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相关概念视频

Preparation of Epoxides03:00

Preparation of Epoxides

Overview
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy acids to...
Olefin Metathesis Polymerization: Overview01:13

Olefin Metathesis Polymerization: Overview

Recently, the development of olefin metathesis polymerization advanced the field of polymer synthesis. Simply put, the reorganization of substituents on their double bonds between two olefins in the presence of a catalyst is known as the olefin metathesis reaction. The use of metathesis reaction for polymer synthesis is called olefin metathesis polymerization.
Ruthenium-based Grubbs catalyst is the most commonly used catalyst for olefin metathesis polymerization. Grubbs catalyst consists of a...
Acid-Catalyzed Ring-Opening of Epoxides02:24

Acid-Catalyzed Ring-Opening of Epoxides

Epoxides that are three-membered ring systems are more reactive than other cyclic and acyclic ethers. The high reactivity of epoxides originates from the strain present in the ring. This ring strain acts as a driving force for epoxides to undergo ring-opening reactions either with halogen acids or weak nucleophiles in the presence of mild acid. The acid catalyst converts the epoxide oxygen, a poor leaving group, into an oxonium ion, a better leaving group, making the reaction feasible. The...
Base-Catalyzed Ring-Opening of Epoxides02:26

Base-Catalyzed Ring-Opening of Epoxides

Due to their highly strained structures, epoxides can readily undergo ring-opening reactions through nucleophilic substitution, either in the presence of an acid or a base. The nucleophilic substitution reactions in the presence of acid are called acid-catalyzed ring-opening reactions, and nucleophilic substitution reactions in the presence of a base are called base-catalyzed ring-opening reactions. Epoxides undergo base-catalyzed ring-opening reactions in the presence of a strong nucleophile...
Sharpless Epoxidation02:57

Sharpless Epoxidation

The conversion of allylic alcohols into epoxides using the chiral catalyst was discovered by K. Barry Sharpless and is known as Sharpless epoxidation. The use of a chiral catalyst enables the formation of one enantiomer of the product in excess. This chiral catalyst is mainly a chiral complex of titanium tetraisopropoxide and tartrate ester (specific stereoisomer). The stereoisomer used in the chiral catalyst dictates the formation of the enantiomer of the product. In other words, the use of...
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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A Simple and Efficient Protocol for the Catalytic Insertion Polymerization of Functional Norbornenes
09:08

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Published on: February 27, 2017

使用双金属催化剂进行选性环氧化物聚合.

Renee M Thomas1, Peter C B Widger, Syud M Ahmed

  • 1Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, United States.

Journal of the American Chemical Society
|November 4, 2010
PubMed
概括

一种新的催化剂使环氧化物的快速,高度立体选择性聚合成为可能,产生异性聚乙烯. 这一突破为合成具有优良热性能的聚合物提供了一种新方法.

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Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes
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Electroactive Polymer Nanoparticles Exhibiting Photothermal Properties
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A Simple and Efficient Protocol for the Catalytic Insertion Polymerization of Functional Norbornenes
09:08

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Published on: February 27, 2017

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes
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Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

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科学领域:

  • 聚合物化学 聚合物化学
  • 有机金属化学 有机金属化学

背景情况:

  • 随机选择性聚合对于制造立体规律的聚合物至关重要.
  • 开发用于立体选择性环氧化物聚合物的高效催化剂仍然是一个挑战.

研究的目的:

  • 探索一个高度活性的enantiopure双金属复合物用于enantioselective环氧化物聚合.
  • 为了优化高速率和立体选择性的聚合条件.
  • 为了研究从racemic环氧化物中合成异性聚乙烯的合成.

主要方法:

  • 使用了一种高度活性的enantiopure双金属复合物.
  • 对各种单替代环氧化物进行了酶选择性聚合.
  • 优化反应条件以实现高立体选择性 (s-因子> 50,有些> 300).
  • 采用了racemic催化剂来制备等离子聚乙烯.

主要成果:

  • 在一系列环氧化物中实现了高聚合率和立体选择性.
  • 产生的高同毒性聚合物 (mm三位 > 95%,有些 > 98%).
  • 合成的异性聚乙烯在定量产量使用的racemic催化剂.
  • 对于得到的同性聚乙烯,证明了高温度 (T(m)).

结论:

  • 双金属复合物对环氧化物快速的enantioselective聚合非常有效.
  • 这项工作介绍了第一份关于从racemic环氧化物中快速合成多种多样,高同位性聚乙烯的报告.
  • 开发的方法为具有理想热性质的立体正规聚乙烯提供了一条有价值的途径.