通过对1,6-heptadiene的两种状态生物协调聚合,对聚1,3-甲基环) 的立体工程
Kaitlyn E Crawford1, Lawrence R Sita
1Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.
Journal of the American Chemical Society
|May 23, 2013
概括
研究人员在1,6-heptadiene聚合过程中控制了动态甲基交换,以创建具有多种微观结构的聚-1,3-甲基环),影响散装特性和阻断共聚合物的行为.
科学领域:
- 聚合物化学 聚合物化学
- 材料科学 材料科学 材料科学
背景情况:
- 生活协调聚合提供了对聚合物架构的精确控制.
- 动态甲基组交换可以影响聚合物的特性和形态.
研究的目的:
- 为了外部控制活跃的甲基组交换在生物协调聚合过程中.
- 为了产生具有系统变化的立体化学微观结构的聚1,3-甲基环) .
- 为了研究微结构对散装性质的影响和阻断共聚合物的行为.
主要方法:
- 1,6-heptadiene的生物协调聚合. 这是一个很好的方法.
- 活跃和休眠物种之间的动态甲基组交换的外部控制.
- 立体化学微观结构的系统变化.
- 聚合物和块共聚物的散体特性和固态微相行为的表征.
主要成果:
- 通过受控的微观结构生成了一系列的多 (1,3-甲环) 物理形式.
- 该策略成功地操纵了聚1,3-甲环的散装特性.
- 聚1,3-甲环) -b-聚1,1-) 块共聚合物的固态微相行为受到影响.
结论:
- 动态甲基组交换的外部控制是调整聚合物微观结构的有效策略.
- 这种控制允许定制聚1,3-甲环的散装性质.
- 该方法适用于修改块共聚合物的行为.
相关概念视频
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
01:26Thermal 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.
00:53Olefin Metathesis Polymerization: Acyclic Diene Metathesis (ADMET)
Acyclic diene metathesis polymerization or ADMET polymerization involves cross-metathesis of terminal dienes, such as 1,8-nonadiene, to give linear unsaturated polymer and ethylene. As ADMET is a reversible process, the formed ethylene gas must be removed from the reaction mixture to complete the polymerization process.
Similar to cross-metathesis, ADMET also involves the formation of metallacyclobutane intermediate by [2+2] cycloaddition of one of the double bonds of a terminal diene with...
Similar to cross-metathesis, ADMET also involves the formation of metallacyclobutane intermediate by [2+2] cycloaddition of one of the double bonds of a terminal diene with...
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...
02:35Free-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.