Kinetic Analysis of “Living” Polymerization Processes Exhibiting Slow Equilibria. 6. Cationic Polymerization Involving Covalent Species, Ion Pairs, and Free Cations

Yan, Deyue; Dong, Hai; Peng, Ye; Müller, Axel H. E.

doi:10.1021/ma9508865

Cited by 17 publications

(13 citation statements)

References 9 publications

(20 reference statements)

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“…In that case α E also becomes concentration-dependent, which explains why the reaction order is higher than the expected value of 0.5. The mathematical treatment of a similar three-state system (cationic polymerization with covalent species, ions, and ion pairs) including MWD has been given elsewhere …”

Section: Resultsmentioning

confidence: 99%

Kinetic Investigation on Metal Free Anionic Polymerization of Methyl Methacrylate Using Tetraphenylphosphonium as the Counterion in Tetrahydrofuran

Baskaran

Müller

1997

Macromolecules

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The anionic polymerization of methyl methacrylate using tetraphenylphosphonium triphenylmethanide as an initiator proceeds in a living manner even at room temperature. The rate constants of propagation were measured between −20 and +20 °C using a flow tube reactor. At 0 °C the reaction half-lives range from 0.3 to 1 s. The polymerization follows first-order kinetics with respect to monomer conversion (with a short induction period) and shows a linear dependence of the number-average degree of polymerization on conversion with high initiator efficiencies and narrow molecular weight distributions (M w/M n < 1.1). The dependence of the measured rate constants on the active center concentration is consistent with the coexistence of ion pairs and free ions. The Arrhenius parameters obtained in the temperature range from −20 °C to +20 °C (activation energy, E a = 28 kJ mol-1 and frequency exponent, log A = 7.9) are similar to those for the Li+ cation. The determined rate constants for the ion pairs are 1−2 orders of magnitude smaller than those expected for such a large cation, indicating a large fraction of dormant species. NMR and quantum-mechanical studies of a model compound confirm the presence of a dormant ylide in equilibrium with a small amount of enolate ion pairs.

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Section: Resultsmentioning

confidence: 99%

Kinetic Investigation on Metal Free Anionic Polymerization of Methyl Methacrylate Using Tetraphenylphosphonium as the Counterion in Tetrahydrofuran

Baskaran

Müller

1997

Macromolecules

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“…The MWD averages and func-tion for a multistate mechanism were derived by Bo ¨hm 26,27 and the results were applied by Schulz et al 28 in order to determine the rate constants of exchange in the anionic polymerization of styrene in polar solvents. The MWD averages for the three-state mechanism of cationic polymerization were derived by Yan et al 29 An important result of both derivations is that the PDI can be expressed as the superposition of the PDI's calculated for the two two-state mechanisms involved: Since most real polymerizations are not living according to the strict definition, the extension to imperfect polymerizations is a necessary step. Litvinenko et al 30 calculated the PDI for transfer to solvent and spontaneous transfer in the presence of direct (bimolecular) activity exchange (degenerative transfer, Scheme 3).…”

Section: Discussionmentioning

confidence: 99%

General Kinetic Analysis and Comparison of Molecular Weight Distributions for Various Mechanisms of Activity Exchange in Living Polymerizations

