Question

The polydispersity index of a polymer containing $10$ molecules with molecular mass $1.0 \times 10^4$ and $10$ molecules with molecular mass $1.0 \times 10^5$ is approximately

• A. 1.67
• B. 0.59
• C. 1.55
• D. 0.83

Answer 1

Answer: (A)

The PDI (polydispersity index) $=\frac{M_{w}}{M_{n}}=1.67$

$M_{w}=$ Weight average molecular weight.

$M_{n}=$ Number average molecular weight.

$M_{n}=\frac{N_{1} M_{1}+N_{2} M_{2}}{N_{1}+N_{2}}=55,000$

$M_{w}=\frac{N_{1} M_{1}^{2}+N_{2} M_{2}^{2}}{N_{1} M_{1}+N_{2} M_{2}}=91818$