建模分支聚乙烯:具有精确放置的乙烯分支的共聚物.
John C Sworen1, Jason A Smith, Jessica M Berg
1The George and Josephine Butler Polymer Research Laboratory, Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, USA.
Journal of the American Chemical Society
|September 10, 2004
概括
精确的乙烯/1-丁烯 (EB) 共聚合物与受控分支被合成和结构性研究. 这些共聚合物中分支的增加导致了较低的点和融合热,以及缺陷的增加.
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
- 有机化学 有机化学
背景情况:
- 对聚合物架构的精确控制对于定制材料特性至关重要.
- 乙烯/1-丁烯 (EB) 共聚合物是重要的工业聚合物,但它们的精确结构-特性关系尚未完全理解.
- 传统的合成方法往往产生随机的共聚物,限制结构控制.
研究的目的:
- 为了合成和结构性地表征模型乙烯/1-丁烯 (EB) 共聚合物,精确控制乙烯分支的位置.
- 研究不同分支频率对共聚合物结构和热性质的影响.
- 为了比较这些精确合成的共聚合物的结构特征与随机合成的.
主要方法:
- 使用阶段聚合化学合成了四种模型EB共聚合物.
- 结构性特征包括对初级和更高层结构的分析.
- 用差分扫描热量计 (DSC) 评估热性能.
- 结晶性和缺陷使用红外 (IR) 光谱学进行了调查.
主要成果:
- 成功合成了EB模型的共聚合物,在每9次,15次和21次碳节点上都有乙烯分支.
- 融点和聚变热量随着乙烯分支频率的增加而减少.
- DSC和IR光谱显示了高度混乱的晶体结构,其中包含了乙烯分支.
- 不管分支的频率如何,EB共聚物表现出高度的曲折和形缺陷.
结论:
- 通过步骤聚合的精确合成,可以控制在EB共聚物中引入分支.
- 分支频率显著影响热性质和晶体乱.
- 乙烯分支的存在会导致显著的结构缺陷,影响材料的行为.
- 与传统的随机共聚物相比,这些模型共聚物提供了宝贵的见解.
相关概念视频
Characteristics and Nomenclature of Homopolymers
Polymers that are made up of identical monomer units are called homopolymers. Only one repeating unit is involved in the construction of the homopolymer structure. For example, as depicted in Figure 1, polypropylene is a homopolymer constituted of propylene monomers. Here, the only repeating unit in the polymer chain is propylene.
Characteristics and Nomenclature of Copolymers
Copolymers are the products obtained from the polymerization of multiple monomer species. So, in a polymer chain itself, there can be multiple repeating units that come from different monomers. The process of synthesizing a polymer from different monomer species is called copolymerization. When two monomers are involved, the polymer is known as a bipolymer. Polymers with three and four monomers are termed terpolymers and quaterpolymers, respectively. Figure 1 depicts the copolymerization of...
Polymer Classification: Architecture
Polymers are classified as linear or branched on the basis of their chain architecture. The polymer chains in linear polymers have a long chain-like structure with minimal to no branching at all. Even if a polymer features large substituent groups on the monomer, which appear as branches to the skeleton, it is not considered a branched polymer. A branched polymer contains secondary polymer chains that arise from the main polymer chain. The branching occurs when the polymer growth shifts from...
Polymer Classification: Crystallinity
Unlike ionic or small covalent molecules, polymers do not form crystalline solids due to the diffusion limitations of their long-chain structures. However, polymers contain microscopic crystalline domains separated by amorphous domains.
Crystalline domains are the regions where polymer chains are aligned in an orderly manner and held together in proximity by intermolecular forces. For example, chains in the crystalline domains of polyethylene and nylon are bound together by van der Waals...
Crystalline domains are the regions where polymer chains are aligned in an orderly manner and held together in proximity by intermolecular forces. For example, chains in the crystalline domains of polyethylene and nylon are bound together by van der Waals...
Polymer 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...
Classification and Mechanical Properties of Synthetic Polymers
Synthetic polymers are classified as elastomers, fibers, or plastics based on their crystallinity. Crystallinity, the degree of long-range order in the solid state, influences the mechanical properties (stretching or contracting) of elastomers. Elastomers are flexible polymers that can expand or contract easily upon the application of an external force. They have numerous crosslinks that pull them back into their original shape when stress is removed. Silicones, for instance, are highly elastic...


