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Videos de Conceptos Relacionados

Fast Reactions01:27

Fast Reactions

Fast reactions occurring in times shorter than the time needed to mix reactants pose a unique challenge for investigation. In a liquid-phase continuous-flow system, reactants A and B are swiftly pushed into the mixing chamber, where mixing occurs within 1 ms. The reaction mixture then flows through an observation tube, and one measures light absorption to determine species concentrations at various points of the tube. This method is most appropriate when relatively large volumes of reactants...
Measuring Reaction Rates03:09

Measuring Reaction Rates

Polarimetry finds application in chemical kinetics to measure the concentration and reaction kinetics of optically active substances during a chemical reaction. Optically active substances have the capability of rotating the plane of polarization of linearly polarized light passing through them—a feature called optical rotation. Optical activity is attributed to the molecular structure of substances. Normal monochromatic light is unpolarized and possesses oscillations of the electrical field in...
Step-Growth Polymerization: Overview01:03

Step-Growth Polymerization: Overview

Step-growth or condensation polymerization is a stepwise reaction of bi or multifunctional monomers to form long-chain polymers. As all the monomers are reactive, most of the monomers are consumed at the early stages of the reaction to form small chains of reactive oligomers, which then combine to form long polymer chains in the late stages. Hence, the reaction has to proceed for a long time to achieve high molecular weight polymers.
Many natural and synthetic polymers are produced by...
Polymers02:34

Polymers

The word polymer is derived from the Greek words “poly” which means “many” and “mer” which means “parts”. Polymers are long chains of molecules composed of repeating units of smaller molecules, known as monomers. They either occur naturally, such as DNA and proteins, or can be constructed synthetically, like plastics. They have varied structural characteristics, such as linear chains, branched chains, or complex networks, that contribute to the properties that they exhibit. Additionally,...
Radical Chain-Growth Polymerization: Mechanism01:09

Radical Chain-Growth Polymerization: Mechanism

The radical chain-growth polymerization mechanism consists of three steps: initiation, propagation, and termination of polymerization. The polymerization initiates when a free radical generated from the radical initiator adds to the unsaturated bond in the monomer. The unpaired electron of the free radical and one π electron in the unsaturated bond creates a σ bond between the free radical and the monomer. As a result, the other π electron in the unsaturated bond converts this species into the...
Free-Radical Chain Reaction and Polymerization of Alkenes02:35

Free-Radical Chain Reaction and Polymerization of Alkenes

The conversion of alkenes to macromolecules called polymers is a reaction of high commercial importance. The structure of the polymer is defined by a repeating unit, while the terminal groups are considered insignificant. The average degree of polymerization represents the number of repeating units in the polymer molecule and is denoted by the subscript n.

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Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization
07:28

Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization

Published on: November 27, 2015

Estudios simultáneos de la cinética de reacción y el desarrollo de la estructura en el procesamiento de polímeros.

W Bras, G E Derbyshire, D Bogg

    Science (New York, N.Y.)
    |February 17, 1995
    PubMed
    Resumen

    Este estudio utilizó técnicas avanzadas para observar la formación de la estructura del polímero durante el procesamiento. La termodinámica de la separación de fases, no el enlace de hidrógeno, impulsa el desarrollo de la estructura en los poliuretanos.

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    Published on: November 27, 2015

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    Área de la Ciencia:

    • La ciencia de los polímeros es la ciencia de los polímeros.
    • Ciencia de los materiales Ciencia de los materiales.
    • Química Física es la química física.

    Sus antecedentes:

    • Comprender el desarrollo de la estructura del polímero es crucial para controlar las propiedades del material.
    • Los poliuretanos exhiben estructuras complejas influenciadas por las condiciones de procesamiento.
    • El análisis cinético y estructural simultáneo ofrece información sobre la formación de polímeros.

    Objetivo del estudio:

    • Investigar las fuerzas motrices detrás del desarrollo de la estructura en los copoliuretanos de bloque segmentado durante el procesamiento.
    • Para correlacionar la evolución de la estructura con la cinética de la reacción utilizando métodos analíticos avanzados.
    • Para aclarar los mecanismos fundamentales que rigen la morfología del poliuretano.

    Principales métodos:

    • Se utilizó la dispersión de rayos X de ángulo pequeño de radiación sincrotrón con resolución temporal (SR-SAXS) para el análisis estructural.
    • Se empleó la espectroscopia infrarroja de la transformada de Fourier (FTIR) para el monitoreo de la cinética de la reacción.
    • Aplicó un enfoque combinado SR-SAXS y FTIR para modelar los copoliuretanos de bloque segmentado.

    Principales resultados:

    • Confirmado que la termodinámica de la separación de fases es el principal motor para el desarrollo de la estructura.
    • Demostró que el enlace de hidrógeno juega un papel secundario en comparación con la separación de fases.
    • Proporcionó datos con resolución temporal que vinculan el procesamiento a la morfología final del polímero.

    Conclusiones:

    • El impulso termodinámico de la separación de fases dicta la formación de la estructura del poliuretano.
    • Los estudios cinéticos y estructurales son esenciales para comprender el procesamiento de polímeros.
    • Esta metodología avanza en la comprensión de las relaciones estructura-propiedad en los poliuretanos.