Question

The polydispersity index of the polymer is always:
(A) 1
(B) < 1
(C) 2
(D) 1 or > 1

Answer 1

Hint: To solve this question we have to first have a clear understanding of what polydispersity index is. It is actually the molecular weight distribution throughout the polymer.

Complete step by step solution:
Macromolecules have a molar mass distribution due to the simplest homopolymers made of homologous chains with a variable number of repeating units. They exhibit average values of two types. We can mathematically express the Poly-dispersity index as the ratio between the weight average molecular weight and the number average molecular weight of a molecule.
It is usually measured by the gel permeation chromatography technique.
When the polymer chains form agglomerates and get entangled, the molecular weight is impossible to measure accurately. In this case the molecular weight distribution is a useful measurement to evaluate a polymer.
Since, the number average molecular weight of a molecule is always greater than the average molecular weight; the polydispersity index is always 1 or more than 1.

Hence, the correct answer is Option (D) 1 or >1.

Additional information:
PDI is employed to point out the distribution of polymer chain molecular weights for a given polymer, with increase in the PDI value, the heterogeneity in cross-linking, network formation, chain length, branching, hyper branching will be more with more random arrangement.

Note: Monodisperse polymers are actually uniform polymers in which all molecules have the same degree of polymerization or relative molecular mass. The polymer has a polydispersity index equal to 1. Many biopolymers, especially proteins, are monodisperse.