain behavior is not as well studied experimentally: [6] α S • 0.5 and i c • 50, [15,16,20] , again in accord with expectation, [21] with oligomer diffusion coefficients, [48] and with measurements on methacrylates with more spherical pendant groups; [9,11] and α L • 0.16, [15,16,20,[44][45][46]49] as predicted by theory. [47] While all this amounts to a highly pleasing chapter of scientific work, unfortunately it does not easily lead to prediction of the overall termination rate coefficient, k t , as measured in the present work, because Equation (8) cannot yield a closed expression for k t .…”

Section: Introductionmentioning

confidence: 69%

“…[17] These values are very much in accord with theoretical expectations [21] and with measurements of oligomer diffusion coefficients. [41] For long ('L') chains there exists a wealth of data [6,17,24,[42][43][44][45][46] supporting the prediction of theory [47] that α L = 0.16. All these values are essentially the same for other n-alkyl methacrylates, [6,9,11] which strongly suggests a family-type behavior.…”

Section: Introductionmentioning

confidence: 74%

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Termination Rate Coefficients for Radical Homopolymerization of Methyl Methacrylate and Styrene at Low Conversion

Taylor

Berkel

Alghamdi

et al. 2010

Macro Chemistry & Physics

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A comprehensive and systematic study of overall termination rate coefficients, k t , in low-conversion radical (homo)polymerization of methyl methacrylate and styrene is presented. Values of k t were determined by gravimetric analysis of steady-state experiments, employing 2,2'-azoisobutyronitrile as initiator. The values delivered by this simple method were found to be in qualitative and quantitative agreement with those from more modern and sophisticated techniques for measuring k t . Accordingly, correlations for bulk, low-conversion k t as a function of temperature are given for each monomer. The effects of initiator concentration, c I , and temperature on bulk k t were studied in a controlled way for both monomers. Additionally, ethyl benzene was used as solvent in order to investigate rigorously the effect of monomer concentration, c M , on styrene k t . The trends found by these systematic studies were considered in the light of what is known about the chain-length dependence of 2 termination. Styrene's behavior was always found to be qualitatively in accord with expectation, although the variations of k t with c I and c M were not as strong as should be the case. However its activation energy, 15 kJ·mol -1 , is shown to be almost perfectly in agreement with theory. Methyl methacrylate, on the other hand, is recalcitrant in that its overall k t does not make manifest the chain-length dependent termination that has been directly measured by other techniques. Possible reasons for these discrepancies are discussed, as are reasons for the difference in values between k t for the two monomers. On the latter topic it is concluded likely that the chain-length dependence of termination at short chain lengths is primarily responsible for styrene having k t that is higher by a factor of about 3, with there also being a contribution that arises from styrene's slower propagation.

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Section: Introductionmentioning

confidence: 69%

Section: Introductionmentioning

confidence: 74%

Termination Rate Coefficients for Radical Homopolymerization of Methyl Methacrylate and Styrene at Low Conversion

Taylor

Berkel

Alghamdi

et al. 2010

Macro Chemistry & Physics

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“…Various experimental techniques may be used to investigate so-called chain-length-dependent termination (CLDT). The best of these are specially designed methods based on controlling the radical chain length either by laser single-pulse initiation [19][20][21] or by reversible additionfragmentation (chain-)transfer (RAFT) polymerization. [22] All going well these techniques induce a narrow size distribution of radicals whose degree of polymerization increases linearly with time or conversion respectively.…”

Section: Introductionmentioning

confidence: 99%

Chain‐Length‐Dependent Termination in Radical Polymerization of Acrylates

Barth

Buback

Russell

et al. 2011

Macro Chemistry & Physics

147

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SUMMARY:The technique of SP PLP EPR, which is single-pulse pulsed-laser polymerization (SP PLP) in conjunction with electron paramagnetic resonance (EPR) spectroscopy, is used to carry out a detailed investigation of secondary (chain-end) radical termination of acrylates. Measurements are performed on methyl acrylate, n-butyl acrylate and dodecyl acrylate in bulk and in toluene solution at -40 °C. The reason for the low temperature is to avoid formation of mid-chain radicals, a complicating factor that has imparted ambiguity to the results of previous studies of this nature. Consistent with these previous studies, composite-model behavior for chain-length-dependent termination rate, is found in this work. However, lower and more reasonable values of α s , the exponent for variation of k t i,i at short chain lengths, are found in the present study.

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“…As the pulsed laser polymerization [1][2][3][4][5][6][7][8] and related pseudostationary polymerization techniques [9][10][11][12] have already proven their usefulness for the direct determination of the kinetic constants for free radical polymerization the idea arose to search for an alternative experimental technique. The quenched instationary polymerization technique [13][14][15] was developed based on the same fundamental idea of counting the number of possible propagation steps that can occur within a given time span.…”

Section: Introductionmentioning

confidence: 99%

The quenched instationary polymerization system, 2. Derivation of the radical and polymer chain length distributions for an incomplete pre-effect

Schnöll‐Bitai¹

2000

Macromol. Theory Simul.

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New aspects of chain-length dependent termination

Cited by 24 publications

References 0 publications

Termination Rate Coefficients for Radical Homopolymerization of Methyl Methacrylate and Styrene at Low Conversion

Termination Rate Coefficients for Radical Homopolymerization of Methyl Methacrylate and Styrene at Low Conversion

Chain‐Length‐Dependent Termination in Radical Polymerization of Acrylates

The quenched instationary polymerization system, 2. Derivation of the radical and polymer chain length distributions for an incomplete pre-effect

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