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Persistent Radical Effect (persistent + radical_effect)

Distribution by Scientific Domains

Polymers and Materials Science	50%

Selected Abstracts

Tin-Free Radical Alkoxyamine Addition and Isomerization Reactions by Using the Persistent Radical Effect: Variation of the Alkoxyamine Structure

CHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2005
Kian Molawi Dipl.-Chem.
Abstract Various C-centered radicals can efficiently be generated through thermal CO-bond homolysis of alkoxyamines. This method is used to perform environmentally benign radical cyclization and intermolecular addition reactions. These alkoxyamine isomerizations and intermolecular carboaminoxylations are mediated by the persistent radical effect (PRE). In the paper, the effect of the variation of the alkoxyamine structure,in particular steric effects in the nitroxide moiety,on the outcome of the PRE mediated radical reactions will be discussed. Fourteen different nitroxides were used in the studies. It will be shown that reaction times can be shortened about 100 times upon careful tuning of the alkoxyamine structure. Activation energies for the CO-bond homolysis of the various alkoxyamines are provided. The kinetic data are used to explain the reaction outcome of the PRE-mediated processes. [source]

Kinetic analysis of the cross reaction between dithioester and alkoxyamine by a Monte Carlo simulation,

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2007
Yong Ao
Abstract A model reaction of dithioester and alkoxyamine is proposed to probe the reversible addition,fragmentation chain transfer (RAFT) process. The kinetics of the model reaction is analyzed and compared with that of pure alkoxyamine homolysis with a Monte Carlo simulation. Although the pure alkoxyamine obeys the law of persistent radical effect, the model reaction results in higher concentration of the persistent radical during the main period of the reaction. However, for a very fast RAFT process or a very low addition rate constant, the time dependence of the persistent radical concentration is quite close to that of pure alkoxyamine. Furthermore, the cross termination between the intermediate and alkyl radicals causes a retardation effect for the model reaction when the intermediate is relatively long-lived. The Monte Carlo simulation indicates that it is feasible to measure the individual rate constants of the RAFT process, such as the rate constant of addition, with a large excess of alkoxyamine. In addition, the special feature of the system with different leaving groups in the alkoxyamine and dithioester is also discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 374,387, 2007 [source]

Kinetics and Molecular Weight Development of Dithiolactone-Mediated Radical Polymerization of Styrene

MACROMOLECULAR REACTION ENGINEERING, Issue 4 2009
Jesús Guillermo Soriano-Moro
Abstract Calculations of polymerization kinetics and molecular weight development in the dithiolactone-mediated polymerization of styrene at 60,°C, using 2,2,-azobisisobutyronitrile (AIBN) as initiator and , -phenyl- , -butirodithiolactone (DTL1) as controller, are presented. The calculations were based on a polymerization mechanism based on the persistent radical effect, considering reverse addition only, implemented in the PREDICI® commercial software. Kinetic rate constants for the reverse addition step were estimated. The equilibrium constant (K,=,kadd/k -add) fell into the range of 105,106 L,·,mol,1. Fairly good agreement between model calculations and experimental data was obtained. [source]