由各种外部刺激引起的光学活性聚乙烯的宏分子螺旋体的切换,带有循环德克斯特林悬挂
Katsuhiro Maeda1, Hiroaki Mochizuki, Masaki Watanabe
1Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan.
Journal of the American Chemical Society
|June 8, 2006
概括
新型螺旋型聚合物具有循环德克斯 (CyD) 组,在对刺激的反应中改变颜色和光学特性. 这些动态聚合物为先进材料应用提供了可调节的特性.
科学领域:
- 聚合物化学 聚合物化学
- 超分子化学 超分子化学
- 石眼材料 石眼材料 石眼材料
背景情况:
- 具有螺旋结构的状聚合物因其独特的光学特性而引起人们的兴趣.
- 循环德克斯特林 (CyDs) 是多功能性性宿主,有可能改变聚合物行为.
研究的目的:
- 为了合成和表征新型的乙烯聚合物,这些聚合物与各种循环二烯残留物功能化.
- 为了研究这些新型聚合物的手术特性和刺激反应行为.
主要方法:
- 合成含有α,β和gamma-CyD残留物的乙烯单体.
- 催化聚合使得高密度的 cis-transoidal 聚 (?? 乙烯) 聚合物产生.
- 紫外线可见吸收和循环二元化 (CD) 光谱分析聚合物构成和光学活性.
主要成果:
- 合成的聚合物 (poly-1alpha, poly-2beta, poly-3gamma, poly-2beta-Me) 由于螺旋形状而表现出诱导的CD信号.
- 棉花效应标志与温度变化,溶剂或客分子相互作用相反,伴随着可见的颜色变化.
- 在多2β固定螺旋形状中的β-CyD单元的交叉连接,抑制反转,但允许基于螺旋距的颜色变化.
结论:
- 用CyD残留物功能化的乙烯聚合物显示出动态的,对刺激有反应的螺旋结构.
- 观察到的手术切换和颜色变化直接与聚合物骨干中的形状过渡有关.
- 内部分子交叉连接提供了一种稳定特定螺旋状态的方法,同时保持一些结构灵活性和颜色变化能力.
相关概念视频
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
01:26Polymer 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...
01:12Cycloaddition Reactions: MO Requirements for Photochemical Activation
Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
01:29Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry
Diels–Alder reactions between cyclic dienes locked in an s-cis configuration and dienophiles yield bridged bicyclic products.