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Radical Chain-Growth Polymerization: Overview
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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...
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Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)
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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...
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Polymers: Molecular Weight Distribution
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For any given polymer, the weight average molecular weight (Mw) is higher than, if not equal to, the number average molecular weight (Mn). The only situation in which the weight average molecular weight and the number average molecular weight are equal is when a polymer consists only of chains with equal molecular weight. However, this never happens in a synthetic polymer, since it is difficult to control the polymerization process up to a molecular level with accuracy to a hundred percent.
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Polymers
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The word polymer is derived from the Greek words “poly” which means “many” and “mer” which means “parts”. Polymers are long chains of molecules composed of repeating units of smaller molecules, known as monomers. They either occur naturally, such as DNA and proteins, or can be constructed synthetically, like plastics. They have varied structural characteristics, such as linear chains, branched chains, or complex networks, that contribute to the...
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Polymers: Defining Molecular Weight
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Unlike small molecules with definite molecular weights, polymers are a mixture of individual polymer chains of varying lengths, each with a unique molecular weight. So, the molecular weight of a polymer is expressed as an average value based on the average size of the polymer chains. The two most common forms of averages used for polymers are the number average molecular weight and weight average molecular weight.
The number average molecular weight (Mn) is the summation of the number...
The number average molecular weight (Mn) is the summation of the number...
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Radical Chain-Growth Polymerization: Mechanism
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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...
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卡拉卡:一个多功能环聚合物分子动力学模拟包
1Chair of Theoretical Chemistry, Friedrich-Alexander University Erlangen-Nürnberg, Egerlandstraße 3, 91058 Erlangen, Bavaria, Germany.
Journal of chemical theory and computation
|August 9, 2023
概括
一个新的开源程序,Caracal,使用环聚合物分子动力学 (RPMD) 为分子系统提供了全面的模拟. 它将先进的RPMD功能与用于化学反应分析的多功能潜在能量表面 (PES) 方法集成在一起.
科学领域:
- 计算化学计算化学
- 分子动力学分子动力学
- 化学物理 化学物理
背景情况:
- 模拟分子系统需要准确的潜在能量表面 (PES) 和高效的动力学方法.
- 环聚合物分子动力学 (RPMD) 是计算反应速率的强大技术.
- 现有的软件包可能缺乏用于PES生成和高级动态模拟的集成功能.
研究的目的:
- 介绍Caracal,一个新的开源软件包用于分子模拟.
- 提供一个全面的方法,将RPMD与各种PES方法结合起来.
- 促进化学反应速率计算和液体系统的研究.
主要方法:
- 使用环聚合物分子动力学 (RPMD) 进行模拟.
- 实施量子力学推导力场 (QMDFF) 和实证价值键 (EVB) -QMDFF方法用于PES构造.
- 采用偏向抽样技术 (雨抽样,回交叉计算) 用于利率常数.
- 支持用于液体系统描述的QMDFF的聚合.
主要成果:
- 卡拉卡尔提供了一个强大的RPMD实现与化学反应速率计算.
- 该包整合了易于设置的PES方法,包括QMDFF和EVB-QMDFF.
- 证明了对反应机制进行分类并获得RPMD速率常数的能力.
- 显示了通过聚合QMDFF描述液体系统的潜力.
结论:
- 卡拉卡尔为先进的分子模拟提供了一个全面和用户友好的平台.
- 整合RPMD和灵活的PES方法提高了化学反应的研究.
- 该软件包适用于气相反应动力学和凝聚相系统分析.


