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Molecular Weight Development (molecular + weight_development)

Distribution by Scientific Domains
Polymers and Materials Science100%

Selected Abstracts

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 PREDICIŽ 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,ˇ,mol,1. Fairly good agreement between model calculations and experimental data was obtained. [source]

Modeling of Polymerization Kinetics and Molecular Weight Development in the Microwave-Activated Nitroxide-Mediated Radical Polymerization of Styrene

MACROMOLECULAR REACTION ENGINEERING, Issue 2-3 2009
Jorge J. Hernández-Meza
Abstract Calculations of the polymerization rate and molecular weight development in the nitroxide-mediated radical polymerization (NMRP) of styrene (STY), using hydroxyl-TEMPO and dibenzoyl peroxide (BPO), and activated by microwave irradiation (MI), are presented. The calculations are based on a kinetic model developed in our group. Microwave activation is modeled by three approaches: microwave-activated production of free radicals from monomer molecules, microwave-enhanced thermal initiation, and microwave-enhanced dormant polymer activation. The results obtained are compared against experimental data from the literature. The first approach is the most adequate. The NMRP of STY using TEMPO, BPO, and conductive heating, and the NMRP of STY activated by MI, without initiator, are also analyzed as reference cases. [source]

Modeling of the Nitroxide-Mediated Radical Copolymerization of Styrene and Divinylbenzene

MACROMOLECULAR REACTION ENGINEERING, Issue 5-6 2009
Julio C. Hernández-Ortiz
Abstract A mathematical model for the copolymerization kinetics with crosslinking of vinyl/divinyl monomers in the presence of nitroxide controllers has been developed and validated using experimental data of TEMPO-mediated copolymerization of styrene (STY) and divinylbenzene (DVB). Polymerization rate, molecular weight development, gelation point, evolution of sol and gel weight fractions, crosslink density, and copolymer composition, as well as concentrations of the species participating in the reaction mechanism can be calculated with the model. Diffusion-controlled effects were assessed and found unimportant. The presence of nitroxide controllers seems to favor the production of more homogeneous polymer networks, but this effect decreases as the initial fraction of crosslinker is increased. [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 PREDICIŽ 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,ˇ,mol,1. Fairly good agreement between model calculations and experimental data was obtained. [source]

Modeling of Polymerization Kinetics and Molecular Weight Development in the Microwave-Activated Nitroxide-Mediated Radical Polymerization of Styrene

MACROMOLECULAR REACTION ENGINEERING, Issue 2-3 2009
Jorge J. Hernández-Meza
Abstract Calculations of the polymerization rate and molecular weight development in the nitroxide-mediated radical polymerization (NMRP) of styrene (STY), using hydroxyl-TEMPO and dibenzoyl peroxide (BPO), and activated by microwave irradiation (MI), are presented. The calculations are based on a kinetic model developed in our group. Microwave activation is modeled by three approaches: microwave-activated production of free radicals from monomer molecules, microwave-enhanced thermal initiation, and microwave-enhanced dormant polymer activation. The results obtained are compared against experimental data from the literature. The first approach is the most adequate. The NMRP of STY using TEMPO, BPO, and conductive heating, and the NMRP of STY activated by MI, without initiator, are also analyzed as reference cases. [source]

Simulation of Styrene Polymerization by Monomolecular and Bimolecular Nitroxide-Mediated Radical Processes over a Range of Reaction Conditions

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2007
Juliana Belincanta-Ximenes
Abstract Simulations of polymerization rate, molecular weight development and evolution of the concentrations of species participating in the reaction mechanism over a range of operating conditions, and a parameter sensitivity analysis showing the effects of temperature, activation/deactivation equilibrium constant and initial concentrations of controller and initiator (if present) on these variables are presented for the nitroxide-mediated radical polymerization of styrene. The simulations were performed with a computer program based on a detailed reaction mechanism. The simulated profiles of conversion, number average molecular weight (), and polydispersity agree well with experimental data. Previously unknown activation energies for reactions involved in the mechanism are estimated. The temperature dependence of the kinetic rate constants obtained in this study will be useful for future modeling and optimization studies. [source]