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Biological membranes show uneven distribution of different types of lipids in the inner and outer layers, resulting in transverse asymmetric membranes. The treatment of the erythrocyte membrane with the enzyme phospholipase confirmed the asymmetric nature of the lipid bilayer. The enzyme hydrolyzes lipids into fatty acids and hydrophilic groups. The phospholipase acts only on the outer layer of the membrane, while the inner layer remains intact. The phospholipase treatment resulted in 80%...
Anionic Chain-Growth Polymerization: Overview01:20

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The polymerization process that involves carbanion as an intermediate is called anionic polymerization. It is also a type of addition or chain-growth polymerization. Anionic polymerization gets initiated by a strong nucleophile such as an organolithium or a Grignard reagent. The most commonly used initiator for anionic polymerization is butyl lithium. Monomers involved in anionic polymerization must possess a vinyl group bonded to one or two electron-withdrawing groups. For instance,...
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The introduction of polyesters has brought major development to the textile industry. The wrinkle-free behavior of polyester blends has eliminated the need for starching and ironing clothes.
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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.
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Anionic Chain-Growth Polymerization: Mechanism01:04

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The mechanism for anionic chain-growth polymerization involves initiation, propagation, and termination steps. In the initiation step, a nucleophilic anion, such as butyl lithium, initiates the polymerization process by attacking the π bond of the vinylic monomer. As a result, a carbanion, stabilized by the electron‐withdrawing group, is generated. The resulting carbanion acts as a Michael donor in the propagation step and attacks the second vinylic monomer, which acts as a Michael acceptor.

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Crecimiento asimétrico en las capas múltiples de polielectrolitos.

Ramy A Ghostine1, Marie Z Markarian, Joseph B Schlenoff

  • 1Department of Chemistry and Biochemistry, The Florida State University, Tallahassee, Florida 32306-4390, USA.

Journal of the American Chemical Society
|May 16, 2013
PubMed
Resumen
Este resumen es generado por máquina.

Los investigadores encontraron que el modelo común de sobrecompensación de carga en polielectrolitos multicapa es incorrecto. El estudio revela un crecimiento asimétrico y la formación de complejos en cloruro de poli (PDADMAC) y sulfonato de poli (PSS) películas.

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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 de las superficies.

Sus antecedentes:

  • Los polielectrolíticos multicapa (PEM) son ampliamente utilizados en diversas aplicaciones.
  • El ensamblaje de los PEM es a menudo descrito por un modelo de sobrecompensación de carga.
  • El sistema específico estudiado incluye el cloruro de poli (diallyldimethylammonium) (PDADMAC) y el sulfonato de poli (styrene) (PSS).

Objetivo del estudio:

  • Para investigar la distribución de carga y el mecanismo de ensamblaje dentro de los polielectrolitos multicapa PDADMAC/PSS.
  • Desafiar el modelo convencional de sobrecompensación de cargos en la formación de PEM.
  • Desarrollar un nuevo modelo que explique el crecimiento observado y la estructura de los PEM.

Principales métodos:

  • Se utilizaron contadores radiactivos para cuantificar la proporción de unidades de polímero positivas y negativas.
  • Se analizó la distribución de la carga a través de la polielectrolita multicapa.
  • Desarrolló un modelo de reacción-difusión para describir el crecimiento asimétrico observado.

Principales resultados:

  • Se encontró que el modelo aceptado de sobrecompensación de carga para cada capa era incorrecto.
  • La sobrecompensación ocurre solo con la adición del policatión (PDADMAC); el polianión (PSS) simplemente compensa.
  • Se observó un crecimiento asimétrico, con un exceso de cargas positivas que se acumulan después de varias capas, lo que lleva a distintas regiones complejas de vidrio y caucho.

Conclusiones:

  • El ensamblaje de PDADMAC/PSS PEM exhibe un crecimiento asimétrico y una formación compleja, que se desvía de los modelos simples de sobrecompensación de carga.
  • Un nuevo modelo de reacción-difusión describe con precisión la formación de distintas capas estequiométricas y ricas en carga.
  • Comprender este crecimiento asimétrico es crucial para predecir y controlar las propiedades de la PEM.