The molecular weight as a function of temperature in heterogeneous radical‐initiated polymerization

Talamini, G.; Vidotto, G.

doi:10.1002/macp.1967.021000107

“…The slight preference for syndiotactic over isotactic placement is caused by steric and/or electrical repulsion between substituents in the chain, although at high temperatures their effects are progressively diminished, due to thermal motion. For example, the fraction of syndiotactic diads of poly(vinyl chloride) changes from 0.67 to 0.51 as the synthesis temperature increases from À78 C to 120 C [15]. For methyl methacrylate, it is 0.86 at À40 C and 0.64 at 250 C [16,17].…”

Section: Propagationmentioning

confidence: 99%

Polymerization Processes, 1. Fundamentals

Tobita

¹

2015

Ullmann's Encyclopedia of Industrial Chemistry

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The article contains sections titled: 1. Introduction 2. Polymerization Mechanisms and Kinetics 3. Kinetics of Step Polymerization 4. Basic Concepts of Molecular Mass Distribution 5. Chain Polymerization 6. Free‐Radical Polymerization 6.1. Elementary Reactions 6.1.1. Initiation 6.1.2. Propagation 6.1.3. Termination 6.1.4. Chain Transfer to Small Molecules 6.2. Kinetics of Free‐Radical Polymerization 6.2.1. Polymerization Rate 6.2.2. Molecular Mass Distribution 6.3. Effect of Temperature 7. Copolymerization 7.1. Copolymer Composition 7.2. Kinetics of Free‐Radical Copolymerization 8. Living Polymerization 8.1. Ideal Living Polymerization 8.2. Reversible‐Deactivation Radical Polymerization 8.2.1. Polymerization Rate 8.2.2. Molecular Mass Distribution 9. Polymers with Branches and Crosslinks 9.1. Crosslinked Polymers 9.2. Branched Polymers 9.3. Note on Nonlinear Polymerization

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“…Therefore, this polymerization proceeds, most probably, by a combination of competitive pathways that involves activation via SET mediated by nascent Cu 0 both in the initiation and propagation steps and by degenerative chain transfer (Scheme ). The resulting PVC obtained in water at 25 °C is free of structural defects, contains two active ∼CHClI chain ends, and has a higher syndiotacticity (62%) than the one obtained by free‐radical polymerization at the same temperature (56%) 57, 82–84. The synthetic process for the LRP of VC here will allow for the time access to the synthesis of PVC with a complex architecture85–88 and unprecedented properties.…”

Section: Discussionmentioning

confidence: 95%

DFT Calculations Suggest a New Type of Self‐Protection and Self‐Inhibition Mechanism in the Mammalian Heme Enzyme Myeloperoxidase: Nucleophilic Addition of a Functional Water rather than One‐Electron Reduction

Sicking

¹

,

Somnitz

²

,

Schmuck

³

2012

Chemistry A European J

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The mammalian heme enzyme myeloperoxidase (MPO) catalyzes the reaction of Cl(-) to the antimicrobial-effective molecule HOCl. During the catalytic cycle, a reactive intermediate "Compound I" (Cpd I) is generated. Cpd I has the ability to destroy the enzyme. Indeed, in the absence of any substrate, Cpd I decays with a half-life of 100 ms to an intermediate called Compound II (Cpd II), which is typically the one-electron reduced Cpd I. However, the nature of Cpd II, its spectroscopic properties, and the source of the additional electron are only poorly understood. On the basis of DFT and time-dependent (TD)-DFT quantum chemical calculations at the PBE0/6-31G* level, we propose an extended mechanism involving a new intermediate, which allows MPO to protect itself from self-oxidation or self-destruction during the catalytic cycle. Because of its similarity in electronic structure to Cpd II, we named this intermediate Cpd II'. However, the suggested mechanism and our proposed functional structure of Cpd II' are based on the hypothesis that the heme is reduced by charge separation caused by reaction with a water molecule, and not, as is normally assumed, by the transfer of an electron. In the course of this investigation, we found a second intermediate, the reduced enzyme, towards which the new mechanism is equally transferable. In analogy to Cpd II', we named it Fe(II'). The proposed new intermediates Cpd II' and Fe(II') allow the experimental findings, which have been well documented in the literature for decades but not so far understood, to be explained for the first time. These encompass a) the spontaneous decay of Cpd I, b) the unusual (chlorin-like) UV/Vis, circular dichroism (CD), and resonance Raman spectra, c) the inability of reduced MPO to bind CO, d) the fact that MPO-Cpd II reduces SCN(-) but not Cl(-), and e) the experimentally observed auto-oxidation/auto-reduction features of the enzyme. Our new mechanism is also transferable to cytochromes, and could well be viable for heme enzymes in general.

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“…Figure 8-9 shows the increase in the fraction of syndiotactic dyads, (r), of poly(vinyl chloride) from 0.51 to 0.67 as the reaction temperature decreases from 120 to À78 C [Talamini and Vidotto, 1967]. Corresponding data for methyl methacrylate show an increase in (r) from 0.64 at 250 C to 0.87 at À78 C [Fox and Schnecko, 1962;Isobe et al, 2000;Otsu et al, 1966].…”

Section: -3a Radical Polymerizationmentioning

confidence: 98%

“…AfterTalamini and Vidotto [1967] (by permission of Huthing and Wepf Verlag, Basel and Wiley-VCH, Weinheim).…”

mentioning

confidence: 99%

Stereochemistry of Polymerization

Odian

¹

2004

Principles of Polymerization

5

0

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Constitutional (formerly: structural) isomerism is encountered when polymers have the same overall chemical composition (i.e., same molecular formula) but differ in connectivitythe order in which the atoms are connected to each other. Polyacetaldehyde, poly(ethylene oxide), and poly(vinyl alcohol) are constitutional isomers. The first two polymers are CH CH 3 O C H 2 CH OH CH 2 CH 2 O n n Polyacetaldehyde Poly(ethylene oxide) Poly(vinyl alcohol) n obtained from isomeric monomers, acetaldehyde and ethylene oxide. The third is obtained by hydrolysis of poly(vinyl acetate) since vinyl alcohol does not exist (it is the enol form of acetaldehyde). Poly(methyl methacrylate) and poly(ethyl acrylate) are isomeric polymers CH 2 C CH 3 CO 2 CH 3 CH 2 CH CO 2 C 2 H 5 n n Poly (methyl methacrylate) Poly (ethyl acrylate) formed from isomeric monomers. Poly(E-caprolactam) and poly(hexamethylene adipamide) are isomeric even though the monomers are not isomeric. Similarly, the 1 : 1 copolymer of Principles of Polymerization, Fourth Edition.

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The molecular weight as a function of temperature in heterogeneous radical‐initiated polymerization

Cited by 52 publications

References 29 publications

Polymerization Processes, 1. Fundamentals

Polymerization Processes, 1. Fundamentals

DFT Calculations Suggest a New Type of Self‐Protection and Self‐Inhibition Mechanism in the Mammalian Heme Enzyme Myeloperoxidase: Nucleophilic Addition of a Functional Water rather than One‐Electron Reduction

Stereochemistry of Polymerization

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