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Videos de Conceptos Relacionados

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...
Radical Chain-Growth Polymerization: Overview01:10

Radical Chain-Growth Polymerization: Overview

Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is...
Radical Chain-Growth Polymerization: Chain Branching01:17

Radical Chain-Growth Polymerization: Chain Branching

The skeletal structure of polymers synthesized via radical polymerization is always branched. For example, the polymerization of ethylene by radical polymerization results in a low-density grade of polyethylene with a heavily branched skeletal structure. Here, the radical site abstracts hydrogen from the growing chain, and the radical site shifts from the end (a primary carbon center) to anywhere within the growing chain (a secondary carbon center). Consequently, the part of the chain from 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.
Cationic Chain-Growth Polymerization: Mechanism00:57

Cationic Chain-Growth Polymerization: Mechanism

The cationic polymerization mechanism consists of three steps: initiation, propagation, and termination. In the initiation step of the polymerization process, the π bond of a monomer gets protonated by the Lewis acid catalyst, which is formed from boron trifluoride and water. The protonation of the π bond generates a carbocation stabilized by the electron‐donating group. In the propagation step, the π bond of the second monomer acts as a nucleophile and attacks the generated carbocation,...
Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)01:16

Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)

Ring-opening metathesis polymerization or ROMP involves strained cycloalkenes as starting materials. The mechanism of ROMP proceeds by reacting cycloalkene with Grubbs catalyst to give metallacyclobutane intermediate which undergoes a ring-opening reaction to form new carbene. The new carbene reacts with another molecule of cycloalkene. Repetition of these steps leads to the formation of an unsaturated open-chain polymer product. All these steps are reversible, however, relieving the ring...

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3D Printing and In Situ Surface Modification via Type I Photoinitiated Reversible Addition-Fragmentation Chain Transfer Polymerization
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Published on: February 18, 2022

Simultánea polimerización radical controlada iniciada en masa y en superficie a partir de sustratos planos.

Salomon Turgman-Cohen1, Jan Genzer

  • 1Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695, United States.

Journal of the American Chemical Society
|October 8, 2011
PubMed
Resumen

Las simulaciones de Monte Carlo revelan que la polimerización a granel es más rápida y produce polímeros con una distribución de peso molecular más estrecha que la polimerización iniciada por la superficie. Las tasas de polimerización superficial dependen de la densidad del iniciador, invalidando las suposiciones comunes sobre la densidad de injerto de polímero.

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Área de la Ciencia:

  • Química de Polímeros La Química de Polímeros es la química de los polímeros.
  • Ciencias de la superficie Ciencias de la superficie.
  • Química computacional es la química computacional.

Sus antecedentes:

  • La polimerización radical controlada es crucial para sintetizar polímeros con propiedades definidas.
  • La polimerización iniciada por la superficie permite la creación de cepillos de polímero y superficies funcionalizadas.
  • La caracterización precisa de los polímeros sujetos a la superficie es esencial para sus aplicaciones.

Objetivo del estudio:

  • Para investigar las diferencias entre la polimerización radical controlada en solución a granel y desde una superficie plana.
  • Determinar los factores que influyen en las tasas de polimerización iniciadas por la superficie.
  • Desafiar el supuesto de igual peso molecular entre los polímeros a granel y los cultivados en superficie.

Principales métodos:

  • Se emplearon simulaciones por computadora de Monte Carlo.
  • Las simulaciones modelaron la polimerización simultánea en solución y desde una superficie plana impenetrable.
  • Se consideraron las variaciones en la densidad del sitio iniciador en la superficie.

Principales resultados:

  • Los polímeros a granel exhibieron tasas de crecimiento más rápidas y distribuciones de peso molecular más estrechas en comparación con los polímeros iniciados en la superficie.
  • Se descubrió que la tasa de polimerización iniciada en la superficie depende de la densidad de los sitios iniciadores.
  • Se observó una discrepancia significativa entre los pesos moleculares de los polímeros a granel y los cultivados en superficie.

Conclusiones:

  • La suposición de que el peso molecular del polímero iniciado en la superficie es igual al peso molecular del polímero a granel es generalmente inválida.
  • Este hallazgo tiene implicaciones para la determinación precisa de la densidad de injerto en sistemas de polímeros sujetos a la superficie.
  • Comprender estas diferencias es clave para diseñar y caracterizar materiales poliméricos avanzados.