在带有氨酸末端组的线性和环状聚钢之间可逆切换
Michel Schappacher1, Alain Deffieux
1CNRS and Université Bordeaux, Laboratoire de Chimie des Polymères Organiques, ENSCBP, 16 Avenue Pey Berland, 33607 Pessac Cedex, France.
Journal of the American Chemical Society
|January 21, 2011
概括
研究人员开发了一种新的单分子环闭方法,用于宏环聚烯合成. 这个过程选择性地将聚合物链末端结合在一起,形成可逆的宏循环,在聚合物化学中具有潜在的应用.
科学领域:
- 聚合物化学 聚合物化学
- 超分子化学 超分子化学
- 有机合成 有机合成
背景情况:
- 宏环聚合物具有独特的特性,但它们的合成仍然具有挑战性.
- 现有的方法往往缺乏选择性或需要严苛的条件.
- 开发高效和可逆循环化策略对于先进的高分子架构至关重要.
研究的目的:
- 研究一种新的单分子环闭工艺,用于合成宏环聚烯.
- 为了探索远程线性聚烯的直接端到端合.
- 描述由此产生的宏环聚合物和循环化的可逆性.
主要方法:
- 通过活体聚合合成合成α,ω-bis[铁(III) 中四烯基氨酸]远线性聚氨酸.
- 链末功能化,引入氨酸单元.
- 通过使用基来实现环闭的分子内凝结.
- 使用稀释的化重新转换宏循环.
- 使用NMR光谱和用二极管阵列探测器进行尺寸排除色谱的表征.
主要成果:
- 通过选择性单分子环闭过程成功合成宏环聚烯.
- 作为关键环关闭单元的二铁 (III) -μ-氧化 (porphyrin) 模体的形成.
- 在添加酸后,证明了循环化过程的完全可逆性.
- 线性前体和宏循环产品的详细结构特征.
结论:
- 已经建立了一个新的和高效的单分子环闭策略,用于宏环聚烯合成.
- 开发的方法具有很高的选择性和完全的可逆性,使得宏观循环结构的受控形成成为可能.
- 这种方法为访问复杂的聚合物结构提供了有价值的工具,这些结构有可能具有量身定制的材料特性.
相关概念视频
01:16Olefin 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...
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
01:17Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
01:17Pericyclic Reactions: Introduction
Pericyclic reactions are organic reactions that occur via a concerted mechanism without generating any intermediates. The reactions proceed through the movement of electrons in a closed loop to form a cyclic transition state, where rearrangement of the σ and π bonds yields specific products.
Pericyclic reactions can be classified into three categories: electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. Electrocyclic reactions and sigmatropic rearrangements are...
Pericyclic reactions can be classified into three categories: electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. Electrocyclic reactions and sigmatropic rearrangements are...
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...