polydispersityindexillä

Polydispersity index, often abbreviated as PDI, is a measure used in polymer science and other fields to describe the distribution of molecular sizes or weights in a sample. A sample with a PDI of 1.0 indicates that all molecules are of the same size or weight, a state known as monodispersity. In reality, most polymer samples are polydisperse, meaning they contain a range of molecular sizes.

A higher PDI value signifies a broader distribution of molecular weights, indicating greater variability in the sizes of the polymer chains. Conversely, a lower PDI value suggests a narrower distribution and more uniform molecular sizes. The PDI is typically calculated as the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn). Therefore, PDI = Mw / Mn.

The PDI is an important parameter as it can significantly influence the physical properties of a material, such as its viscosity, mechanical strength, and solubility. For instance, polymers with a narrow PDI often exhibit more predictable and reproducible properties compared to those with a broad PDI. In many applications, a low PDI is desirable to ensure consistent material performance. The method of synthesis or processing can greatly affect the PDI of a polymer sample.