Chain Length Dependent Termination in Pulsed-Laser Polymerization. 9. The Influence of Solvent on the Rate Coefficient of Bimolecular Termination in the Polymerization of Styrene

Olaj, Oskar Friedrich; Zoder, Monika; Vana, Philipp

doi:10.1021/ma0012651

Cited by 24 publications

(21 citation statements)

References 29 publications

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“…This means that k t 1,1 will change, providing a second avenuei.e., in addition to c M -through which k t is altered (see Equation (10)). Further, solvent power will also change, which has been shown to bring about change in α, [60] also affecting k t .…”

Section: Variation Of K T With Monomer Concentrationmentioning

confidence: 99%

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: Variation Of K T With Monomer Concentrationmentioning

confidence: 99%

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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“…Considering all the experimental [2][3][4][5][6][7] and theoretical [12][13][14] evidence outlined above, one must conclude that for termination of long radicals e L % 0.16 (corresponding to the best data of Table 1), although we recognize that this value will depend somewhat on the monomer, temperature [24] and solvent quality. [25] Hence e L ¼ 0.16 will be used in the calculations of this paper.…”

Section: Homotermination Rate Coefficientsmentioning

confidence: 99%

“…Substituting this equation into Equation (25), then using Equation (2a) and (2b) for k t j, j , and then evaluating the integral, one obtains…”

Section: Steady State Solutionsmentioning

confidence: 99%

“…The simulation is then carried out for one further time period t d , and the results from this time period only are saved, as it corresponds most closely to the results of an actual PLP lasting hundreds or even thousands of laser pulses. The values of [D i ] from this single time period of pseudo-steady state polymerization are used to calculate DP n and DP w (Equation (19) and (20) [33,50,51] and used [3,4,24,25] the following two ways for obtaining a hk t i which is representative of the termination occurring in a PLP:…”

Section: Pulsed-laser Polymerization Simulationsmentioning

confidence: 99%

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Termination in Dilute‐Solution Free‐Radical Polymerization: A Composite Model

Smith

Russell

Heuts

2003

Macro Theory & Simulations

135

201

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Literature data are summarized for the chain‐length‐dependence of the termination rate coefficient in dilute solution free‐radical polymerizations. In essence such experiments have yielded two parameter values: the rate coefficient for termination between monomeric free radicals, k, and a power‐law exponent e quantifying how kt values decrease with increasing chain length. All indications are that the value e ≈ 0.16 in good solvent is accurate, however the values of k which have been deduced are considerably lower than well‐established values for small molecule radicals. This seeming impasse is resolved by putting forward a ‘composite’ model of termination: it is proposed that the value e ≈ 0.16 holds only for long chains, with e being higher for small chains – the value 0.5 is used in this paper, although it is not held to dogmatically. It is then investigated whether this model is consistent with experimental data. This is a non‐trivial task, because although the experiments themselves and the ways in which they are analyzed are elegant and not too complicated, the underlying theory is sophisticated, as is outlined. Simulations of steady‐state polymerization experiments are first of all carried out, and it is shown that the composite model of termination both recovers the e values which have been found and beautifully explains why these experiments considerably underestimate the true value of k. Simulations of pulsed‐laser polymerizations find the same, although not quite so strikingly. It is therefore concluded that our new termination model, which retains the virtue of simplicity and in which all parameter values are physically reasonable, is consistent with experimental data. Taking a wider view, it seems likely that the situation of the exponent e varying with chain length will not just be the case in dilute solution, but will be the norm for all conditions, which would give our model and our work a general relevance.Normalized chain length distributions from PLP simulations.imageNormalized chain length distributions from PLP simulations.

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“…of monomers [4] as well as a systematic investigation of copolymerization [5][6][7] systems and the influence of solvent [4,[8][9][10][11][12][13][14][15] on the kinetic constants. Two recent review articles [4,16] give an impressive survey of the relevant literature published on this subject.…”

Section: Introductionmentioning

confidence: 99%

Pseudostationary Pulsed Laser Polymerization: A Simple Method for the Direct Determination of Axial Dispersion as Occurring in Size Exclusion Chromatography

Kornherr¹,

Olaj²,

Schnöll‐Bitai³

et al. 2003

Macro Theory & Simulations

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Theoretical distribution curves were calculated for several values of pulse separation t0 and concentrations of initiating radicals ρ formed by each pulse for both types of termination (disproportionation and combination). The absolute and relative peak widths of the additional peaks for the number, molar mass, and hyperdistribution were determined and compared. In all cases, the peak widths of these different distributions became the same with increasing values of C = ktρt0 and/or L0 = kp[M]t0, with [M] = monomer concentration and kt and kp are the rate constants of termination and propagation, respectively. This is similar to the behavior of Poisson distributions if only the degrees of polymerization are fairly high (P̄n ≥ 50). The analogy is further supported by the finding that under the same conditions the peak widths themselves approach the theoretical ones for Poisson distributions. Thus, the fulfilment of these two criteria suggests that the various peaks in multimodal distributions should be treated in the same formal way as Poissonian peaks although they clearly originate from a superposition of adjacent Poissonian peaks of different amplitude and, on the whole have a peak width somewhat in excess of the theoretical one of true Poisson peaks of the same P̄n. The point of inflection can be used as a measure of L0 without reservation only if the first criterion is not fulfilled. The influence of axial dispersion on the location of the extrema was calculated by use of standard deviations σad,k (0.05 and 0.025) to give “experimental curves” for which a pronounced increase in the absolute and relative peak widths was observed. Based on an assumed additivity of the peak variances, a simple procedure was tested for the direct determination of σad,k. The accuracy increased with increasing peak chain lengths and C values for those values determined from the first peak. The values determined from the second peak in the chain length region between 400–700 were closest to the input value.The points of inflection on the low and high molecular weight side of the additional first three peaks are given as a function of the peak maximum. The lower and upper lines were calculated with Equation (11) and (12), respectively.imageThe points of inflection on the low and high molecular weight side of the additional first three peaks are given as a function of the peak maximum. The lower and upper lines were calculated with Equation (11) and (12), respectively.

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Chain Length Dependent Termination in Pulsed-Laser Polymerization. 9. The Influence of Solvent on the Rate Coefficient of Bimolecular Termination in the Polymerization of Styrene

Cited by 24 publications

References 29 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

Termination in Dilute‐Solution Free‐Radical Polymerization: A Composite Model

Pseudostationary Pulsed Laser Polymerization: A Simple Method for the Direct Determination of Axial Dispersion as Occurring in Size Exclusion Chromatography

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