Video Experimental Relacionado
Updated: Jul 14, 2026
09:15
Growing Protein Crystals with Distinct Dimensions Using Automated Crystallization Coupled with In Situ Dynamic Light Scattering
Published on: August 14, 2018
La base molecular de la morfología shish-kebab en la cristalización de polímeros
Shuichi Kimata1, Takashi Sakurai, Yoshinobu Nozue
1Petrochemicals Research Laboratory, Sumitomo Chemical, 2-1 Kitasode, Sodegaura, Chiba 299-0295, Japan.
Science (New York, N.Y.)
|May 19, 2007
Resumen
Las cadenas de polímero más largas no dominan la estructura de la cápsula durante la cristalización inducida por flujo. En cambio, actúan catalíticamente, reclutando cadenas adyacentes para formar el precursor shish. Este hallazgo impacta la comprensión de la ciencia de los polímeros.
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:
- La cristalización inducida por flujo es crucial para el procesamiento de polímeros.
- La estructura "shish" es un precursor clave en este proceso.
- Se cree ampliamente que las cadenas de polímero más largas forman el shish.
Objetivo del estudio:
- Examinar críticamente el papel de la longitud de la cadena en la formación de shish.
- Para determinar si las cadenas más largas se incorporan preferentemente en el shish.
- Para dilucidar el mecanismo molecular de la nucleación shish.
Principales métodos:
- Etiquetado de deuterio para diferenciar las longitudes de las cadenas poliméricas.
- Diseminación de neutrones de ángulo pequeño (SANS) para analizar la composición del shish.
- Investigando la fusión de polímeros bajo condiciones de flujo.
Principales resultados:
- Las largas cadenas de polímero no están sobrerrepresentadas en el shish.
- La concentración de cadenas largas en el shish refleja su concentración masiva.
- La evidencia sugiere que las cadenas más largas actúan catalíticamente en la formación de shish.
Conclusiones:
- Se desafía la visión ampliamente difundida del dominio de la cadena más larga en shish.
- Las cadenas más largas parecen desempeñar un papel catalítico, no uno de composición.
- Esta investigación refina nuestra comprensión de los mecanismos de cristalización de polímeros.
Videos de Conceptos Relacionados
01:21Polymer Classification: Crystallinity
Unlike ionic or small covalent molecules, polymers do not form crystalline solids due to the diffusion limitations of their long-chain structures. However, polymers contain microscopic crystalline domains separated by amorphous domains.
Crystalline domains are the regions where polymer chains are aligned in an orderly manner and held together in proximity by intermolecular forces. For example, chains in the crystalline domains of polyethylene and nylon are bound together by van der Waals...
Crystalline domains are the regions where polymer chains are aligned in an orderly manner and held together in proximity by intermolecular forces. For example, chains in the crystalline domains of polyethylene and nylon are bound together by van der Waals...
01:26Polymer Classification: Stereospecificity
Polymerization generates chiral centers along the entire backbone of a polymer chain. Accordingly, the stereochemistry of the substituent group has a significant effect on polymer properties. Polymers formed from monosubstituted alkene monomers feature chiral carbons at every alternate position in the polymer backbone. Relative to the predominant orientation of substituents at the adjacent chiral carbons, the polymer can exist in three different configurations: isotactic, syndiotactic, and...
01:08Molecular Weight of Step-Growth Polymers
Step growth polymerization involves bi or multifunctional monomers. Bifunctional monomers react to form linear step growth polymers, whereas multifunctional monomers react to form non-linear or branched polymers.
As the step-growth polymerization involves step-wise condensation of monomers, the molecular weight also builds up eventually. Consequently, high molecular weight polymers are obtained at the late stages of the polymerization, where 99% of monomers have been consumed.
The extent of the...
As the step-growth polymerization involves step-wise condensation of monomers, the molecular weight also builds up eventually. Consequently, high molecular weight polymers are obtained at the late stages of the polymerization, where 99% of monomers have been consumed.
The extent of the...
01:24Determination of Molar Masses of Polymers I
Polymerization produces macromolecules with a range of chain lengths due to the random nature of molecular growth processes. As chains form and terminate at different stages, a single polymer sample contains molecules of varying sizes rather than a uniform structure. This variability is described using average molar masses and distribution-related parameters, which together provide a comprehensive understanding of polymer characteristics.The distribution of molar masses plays a critical role in...
01:03Step-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...
Many natural and synthetic polymers are produced by...
00:57Cationic 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,...