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polymer fractionation
Polymers are chainlike molecules that are made of the same repetition unit. With a few exceptions such as proteins, a polymer consists of a mix of molecules with different chain lengths. Therefore average values are given for the molecular weight like the number average, the weight average or the viscosity average molar mass. A measure for the width of the molecular weight distribution is the polydispersity index. The targeted manipulation of the molecular weight distribution of a polymer by removing short and/or long chain material is called polymer fractionation.
== Reasons for polymer fractionation ==
The molecular weight of polymers has a large influence on their properties and therefore determines the applications. Among others the flow behavior, the solubility, the mechanical properties but also the lifetime are influenced by the molecular weight. For high duty polymers – polymers that have to fulfill elevated demands – not only the molecular weight but also the molecular weight distribution is important. This especially holds true if low and/or high molecular material disturbs a given task.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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