Question

For natural polymers, PDI value is always equal to unity.
(2): The ratio $\dfrac{\overset{-}{\mathop{{{M}_{n}}}}\,}{\overset{-}{\mathop{{{M}_{w}}}}\,}$
 of a polymer is called PDI.
A. Both 1 and 2 are correct and 2 is the correct explanation of the 1
B. Both 1 and 2 are correct and 2 is the correct explanation of the 1
C. 1 is correct but 2 is incorrect
D. 1 is incorrect but 2 is correct

Answer 1

Hint: As we know that a polymer material is shown by the term non-uniform or disperse, it is found that the man-made polymers, their chain lengths vary over a wide range of molecular masses. Whereas, natural organic matter is being produced by the decomposition of plants and wood debris.

Complete Solution :
- As we know that for natural polymers the value of PDI that is (polymer dispersity index) is equal to one because they are basically straight and uniform in length.
- The polydispersity index or PDI is a measure of the distribution of molecular mass in a given polymer sample. The PDI is the ratio of the weight average molecular weight and the number average molecular weight. PDI is denoted as:
$PDI=\dfrac{\overset{-}{\mathop{{{M}_{n}}}}\,}{\overset{-}{\mathop{{{M}_{w}}}}\,}$
- Hence, we can conclude that the correct option is (b), that both 1and 2 are correct and 2 is the correct explanation of the 1.
So, the correct answer is “Option B”.

Note: - As we know that the dispersity shows the distribution of particular molecular masses in a group of polymers. The polydispersity index has a value greater to or equal to one, but as the polymer chains approach towards the uniform chain length, the value of PDI becomes 1.