# What are Polydispersity Index

What are Polydispersity Index

It is the ratio of the mass average molecular mass  to the number average molecular mass PDI = Mw / Mn

For natural polymers, PDI is usually equal to one  which means that they are monodisperse.

In other words, such polymers are more homogeneous. On the contrary, synthetic polymers generally have PDI > 1 which means that they are less homogeneous.