PEROXIDE CROSS-LINKING OF EPDMs HAVING HIGH FRACTIONS OF ETHYLENIC UNITS

ABSTRACT The considerable amount of research in the literature has practically allowed the elucidation of the mechanism of peroxide cross-linking of ethylene–propylene–diene–monomer rubber (EPDM), which occurs through a radical chain reaction initiated by the thermal decomposition of the peroxide molecule. According to this radical chain reaction, all types of labile hydrocarbon bonds (i.e., allylic, methynic, and methylenic CH bonds) would be exposed to alkoxy radicals and involved in the formation of the elastomeric network. However, for high fractions of ethylenic units (typically ≥60 mol.%), simple chemical kinetics and thermochemical analyses have shown that the radical attack would essentially occur on the methylenic CH bonds. Starting from this assertion, a simplified mechanistic scheme has been proposed for the three commercial EPDMs under study. The corresponding kinetic model, derived from this new scheme by using the basic concepts of the chemical kinetics, provides access to the changes in concentration of the main reactive chemical functions (against exposure time), among which are double bonds and changes in cross-linking density. The validity of these predictions has been eventually successfully verified by five distinct analytical techniques frequently used for studying the cross-linking of rubbers.

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Catalyst- and Silane- Controlled Enantioselective Hydrofunctionalization of Alkenes by Cobalt-Catalyzed Hydrogen Atom Transfer and Radical-Polar Crossover

10.26434/chemrxiv.9981395 ◽

2020 ◽

Author(s):

Kousuke Ebisawa ◽

Kana Izumi ◽

Yuka Ooka ◽

Hiroaki Kato ◽

Sayori Kanazawa ◽

...

Keyword(s):

Hydrogen Atom ◽

Absolute Configuration ◽

Kinetic Resolution ◽

Hydrogen Atom Transfer ◽

Biologically Active ◽

Atom Transfer ◽

High Concentration ◽

Chain Reaction ◽

Radical Chain ◽

Radical Chain Reaction

Catalytic enantioselective synthesis of tetrahydrofurans, which are found in the structures of many biologically active natural products, via a transition-metal catalyzed-hydrogen atom transfer (TM-HAT) and radical-polar crossover (RPC) mechanism is described herein. Hydroalkoxylation of non-conjugated alkenes proceeded efficiently with excellent enantioselectivity (up to 94% ee) using a suitable chiral cobalt catalyst, <i>N</i>-fluoro-2,4,6-collidinium tetrafluoroborate, and diethylsilane. Surprisingly, absolute configuration of the product was highly dependent on the steric hindrance of the silane. Slow addition of the silane, the dioxygen effect in the solvent, thermal dependency, and DFT calculation results supported the unprecedented scenario of two competing selective mechanisms. For the less-hindered diethylsilane, a high concentration of diffused carbon-centered radicals invoked diastereoenrichment of an alkylcobalt(III) intermediate by a radical chain reaction, which eventually determined the absolute configuration of the product. On the other hand, a more hindered silane resulted in less opportunity for radical chain reaction, instead facilitating enantioselective kinetic resolution during the late-stage nucleophilic displacement of the alkylcobalt(IV) intermediate.

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The reaction of thionitrites with barton esters: a convenient free radical chain reaction for decarboxylative nitrosation

Tetrahedron ◽

10.1016/s0040-4020(98)01164-8 ◽

1999 ◽

Vol 55 (12) ◽

pp. 3573-3584 ◽

Cited By ~ 16

Author(s):

Pierre Girard ◽

Nadine Guillot ◽

William B. Motherwell ◽

Robyn S. Hay-Motherwell ◽

Pierre Potier

Keyword(s):

Free Radical ◽

Chain Reaction ◽

Radical Chain ◽

Free Radical Chain Reaction ◽

Radical Chain Reaction

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ChemInform Abstract: A FREE-RADICAL CHAIN REACTION INVOLVING ELECTRON TRANSFER. THE REPLACEMENT OF THE NITRO GROUP BY HYDROGEN USING TRIALKYLTIN HYDRIDE, A VARIATION OF THE KORNBLUM REACTION

Chemischer Informationsdienst ◽

10.1002/chin.198127133 ◽

1981 ◽

Vol 12 (27) ◽

Author(s):

D. D. TANNER ◽

E. V. BLACKBURN ◽

G. E. DIAZ

Keyword(s):

Electron Transfer ◽

Free Radical ◽

Nitro Group ◽

Chain Reaction ◽

Radical Chain ◽

Kornblum Reaction ◽

Free Radical Chain Reaction ◽

Radical Chain Reaction

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Radical Chain Reaction of Alkene Molecule on H-terminated Si(100)-2×1 Surface

Acta Physico-Chimica Sinica ◽

10.3866/pku.whxb20080102 ◽

2008 ◽

Vol 24 (01) ◽

pp. 8-12

Author(s):

YAN Hui ◽

◽

YUAN Shi-Ling ◽

LIU Cheng-Bu

Keyword(s):

Chain Reaction ◽

Radical Chain ◽

Radical Chain Reaction

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Future Therapeutic Perspectives into the Alzheimer’s Disease Targeting the Oxidative Stress Hypothesis

Molecules ◽

10.3390/molecules24234410 ◽

2019 ◽

Vol 24 (23) ◽

pp. 4410 ◽

Cited By ~ 10

Author(s):

Jéssika P. Teixeira ◽

Alexandre A. de Castro ◽

Flávia V. Soares ◽

Elaine F. F. da Cunha ◽

Teodorico C. Ramalho

Keyword(s):

Oxidative Stress ◽

Alzheimer’S Disease ◽

Alzheimer's Disease ◽

Neuronal Cell ◽

The Elderly ◽

Oxygen Species ◽

Chain Reaction ◽

Radical Chain ◽

App Metabolism ◽

Radical Chain Reaction

Alzheimer’s disease (AD) is a neurodegenerative disease that is usually accompanied by aging, increasingly being the most common cause of dementia in the elderly. This disorder is characterized by the accumulation of beta amyloid plaques (Aβ) resulting from impaired amyloid precursor protein (APP) metabolism, together with the formation of neurofibrillary tangles and tau protein hyperphosphorylation. The exacerbated production of reactive oxygen species (ROS) triggers the process called oxidative stress, which increases neuronal cell abnormalities, most often followed by apoptosis, leading to cognitive dysfunction and dementia. In this context, the development of new therapies for the AD treatment is necessary. Antioxidants, for instance, are promising species for prevention and treatment because they are capable of disrupting the radical chain reaction, reducing the production of ROS. These species have also proven to be adjunctive to conventional treatments making them more effective. In this sense, several recently published works have focused their attention on oxidative stress and antioxidant species. Therefore, this review seeks to show the most relevant findings of these studies.

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