概括
高分子量聚钢的特征是使用光散射和超离心. 马克-霍温克方程仅在特定的溶剂和温度条件下 (甲溶剂/温度) 适用于柔性聚合物.
科学领域:
- 聚合物科学 聚合物科学
- 物理化学 物理化学
背景情况:
- 描述高分子量聚合物对于理解它们的特性至关重要.
- 分子重量和粘度之间的关系在聚合物科学中是至关重要的.
研究的目的:
- 为了表征具有非常高分子量的聚乙烯.
- 调查马克-霍温克方程对这些聚合物的适用性.
主要方法:
- 对光散射进行测量.
- 平衡超离心法. 在平衡超离心法中.
- 在theta溶剂中的粘度测量.
主要成果:
- 分子重量高达44 x 10^6 g/mol的聚乙烯的特征已经成功确定.
- 马克-霍温克方程需要在theta温度下在theta溶剂中进行测量,以获得灵活聚合物的准确结果.
结论:
- 使用已确定的物理方法,可以可靠地描述高分子量聚钢.
- 严格遵守theta溶剂和theta温度条件是必要的,以使Mark-Houwink方程在聚合物分子量测定中的有效应用.
相关概念视频
01:08Molecular Weight of Step-Growth Polymers
Step growth polymerization involves bi or multifunctional monomers. Bifunctional monomers react to form linear step growth polymers, whereas multifunctional monomers react to form non-linear or branched polymers.
As the step-growth polymerization involves step-wise condensation of monomers, the molecular weight also builds up eventually. Consequently, high molecular weight polymers are obtained at the late stages of the polymerization, where 99% of monomers have been consumed.
The extent of the...
As the step-growth polymerization involves step-wise condensation of monomers, the molecular weight also builds up eventually. Consequently, high molecular weight polymers are obtained at the late stages of the polymerization, where 99% of monomers have been consumed.
The extent of the...
01:14Polymer 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...
01:10Polymers: Molecular Weight Distribution
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.
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...
01:24Determination of Molar Masses of Polymers I
Polymerization produces macromolecules with a range of chain lengths due to the random nature of molecular growth processes. As chains form and terminate at different stages, a single polymer sample contains molecules of varying sizes rather than a uniform structure. This variability is described using average molar masses and distribution-related parameters, which together provide a comprehensive understanding of polymer characteristics.The distribution of molar masses plays a critical role in...
01:01Polymers: Defining Molecular Weight
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...