1997

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The molecular weight distributions in many living (e.g. anionic, group transfer, cationic, and radical) polymerizations strongly depend on the dynamics of various equilibria between chain ends of different reactivity. A very important special case is equilibria between active and dormant centers. Various mechanisms including uni- and bimolecular isomerization (or activation/deactivation), aggregation, and direct bimolecular activity exchange (“degenerative transfer”) are discussed and compared. For all these mechanisms (and for both fast and slow monomer addition), the averages of the molecular weight distribution and the polydispersity index (DPI), P̄ w/P̄ n, are derived in a unified way. Their dependencies on three universal parameters are analyzed: (i) on the reactivity ratio of the two species, λ = k‘p/k*p, (ii) on the fraction of the more active species, α = P*/I 0, which is determined by the initial concentrations of reagents, and (iii) on a generalized exchange rate parameter, β, which quantifies the rate of exchange relative to that of propagation. The dependence of β on the initial concentrations of reagents is defined by the mechanism of exchange and can be used as a mechanistic criterion to distinguish between various possible mechanisms. For the typical case β > 1, the PDI decreases with monomer conversion, which is a common observation in many living polymerizations where 10 ≤ β ≤ 100 was determined. At full conversion, a simple relation, P̄ w/P̄ n ≈ 1 + ϑ/β, is valid, where ϑ depends on α and λ. For the common case where one species is dormant this simplifies further to P̄ w/P̄ n ≈ 1 + 1/β. Generally, the molecular weight distribution is narrower if monomer is added slowly.

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“…There were two characteristic peaks between 263 and 331 °C and 331 and 400 °C of PAA-AM/St, and the significant weight loss occurred at 316 °C and 342 °C, respectively (as shown in Figure 6). The weight loss between 263 and 331 °C corresponded to the collapse of the main structure of starch, while the weight loss between 331 and 400 °C was due to the collapse of the chain structure of PAA-AM copolymers [27,28]. The results show that the poly (acrylicacrylamide) chain was successfully grafted onto the starch structure.…”

Section: Thermal Stabilitymentioning

confidence: 89%

“…PDI is defined as the ratio of Mw to Mn [27]. Generally speaking, the larger the PDI value is, the wider the molecular weight distribution is, the smaller the PDI value is, the narrower the molecular weight distribution is [28]. The PDI values of starch and PAA-AM/St composite calculated from Table 1 are 1.06 and 1.07, respectively.…”

Section: Measurement Of Molecular Weightmentioning

confidence: 98%

Preparation of Poly(acrylic acid-acrylamide/starch) Composite and Its Adsorption Properties for Mercury (II)

et al. 2021

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The poly (acrylic acid-acrylamide/starch) composite was synthesized by solution polymerization, aiming to adsorb mercury (II) in water. The resulted copolymer was characterized by particle size exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), scanning electron microscopy (SEM) and dynamic light scattering particle size analyzer (DLS). It turned out that starch was successfully incorporated with the macromolecular polymer matrix and played a key role for improving the performance of the composites. These characterization results showed that the graft copolymer exhibited narrow molecular weight distribution, rough but uniform morphology, good thermal stability and narrow particle size distribution. The graft copolymer was used to remove Hg(II) ions from aqueous solution. The effects of contact time, pH value, initial mercury (II) concentration and temperature on the adsorption capacity of Hg(II) ions were researched. It was found that after 120 min of interaction, poly (acrylic acid-acrylamide/starch) composite achieved the maximum adsorption capacity of 19.23 mg·g−1 to Hg(II) ions with initial concentration of 15 mg·L−1, pH of 5.5 at 45 °C. Compared with other studies with the same purpose, the composites synthesized in this study present high adsorption properties for Hg(II) ion in dilute solution. The adsorption kinetics of Hg(II) on the poly (acrylic acid-acrylamide/starch) composite fits well with the pseudo second order model.

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Kinetic Analysis of “Living” Polymerization Processes Exhibiting Slow Equilibria. 6. Cationic Polymerization Involving Covalent Species, Ion Pairs, and Free Cations

Cited by 17 publications

References 9 publications

Kinetic Investigation on Metal Free Anionic Polymerization of Methyl Methacrylate Using Tetraphenylphosphonium as the Counterion in Tetrahydrofuran

Kinetic Investigation on Metal Free Anionic Polymerization of Methyl Methacrylate Using Tetraphenylphosphonium as the Counterion in Tetrahydrofuran

General Kinetic Analysis and Comparison of Molecular Weight Distributions for Various Mechanisms of Activity Exchange in Living Polymerizations

Preparation of Poly(acrylic acid-acrylamide/starch) Composite and Its Adsorption Properties for Mercury (II)

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