使用双光电化学催化剂进行可交换的活基和阴离子聚合
Andrei Nikolaev1, Zhipeng Lu1, Arunavo Chakraborty1
1Department of Chemistry and Biochemistry, University of California at Santa Barbara, Santa Barbara, California 93106, United States.
Journal of the American Chemical Society
|July 27, 2021
概括
这项研究引入了可控聚合物合成的双响应催化剂,可在活基和阴离子聚合方法之间按需切换,以获得更广泛的单体范围.
科学领域:
- 聚合物化学
- 有机合成
- 材料科学
背景情况:
- 控制的聚合物合成通常需要特定的催化剂,限制可以使用的单体的范围.
- 实现多样化的聚合物架构,如块共聚物,通常涉及多种不同的聚合技术.
研究的目的:
- 开发一种单一的催化剂,能够调解活基和离子聚合.
- 使用不同的刺激来证明对聚合路径的正交控制.
- 扩大在温和条件下合成块共聚物的基质范围.
主要方法:
- 使用双光和电响应催化剂 (10-)
- 使用直角光化学和电化学刺激来激活常见的休眠物种.
- 交替刺激以控制不同类型的单体 (烯酸和乙烯基乙烯) 的顺序结合.
主要成果:
- 在活激素和阴离子聚合物之间实现了按需的相互转换.
- 精确控制聚合物分子质量和块组成.
- 合成的区块共聚物,具有明显的根性和阴性聚合段.
- 在整个过程中保持终端群忠实性和低分散性.
结论:
- 一个单一的双反应催化剂可以有效控制不同的聚合机制.
- 正角刺激使复杂的聚合物结构能够按需合成.
- 这种方法在无金属条件下显著扩大了块共聚合物合成的单体基材范围.
相关概念视频
01:26Photochemical Electrocyclic Reactions: Stereochemistry
2.0K
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
2.0K
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
2.6K
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.
2.6K
00:57Cationic Chain-Growth Polymerization: Mechanism
2.5K
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...
2.5K
01:09Radical Chain-Growth Polymerization: Mechanism
2.9K
The radical chain-growth polymerization mechanism consists of three steps: initiation, propagation, and termination of polymerization. The polymerization initiates when a free radical generated from the radical initiator adds to the unsaturated bond in the monomer. The unpaired electron of the free radical and one π electron in the unsaturated bond creates a σ bond between the free radical and the monomer. As a result, the other π electron in the unsaturated bond converts this...
2.9K
01:10Radical Chain-Growth Polymerization: Overview
2.8K
Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is...
2.8K
01:04Anionic Chain-Growth Polymerization: Mechanism
2.2K
The mechanism for anionic chain-growth polymerization involves initiation, propagation, and termination steps. In the initiation step, a nucleophilic anion, such as butyl lithium, initiates the polymerization process by attacking the π bond of the vinylic monomer. As a result, a carbanion, stabilized by the electron‐withdrawing group, is generated. The resulting carbanion acts as a Michael donor in the propagation step and attacks the second vinylic monomer, which acts as a Michael...
2.2K