基于尿素的双功能器官催化:对活聚合物的超分子识别
Andrew P Dove1, Russell C Pratt, Bas G G Lohmeijer
1IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA.
Journal of the American Chemical Society
|October 6, 2005
概括
一种新型的有机催化剂使得无金属,活环开放聚合乳化物. 这种双功能催化剂实现了高选择性和控制性,产生了具有非常狭窄分子量分布的多分子乳化物.
科学领域:
- 聚合物化学 聚合物化学
- 机体催化剂是有机催化剂.
- 材料科学 材料科学 材料科学
背景情况:
- 环开聚合 (ROP) 对于合成诸如聚乳酸之类的聚而言至关重要.
- 传统的ROP通常依赖于基于金属的催化剂,这引发了人们对残留金属污染和环境影响的担忧.
- 开发无金属催化系统用于控制的ROP仍然是一个重大挑战.
研究的目的:
- 引入一种多功能,无金属的有机催化方法,用于活环开放的乳化物聚合.
- 为了研究乳酸聚合物聚合过程中双功能氨酸-三级胺催化剂的机制和效率.
- 为了实现对聚合物分子重量的高度控制和低的聚分散性.
主要方法:
- 使用双功能的硫尿酸-三级胺催化剂进行乳酸盐聚合.
- 在温和和选择性条件下进行聚合.
- 分析了由此产生的多乳酸) 的分子量和多分散性.
主要成果:
- 实现了具有可预测分子重量的乳化物的活环开放聚合.
- 产生了具有极其狭窄的多分散度 (Đ ≈1.05) 的多乳酸.
- 对于聚合而非转化而具有非凡的选择性,归因于催化剂设计和乳环应变.
结论:
- 开发的双功能器官催化剂提供了一种高效的无金属途径,用于控制的聚乳酸合成.
- 催化剂的独特结构促进了启动器和单体的同时激活,确保了高选择性和生活特征.
- 这种方法提供了一种可持续和高效的替代品,用于生产高质量的聚乳酸.
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.
01:04Anionic Chain-Growth Polymerization: Mechanism
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 acceptor.
00:57Cationic Chain-Growth Polymerization: Mechanism
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 generated carbocation,...
01:13Olefin 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...
Ruthenium-based Grubbs catalyst is the most commonly used catalyst for olefin metathesis polymerization. Grubbs catalyst consists of a...
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...
01:16Cycloaddition Reactions: MO Requirements for Thermal Activation
Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.